From 9544fb353c6c730730e96bb03f60a459850232bb Mon Sep 17 00:00:00 2001
From: SarthakWade <sarthakssg5@gmail.com>
Date: Tue, 22 Sep 2026 17:56:34 +0530
Subject: [PATCH] feat: add region screenshot series

---
 .agents/skills/headless-computer-use/SKILL.md |   1 +
 .../references/commands.md                    |   5 +-
 CHANGELOG.md                                  |   4 +
 README.md                                     |  12 +
 apps/headless-rs/src/protocol.rs              |  20 +-
 apps/headless-rs/tests/protocol_tests.rs      |  19 ++
 apps/headless/Host/AgentBridge.swift          | 137 +++++++--
 apps/headless/LinuxHost/BrowserProcess.swift  |  67 ++++-
 apps/headless/LinuxHost/main.swift            |  21 +-
 .../Sources/HeadlessProtocol/CLI.swift        |  17 +-
 .../HeadlessProtocol/Capabilities.swift       |   2 +-
 .../Sources/HeadlessProtocol/HostCore.swift   |  52 +++-
 .../Sources/HeadlessProtocol/Protocol.swift   |  14 +-
 .../HeadlessProtocol/ProtocolSchema.swift     |  11 +-
 .../Resources/AgentRuntime.js                 | 118 +++++++-
 .../HeadlessProtocol/ScreenshotSeries.swift   | 188 +++++++++++-
 .../Tests/Fixtures/region-capture.html        |  30 ++
 .../HeadlessProtocolTests/ProtocolTests.swift | 273 +++++++++++++++++-
 apps/headless/Tests/agent-runtime.test.mjs    | 151 ++++++++++
 apps/headless/Tests/fixture-server.mjs        |   1 +
 apps/headless/Tests/linux-e2e.sh              |  61 +++-
 apps/headless/Tests/macos-e2e.sh              |  57 ++++
 apps/headless/docs/COMMANDS.md                |  10 +-
 apps/headless/docs/P1.md                      |   8 +
 docs/roadmap/architecture-decisions.md        |  45 +++
 docs/roadmap/improvements-backlog.md          |   8 +-
 packages/headless-npm/src/generated.ts        |  52 +++-
 packages/headless-npm/src/protocol.ts         |  42 +++
 packages/headless-npm/test/protocol.test.mjs  |  19 ++
 .../src/headless_sdk/_protocol.py             |  39 +++
 .../src/headless_sdk/generated.py             |  47 ++-
 .../headless-python/tests/test_protocol.py    |  12 +
 sdk/protocol-fixtures.json                    |  30 ++
 sdk/protocol-schema.json                      |   2 +-
 34 files changed, 1483 insertions(+), 92 deletions(-)
 create mode 100644 apps/headless/Tests/Fixtures/region-capture.html

diff --git a/.agents/skills/headless-computer-use/SKILL.md b/.agents/skills/headless-computer-use/SKILL.md
index 5a877cf..f6935a7 100644
--- a/.agents/skills/headless-computer-use/SKILL.md
+++ b/.agents/skills/headless-computer-use/SKILL.md
@@ -87,6 +87,7 @@ headless --session agent-qa screenshot --full-page --output before.png
 headless --session agent-qa screenshot --format jpg --output before.jpg
 headless --session agent-qa screenshot --every-viewport --output page-scroll
 headless --session agent-qa screenshot --by-section --output page-sections
+headless --session agent-qa screenshot --by-region @r4 --output focused-region
 headless --session agent-qa click --role button --name Continue
 headless --session agent-qa wait --url /next --text "Designer details" --settled
 headless --session agent-qa screenshot --full-page --output after.png
diff --git a/.agents/skills/headless-computer-use/references/commands.md b/.agents/skills/headless-computer-use/references/commands.md
index a0cca41..7bb75a8 100644
--- a/.agents/skills/headless-computer-use/references/commands.md
+++ b/.agents/skills/headless-computer-use/references/commands.md
@@ -82,6 +82,7 @@ headless --session NAME screenshot REF --output element.png
 headless --session NAME screenshot --role button --name Continue --output button.png
 headless --session NAME screenshot --every-viewport --format jpg --output page-scroll
 headless --session NAME screenshot --by-section --output page-sections
+headless --session NAME screenshot --by-region @r4 --output focused-region
 headless --session NAME record start --fps 10 --format mp4 --quality balanced
 headless --session NAME record status
 headless --session NAME record stop --output flow.mp4
@@ -117,8 +118,8 @@ For human-reviewable evidence:
 
 1. Start recording before the action under test.
 2. Use `tour --full-page --pace 500` when scrolling is part of the evidence.
-3. Capture key-state screenshots, plus `--every-viewport` or `--by-section`
-   screenshots for long scrollable pages.
+3. Capture key-state screenshots, plus `--every-viewport`, `--by-section`, or
+   an outline-scoped `--by-region @rN` series for broader visual evidence.
 4. Stop recording on both success and failure paths.
 5. List the artifact metadata.
 6. Verify the copied file independently when tools are available:
diff --git a/CHANGELOG.md b/CHANGELOG.md
index 95bb710..eaf9922 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -18,6 +18,10 @@ Two versions travel independently, on purpose:
 
 ## [Unreleased]
 
+- Add bounded cross-engine `screenshot --by-region @rN` series with exact
+  border-box crops, document and geometry revalidation, atomic artifacts, and
+  enforced scroll restoration.
+
 ### Added
 
 - macOS Command-, opens one Settings window built from the typed registry and
diff --git a/README.md b/README.md
index e4e4bea..8b1eebb 100644
--- a/README.md
+++ b/README.md
@@ -87,6 +87,7 @@ headless --session qa screenshot --format jpg --output next-page.jpg --clipboard
 headless --session qa screenshot --format pdf --full-page --output next-page.pdf
 headless --session qa screenshot --every-viewport --output dashboard-scroll
 headless --session qa screenshot --by-section --output dashboard-sections
+headless --session qa screenshot --by-region @r4 --output checkout-region
 headless --session qa qa report
 headless --session qa console list --level error
 headless --session qa network list --failed
@@ -143,6 +144,17 @@ jpg` for JPEG series; PDF requires `--full-page` and is not a series format. The
 output prefix creates numbered artifacts such as `dashboard-scroll-001.png` or
 `dashboard-scroll-001.jpg`.
 
+After `inspect --context outline`, use `screenshot --by-region @rN --output
+PREFIX` to capture only that region element's rendered border box as bounded
+vertical slices. The region must fit horizontally in the viewport and cannot
+exceed the portable 4096 CSS-pixel capture width. Nested
+scroll-container content outside the rendered box is not expanded. Unknown,
+expired, hidden, clipped, or changing regions fail without keeping partial
+artifacts. A series with `truncated: true` contains the first 79 slices and the
+final slice, so its omitted middle is explicit rather than presented as full
+coverage. Scroll restoration is enforced while the original document remains
+active.
+
 When an action fails, use the on-demand diagnostic commands instead of an
 interactive DevTools UI: `console list`, `network list|get`, `styles get`,
 `cookies list`, and `storage list`. Cookie and storage values stay redacted
diff --git a/apps/headless-rs/src/protocol.rs b/apps/headless-rs/src/protocol.rs
index 2c9cc7d..9f83d6a 100644
--- a/apps/headless-rs/src/protocol.rs
+++ b/apps/headless-rs/src/protocol.rs
@@ -537,7 +537,7 @@ impl CommandRequest {
     fn validate_screenshot(&self) -> Result<(), ValidationError> {
         self.allow(&[
             "fullPage", "target", "role", "name", "output", "series", "outputPrefix", "format",
-            "clipboard",
+            "clipboard", "region",
         ])?;
         self.boolean("fullPage")?;
         self.boolean("clipboard")?;
@@ -546,12 +546,28 @@ impl CommandRequest {
             self.parameter("target").is_some() || self.parameter("role").is_some() || self.parameter("name").is_some();
         let series = self.string("series", false, 32)?;
         if let Some(series) = &series {
-            if !["viewport", "section"].contains(&series.as_str()) {
+            if !["viewport", "section", "region"].contains(&series.as_str()) {
                 return Err(ValidationError::InvalidParameter(
                     "Invalid screenshot series".to_string(),
                 ));
             }
         }
+        let region = self.string("region", false, 16)?;
+        if let Some(region) = &region {
+            let digits = region.strip_prefix("@r").map(|rest| {
+                !rest.is_empty() && rest.bytes().all(|byte| byte.is_ascii_digit())
+            });
+            if digits != Some(true) {
+                return Err(ValidationError::InvalidParameter(
+                    "Invalid screenshot region reference".to_string(),
+                ));
+            }
+        }
+        if (series.as_deref() == Some("region")) != region.is_some() {
+            return Err(ValidationError::InvalidParameter(
+                "Region screenshot series requires exactly one region reference".to_string(),
+            ));
+        }
         let format = screenshot_format(
             self.string("format", false, 16)?.as_deref(),
             self.parameter("output").and_then(|v| v.string_value()),
diff --git a/apps/headless-rs/tests/protocol_tests.rs b/apps/headless-rs/tests/protocol_tests.rs
index 0dfbb1d..2b1e93c 100644
--- a/apps/headless-rs/tests/protocol_tests.rs
+++ b/apps/headless-rs/tests/protocol_tests.rs
@@ -189,6 +189,25 @@ fn command_parameter_validation() {
         params(&[("format", json!("pdf")), ("fullPage", json!(true)), ("output", json!("page.pdf"))]),
     );
     request.validate().unwrap();
+    let request = valid_request(
+        CommandName::Screenshot,
+        params(&[
+            ("series", json!("region")),
+            ("region", json!("@r4")),
+            ("outputPrefix", json!("checkout")),
+        ]),
+    );
+    request.validate().unwrap();
+    let request = valid_request(
+        CommandName::Screenshot,
+        params(&[("series", json!("region"))]),
+    );
+    assert!(request.validate().is_err());
+    let request = valid_request(
+        CommandName::Screenshot,
+        params(&[("series", json!("viewport")), ("region", json!("@r4"))]),
+    );
+    assert!(request.validate().is_err());
 
     // visual compare only accepts private PNG artifacts
     let request = valid_request(
diff --git a/apps/headless/Host/AgentBridge.swift b/apps/headless/Host/AgentBridge.swift
index ed06f89..bbbde02 100644
--- a/apps/headless/Host/AgentBridge.swift
+++ b/apps/headless/Host/AgentBridge.swift
@@ -208,8 +208,10 @@ extension BrowserWindowController {
         format: ScreenshotFormat,
         copyToClipboard: Bool
     ) throws -> ScreenshotArtifactData {
-        let image = try agentScreenshotImage(parameters: parameters)
-        guard let data = encodeScreenshot(image, format: format) else {
+        let capture = try agentScreenshotImage(parameters: parameters)
+        guard let data = encodeScreenshot(
+            capture.image, format: format, pixelSize: capture.regionPixelSize
+        ) else {
             throw HostError(code: .operationFailed, message: "Browser returned an invalid agent result")
         }
         if copyToClipboard {
@@ -218,16 +220,53 @@ extension BrowserWindowController {
             }
             onMain {
                 NSPasteboard.general.clearContents()
-                NSPasteboard.general.writeObjects([image])
+                NSPasteboard.general.writeObjects([capture.image])
             }
         }
         return ScreenshotArtifactData(data: data, clipboardCopied: copyToClipboard)
     }
 
-    private func agentScreenshotImage(parameters: [String: JSONValue]) throws -> NSImage {
+    private func agentScreenshotImage(
+        parameters: [String: JSONValue]
+    ) throws -> (image: NSImage, regionPixelSize: CGSize?) {
         var requestedRect: CGRect?
+        var regionSliceArguments: [String: Any]?
         let hasTarget = parameters["target"] != nil || parameters["role"] != nil || parameters["name"] != nil
-        if hasTarget {
+        let hasRegionSlice = ["_region", "_document", "_geometry", "_sliceTop", "_sliceHeight"]
+            .contains { parameters[$0] != nil }
+        if hasRegionSlice {
+            guard let reference = parameters["_region"]?.stringValue,
+                  let document = parameters["_document"]?.stringValue,
+                  case .object(let geometry)? = parameters["_geometry"],
+                  let x = geometry["x"]?.numberValue,
+                  let y = geometry["y"]?.numberValue,
+                  let width = geometry["width"]?.numberValue,
+                  let height = geometry["height"]?.numberValue,
+                  let sliceTop = parameters["_sliceTop"]?.numberValue,
+                  let sliceHeight = parameters["_sliceHeight"]?.numberValue else {
+                throw ScreenshotSeriesError.invalidPlan
+            }
+            var args: [String: Any] = [
+                "region": reference, "document": document,
+                "geometry": ["x": x, "y": y, "width": width, "height": height],
+                "sliceTop": sliceTop, "sliceHeight": sliceHeight,
+            ]
+            let value = try callAgent(
+                "return globalThis.__headlessAgent.regionSlice(args);",
+                arguments: ["args": args]
+            )
+            guard case .object(let outer) = value, case .object(let rect)? = outer["viewport"] else {
+                throw HostError(code: .operationFailed, message: "Browser returned an invalid agent result")
+            }
+            requestedRect = try screenshotRect(rect)
+            if let requestedRect {
+                args["viewport"] = [
+                    "x": requestedRect.origin.x, "y": requestedRect.origin.y,
+                    "width": requestedRect.width, "height": requestedRect.height,
+                ]
+            }
+            regionSliceArguments = args
+        } else if hasTarget {
             let args = try browserTargetArguments(parameters)
             let value = try callAgent(
                 "return globalThis.__headlessAgent.rectangle(args);", arguments: ["args": args]
@@ -279,15 +318,26 @@ extension BrowserWindowController {
         guard let image = try result?.get() else {
             throw HostError(code: .operationFailed, message: "Browser returned an invalid agent result")
         }
-        return image
+        if let regionSliceArguments {
+            _ = try callAgent(
+                "return globalThis.__headlessAgent.regionSlice(args);",
+                arguments: ["args": regionSliceArguments]
+            )
+        }
+        return (image, regionSliceArguments == nil ? nil : requestedRect?.size)
     }
 
-    private func encodeScreenshot(_ image: NSImage, format: ScreenshotFormat) -> Data? {
+    private func encodeScreenshot(
+        _ image: NSImage, format: ScreenshotFormat, pixelSize: CGSize? = nil
+    ) -> Data? {
         switch format {
         case .png:
-            return bitmapData(for: image, type: .png, properties: [:])
+            return bitmapData(for: image, pixelSize: pixelSize, type: .png, properties: [:])
         case .jpeg:
-            return bitmapData(for: image, type: .jpeg, properties: [.compressionFactor: 0.88])
+            return bitmapData(
+                for: image, pixelSize: pixelSize,
+                type: .jpeg, properties: [.compressionFactor: 0.88]
+            )
         case .pdf:
             return pdfData(for: image)
         }
@@ -295,9 +345,45 @@ extension BrowserWindowController {
 
     private func bitmapData(
         for image: NSImage,
+        pixelSize: CGSize?,
         type: NSBitmapImageRep.FileType,
         properties: [NSBitmapImageRep.PropertyKey: Any]
     ) -> Data? {
+        if let pixelSize {
+            let width = Int(ceil(pixelSize.width))
+            let height = Int(ceil(pixelSize.height))
+            guard width > 0, height > 0,
+                  width <= Int(ProtocolBounds.screenshotDimension),
+                  height <= Int(ProtocolBounds.screenshotDimension),
+                  Double(width * height) <= ProtocolBounds.screenshotPixels,
+                  let bitmap = NSBitmapImageRep(
+                      bitmapDataPlanes: nil,
+                      pixelsWide: width,
+                      pixelsHigh: height,
+                      bitsPerSample: 8,
+                      samplesPerPixel: 4,
+                      hasAlpha: true,
+                      isPlanar: false,
+                      colorSpaceName: .deviceRGB,
+                      bytesPerRow: 0,
+                      bitsPerPixel: 0
+                  ),
+                  let context = NSGraphicsContext(bitmapImageRep: bitmap) else {
+                return nil
+            }
+            bitmap.size = NSSize(width: width, height: height)
+            NSGraphicsContext.saveGraphicsState()
+            NSGraphicsContext.current = context
+            image.draw(
+                in: NSRect(x: 0, y: 0, width: width, height: height),
+                from: NSRect(origin: .zero, size: image.size),
+                operation: .copy,
+                fraction: 1
+            )
+            context.flushGraphics()
+            NSGraphicsContext.restoreGraphicsState()
+            return bitmap.representation(using: type, properties: properties)
+        }
         guard let representation = image.tiffRepresentation,
               let bitmap = NSBitmapImageRep(data: representation) else { return nil }
         return bitmap.representation(using: type, properties: properties)
@@ -319,17 +405,19 @@ extension BrowserWindowController {
         return data as Data
     }
 
-    func agentScreenshotSeriesPlan(mode: String) throws -> JSONValue {
-        try callAgent(
+    func agentScreenshotSeriesPlan(mode: String, region: String?) throws -> JSONValue {
+        var args: [String: Any] = ["mode": mode]
+        if let region { args["region"] = region }
+        return try callAgent(
             "return globalThis.__headlessAgent.screenshotPlan(args);",
-            arguments: ["args": ["mode": mode]]
+            arguments: ["args": args]
         )
     }
 
-    func agentScrollToCapturePoint(y: Double) throws -> JSONValue {
+    func agentScrollToCapturePoint(y: Double, document: String) throws -> JSONValue {
         try callAgent(
             "return await globalThis.__headlessAgent.scrollToCapturePoint(args);",
-            arguments: ["args": ["y": y]]
+            arguments: ["args": ["y": y, "document": document]]
         )
     }
 
@@ -595,12 +683,25 @@ extension BrowserWindowController: BrowserEngineSession {
             data: screenshot.data, clipboardCopied: screenshot.clipboardCopied
         )
     }
+    func hostScreenshotRegionSlice(
+        reference: String, document: String, geometry: ScreenshotRegionGeometry,
+        point: ScreenshotSeriesPoint, format: ScreenshotFormat
+    ) throws -> BrowserScreenshot {
+        guard let sliceTop = point.sliceTop, let sliceHeight = point.sliceHeight else {
+            throw ScreenshotSeriesError.invalidPlan
+        }
+        return BrowserScreenshot(data: try agentScreenshotData(parameters: [
+            "_region": .string(reference), "_document": .string(document),
+            "_geometry": .object(geometry.parameters),
+            "_sliceTop": .number(sliceTop), "_sliceHeight": .number(sliceHeight),
+        ], format: format, copyToClipboard: false).data)
+    }
     func hostRecordingFrame() throws -> Data { try agentScreenshot(parameters: [:]) }
-    func hostScreenshotSeriesPlan(mode: String) throws -> JSONValue {
-        try agentScreenshotSeriesPlan(mode: mode)
+    func hostScreenshotSeriesPlan(mode: String, region: String?) throws -> JSONValue {
+        try agentScreenshotSeriesPlan(mode: mode, region: region)
     }
-    func hostScrollToCapturePoint(y: Double) throws -> JSONValue {
-        try agentScrollToCapturePoint(y: y)
+    func hostScrollToCapturePoint(y: Double, document: String) throws -> JSONValue {
+        try agentScrollToCapturePoint(y: y, document: document)
     }
     func hostQAReport() throws -> JSONValue { agentQAReport() }
     func hostQAClear() throws -> JSONValue { agentQAClear() }
diff --git a/apps/headless/LinuxHost/BrowserProcess.swift b/apps/headless/LinuxHost/BrowserProcess.swift
index ff915e3..8888489 100644
--- a/apps/headless/LinuxHost/BrowserProcess.swift
+++ b/apps/headless/LinuxHost/BrowserProcess.swift
@@ -914,8 +914,23 @@ final class LinuxBrowserSession: @unchecked Sendable {
             "format": format.browserScreenshotFormat, "fromSurface": true, "captureBeyondViewport": false,
         ]
         if format == .jpeg { capture["quality"] = 88 }
+        var regionSliceArguments = try screenshotRegionSliceArguments(parameters)
         let hasTarget = parameters["target"] != nil || parameters["role"] != nil || parameters["name"] != nil
-        if hasTarget {
+        if var arguments = regionSliceArguments {
+            capture["captureBeyondViewport"] = true
+            let rectangle = try evaluate(
+                "return globalThis.__headlessAgent.regionSlice(args);",
+                input: ["args": arguments]
+            )
+            guard case .object(let outer) = rectangle,
+                  case .object(let rect)? = outer["document"],
+                  case .object(let viewport)? = outer["viewport"] else {
+                throw CDPError.invalidResponse("region slice rectangle")
+            }
+            capture["clip"] = try screenshotClip(rect)
+            arguments["viewport"] = try screenshotRectangleArguments(viewport)
+            regionSliceArguments = arguments
+        } else if hasTarget {
             capture["captureBeyondViewport"] = true
             let args = try browserTargetArguments(parameters)
             let rectangle = try evaluate(
@@ -946,9 +961,39 @@ final class LinuxBrowserSession: @unchecked Sendable {
         guard let base64 = response["data"] as? String, let data = Data(base64Encoded: base64) else {
             throw CDPError.invalidResponse("Page.captureScreenshot data")
         }
+        if let regionSliceArguments {
+            _ = try evaluate(
+                "return globalThis.__headlessAgent.regionSlice(args);",
+                input: ["args": regionSliceArguments]
+            )
+        }
         return data
     }
 
+    private func screenshotRegionSliceArguments(
+        _ parameters: [String: JSONValue]
+    ) throws -> [String: Any]? {
+        let hasRegionSlice = ["_region", "_document", "_geometry", "_sliceTop", "_sliceHeight"]
+            .contains { parameters[$0] != nil }
+        guard hasRegionSlice else { return nil }
+        guard let reference = parameters["_region"]?.stringValue,
+              let document = parameters["_document"]?.stringValue,
+              case .object(let geometry)? = parameters["_geometry"],
+              let x = geometry["x"]?.numberValue,
+              let y = geometry["y"]?.numberValue,
+              let width = geometry["width"]?.numberValue,
+              let height = geometry["height"]?.numberValue,
+              let sliceTop = parameters["_sliceTop"]?.numberValue,
+              let sliceHeight = parameters["_sliceHeight"]?.numberValue else {
+            throw CDPError.invalidResponse("region slice parameters")
+        }
+        return [
+            "region": reference, "document": document,
+            "geometry": ["x": x, "y": y, "width": width, "height": height],
+            "sliceTop": sliceTop, "sliceHeight": sliceHeight,
+        ]
+    }
+
     private func printPDF(
         parameters: [String: JSONValue],
         timeoutMilliseconds: Int32
@@ -972,17 +1017,19 @@ final class LinuxBrowserSession: @unchecked Sendable {
         return data
     }
 
-    func screenshotSeriesPlan(mode: String) throws -> JSONValue {
-        try evaluate(
+    func screenshotSeriesPlan(mode: String, region: String?) throws -> JSONValue {
+        var args: [String: Any] = ["mode": mode]
+        if let region { args["region"] = region }
+        return try evaluate(
             "return globalThis.__headlessAgent.screenshotPlan(args);",
-            input: ["args": ["mode": mode]]
+            input: ["args": args]
         )
     }
 
-    func scrollToCapturePoint(y: Double) throws -> JSONValue {
+    func scrollToCapturePoint(y: Double, document: String) throws -> JSONValue {
         try evaluate(
             "return await globalThis.__headlessAgent.scrollToCapturePoint(args);",
-            input: ["args": ["y": y]]
+            input: ["args": ["y": y, "document": document]]
         )
     }
 
@@ -1279,10 +1326,16 @@ final class LinuxBrowserSession: @unchecked Sendable {
     }
 
     private func screenshotClip(_ rect: [String: JSONValue]) throws -> [String: Any] {
+        var result = try screenshotRectangleArguments(rect)
+        result["scale"] = 1
+        return result
+    }
+
+    private func screenshotRectangleArguments(_ rect: [String: JSONValue]) throws -> [String: Any] {
         let rectangle = try BoundedScreenshotRectangle(rect)
         return [
             "x": rectangle.x, "y": rectangle.y,
-            "width": rectangle.width, "height": rectangle.height, "scale": 1,
+            "width": rectangle.width, "height": rectangle.height,
         ]
     }
 
diff --git a/apps/headless/LinuxHost/main.swift b/apps/headless/LinuxHost/main.swift
index f1d0fe3..3168c83 100644
--- a/apps/headless/LinuxHost/main.swift
+++ b/apps/headless/LinuxHost/main.swift
@@ -134,12 +134,25 @@ final class ChromiumBrowserEngineSession: BrowserEngineSession {
         }
         return BrowserScreenshot(data: try browserSession.screenshot(parameters: parameters, format: format))
     }
+    func hostScreenshotRegionSlice(
+        reference: String, document: String, geometry: ScreenshotRegionGeometry,
+        point: ScreenshotSeriesPoint, format: ScreenshotFormat
+    ) throws -> BrowserScreenshot {
+        guard let sliceTop = point.sliceTop, let sliceHeight = point.sliceHeight else {
+            throw ScreenshotSeriesError.invalidPlan
+        }
+        return BrowserScreenshot(data: try browserSession.screenshot(parameters: [
+            "_region": .string(reference), "_document": .string(document),
+            "_geometry": .object(geometry.parameters),
+            "_sliceTop": .number(sliceTop), "_sliceHeight": .number(sliceHeight),
+        ], format: format))
+    }
     func hostRecordingFrame() throws -> Data { try browserSession.recordingFrame() }
-    func hostScreenshotSeriesPlan(mode: String) throws -> JSONValue {
-        try browserSession.screenshotSeriesPlan(mode: mode)
+    func hostScreenshotSeriesPlan(mode: String, region: String?) throws -> JSONValue {
+        try browserSession.screenshotSeriesPlan(mode: mode, region: region)
     }
-    func hostScrollToCapturePoint(y: Double) throws -> JSONValue {
-        try browserSession.scrollToCapturePoint(y: y)
+    func hostScrollToCapturePoint(y: Double, document: String) throws -> JSONValue {
+        try browserSession.scrollToCapturePoint(y: y, document: document)
     }
     func hostQAReport() throws -> JSONValue { try browserSession.qaReport() }
     func hostQAClear() throws -> JSONValue { browserSession.diagnostics.clear() }
diff --git a/apps/headless/Sources/HeadlessProtocol/CLI.swift b/apps/headless/Sources/HeadlessProtocol/CLI.swift
index c98ca76..9bd481d 100644
--- a/apps/headless/Sources/HeadlessProtocol/CLI.swift
+++ b/apps/headless/Sources/HeadlessProtocol/CLI.swift
@@ -506,23 +506,32 @@ public struct CLIParser {
         let fullPage = removeFlag("--full-page", from: &args)
         let everyViewport = removeFlag("--every-viewport", from: &args)
         let bySection = removeFlag("--by-section", from: &args)
+        let byRegion = try removeOption("--by-region", from: &args)
         let role = try removeOption("--role", from: &args)
         let name = try removeOption("--name", from: &args)
         let output = try removeOption("--output", from: &args)
         let formatText = try removeOption("--format", from: &args)
         let clipboard = removeFlag("--clipboard", from: &args)
         let format = try screenshotFormat(explicit: formatText, output: output)
-        if everyViewport && bySection { throw CLIParseError.conflictingTarget }
-        if everyViewport || bySection {
+        let seriesModes = (everyViewport ? 1 : 0) + (bySection ? 1 : 0) + (byRegion == nil ? 0 : 1)
+        if seriesModes > 1 { throw CLIParseError.conflictingTarget }
+        if seriesModes == 1 {
             try requireEmpty(args)
             guard !fullPage, role == nil, name == nil else { throw CLIParseError.conflictingTarget }
             guard format.isImage else { throw CLIParseError.invalidOption("--format pdf") }
             guard !clipboard else { throw CLIParseError.invalidOption("--clipboard") }
+            if let byRegion {
+                guard byRegion.hasPrefix("@r"), !byRegion.dropFirst(2).isEmpty,
+                      byRegion.dropFirst(2).allSatisfy({ $0.isASCII && $0.isNumber }) else {
+                    throw CLIParseError.invalidOption(byRegion)
+                }
+            }
             var parameters: [String: JSONValue] = [
                 "fullPage": .bool(false),
-                "series": .string(everyViewport ? "viewport" : "section"),
+                "series": .string(everyViewport ? "viewport" : (bySection ? "section" : "region")),
                 "format": .string(format.rawValue),
             ]
+            if let byRegion { parameters["region"] = .string(byRegion) }
             if let output {
                 let prefix = try screenshotSeriesPrefix(output)
                 parameters["outputPrefix"] = .string(prefix)
@@ -886,7 +895,7 @@ Commands:
   capture-info
   screenshot [REF | --role ROLE --name NAME | --full-page] [--format png|jpg|jpeg] [--output FILE] [--clipboard]
   screenshot --full-page --format pdf [--output FILE.pdf]
-  screenshot --every-viewport|--by-section [--format png|jpg|jpeg] [--output PREFIX]
+  screenshot --every-viewport|--by-section|--by-region @rN [--format png|jpg|jpeg] [--output PREFIX]
   artifacts list [--limit N] [--cursor CURSOR]
   record start [--fps N] [--format mp4|mov|webm|gif] [--quality fast|balanced|high] [--output FILE]
   record status | record stop [--output FILE]
diff --git a/apps/headless/Sources/HeadlessProtocol/Capabilities.swift b/apps/headless/Sources/HeadlessProtocol/Capabilities.swift
index 759880d..c1a8169 100644
--- a/apps/headless/Sources/HeadlessProtocol/Capabilities.swift
+++ b/apps/headless/Sources/HeadlessProtocol/Capabilities.swift
@@ -215,7 +215,7 @@ public let capabilitiesDocument: JSONValue = {
             "budgetRangeEstimatedTokens": .array([.number(256), .number(16_000)]),
             "maximumOutlineDepth": .number(8),
         ]),
-        "screenshotSeries": stringArray(["viewport", "section"]),
+        "screenshotSeries": stringArray(["viewport", "section", "region"]),
         "localCommands": stringArray([
             "config.describe", "config.get", "config.list", "config.reset", "config.set",
             "credentials.add", "credentials.list", "credentials.remove", "credentials.rename",
diff --git a/apps/headless/Sources/HeadlessProtocol/HostCore.swift b/apps/headless/Sources/HeadlessProtocol/HostCore.swift
index c4dc887..cb45172 100644
--- a/apps/headless/Sources/HeadlessProtocol/HostCore.swift
+++ b/apps/headless/Sources/HeadlessProtocol/HostCore.swift
@@ -48,9 +48,13 @@ public protocol BrowserEngineSession: AnyObject {
     func hostScreenshot(
         parameters: [String: JSONValue], format: ScreenshotFormat, copyToClipboard: Bool
     ) throws -> BrowserScreenshot
+    func hostScreenshotRegionSlice(
+        reference: String, document: String, geometry: ScreenshotRegionGeometry,
+        point: ScreenshotSeriesPoint, format: ScreenshotFormat
+    ) throws -> BrowserScreenshot
     func hostRecordingFrame() throws -> Data
-    func hostScreenshotSeriesPlan(mode: String) throws -> JSONValue
-    func hostScrollToCapturePoint(y: Double) throws -> JSONValue
+    func hostScreenshotSeriesPlan(mode: String, region: String?) throws -> JSONValue
+    func hostScrollToCapturePoint(y: Double, document: String) throws -> JSONValue
     func hostQAReport() throws -> JSONValue
     func hostQAClear() throws -> JSONValue
     func hostConsole(level: String, limit: Int, cursor: String?) throws -> JSONValue
@@ -887,28 +891,50 @@ public final class HostCore<Engine: BrowserEngine>: @unchecked Sendable {
     ) throws -> JSONValue {
         let mode = parameters["series"]?.stringValue ?? "viewport"
         let format = try screenshotFormat(explicit: parameters["format"]?.stringValue, output: nil)
-        let plan = try parseScreenshotSeriesPlan(try session.hostScreenshotSeriesPlan(mode: mode))
+        let regionReference = parameters["region"]?.stringValue
+        let rawPlan = try session.hostScreenshotSeriesPlan(
+            mode: mode, region: regionReference
+        )
+        let plan = try parseScreenshotSeriesPlan(rawPlan, regionReference: regionReference)
         let prefix = try screenshotSeriesPrefix(parameters: parameters, mode: mode)
-        defer { _ = try? session.hostScrollToCapturePoint(y: plan.initialY) }
         let reserved = try reserveScreenshotSeriesArtifacts(
             store: artifacts, points: plan.points, prefix: prefix, mode: mode, format: format
         )
+        var metadata: [JSONValue] = []
+        var captureError: Error?
         do {
-            let metadata = try plan.points.enumerated().map { index, point -> JSONValue in
-                _ = try session.hostScrollToCapturePoint(y: point.y)
-                let screenshot = try session.hostScreenshot(
-                    parameters: [:], format: format, copyToClipboard: false
-                )
+            metadata = try plan.points.enumerated().map { index, point -> JSONValue in
+                _ = try session.hostScrollToCapturePoint(y: point.y, document: plan.document)
+                let screenshot: BrowserScreenshot
+                if let regionReference, let geometry = plan.region {
+                    screenshot = try session.hostScreenshotRegionSlice(
+                        reference: regionReference, document: plan.document,
+                        geometry: geometry, point: point, format: format
+                    )
+                } else {
+                    screenshot = try session.hostScreenshot(
+                        parameters: [:], format: format, copyToClipboard: false
+                    )
+                }
                 return try artifacts.writeReserved(screenshot.data, to: reserved[index])
             }
-            return screenshotSeriesSummary(
-                mode: mode, points: plan.points, artifacts: metadata,
-                truncated: plan.truncated, totalPoints: plan.totalPoints
-            )
+        } catch {
+            captureError = error
+        }
+        do {
+            _ = try session.hostScrollToCapturePoint(y: plan.initialY, document: plan.document)
         } catch {
             artifacts.discardReserved(reserved)
             throw error
         }
+        if let captureError {
+            artifacts.discardReserved(reserved)
+            throw captureError
+        }
+        return screenshotSeriesSummary(
+            mode: mode, points: plan.points, artifacts: metadata,
+            truncated: plan.truncated, totalPoints: plan.totalPoints
+        )
     }
 
     private func startRecording(
diff --git a/apps/headless/Sources/HeadlessProtocol/Protocol.swift b/apps/headless/Sources/HeadlessProtocol/Protocol.swift
index bd13d9d..ef08ce0 100644
--- a/apps/headless/Sources/HeadlessProtocol/Protocol.swift
+++ b/apps/headless/Sources/HeadlessProtocol/Protocol.swift
@@ -306,9 +306,21 @@ public struct CommandRequest: Codable, Equatable, Sendable {
             try target(allowValue: false, required: false)
             let hasTarget = parameters["target"] != nil || parameters["role"] != nil || parameters["name"] != nil
             let series = try string("series", maximumBytes: 32)
-            if let series, !["viewport", "section"].contains(series) {
+            if let series, !["viewport", "section", "region"].contains(series) {
                 throw ProtocolValidationError.invalidParameter("Invalid screenshot series")
             }
+            let region = try string("region", maximumBytes: 16)
+            if let region {
+                guard region.hasPrefix("@r"), !region.dropFirst(2).isEmpty,
+                      region.dropFirst(2).allSatisfy({ $0.isASCII && $0.isNumber }) else {
+                    throw ProtocolValidationError.invalidParameter("Invalid screenshot region reference")
+                }
+            }
+            if (series == "region") != (region != nil) {
+                throw ProtocolValidationError.invalidParameter(
+                    "Region screenshot series requires exactly one region reference"
+                )
+            }
             let format = try screenshotFormat(
                 explicit: string("format", maximumBytes: 16),
                 output: parameters["output"]?.stringValue
diff --git a/apps/headless/Sources/HeadlessProtocol/ProtocolSchema.swift b/apps/headless/Sources/HeadlessProtocol/ProtocolSchema.swift
index 867826c..4901531 100644
--- a/apps/headless/Sources/HeadlessProtocol/ProtocolSchema.swift
+++ b/apps/headless/Sources/HeadlessProtocol/ProtocolSchema.swift
@@ -351,7 +351,14 @@ public func protocolResultDefinition(for command: CommandName) -> ProtocolResult
             resultField("bytes", .number, required: false),
             resultField("createdAt", .number, required: false),
             resultField("artifacts", .array, required: false),
+            resultField(
+                "series", .string, required: false, values: ["viewport", "section", "region"]
+            ),
+            resultField("count", .number, required: false),
+            resultField("positions", .array, required: false),
             resultField("truncated", .boolean, required: false),
+            resultField("totalPoints", .number, required: false),
+            resultField("untrustedContent", .boolean, required: false),
         ])
     case .artifactList:
         return result("ArtifactList", [
@@ -747,7 +754,8 @@ public let protocolCommandDefinitions: [CommandName: ProtocolCommandDefinition]
         command(.captureInfo, untrusted: true),
         command(.screenshot, targetParameters + [
             boolean("fullPage"), string("output", maximumBytes: 128),
-            string("series", maximumBytes: 32, values: ["viewport", "section"]),
+            string("series", maximumBytes: 32, values: ["viewport", "section", "region"]),
+            string("region", maximumBytes: 16),
             string("outputPrefix", maximumBytes: 80),
             string(
                 "format", maximumBytes: 16, values: ["png", "jpg", "jpeg", "pdf"],
@@ -756,6 +764,7 @@ public let protocolCommandDefinitions: [CommandName: ProtocolCommandDefinition]
             boolean("clipboard"),
         ], capabilityNegotiated: true, constraints: [
             "target, full-page, and series modes are mutually constrained",
+            "region is required only for region series and must be an @rN reference",
             "PDF requires full-page mode and no clipboard",
         ]),
         command(.artifactList, [
diff --git a/apps/headless/Sources/HeadlessProtocol/Resources/AgentRuntime.js b/apps/headless/Sources/HeadlessProtocol/Resources/AgentRuntime.js
index f2ab9fc..1b33eb4 100644
--- a/apps/headless/Sources/HeadlessProtocol/Resources/AgentRuntime.js
+++ b/apps/headless/Sources/HeadlessProtocol/Resources/AgentRuntime.js
@@ -13,6 +13,10 @@ if (!globalThis.__headlessAgent) {
     const issuedRefs = new Set();
     const issuedRegionRefs = new Set();
     const maximumTrackedRegions = 256;
+    const maximumScreenshotDimension = 16384;
+    const maximumScreenshotPixels = 64000000;
+    const maximumRegionCaptureWidth = 4096;
+    const maximumRegionExtent = 100000000;
     let lastMutation = performance.now();
     new MutationObserver(() => { lastMutation = performance.now(); })
       .observe(document, {subtree: true, childList: true, attributes: true, characterData: true});
@@ -94,6 +98,27 @@ if (!globalThis.__headlessAgent) {
       const rect = element.getBoundingClientRect();
       return rect.width > 0 && rect.height > 0;
     };
+    const regionIsFullyRenderable = element => {
+      const target = element.getBoundingClientRect();
+      for (let current = element.parentElement; current instanceof Element;
+        current = current.parentElement) {
+        const style = getComputedStyle(current);
+        const ancestor = current.getBoundingClientRect();
+        const overflow = style.overflow || '';
+        const overflowX = style.overflowX || overflow;
+        const overflowY = style.overflowY || overflow;
+        const clipsX = /^(auto|clip|hidden|scroll)$/.test(overflowX);
+        const clipsY = /^(auto|clip|hidden|scroll)$/.test(overflowY);
+        if ((clipsX && (target.left < ancestor.left - 0.5 || target.right > ancestor.right + 0.5)) ||
+            (clipsY && (target.top < ancestor.top - 0.5 || target.bottom > ancestor.bottom + 0.5))) {
+          return false;
+        }
+        const clipPath = style.clipPath || style.getPropertyValue?.('clip-path') || 'none';
+        const contain = style.contain || style.getPropertyValue?.('contain') || 'none';
+        if (clipPath !== 'none' || /(^|\s)(content|paint|strict)(\s|$)/.test(contain)) return false;
+      }
+      return true;
+    };
     const uploadVisible = element => {
       if (!visible(element)) return false;
       const viewportWidth = document.documentElement.clientWidth || globalThis.innerWidth || 0;
@@ -1005,10 +1030,49 @@ if (!globalThis.__headlessAgent) {
       return {points: result, truncated, totalPoints: truncated ? points.length : result.length};
     };
     const screenshotPlan = args => {
-      const mode = args.mode === 'section' ? 'section' : 'viewport';
+      const mode = ['section', 'region'].includes(args.mode) ? args.mode : 'viewport';
       const root = document.documentElement;
       const maximum = Math.max(0, root.scrollHeight - innerHeight);
       const initialY = Math.round(scrollY);
+      if (mode === 'region') {
+        const element = resolveRegion(args.region);
+        const rect = element.getBoundingClientRect();
+        const x = rect.left + scrollX;
+        const y = rect.top + scrollY;
+        const width = rect.width;
+        const height = rect.height;
+        if (![x, y, width, height].every(Number.isFinite) || x < 0 || y < 0 ||
+            width <= 0 || height <= 0 || width > maximumRegionCaptureWidth ||
+            x > maximumRegionExtent || y > maximumRegionExtent || height > maximumRegionExtent ||
+            rect.left < -0.5 || rect.right > innerWidth + 0.5 ||
+            !regionIsFullyRenderable(element)) {
+          fail('REGION_NOT_FOUND', `REGION_NOT_FOUND:${args.region} (invalid capture geometry)`);
+        }
+        const sliceHeight = Math.min(
+          innerHeight, maximumScreenshotDimension, Math.floor(maximumScreenshotPixels / width)
+        );
+        if (!Number.isFinite(sliceHeight) || sliceHeight < 1) {
+          fail('REGION_NOT_FOUND', `REGION_NOT_FOUND:${args.region} (invalid capture geometry)`);
+        }
+        const totalPoints = Math.max(1, Math.ceil(height / sliceHeight));
+        const truncated = totalPoints > 80;
+        const points = [];
+        const leadingCount = truncated ? 79 : totalPoints;
+        for (let index = 0; index < leadingCount; index += 1) {
+          const sliceTop = y + index * sliceHeight;
+          points.push({...capturePoint(Math.min(maximum, sliceTop), `region ${index + 1}`, 'region'),
+            sliceTop, sliceHeight: Math.min(sliceHeight, y + height - sliceTop)});
+        }
+        if (truncated) {
+          const finalHeight = Math.min(sliceHeight, height);
+          const sliceTop = y + height - finalHeight;
+          points.push({...capturePoint(Math.min(maximum, sliceTop), `region ${totalPoints}`, 'region'),
+            sliceTop, sliceHeight: finalHeight});
+        }
+        return {mode, document: authenticationDocument, initialY,
+          viewportHeight: innerHeight, contentHeight: root.scrollHeight,
+          region: {x, y, width, height}, points, truncated, totalPoints};
+      }
       if (mode === 'viewport') {
         const step = Math.max(1, innerHeight);
         const totalPoints = maximum === 0 ? 1 : Math.ceil(maximum / step) + 1;
@@ -1021,7 +1085,8 @@ if (!globalThis.__headlessAgent) {
         if (points.length === 0 || points[points.length - 1].y !== maximum) {
           points.push(capturePoint(maximum, `viewport ${totalPoints}`, 'viewport'));
         }
-        return {mode, initialY, viewportHeight: innerHeight, contentHeight: root.scrollHeight,
+        return {mode, document: authenticationDocument, initialY,
+          viewportHeight: innerHeight, contentHeight: root.scrollHeight,
           points, truncated, totalPoints};
       }
       const candidates = Array.from(document.querySelectorAll('main h1,main h2,main h3,h1,h2,h3,section,[role="region"]'));
@@ -1032,10 +1097,55 @@ if (!globalThis.__headlessAgent) {
         return capturePoint(rect.top + scrollY - 16, label, kind);
       }).sort((left, right) => left.y - right.y);
       const deduped = dedupePoints(points);
-      return {mode, initialY, viewportHeight: innerHeight, contentHeight: root.scrollHeight,
+      return {mode, document: authenticationDocument, initialY,
+        viewportHeight: innerHeight, contentHeight: root.scrollHeight,
         points: deduped.points, truncated: deduped.truncated, totalPoints: deduped.totalPoints};
     };
+    const regionSlice = args => {
+      if (args.document !== authenticationDocument) {
+        fail('REGION_NOT_FOUND', `REGION_NOT_FOUND:${args.region} (document changed: inspect again)`);
+      }
+      const element = resolveRegion(args.region);
+      const rect = element.getBoundingClientRect();
+      if (!regionIsFullyRenderable(element)) {
+        fail('REGION_NOT_FOUND', `REGION_NOT_FOUND:${args.region} (region is clipped by an ancestor)`);
+      }
+      const current = {
+        x: rect.left + scrollX, y: rect.top + scrollY,
+        width: rect.width, height: rect.height
+      };
+      const expected = args.geometry || {};
+      if (![current.x, current.y, current.width, current.height].every(Number.isFinite) ||
+          ['x', 'y', 'width', 'height'].some(key =>
+            !Number.isFinite(Number(expected[key])) || Math.abs(current[key] - Number(expected[key])) > 0.5)) {
+        fail('REGION_NOT_FOUND', `REGION_NOT_FOUND:${args.region} (geometry changed: inspect again)`);
+      }
+      const top = Number(args.sliceTop);
+      const height = Number(args.sliceHeight);
+      if (!Number.isFinite(top) || !Number.isFinite(height) || height <= 0 ||
+          top < current.y - 0.5 || top + height > current.y + current.height + 0.5) {
+        fail('REGION_NOT_FOUND', `REGION_NOT_FOUND:${args.region} (invalid capture slice)`);
+      }
+      const viewport = {x: current.x - scrollX, y: top - scrollY, width: current.width, height};
+      const expectedViewport = args.viewport;
+      if (expectedViewport && ['x', 'y', 'width', 'height'].some(key =>
+          !Number.isFinite(Number(expectedViewport[key])) ||
+          Math.abs(viewport[key] - Number(expectedViewport[key])) > 0.5)) {
+        fail('REGION_NOT_FOUND', `REGION_NOT_FOUND:${args.region} (viewport changed during capture)`);
+      }
+      if (viewport.x < -0.5 || viewport.x + viewport.width > innerWidth + 0.5 ||
+          viewport.y < -0.5 || viewport.y + viewport.height > innerHeight + 0.5) {
+        fail('REGION_NOT_FOUND', `REGION_NOT_FOUND:${args.region} (slice is outside the viewport)`);
+      }
+      return {
+        viewport,
+        document: {x: current.x, y: top, width: current.width, height}
+      };
+    };
     const scrollToCapturePoint = async args => {
+      if (args.document !== authenticationDocument) {
+        fail('OPERATION_FAILED', 'SCREENSHOT_DOCUMENT_CHANGED');
+      }
       const maximum = Math.max(0, document.documentElement.scrollHeight - innerHeight);
       const requestedY = Math.min(maximum, Math.max(0, Number(args.y || 0)));
       scrollTo({top: requestedY, behavior: 'instant'});
@@ -1090,7 +1200,7 @@ if (!globalThis.__headlessAgent) {
     };
     return {
       snapshot, click, fill, select, credentialFill, finishCredentialFill, press, inputTarget, fileInput, fileInputMetadata,
-      authentication, scroll, state, tour, screenshotPlan, scrollToCapturePoint, rectangle, styles, storage,
+      authentication, scroll, state, tour, screenshotPlan, regionSlice, scrollToCapturePoint, rectangle, styles, storage,
       performance: performanceSummary, animations
     };
   })();
diff --git a/apps/headless/Sources/HeadlessProtocol/ScreenshotSeries.swift b/apps/headless/Sources/HeadlessProtocol/ScreenshotSeries.swift
index 0cd8c82..a75d2bc 100644
--- a/apps/headless/Sources/HeadlessProtocol/ScreenshotSeries.swift
+++ b/apps/headless/Sources/HeadlessProtocol/ScreenshotSeries.swift
@@ -16,61 +16,214 @@ public struct ScreenshotSeriesPoint: Equatable, Sendable {
     public let y: Double
     public let label: String
     public let kind: String
+    public let sliceTop: Double?
+    public let sliceHeight: Double?
 
-    public init(y: Double, label: String, kind: String) {
+    public init(
+        y: Double, label: String, kind: String,
+        sliceTop: Double? = nil, sliceHeight: Double? = nil
+    ) {
         self.y = y
         self.label = label
         self.kind = kind
+        self.sliceTop = sliceTop
+        self.sliceHeight = sliceHeight
+    }
+}
+
+public struct ScreenshotRegionGeometry: Equatable, Sendable {
+    public static let maximumDocumentExtent = 100_000_000.0
+    public static let maximumCaptureWidth = 4_096.0
+
+    public let x: Double
+    public let y: Double
+    public let width: Double
+    public let height: Double
+
+    public init(_ object: [String: JSONValue]) throws {
+        guard let x = object["x"]?.numberValue, let y = object["y"]?.numberValue,
+              let width = object["width"]?.numberValue,
+              let height = object["height"]?.numberValue,
+              x.isFinite, y.isFinite, width.isFinite, height.isFinite,
+              x >= 0, y >= 0, width > 0, height > 0,
+              x <= Self.maximumDocumentExtent, y <= Self.maximumDocumentExtent,
+              width <= Self.maximumCaptureWidth,
+              height <= Self.maximumDocumentExtent else {
+            throw ScreenshotSeriesError.invalidPlan
+        }
+        self.x = x
+        self.y = y
+        self.width = width
+        self.height = height
+    }
+
+    public var parameters: [String: JSONValue] {
+        [
+            "x": .number(x), "y": .number(y),
+            "width": .number(width), "height": .number(height),
+        ]
     }
 }
 
 public struct ScreenshotSeriesPlan: Equatable, Sendable {
+    public let document: String
     public let initialY: Double
     public let points: [ScreenshotSeriesPoint]
     public let truncated: Bool
     public let totalPoints: Int
+    public let region: ScreenshotRegionGeometry?
 
-    public init(initialY: Double, points: [ScreenshotSeriesPoint], truncated: Bool, totalPoints: Int) {
+    public init(
+        document: String, initialY: Double, points: [ScreenshotSeriesPoint], truncated: Bool,
+        totalPoints: Int, region: ScreenshotRegionGeometry? = nil
+    ) {
+        self.document = document
         self.initialY = initialY
         self.points = points
         self.truncated = truncated
         self.totalPoints = totalPoints
+        self.region = region
     }
 }
 
-public func parseScreenshotSeriesPlan(_ plan: JSONValue) throws -> ScreenshotSeriesPlan {
+public func parseScreenshotSeriesPlan(
+    _ plan: JSONValue, regionReference: String? = nil
+) throws -> ScreenshotSeriesPlan {
     guard case .object(let object) = plan,
           case .array(let values)? = object["points"] else {
         throw ScreenshotSeriesError.invalidPlan
     }
+    guard let document = object["document"]?.stringValue,
+          document.count == 32,
+          document.allSatisfy({ $0.isHexDigit }) else {
+        throw ScreenshotSeriesError.invalidPlan
+    }
     let initialY = object["initialY"]?.numberValue ?? 0
     guard initialY.isFinite, initialY >= 0 else { throw ScreenshotSeriesError.invalidPlan }
-    let points = try values.prefix(80).map { value -> ScreenshotSeriesPoint in
+    let region: ScreenshotRegionGeometry?
+    if case .object(let rawRegion)? = object["region"] {
+        region = try ScreenshotRegionGeometry(rawRegion)
+    } else {
+        region = nil
+    }
+    guard (regionReference != nil) == (region != nil) else {
+        throw ScreenshotSeriesError.invalidPlan
+    }
+    guard values.count <= 80 else { throw ScreenshotSeriesError.invalidPlan }
+    let points = try values.map { value -> ScreenshotSeriesPoint in
         guard case .object(let item) = value,
               let y = item["y"]?.numberValue, y.isFinite else {
             throw ScreenshotSeriesError.invalidPlan
         }
+        let sliceTop = item["sliceTop"]?.numberValue
+        let sliceHeight = item["sliceHeight"]?.numberValue
+        guard (sliceTop == nil) == (sliceHeight == nil) else {
+            throw ScreenshotSeriesError.invalidPlan
+        }
+        if let region, let sliceTop, let sliceHeight {
+            guard sliceTop.isFinite, sliceHeight.isFinite,
+                  sliceTop >= region.y, sliceHeight > 0,
+                  sliceTop + sliceHeight <= region.y + region.height + 0.5 else {
+                throw ScreenshotSeriesError.invalidPlan
+            }
+            _ = try BoundedScreenshotRectangle([
+                "x": .number(region.x), "y": .number(sliceTop),
+                "width": .number(region.width), "height": .number(sliceHeight),
+            ])
+        } else if region != nil || sliceTop != nil {
+            throw ScreenshotSeriesError.invalidPlan
+        }
         return ScreenshotSeriesPoint(
             y: y,
             label: String((item["label"]?.stringValue ?? "viewport").prefix(80)),
-            kind: String((item["kind"]?.stringValue ?? "viewport").prefix(32))
+            kind: String((item["kind"]?.stringValue ?? "viewport").prefix(32)),
+            sliceTop: sliceTop, sliceHeight: sliceHeight
         )
     }
     guard !points.isEmpty else { throw ScreenshotSeriesError.emptyPlan }
-    let truncated = object["truncated"]?.boolValue ?? (values.count > points.count)
-    let totalPointsValue = object["totalPoints"]?.numberValue ?? Double(values.count)
+    guard let truncated = object["truncated"]?.boolValue,
+          let totalPointsValue = object["totalPoints"]?.numberValue else {
+        throw ScreenshotSeriesError.invalidPlan
+    }
     guard totalPointsValue.isFinite, totalPointsValue.rounded(.towardZero) == totalPointsValue,
           totalPointsValue >= Double(points.count), totalPointsValue <= 100_000_000 else {
         throw ScreenshotSeriesError.invalidPlan
     }
+    guard truncated == (totalPointsValue > Double(points.count)) else {
+        throw ScreenshotSeriesError.invalidPlan
+    }
+    if let region {
+        try validateRegionTiling(
+            points: points, region: region,
+            truncated: truncated, totalPoints: Int(totalPointsValue)
+        )
+    }
     return ScreenshotSeriesPlan(
-        initialY: initialY,
+        document: document, initialY: initialY,
         points: points,
-        truncated: truncated || values.count > points.count,
-        totalPoints: Int(totalPointsValue)
+        truncated: truncated,
+        totalPoints: Int(totalPointsValue),
+        region: region
     )
 }
 
+private func validateRegionTiling(
+    points: [ScreenshotSeriesPoint], region: ScreenshotRegionGeometry,
+    truncated: Bool, totalPoints: Int
+) throws {
+    let tolerance = 0.5
+    guard let firstHeight = points.first?.sliceHeight,
+          let firstTop = points.first?.sliceTop,
+          abs(firstTop - region.y) <= tolerance,
+          firstHeight > 0 else {
+        throw ScreenshotSeriesError.invalidPlan
+    }
+    let leadingCount = max(0, points.count - 1)
+    guard !truncated || (points.count == 80 && totalPoints > points.count) else {
+        throw ScreenshotSeriesError.invalidPlan
+    }
+    for index in 0..<leadingCount {
+        guard let top = points[index].sliceTop,
+              let height = points[index].sliceHeight,
+              abs(height - firstHeight) <= tolerance else {
+            throw ScreenshotSeriesError.invalidPlan
+        }
+        if index == 0 {
+            guard abs(top - region.y) <= tolerance else {
+                throw ScreenshotSeriesError.invalidPlan
+            }
+        } else if let previousTop = points[index - 1].sliceTop,
+                  let previousHeight = points[index - 1].sliceHeight {
+            guard abs(top - (previousTop + previousHeight)) <= tolerance else {
+                throw ScreenshotSeriesError.invalidPlan
+            }
+        } else {
+            throw ScreenshotSeriesError.invalidPlan
+        }
+    }
+    guard let lastTop = points.last?.sliceTop,
+          let lastHeight = points.last?.sliceHeight,
+          abs(lastTop + lastHeight - (region.y + region.height)) <= tolerance,
+          lastHeight <= firstHeight + tolerance else {
+        throw ScreenshotSeriesError.invalidPlan
+    }
+    let expectedTotal = Int(ceil(region.height / firstHeight))
+    guard totalPoints == expectedTotal else { throw ScreenshotSeriesError.invalidPlan }
+    if truncated {
+        guard let previousTop = points[points.count - 2].sliceTop,
+              let previousHeight = points[points.count - 2].sliceHeight,
+              lastTop > previousTop + previousHeight else {
+            throw ScreenshotSeriesError.invalidPlan
+        }
+    } else if points.count > 1,
+              let previousTop = points[points.count - 2].sliceTop,
+              let previousHeight = points[points.count - 2].sliceHeight {
+        guard abs(lastTop - (previousTop + previousHeight)) <= tolerance else {
+            throw ScreenshotSeriesError.invalidPlan
+        }
+    }
+}
+
 public func screenshotSeriesPrefix(parameters: [String: JSONValue], mode: String) throws -> String {
     if let requested = parameters["outputPrefix"]?.stringValue {
         try validateArtifactPrefix(requested)
@@ -110,12 +263,14 @@ public func screenshotSeriesSummary(
     totalPoints: Int? = nil
 ) -> JSONValue {
     let positions = points.enumerated().map { index, point in
-        JSONValue.object([
-            "index": .number(Double(index + 1)),
-            "y": .number(point.y),
-            "label": .string(point.label),
-            "kind": .string(point.kind),
-        ])
+        var position: [String: JSONValue] = [
+            "index": .number(Double(index + 1)), "kind": .string(point.kind),
+        ]
+        if mode != "region" {
+            position["y"] = .number(point.y)
+            position["label"] = .string(point.label)
+        }
+        return JSONValue.object(position)
     }
     return .object([
         "series": .string(mode),
@@ -124,6 +279,7 @@ public func screenshotSeriesSummary(
         "positions": .array(positions),
         "truncated": .bool(truncated),
         "totalPoints": .number(Double(totalPoints ?? points.count)),
+        "untrustedContent": .bool(mode == "section" || mode == "region"),
     ])
 }
 
diff --git a/apps/headless/Tests/Fixtures/region-capture.html b/apps/headless/Tests/Fixtures/region-capture.html
new file mode 100644
index 0000000..6b2022e
--- /dev/null
+++ b/apps/headless/Tests/Fixtures/region-capture.html
@@ -0,0 +1,30 @@
+<!doctype html>
+<html lang="en">
+<head>
+  <meta charset="utf-8">
+  <meta name="viewport" content="width=device-width,initial-scale=1">
+  <title>Region capture fixture</title>
+  <style>
+    html, body { margin: 0; min-height: 100%; }
+    body { background: rgb(220, 20, 60); font: 16px sans-serif; }
+    main { padding: 120px 40px 240px; }
+    section {
+      box-sizing: border-box;
+      width: 640px;
+      height: 1600px;
+      padding: 32px;
+      overflow: hidden;
+      background: rgb(0, 180, 190);
+      color: rgb(5, 35, 40);
+    }
+  </style>
+</head>
+<body>
+  <main>
+    <section aria-label="Capture target">
+      <h1>Capture target</h1>
+      <p>The red page background must not appear in region artifacts.</p>
+    </section>
+  </main>
+</body>
+</html>
diff --git a/apps/headless/Tests/HeadlessProtocolTests/ProtocolTests.swift b/apps/headless/Tests/HeadlessProtocolTests/ProtocolTests.swift
index 84f67b6..a529837 100644
--- a/apps/headless/Tests/HeadlessProtocolTests/ProtocolTests.swift
+++ b/apps/headless/Tests/HeadlessProtocolTests/ProtocolTests.swift
@@ -318,6 +318,9 @@ private final class TestBrowserSession: BrowserEngineSession {
     var saveAlias: CredentialAlias?
     private(set) var credentialPromptCount = 0
     private(set) var savePromptCount = 0
+    private(set) var screenshotScrollCount = 0
+    var screenshotScrollFailureCall: Int?
+    var screenshotRegionFailure = false
 
     init(isolated: Bool = false) {
         hostIsolated = isolated
@@ -361,14 +364,40 @@ private final class TestBrowserSession: BrowserEngineSession {
     func hostScreenshot(
         parameters: [String: JSONValue], format: ScreenshotFormat, copyToClipboard: Bool
     ) throws -> BrowserScreenshot { BrowserScreenshot(data: Data("image".utf8)) }
+    func hostScreenshotRegionSlice(
+        reference: String, document: String, geometry: ScreenshotRegionGeometry,
+        point: ScreenshotSeriesPoint, format: ScreenshotFormat
+    ) throws -> BrowserScreenshot {
+        if screenshotRegionFailure {
+            throw HostError(code: .operationFailed, message: "region capture failed")
+        }
+        return BrowserScreenshot(data: Data("region".utf8))
+    }
     func hostRecordingFrame() throws -> Data { Data("frame".utf8) }
-    func hostScreenshotSeriesPlan(mode: String) throws -> JSONValue {
-        .object([
+    func hostScreenshotSeriesPlan(mode: String, region: String?) throws -> JSONValue {
+        var plan: [String: JSONValue] = [
+            "document": .string(String(repeating: "a", count: 32)),
             "initialY": .number(0), "totalPoints": .number(1), "truncated": .bool(false),
             "points": .array([.object(["y": .number(0), "label": .string("viewport")])]),
-        ])
+        ]
+        if mode == "region", region != nil {
+            plan["region"] = .object([
+                "x": .number(0), "y": .number(0), "width": .number(100), "height": .number(100),
+            ])
+            plan["points"] = .array([.object([
+                "y": .number(0), "label": .string("region 1"), "kind": .string("region"),
+                "sliceTop": .number(0), "sliceHeight": .number(100),
+            ])])
+        }
+        return .object(plan)
+    }
+    func hostScrollToCapturePoint(y: Double, document: String) throws -> JSONValue {
+        screenshotScrollCount += 1
+        if screenshotScrollFailureCall == screenshotScrollCount {
+            throw HostError(code: .operationFailed, message: "scroll restoration failed")
+        }
+        return .object(["y": .number(y)])
     }
-    func hostScrollToCapturePoint(y: Double) throws -> JSONValue { .object(["y": .number(y)]) }
     func hostQAReport() throws -> JSONValue { .object(["issues": .array([])]) }
     func hostQAClear() throws -> JSONValue { .object(["cleared": .bool(true)]) }
     func hostConsole(level: String, limit: Int, cursor: String?) throws -> JSONValue {
@@ -1009,6 +1038,37 @@ struct ProtocolTests {
             id: "valid-screenshot-series", command: .screenshot,
             parameters: ["series": .string("viewport"), "outputPrefix": .string("dashboard-scroll")]
         ).validate()
+        try CommandRequest(
+            id: "valid-region-screenshot-series", command: .screenshot,
+            parameters: [
+                "series": .string("region"), "region": .string("@r4"),
+                "outputPrefix": .string("checkout"),
+            ]
+        ).validate()
+        try expectThrows("region series should require a region reference") {
+            try CommandRequest(
+                id: "missing-region", command: .screenshot,
+                parameters: ["series": .string("region")]
+            ).validate()
+        }
+        try expectThrows("region references should require region series mode") {
+            try CommandRequest(
+                id: "unused-region", command: .screenshot,
+                parameters: ["series": .string("viewport"), "region": .string("@r4")]
+            ).validate()
+        }
+        try expectThrows("malformed screenshot region references should fail") {
+            try CommandRequest(
+                id: "bad-region", command: .screenshot,
+                parameters: ["series": .string("region"), "region": .string("@r../4")]
+            ).validate()
+        }
+        try expectThrows("screenshot region references should require ASCII digits") {
+            try CommandRequest(
+                id: "unicode-region", command: .screenshot,
+                parameters: ["series": .string("region"), "region": .string("@r٤")]
+            ).validate()
+        }
         try CommandRequest(
             id: "valid-jpeg-screenshot", command: .screenshot,
             parameters: ["format": .string("jpeg"), "output": .string("dashboard.jpeg")]
@@ -1396,6 +1456,20 @@ struct ProtocolTests {
         ])
         try expect(sectionSeries.request?.parameters["series"] == .string("section"), "section series should parse")
         try expect(sectionSeries.request?.parameters["outputPrefix"] == .string("dashboard-sections"), "series prefix should strip image extension")
+        let regionSeries = try CLIParser().parse([
+            "screenshot", "--by-region", "@r4", "--output", "checkout",
+        ])
+        try expect(regionSeries.request?.parameters["series"] == .string("region"), "region series should parse")
+        try expect(regionSeries.request?.parameters["region"] == .string("@r4"), "region reference should parse")
+        try expectThrows("region screenshot must reject malformed references") {
+            _ = try CLIParser().parse(["screenshot", "--by-region", "main"])
+        }
+        try expectThrows("region screenshot must reject Unicode digits") {
+            _ = try CLIParser().parse(["screenshot", "--by-region", "@r٤"])
+        }
+        try expectThrows("region screenshot must reject another series mode") {
+            _ = try CLIParser().parse(["screenshot", "--by-region", "@r4", "--by-section"])
+        }
         try expectThrows("series screenshot must reject element targets") {
             _ = try CLIParser().parse(["screenshot", "--every-viewport", "@e1"])
         }
@@ -3385,6 +3459,7 @@ struct ProtocolTests {
 
     static func screenshotSeriesHelpers() throws {
         let rawPlan = JSONValue.object([
+            "document": .string(String(repeating: "a", count: 32)),
             "initialY": .number(240),
             "truncated": .bool(true),
             "totalPoints": .number(100),
@@ -3399,10 +3474,136 @@ struct ProtocolTests {
         try expect(plan.truncated && plan.totalPoints == 100, "series plans should report truncation")
         try expectThrows("invalid initial scroll positions should fail") {
             _ = try parseScreenshotSeriesPlan(.object([
+                "document": .string(String(repeating: "a", count: 32)),
                 "initialY": .number(-1),
                 "points": .array([.object(["y": .number(0)])]),
             ]))
         }
+        let regionPlan = try parseScreenshotSeriesPlan(.object([
+            "document": .string(String(repeating: "b", count: 32)),
+            "initialY": .number(20), "totalPoints": .number(2),
+            "truncated": .bool(false),
+            "region": .object([
+                "x": .number(10), "y": .number(100),
+                "width": .number(500), "height": .number(900),
+            ]),
+            "points": .array([
+                .object([
+                    "y": .number(100), "kind": .string("region"),
+                    "sliceTop": .number(100), "sliceHeight": .number(600),
+                ]),
+                .object([
+                    "y": .number(700), "kind": .string("region"),
+                    "sliceTop": .number(700), "sliceHeight": .number(300),
+                ]),
+            ]),
+        ]), regionReference: "@r4")
+        try expect(regionPlan.region?.width == 500, "region geometry should remain bounded")
+        let fractionalSliceHeight = 10.0
+        let fractionalRegionHeight = fractionalSliceHeight * 80 + 0.25
+        var fractionalPoints = (0..<79).map { index in
+            JSONValue.object([
+                "y": .number(Double(index) * fractionalSliceHeight),
+                "sliceTop": .number(Double(index) * fractionalSliceHeight),
+                "sliceHeight": .number(fractionalSliceHeight),
+            ])
+        }
+        fractionalPoints.append(.object([
+            "y": .number(fractionalRegionHeight - fractionalSliceHeight),
+            "sliceTop": .number(fractionalRegionHeight - fractionalSliceHeight),
+            "sliceHeight": .number(fractionalSliceHeight),
+        ]))
+        let fractionalPlan = try parseScreenshotSeriesPlan(.object([
+            "document": .string(String(repeating: "c", count: 32)),
+            "totalPoints": .number(81), "truncated": .bool(true),
+            "region": .object([
+                "x": .number(0), "y": .number(0),
+                "width": .number(500), "height": .number(fractionalRegionHeight),
+            ]),
+            "points": .array(fractionalPoints),
+        ]), regionReference: "@r5")
+        try expect(
+            fractionalPlan.truncated && fractionalPlan.totalPoints == 81,
+            "fractional omitted spans should remain valid truncated plans"
+        )
+        let regionSummary = screenshotSeriesSummary(
+            mode: "region", points: regionPlan.points, artifacts: []
+        )
+        guard case .object(let regionSummaryObject) = regionSummary,
+              case .array(let positions)? = regionSummaryObject["positions"],
+              case .object(let firstPosition)? = positions.first else {
+            throw TestFailure(description: "region summary should contain bounded positions")
+        }
+        try expect(firstPosition["y"] == nil, "region summaries must not expose page coordinates")
+        try expect(firstPosition["label"] == nil, "region summaries must not expose page labels")
+        try expectThrows("region plans with gaps should fail") {
+            _ = try parseScreenshotSeriesPlan(.object([
+                "document": .string(String(repeating: "b", count: 32)),
+                "totalPoints": .number(2), "truncated": .bool(false),
+                "region": .object([
+                    "x": .number(10), "y": .number(100),
+                    "width": .number(500), "height": .number(900),
+                ]),
+                "points": .array([
+                    .object([
+                        "y": .number(100), "sliceTop": .number(100),
+                        "sliceHeight": .number(600),
+                    ]),
+                    .object([
+                        "y": .number(750), "sliceTop": .number(750),
+                        "sliceHeight": .number(250),
+                    ]),
+                ]),
+            ]), regionReference: "@r4")
+        }
+        try expectThrows("region plans with overlaps should fail") {
+            _ = try parseScreenshotSeriesPlan(.object([
+                "document": .string(String(repeating: "b", count: 32)),
+                "totalPoints": .number(2), "truncated": .bool(false),
+                "region": .object([
+                    "x": .number(10), "y": .number(100),
+                    "width": .number(500), "height": .number(900),
+                ]),
+                "points": .array([
+                    .object([
+                        "y": .number(100), "sliceTop": .number(100),
+                        "sliceHeight": .number(600),
+                    ]),
+                    .object([
+                        "y": .number(650), "sliceTop": .number(650),
+                        "sliceHeight": .number(350),
+                    ]),
+                ]),
+            ]), regionReference: "@r4")
+        }
+        try expectThrows("region plans wider than the portable capture bound should fail") {
+            _ = try parseScreenshotSeriesPlan(.object([
+                "document": .string(String(repeating: "b", count: 32)),
+                "totalPoints": .number(1), "truncated": .bool(false),
+                "region": .object([
+                    "x": .number(10), "y": .number(100),
+                    "width": .number(4097), "height": .number(600),
+                ]),
+                "points": .array([.object([
+                    "y": .number(100), "sliceTop": .number(100),
+                    "sliceHeight": .number(600),
+                ])]),
+            ]), regionReference: "@r4")
+        }
+        try expectThrows("region slices outside frozen geometry should fail") {
+            _ = try parseScreenshotSeriesPlan(.object([
+                "document": .string(String(repeating: "b", count: 32)),
+                "totalPoints": .number(1), "truncated": .bool(false),
+                "region": .object([
+                    "x": .number(10), "y": .number(100),
+                    "width": .number(500), "height": .number(900),
+                ]),
+                "points": .array([.object([
+                    "y": .number(100), "sliceTop": .number(900),
+                    "sliceHeight": .number(200),
+                ])]),
+            ]), regionReference: "@r4")
+        }
 
         let root = "/tmp/headless-series-test-\(UUID().uuidString)"
         defer { try? FileManager.default.removeItem(atPath: root) }
@@ -3428,6 +3629,70 @@ struct ProtocolTests {
             !FileManager.default.fileExists(atPath: root + "/" + firstName),
             "partial series reservations should be removed after a later collision"
         )
+        let atomicRoot = root + "/atomic"
+        let successSession = TestBrowserSession()
+        let successCore = HostCore(
+            engine: TestBrowserEngine(),
+            artifacts: try ArtifactStore(environment: ["HEADLESS_ARTIFACT_DIR": atomicRoot]),
+            defaultSession: successSession,
+            shutdownHandler: {}
+        )
+        let successfulCapture = successCore.handle(CommandRequest(
+            command: .screenshot,
+            parameters: [
+                "series": .string("region"), "region": .string("@r4"),
+                "outputPrefix": .string("capture-success"),
+            ]
+        ))
+        successCore.stop()
+        try expect(successfulCapture.ok, "valid region capture should succeed")
+        try expect(successSession.screenshotScrollCount == 2, "successful capture must restore scroll")
+
+        let restorationSession = TestBrowserSession()
+        restorationSession.screenshotScrollFailureCall = 2
+        let restorationCore = HostCore(
+            engine: TestBrowserEngine(),
+            artifacts: try ArtifactStore(environment: ["HEADLESS_ARTIFACT_DIR": atomicRoot]),
+            defaultSession: restorationSession,
+            shutdownHandler: {}
+        )
+        let restorationFailure = restorationCore.handle(CommandRequest(
+            command: .screenshot,
+            parameters: [
+                "series": .string("viewport"), "outputPrefix": .string("restore-failure"),
+            ]
+        ))
+        restorationCore.stop()
+        try expect(!restorationFailure.ok, "scroll restoration failure must fail the series")
+        let restorationArtifacts = try FileManager.default.contentsOfDirectory(atPath: atomicRoot)
+        try expect(
+            !restorationArtifacts.contains(where: { $0.hasPrefix("restore-failure") }),
+            "scroll restoration failure must remove completed artifacts"
+        )
+
+        let captureSession = TestBrowserSession()
+        captureSession.screenshotRegionFailure = true
+        let captureCore = HostCore(
+            engine: TestBrowserEngine(),
+            artifacts: try ArtifactStore(environment: ["HEADLESS_ARTIFACT_DIR": atomicRoot]),
+            defaultSession: captureSession,
+            shutdownHandler: {}
+        )
+        let captureFailure = captureCore.handle(CommandRequest(
+            command: .screenshot,
+            parameters: [
+                "series": .string("region"), "region": .string("@r4"),
+                "outputPrefix": .string("capture-failure"),
+            ]
+        ))
+        captureCore.stop()
+        try expect(!captureFailure.ok, "region capture failure must fail the series")
+        try expect(captureSession.screenshotScrollCount == 2, "failed capture must still restore scroll")
+        let captureArtifacts = try FileManager.default.contentsOfDirectory(atPath: atomicRoot)
+        try expect(
+            !captureArtifacts.contains(where: { $0.hasPrefix("capture-failure") }),
+            "region capture failure must remove every reservation"
+        )
         try expect(RecordingFormat.webm.videoCodec == "vp9", "recording metadata should report the codec, not encoder")
         try expect(
             agentRuntimeJavaScript.contains("hints.push('select')"),
diff --git a/apps/headless/Tests/agent-runtime.test.mjs b/apps/headless/Tests/agent-runtime.test.mjs
index 8652d1d..04ecc6b 100644
--- a/apps/headless/Tests/agent-runtime.test.mjs
+++ b/apps/headless/Tests/agent-runtime.test.mjs
@@ -29,6 +29,11 @@ window.getComputedStyle = element => ({
   display: element.style?.display || 'block',
   visibility: element.style?.visibility || 'visible',
   opacity: element.style?.opacity || '1',
+  overflow: element.style?.overflow || 'visible',
+  overflowX: element.style?.overflowX || element.style?.overflow || 'visible',
+  overflowY: element.style?.overflowY || element.style?.overflow || 'visible',
+  clipPath: element.style?.clipPath || 'none',
+  contain: element.style?.contain || 'none',
   getPropertyValue(property) { return element.style?.getPropertyValue(property) || ''; },
 });
 const positions = new WeakMap();
@@ -530,6 +535,152 @@ for (let index = 1; index < sectionPlan.points.length; index += 1) {
   );
 }
 
+// Region series bind an outline ref and one document to exact vertical slices.
+const captureRegion = window.document.createElement('section');
+captureRegion.setAttribute('aria-label', 'Region capture fixture');
+captureRegion.textContent = 'Only these pixels belong in the region series.';
+const captureRegionContainer = window.document.createElement('div');
+window.document.body.append(captureRegionContainer);
+captureRegionContainer.append(captureRegion);
+let captureRegionTop = 400;
+let captureRegionLeft = 40;
+let captureRegionWidth = 700;
+let captureRegionHeight = window.innerHeight * 2 + 100;
+let captureRegionContainerHeight = captureRegionHeight + 100;
+captureRegionContainer.getBoundingClientRect = () => ({
+  x: captureRegionLeft,
+  y: captureRegionTop - window.scrollY,
+  top: captureRegionTop - window.scrollY,
+  left: captureRegionLeft,
+  right: captureRegionLeft + captureRegionWidth,
+  bottom: captureRegionTop - window.scrollY + captureRegionContainerHeight,
+  width: captureRegionWidth,
+  height: captureRegionContainerHeight,
+});
+captureRegion.getBoundingClientRect = () => ({
+  x: captureRegionLeft,
+  y: captureRegionTop - window.scrollY,
+  top: captureRegionTop - window.scrollY,
+  left: captureRegionLeft,
+  right: captureRegionLeft + captureRegionWidth,
+  bottom: captureRegionTop - window.scrollY + captureRegionHeight,
+  width: captureRegionWidth,
+  height: captureRegionHeight,
+});
+const captureOutline = agent.snapshot(false, false, {
+  context: 'outline', task: 'Region capture fixture', limit: 20, budget: 1200,
+});
+const captureRegionRef = captureOutline.regions.find(
+  region => region.name === 'Region capture fixture',
+)?.ref;
+assert.match(captureRegionRef ?? '', /^@r\d+$/);
+window.scrollY = 0;
+const regionPlan = agent.screenshotPlan({mode: 'region', region: captureRegionRef});
+assert.equal(regionPlan.points.length, 3);
+assert.equal(regionPlan.truncated, false);
+assert.equal(regionPlan.region.height, captureRegionHeight);
+assert.equal(regionPlan.points.at(-1).sliceTop + regionPlan.points.at(-1).sliceHeight,
+  captureRegionTop + captureRegionHeight);
+const firstRegionPoint = regionPlan.points[0];
+await agent.scrollToCapturePoint({y: firstRegionPoint.y, document: regionPlan.document});
+const firstRegionSlice = agent.regionSlice({
+  region: captureRegionRef,
+  document: regionPlan.document,
+  geometry: regionPlan.region,
+  sliceTop: firstRegionPoint.sliceTop,
+  sliceHeight: firstRegionPoint.sliceHeight,
+});
+assert.equal(firstRegionSlice.viewport.x, captureRegionLeft);
+assert.equal(firstRegionSlice.viewport.y, 0);
+assert.equal(firstRegionSlice.viewport.width, captureRegionWidth);
+assert.equal(firstRegionSlice.viewport.height, window.innerHeight);
+window.scrollY += 10;
+assert.throws(
+  () => agent.regionSlice({
+    region: captureRegionRef,
+    document: regionPlan.document,
+    geometry: regionPlan.region,
+    sliceTop: firstRegionPoint.sliceTop,
+    sliceHeight: firstRegionPoint.sliceHeight,
+    viewport: firstRegionSlice.viewport,
+  }),
+  error => error.headlessCode === 'REGION_NOT_FOUND' && /viewport changed/.test(error.message),
+);
+window.scrollY -= 10;
+assert.throws(
+  () => agent.regionSlice({
+    region: captureRegionRef,
+    document: '0'.repeat(32),
+    geometry: regionPlan.region,
+    sliceTop: firstRegionPoint.sliceTop,
+    sliceHeight: firstRegionPoint.sliceHeight,
+  }),
+  error => error.headlessCode === 'REGION_NOT_FOUND' && /document changed/.test(error.message),
+);
+captureRegionHeight += 10;
+assert.throws(
+  () => agent.regionSlice({
+    region: captureRegionRef,
+    document: regionPlan.document,
+    geometry: regionPlan.region,
+    sliceTop: firstRegionPoint.sliceTop,
+    sliceHeight: firstRegionPoint.sliceHeight,
+  }),
+  error => error.headlessCode === 'REGION_NOT_FOUND' && /geometry changed/.test(error.message),
+);
+captureRegionHeight = window.innerHeight * 100;
+const truncatedRegionPlan = agent.screenshotPlan({mode: 'region', region: captureRegionRef});
+assert.equal(truncatedRegionPlan.points.length, 80);
+assert.equal(truncatedRegionPlan.truncated, true);
+assert(truncatedRegionPlan.totalPoints > truncatedRegionPlan.points.length);
+assert.equal(
+  truncatedRegionPlan.points.at(-1).sliceTop + truncatedRegionPlan.points.at(-1).sliceHeight,
+  captureRegionTop + captureRegionHeight,
+);
+captureRegionHeight = window.innerHeight * 2 + 100;
+captureRegionWidth = 4097;
+assert.throws(
+  () => agent.screenshotPlan({mode: 'region', region: captureRegionRef}),
+  error => error.headlessCode === 'REGION_NOT_FOUND' && /invalid capture geometry/.test(error.message),
+);
+captureRegionWidth = 700;
+captureRegionContainer.style.overflow = 'hidden';
+captureRegionContainerHeight = captureRegionHeight - 1;
+assert.throws(
+  () => agent.screenshotPlan({mode: 'region', region: captureRegionRef}),
+  error => error.headlessCode === 'REGION_NOT_FOUND' && /invalid capture geometry/.test(error.message),
+);
+captureRegionContainer.style.overflow = 'visible';
+captureRegionContainerHeight = captureRegionHeight + 100;
+captureRegionLeft = -1;
+assert.throws(
+  () => agent.screenshotPlan({mode: 'region', region: captureRegionRef}),
+  error => error.headlessCode === 'REGION_NOT_FOUND' && /invalid capture geometry/.test(error.message),
+);
+captureRegionLeft = 40;
+captureRegion.style.display = 'none';
+assert.throws(
+  () => agent.screenshotPlan({mode: 'region', region: captureRegionRef}),
+  error => error.headlessCode === 'REGION_NOT_FOUND' && /no longer visible/.test(error.message),
+);
+captureRegion.style.display = '';
+assert.throws(
+  () => agent.screenshotPlan({mode: 'region', region: '@r999999'}),
+  error => error.headlessCode === 'REGION_NOT_FOUND' && /unknown/.test(error.message),
+);
+const refreshedCaptureOutline = agent.snapshot(false, false, {
+  context: 'outline', task: 'Region capture fixture', limit: 20, budget: 1200,
+});
+const refreshedCaptureRegionRef = refreshedCaptureOutline.regions.find(
+  region => region.name === 'Region capture fixture',
+)?.ref;
+assert.equal(refreshedCaptureRegionRef, captureRegionRef);
+captureRegion.remove();
+assert.throws(
+  () => agent.screenshotPlan({mode: 'region', region: refreshedCaptureRegionRef}),
+  error => error.headlessCode === 'REGION_NOT_FOUND' && /no longer visible/.test(error.message),
+);
+
 // Once result arrays are exhausted, budget pruning must fall back to chopping
 // page text instead of returning an oversized response.
 const budgetedText = agent.snapshot(false, true, {context: 'full', limit: 1, budget: 256});
diff --git a/apps/headless/Tests/fixture-server.mjs b/apps/headless/Tests/fixture-server.mjs
index 4dbf90c..4f8fc1c 100644
--- a/apps/headless/Tests/fixture-server.mjs
+++ b/apps/headless/Tests/fixture-server.mjs
@@ -11,6 +11,7 @@ const routes = new Map([
   ['/large-document', 'large-document.html'],
   ['/select', 'select.html'],
   ['/network-idle', 'network-idle.html'],
+  ['/region-capture', 'region-capture.html'],
   ['/auth-state', 'auth-state.html'],
   ['/auth-login', 'auth-login.html'],
   ['/file-upload', 'file-upload.html'],
diff --git a/apps/headless/Tests/linux-e2e.sh b/apps/headless/Tests/linux-e2e.sh
index 949cde5..49fc31a 100755
--- a/apps/headless/Tests/linux-e2e.sh
+++ b/apps/headless/Tests/linux-e2e.sh
@@ -12,11 +12,12 @@ SUPERVISED_LAUNCHER_PID=""
 
 FIXTURE_ROOT="$(mktemp -d /tmp/headless-fixture.XXXXXX)"
 INSTALL_ROOT="$(mktemp -d /tmp/headless-install.XXXXXX)"
-mkdir -p "$FIXTURE_ROOT/designers/dashboard" "$FIXTURE_ROOT/next" "$FIXTURE_ROOT/hostile" "$FIXTURE_ROOT/large-document" "$FIXTURE_ROOT/select" "$FIXTURE_ROOT/network-idle" "$FIXTURE_ROOT/trusted-input" "$FIXTURE_ROOT/auth-state" "$FIXTURE_ROOT/auth-login" "$FIXTURE_ROOT/file-upload" "$FIXTURE_ROOT/api" "$FIXTURE_ROOT/allowlist-exits" "$FIXTURE_ROOT/allowlist-redirect"
+mkdir -p "$FIXTURE_ROOT/designers/dashboard" "$FIXTURE_ROOT/next" "$FIXTURE_ROOT/hostile" "$FIXTURE_ROOT/large-document" "$FIXTURE_ROOT/region-capture" "$FIXTURE_ROOT/select" "$FIXTURE_ROOT/network-idle" "$FIXTURE_ROOT/trusted-input" "$FIXTURE_ROOT/auth-state" "$FIXTURE_ROOT/auth-login" "$FIXTURE_ROOT/file-upload" "$FIXTURE_ROOT/api" "$FIXTURE_ROOT/allowlist-exits" "$FIXTURE_ROOT/allowlist-redirect"
 cp /opt/headless/fixtures/dashboard.html "$FIXTURE_ROOT/designers/dashboard/index.html"
 cp /opt/headless/fixtures/next.html "$FIXTURE_ROOT/next/index.html"
 cp /opt/headless/fixtures/hostile.html "$FIXTURE_ROOT/hostile/index.html"
 cp /opt/headless/fixtures/large-document.html "$FIXTURE_ROOT/large-document/index.html"
+cp /opt/headless/fixtures/region-capture.html "$FIXTURE_ROOT/region-capture/index.html"
 cp /opt/headless/fixtures/select.html "$FIXTURE_ROOT/select/index.html"
 cp /opt/headless/fixtures/network-idle.html "$FIXTURE_ROOT/network-idle/index.html"
 cp /opt/headless/fixtures/trusted-input.html "$FIXTURE_ROOT/trusted-input/index.html"
@@ -509,6 +510,7 @@ if headless --session qa screenshot --format pdf --role button --name Continue -
   echo "element PDF capture was not rejected" >&2
   exit 1
 fi
+STEP="screenshot-series"
 VIEWPORT_SERIES="$(headless --session qa screenshot --every-viewport --format jpg --output scroll-capture)"
 echo "$VIEWPORT_SERIES" | grep -q '"series":"viewport"'
 echo "$VIEWPORT_SERIES" | grep -q '"name":"scroll-capture-001.jpg"'
@@ -519,6 +521,63 @@ SECTION_SERIES="$(headless --session qa screenshot --by-section --output section
 echo "$SECTION_SERIES" | grep -q '"series":"section"'
 SECTION_CAPTURE_COUNT="$(find "$HEADLESS_ARTIFACT_DIR" -maxdepth 1 -name 'section-capture-*.png' | wc -l | tr -d ' ')"
 test "$SECTION_CAPTURE_COUNT" -ge 3
+headless --session qa visit http://127.0.0.1:41739/region-capture | grep -q 'Region capture fixture'
+REGION_OUTLINE="$(headless --session qa inspect --context outline --task 'Capture target' --limit 8 --budget 900)"
+CAPTURE_REGION="$(printf %s "$REGION_OUTLINE" | python3 -c '
+import json, sys
+regions = json.load(sys.stdin)["result"]["regions"]
+print(next(region["ref"] for region in regions
+           if region.get("role") == "region" and region.get("name") == "Capture target"))
+')"
+test -n "$CAPTURE_REGION"
+REGION_SERIES="$(headless --session qa screenshot --by-region "$CAPTURE_REGION" --output region-capture)"
+echo "$REGION_SERIES" | grep -q '"series":"region"'
+echo "$REGION_SERIES" | grep -q '"count":3'
+echo "$REGION_SERIES" | grep -q '"totalPoints":3'
+echo "$REGION_SERIES" | grep -q '"untrustedContent":true'
+if echo "$REGION_SERIES" | grep -q '"label"\|"y"'; then
+  echo "region screenshot response exposed page labels or coordinates" >&2
+  exit 1
+fi
+REGION_CAPTURE_COUNT="$(find "$HEADLESS_ARTIFACT_DIR" -maxdepth 1 -name 'region-capture-*.png' | wc -l | tr -d ' ')"
+test "$REGION_CAPTURE_COUNT" -eq 3
+python3 - "$HEADLESS_ARTIFACT_DIR" <<'PY'
+import glob
+import os
+import struct
+import sys
+
+paths = sorted(glob.glob(os.path.join(sys.argv[1], "region-capture-*.png")))
+dimensions = []
+for path in paths:
+    with open(path, "rb") as artifact:
+        header = artifact.read(24)
+    dimensions.append(struct.unpack(">II", header[16:24]))
+assert len(dimensions) == 3, dimensions
+assert all(width == 640 for width, _ in dimensions), dimensions
+assert sum(height for _, height in dimensions) == 1600, dimensions
+assert dimensions[0][1] == dimensions[1][1], dimensions
+assert 0 < dimensions[-1][1] < dimensions[0][1], dimensions
+PY
+for artifact in "$HEADLESS_ARTIFACT_DIR"/region-capture-*.png; do
+  if ! ffmpeg -v error -i "$artifact" \
+      -f rawvideo -pix_fmt rgb24 - 2>/dev/null | python3 -c '
+import sys
+pixels = sys.stdin.buffer.read()
+has_page_red = any(pixels[index] > 180 and pixels[index + 1] < 80 and pixels[index + 2] < 100
+                   for index in range(0, len(pixels) - 2, 3))
+sys.exit(0 if pixels and not has_page_red else 1)
+'; then
+    echo "region screenshot included pixels outside the target: $artifact" >&2
+    exit 1
+  fi
+done
+if REGION_ERROR="$(headless --session qa screenshot --by-region @r999999 --output missing-region 2>&1)"; then
+  echo "unknown screenshot region unexpectedly succeeded" >&2
+  exit 1
+fi
+echo "$REGION_ERROR" | grep -q 'REGION_NOT_FOUND'
+headless --session qa visit http://127.0.0.1:41739/designers/dashboard | grep -q 'Designers Dashboard'
 headless --session qa visual compare viewport.png viewport.png --output visual-diff.png | grep -q '"name":"visual-diff.png"'
 test -s "$HEADLESS_ARTIFACT_DIR/visual-diff.png"
 headless --session qa performance get | grep -q '"webVitals"'
diff --git a/apps/headless/Tests/macos-e2e.sh b/apps/headless/Tests/macos-e2e.sh
index 6b02c37..3503f92 100755
--- a/apps/headless/Tests/macos-e2e.sh
+++ b/apps/headless/Tests/macos-e2e.sh
@@ -1445,6 +1445,63 @@ SECTION_SERIES="$("$CLI" --session qa screenshot --by-section --output section-c
 echo "$SECTION_SERIES" | grep -q '"series":"section"'
 SECTION_CAPTURE_COUNT="$(find "$HEADLESS_ARTIFACT_DIR" -maxdepth 1 -name 'section-capture-*.png' | wc -l | tr -d ' ')"
 test "$SECTION_CAPTURE_COUNT" -ge 3
+"$CLI" --session qa visit "http://127.0.0.1:$PORT/region-capture" | grep -q 'Region capture fixture'
+REGION_OUTLINE="$("$CLI" --session qa inspect --context outline --task 'Capture target' --limit 8 --budget 900)"
+CAPTURE_REGION="$(printf %s "$REGION_OUTLINE" | python3 -c '
+import json, sys
+regions = json.load(sys.stdin)["result"]["regions"]
+print(next(region["ref"] for region in regions
+           if region.get("role") == "region" and region.get("name") == "Capture target"))
+')"
+test -n "$CAPTURE_REGION"
+REGION_SERIES="$("$CLI" --session qa screenshot --by-region "$CAPTURE_REGION" --output region-capture)"
+echo "$REGION_SERIES" | grep -q '"series":"region"'
+echo "$REGION_SERIES" | grep -q '"count":3'
+echo "$REGION_SERIES" | grep -q '"totalPoints":3'
+echo "$REGION_SERIES" | grep -q '"untrustedContent":true'
+if echo "$REGION_SERIES" | grep -q '"label"\|"y"'; then
+  echo "region screenshot response exposed page labels or coordinates" >&2
+  fail
+fi
+REGION_CAPTURE_COUNT="$(find "$HEADLESS_ARTIFACT_DIR" -maxdepth 1 -name 'region-capture-*.png' | wc -l | tr -d ' ')"
+test "$REGION_CAPTURE_COUNT" -eq 3
+python3 - "$HEADLESS_ARTIFACT_DIR" <<'PY'
+import glob
+import os
+import struct
+import sys
+
+paths = sorted(glob.glob(os.path.join(sys.argv[1], "region-capture-*.png")))
+dimensions = []
+for path in paths:
+    with open(path, "rb") as artifact:
+        header = artifact.read(24)
+    dimensions.append(struct.unpack(">II", header[16:24]))
+assert len(dimensions) == 3, dimensions
+assert all(width == 640 for width, _ in dimensions), dimensions
+assert sum(height for _, height in dimensions) == 1600, dimensions
+assert dimensions[0][1] == dimensions[1][1], dimensions
+assert 0 < dimensions[-1][1] < dimensions[0][1], dimensions
+PY
+for artifact in "$HEADLESS_ARTIFACT_DIR"/region-capture-*.png; do
+  if ! ffmpeg -v error -i "$artifact" \
+      -f rawvideo -pix_fmt rgb24 - 2>/dev/null | python3 -c '
+import sys
+pixels = sys.stdin.buffer.read()
+has_page_red = any(pixels[index] > 180 and pixels[index + 1] < 80 and pixels[index + 2] < 100
+                   for index in range(0, len(pixels) - 2, 3))
+sys.exit(0 if pixels and not has_page_red else 1)
+'; then
+    echo "region screenshot included pixels outside the target: $artifact" >&2
+    fail
+  fi
+done
+if REGION_ERROR="$("$CLI" --session qa screenshot --by-region @r999999 --output missing-region 2>&1)"; then
+  echo "unknown screenshot region unexpectedly succeeded" >&2
+  fail
+fi
+echo "$REGION_ERROR" | grep -q 'REGION_NOT_FOUND'
+"$CLI" --session qa visit "http://127.0.0.1:$PORT/designers/dashboard" | grep -q 'Designers Dashboard'
 "$CLI" --session qa visual compare viewport.png viewport.png --output visual-diff.png | grep -q '"name":"visual-diff.png"'
 test -s "$HEADLESS_ARTIFACT_DIR/visual-diff.png"
 "$CLI" --session qa performance get | grep -q '"webVitals"'
diff --git a/apps/headless/docs/COMMANDS.md b/apps/headless/docs/COMMANDS.md
index b7159e8..b224808 100644
--- a/apps/headless/docs/COMMANDS.md
+++ b/apps/headless/docs/COMMANDS.md
@@ -274,7 +274,7 @@ back | reload
 capture-info
 screenshot [REF | --role ROLE --name NAME | --full-page] [--format png|jpg|jpeg] [--output FILE] [--clipboard]
 screenshot --full-page --format pdf [--output FILE.pdf]
-screenshot --every-viewport|--by-section [--format png|jpg|jpeg] [--output PREFIX]
+screenshot --every-viewport|--by-section|--by-region @rN [--format png|jpg|jpeg] [--output PREFIX]
 artifacts list [--limit N] [--cursor CURSOR]
 record start [--fps N] [--format mp4|mov|webm|gif] [--quality fast|balanced|high] [--output FILE]
 record status | record stop [--output FILE]
@@ -290,6 +290,14 @@ report create [--output REPORT.json]
   file reader or a download manager.
 - `--clipboard` capture is macOS only. Linux rejects clipboard capture because
   VM clipboards are not a reliable boundary.
+- `--by-region @rN` captures the referenced outline region's rendered border
+  box as vertical slices on both engines. The region must fit horizontally in
+  the viewport and cannot exceed 4096 CSS pixels in width; nested overflow is
+  not expanded. Region refs that are stale,
+  hidden, clipped, or change geometry during capture fail the whole series.
+- Region series reserve every artifact before capture and remove them all on
+  capture, write, validation, or scroll-restoration failure. `truncated: true`
+  means the first 79 and final slices were returned with the middle omitted.
 - PDF screenshots and element-scoped capture follow the engine matrix reported
   by `capabilities`.
 - The recorder captures browser pixels through ffmpeg only: no OS chrome, no
diff --git a/apps/headless/docs/P1.md b/apps/headless/docs/P1.md
index 8691afb..d85d307 100644
--- a/apps/headless/docs/P1.md
+++ b/apps/headless/docs/P1.md
@@ -87,6 +87,7 @@ headless --session qa inspect --context full --text
 headless --session qa screenshot --full-page --output dashboard.png
 headless --session qa screenshot --every-viewport --output dashboard-scroll
 headless --session qa screenshot --by-section --output dashboard-sections
+headless --session qa screenshot --by-region @r4 --output checkout-region
 headless --session qa record start --fps 10
 headless --session qa record status
 headless --session qa record stop --output dashboard-flow.mp4
@@ -131,6 +132,13 @@ around visible headings, sections, and regions. Series output uses a prefix, not
 a single filename, restores the original scroll position, and still refuses
 paths or overwrites. Series screenshots support PNG and JPG/JPEG; PDF requires
 `--full-page` and cannot target an element.
+`screenshot --by-region @rN --output PREFIX` instead captures the referenced
+element's exact rendered border box as bounded vertical slices, with a portable
+4096 CSS-pixel width ceiling. It rejects stale, hidden, horizontally clipped,
+or changing regions and removes every
+artifact if capture or scroll restoration fails. Nested overflow outside the
+border box is not included. Truncated output contains the first 79 slices and
+the final slice, with `totalPoints` reporting the full plan.
 
 ## Context pruning
 
diff --git a/docs/roadmap/architecture-decisions.md b/docs/roadmap/architecture-decisions.md
index e181d14..acd928f 100644
--- a/docs/roadmap/architecture-decisions.md
+++ b/docs/roadmap/architecture-decisions.md
@@ -1124,6 +1124,50 @@ for logging, even though callers still control their own CLI process arguments.
 
 ---
 
+## 36. Region screenshots are bounded, exact-crop series
+
+**Decision:** `screenshot --by-region @rN` is a third screenshot-series mode
+alongside viewport and section series. It accepts only an opaque region
+reference issued by the current page runtime. It never accepts selectors,
+element references, roles, or names.
+
+The isolated runtime freezes the region's document geometry and divides its
+vertical extent into at most 80 bounded image slices. Each slice is no taller
+than the viewport or the shared screenshot pixel limit permits, and the final
+region extent is included when truncation is not required. Before each capture,
+the runtime resolves the same region reference again, requires it to remain
+connected and visible, verifies that its geometry has not changed, and returns
+only the exact slice rectangle. Regions that are horizontally outside the
+viewport, exceed the portable 4096 CSS-pixel width bound, mutate during
+capture, or produce invalid geometry fail closed.
+
+A region reference means the referenced element's rendered border box, not the
+broader logical scope used by `inspect --within`. Nested scroll-container
+content outside that border box is not expanded. If more than 80 slices are
+required, Headless captures the first 79 and final slice and reports both
+`truncated: true` and the complete `totalPoints`; the missing middle is not
+represented as complete coverage.
+
+HostCore reserves the complete artifact set before capture, discards every
+reservation on failure, and requires restoration of the original scroll
+position after both success and failure while the original document identity
+remains active. WebKit captures the validated viewport rectangle;
+Chromium captures the corresponding document rectangle through CDP. Both use
+the same plan, artifact, truncation, and response contract. Region capture
+does not add selectors, arbitrary JavaScript, page content, or coordinates to
+logs or flows. Screenshot-series metadata is marked untrusted because section
+labels originate in the page.
+
+**Status:** implemented for
+[#211](https://github.com/LockInTime/headless/issues/211).
+
+**Consequences:** an agent can progress from outline inspection to visual
+evidence for one semantic region without broad full-page capture. Very wide,
+moving, sticky, or dynamically resizing regions require a fresh inspection or
+a narrower region instead of yielding partial or misleading evidence.
+
+---
+
 ## Decision log
 
 | #   | Decision                                                    | Status                                                    | Date       |
@@ -1156,5 +1200,6 @@ for logging, even though callers still control their own CLI process arguments.
 | 33  | Keep heavy agent benchmarks outside the product repository  | Proposed                                                  | 2026-09-19 |
 | 34  | CDP-backed bounded network-idle wait                        | Implemented                                               | 2026-09-20 |
 | 35  | Fixed native single-select operation                        | Implemented                                               | 2026-09-20 |
+| 36  | Bounded exact-crop region screenshot series                 | Implemented                                               | 2026-09-22 |
 
 New decisions append here with the same format.
diff --git a/docs/roadmap/improvements-backlog.md b/docs/roadmap/improvements-backlog.md
index 8bf57ee..456342f 100644
--- a/docs/roadmap/improvements-backlog.md
+++ b/docs/roadmap/improvements-backlog.md
@@ -491,8 +491,12 @@ get an architecture-decision entry:
   **Done:** Chromium tracks bounded in-flight CDP requests and requires a
   500 ms quiet window; WebKit declares and returns an explicit unsupported
   capability instead of approximating network state.
-- **G6. Element screenshot on Linux `--by-region @rN`** — region-scoped series
-  capture, pairs naturally with the pruning ladder.
+- **G6. Region screenshot series** ([#211](https://github.com/LockInTime/headless/issues/211)) —
+  ~~add bounded exact-crop `screenshot --by-region @rN` capture that pairs with
+  the pruning ladder and uses the portable series pipeline on both engines.~~
+  **Done:** opaque current-document region refs produce an atomic, bounded
+  vertical series on both engines, with per-slice geometry revalidation,
+  enforced scroll restoration, explicit truncation, and untrusted metadata.
 - **G7. Trace export** — `capture-info` already returns an action trace;
   `report create` bundles it; a `--format junit`/markdown export would slot
   into CI comments.
diff --git a/packages/headless-npm/src/generated.ts b/packages/headless-npm/src/generated.ts
index 08b27a2..aa38c01 100644
--- a/packages/headless-npm/src/generated.ts
+++ b/packages/headless-npm/src/generated.ts
@@ -7,8 +7,8 @@ export type Untrusted<T> = Readonly<{ readonly untrustedContent: true; readonly
 export const PROTOCOL_VERSION = "0.5" as const;
 export const PROTOCOL_SCHEMA_VERSION = 1 as const;
 export const MAXIMUM_MESSAGE_BYTES = 1048576 as const;
-export const PROTOCOL_SCHEMA_SHA256 = "f82b2ea0d7e8b5d2db0a841c5d22976aec6f774303cd81791921977899679f1e" as const;
-export const PROTOCOL_FIXTURES_SHA256 = "0b51ffaa2d3e3aaf0c32adcfeb02c180dcbe44face0d49e1c332b69f403ae062" as const;
+export const PROTOCOL_SCHEMA_SHA256 = "db70dc1b07b034624e85ab8f07ac420d5af5b948edf999cd11e5445ed07d7a17" as const;
+export const PROTOCOL_FIXTURES_SHA256 = "76bbee05cacd7ed16452176ad2973bf4604f4b864f8de1277664880c079a5435" as const;
 export const RESPONSE_ADDITIONAL_PROPERTIES = true as const;
 export const MAXIMUM_COMMAND_TIMEOUT_MS = 125000 as const;
 export const LOCAL_LIFECYCLE = {
@@ -223,7 +223,8 @@ export interface ScreenshotParameters {
   readonly "name"?: string;
   readonly "fullPage"?: boolean;
   readonly "output"?: string;
-  readonly "series"?: "viewport" | "section";
+  readonly "series"?: "viewport" | "section" | "region";
+  readonly "region"?: string;
   readonly "outputPrefix"?: string;
   readonly "format"?: string;
   readonly "clipboard"?: boolean;
@@ -479,7 +480,12 @@ export interface Screenshot {
   readonly "bytes"?: number;
   readonly "createdAt"?: number;
   readonly "artifacts"?: readonly JsonValue[];
+  readonly "series"?: "viewport" | "section" | "region";
+  readonly "count"?: number;
+  readonly "positions"?: readonly JsonValue[];
   readonly "truncated"?: boolean;
+  readonly "totalPoints"?: number;
+  readonly "untrustedContent"?: boolean;
   readonly [key: string]: JsonValue;
 }
 
@@ -1998,9 +2004,17 @@ export const COMMAND_METADATA = {
         "type": "string",
         "values": [
           "viewport",
-          "section"
+          "section",
+          "region"
         ]
       },
+      {
+        "maximumBytes": 16,
+        "name": "region",
+        "required": false,
+        "sensitive": false,
+        "type": "string"
+      },
       {
         "maximumBytes": 80,
         "name": "outputPrefix",
@@ -2064,10 +2078,40 @@ export const COMMAND_METADATA = {
             "required": false,
             "type": "array"
           },
+          {
+            "name": "series",
+            "required": false,
+            "type": "string",
+            "values": [
+              "viewport",
+              "section",
+              "region"
+            ]
+          },
+          {
+            "name": "count",
+            "required": false,
+            "type": "number"
+          },
+          {
+            "name": "positions",
+            "required": false,
+            "type": "array"
+          },
           {
             "name": "truncated",
             "required": false,
             "type": "boolean"
+          },
+          {
+            "name": "totalPoints",
+            "required": false,
+            "type": "number"
+          },
+          {
+            "name": "untrustedContent",
+            "required": false,
+            "type": "boolean"
           }
         ],
         "name": "Screenshot",
diff --git a/packages/headless-npm/src/protocol.ts b/packages/headless-npm/src/protocol.ts
index 90e933f..845b1d1 100644
--- a/packages/headless-npm/src/protocol.ts
+++ b/packages/headless-npm/src/protocol.ts
@@ -153,6 +153,48 @@ export function validateParameters<C extends CommandName>(
       validateParameter(command, definition, value);
     }
   }
+  if (command === "screenshot") {
+    const values = parameters as Readonly<Record<string, unknown>>;
+    const targetPresent = values.target !== undefined;
+    const semanticTargetPresent = values.role !== undefined || values.name !== undefined;
+    if (targetPresent && semanticTargetPresent) {
+      throw new ValidationError("screenshot element targets are mutually exclusive");
+    }
+    if (targetPresent && !/^@e\d+$/.test(String(values.target))) {
+      throw new ValidationError("screenshot.target must be an element reference");
+    }
+    if ((values.role !== undefined && values.role === "")
+      || (values.name !== undefined && values.name === "")) {
+      throw new ValidationError("screenshot semantic target values must not be empty");
+    }
+    const hasTarget = targetPresent || semanticTargetPresent;
+    const series = typeof values.series === "string" ? values.series : undefined;
+    const regionPresent = values.region !== undefined;
+    if (regionPresent && !/^@r\d+$/.test(String(values.region))) {
+      throw new ValidationError("screenshot.region must be a region reference");
+    }
+    if ((series === "region") !== regionPresent) {
+      throw new ValidationError("region screenshot series requires exactly one region reference");
+    }
+    if (series !== undefined && (values.fullPage === true || hasTarget || values.output !== undefined)) {
+      throw new ValidationError("screenshot series conflicts with full-page, output, or element target");
+    }
+    if (values.fullPage === true && hasTarget) {
+      throw new ValidationError("full-page and element screenshots are mutually exclusive");
+    }
+    if (values.outputPrefix !== undefined && series === undefined) {
+      throw new ValidationError("screenshot.outputPrefix requires a screenshot series");
+    }
+    const explicitFormat = typeof values.format === "string" ? values.format.toLowerCase() : "";
+    const output = typeof values.output === "string" ? values.output.toLowerCase() : "";
+    const pdf = explicitFormat === "pdf" || (!explicitFormat && output.endsWith(".pdf"));
+    if (series !== undefined && (pdf || values.clipboard === true)) {
+      throw new ValidationError("screenshot series does not support PDF or clipboard output");
+    }
+    if (pdf && (values.fullPage !== true || hasTarget || values.clipboard === true)) {
+      throw new ValidationError("PDF screenshots require full-page mode without a target or clipboard");
+    }
+  }
   if (command === "session.create") {
     validateSession(String(parameters.name));
   }
diff --git a/packages/headless-npm/test/protocol.test.mjs b/packages/headless-npm/test/protocol.test.mjs
index a766349..01e565b 100644
--- a/packages/headless-npm/test/protocol.test.mjs
+++ b/packages/headless-npm/test/protocol.test.mjs
@@ -85,6 +85,25 @@ test("schema-driven validation mirrors portable Swift bounds", () => {
     () => validateParameters("auth.login", { challenge: "id", account: "work", password: "secret" }),
     /unknown parameter password/,
   );
+  assert.doesNotThrow(() => validateParameters("screenshot", {
+    series: "region", region: "@r4", outputPrefix: "checkout", format: "png",
+  }));
+  assert.throws(
+    () => validateParameters("screenshot", { series: "region" }),
+    /requires exactly one region reference/,
+  );
+  assert.throws(
+    () => validateParameters("screenshot", { series: "viewport", region: "@r4" }),
+    /requires exactly one region reference/,
+  );
+  assert.throws(
+    () => validateParameters("screenshot", { series: "region", region: "@r4", clipboard: true }),
+    /does not support PDF or clipboard/,
+  );
+  assert.throws(
+    () => validateParameters("screenshot", { fullPage: true, target: "@e1" }),
+    /mutually exclusive/,
+  );
 });
 
 test("generated scopes and timeout policies drive the SDK", () => {
diff --git a/packages/headless-python/src/headless_sdk/_protocol.py b/packages/headless-python/src/headless_sdk/_protocol.py
index cf0304a..0900b00 100644
--- a/packages/headless-python/src/headless_sdk/_protocol.py
+++ b/packages/headless-python/src/headless_sdk/_protocol.py
@@ -153,6 +153,45 @@ def validate_parameters(command: CommandName, parameters: Mapping[str, object])
                 raise ValidationError(f"{command} requires {name}")
         else:
             _validate_parameter(command, definition, parameters[name])
+    if command == "screenshot":
+        target_present = "target" in parameters
+        semantic_target_present = "role" in parameters or "name" in parameters
+        if target_present and semantic_target_present:
+            raise ValidationError("screenshot element targets are mutually exclusive")
+        if target_present and re.fullmatch(r"@e\d+", cast(str, parameters["target"])) is None:
+            raise ValidationError("screenshot.target must be an element reference")
+        if parameters.get("role") == "" or parameters.get("name") == "":
+            raise ValidationError("screenshot semantic target values must not be empty")
+        has_target = target_present or semantic_target_present
+        series = parameters.get("series")
+        region_present = "region" in parameters
+        if region_present and re.fullmatch(r"@r\d+", cast(str, parameters["region"])) is None:
+            raise ValidationError("screenshot.region must be a region reference")
+        if (series == "region") != region_present:
+            raise ValidationError("region screenshot series requires exactly one region reference")
+        if series is not None and (
+            parameters.get("fullPage") is True or has_target or "output" in parameters
+        ):
+            raise ValidationError(
+                "screenshot series conflicts with full-page, output, or element target"
+            )
+        if parameters.get("fullPage") is True and has_target:
+            raise ValidationError("full-page and element screenshots are mutually exclusive")
+        if "outputPrefix" in parameters and series is None:
+            raise ValidationError("screenshot.outputPrefix requires a screenshot series")
+        explicit_format = cast(str, parameters.get("format", "")).lower()
+        output = cast(str, parameters.get("output", "")).lower()
+        pdf = explicit_format == "pdf" or (not explicit_format and output.endswith(".pdf"))
+        if series is not None and (pdf or parameters.get("clipboard") is True):
+            raise ValidationError("screenshot series does not support PDF or clipboard output")
+        if pdf and (
+            parameters.get("fullPage") is not True
+            or has_target
+            or parameters.get("clipboard") is True
+        ):
+            raise ValidationError(
+                "PDF screenshots require full-page mode without a target or clipboard"
+            )
     if command == "session.create":
         validate_session(cast(str, parameters["name"]))
 
diff --git a/packages/headless-python/src/headless_sdk/generated.py b/packages/headless-python/src/headless_sdk/generated.py
index 8c59797..d455b4f 100644
--- a/packages/headless-python/src/headless_sdk/generated.py
+++ b/packages/headless-python/src/headless_sdk/generated.py
@@ -13,8 +13,8 @@
 PROTOCOL_SCHEMA_VERSION = 1
 MAXIMUM_MESSAGE_BYTES = 1048576
 MAXIMUM_COMMAND_TIMEOUT_SECONDS = 125.0
-PROTOCOL_SCHEMA_SHA256 = 'f82b2ea0d7e8b5d2db0a841c5d22976aec6f774303cd81791921977899679f1e'
-PROTOCOL_FIXTURES_SHA256 = '0b51ffaa2d3e3aaf0c32adcfeb02c180dcbe44face0d49e1c332b69f403ae062'
+PROTOCOL_SCHEMA_SHA256 = 'db70dc1b07b034624e85ab8f07ac420d5af5b948edf999cd11e5445ed07d7a17'
+PROTOCOL_FIXTURES_SHA256 = '76bbee05cacd7ed16452176ad2973bf4604f4b864f8de1277664880c079a5435'
 RESPONSE_ADDITIONAL_PROPERTIES = True
 COMMAND_ERROR_CODES = ('ARTIFACT_ERROR', 'AUTH_ACCOUNT_NOT_FOUND', 'AUTH_CHALLENGE_CONSUMED', 'AUTH_CHALLENGE_EXPIRED', 'AUTH_CHALLENGE_NOT_FOUND', 'AUTH_FORM_CHANGED', 'AUTH_ORIGIN_CHANGED', 'AUTH_REQUIRED', 'CREDENTIAL_ALIAS_EXISTS', 'ELEMENT_NOT_FOUND', 'FLOW_FAILED', 'HOST_STOPPING', 'HOST_UNAVAILABLE', 'INTERNAL_ERROR', 'INVALID_CAPTURE_FORMAT', 'INVALID_COMMAND', 'INVALID_FLOW', 'INVALID_INPUT', 'INVALID_REQUEST', 'INVALID_SESSION', 'MISSING_PARAMETER', 'OPERATION_FAILED', 'PAGINATION_CURSOR_EXPIRED', 'PAGINATION_CURSOR_INVALID', 'PAGINATION_CURSOR_SCOPE_MISMATCH', 'PAGINATION_CURSOR_STALE', 'PEER_DENIED', 'RECORDER_UNAVAILABLE', 'RECORDING_ACTIVE', 'RECORDING_FAILED', 'RECORDING_NOT_ACTIVE', 'REGION_NOT_FOUND', 'RESPONSE_TOO_LARGE', 'SENSITIVE_DIAGNOSTICS_DISABLED', 'SESSION_EXISTS', 'SESSION_NOT_FOUND', 'TIMEOUT', 'UNSAFE_NAVIGATION', 'UNSAFE_RESOURCE_TYPE', 'UNSUPPORTED_CAPABILITY', 'USER_PRESENCE_DENIED', 'USER_PRESENCE_UNAVAILABLE', 'VAULT_LOCKED', 'VAULT_OPERATION_FAILED', 'VAULT_RESPONSE_INVALID', 'VAULT_UNAVAILABLE')
 CommandErrorCode = Literal['ARTIFACT_ERROR', 'AUTH_ACCOUNT_NOT_FOUND', 'AUTH_CHALLENGE_CONSUMED', 'AUTH_CHALLENGE_EXPIRED', 'AUTH_CHALLENGE_NOT_FOUND', 'AUTH_FORM_CHANGED', 'AUTH_ORIGIN_CHANGED', 'AUTH_REQUIRED', 'CREDENTIAL_ALIAS_EXISTS', 'ELEMENT_NOT_FOUND', 'FLOW_FAILED', 'HOST_STOPPING', 'HOST_UNAVAILABLE', 'INTERNAL_ERROR', 'INVALID_CAPTURE_FORMAT', 'INVALID_COMMAND', 'INVALID_FLOW', 'INVALID_INPUT', 'INVALID_REQUEST', 'INVALID_SESSION', 'MISSING_PARAMETER', 'OPERATION_FAILED', 'PAGINATION_CURSOR_EXPIRED', 'PAGINATION_CURSOR_INVALID', 'PAGINATION_CURSOR_SCOPE_MISMATCH', 'PAGINATION_CURSOR_STALE', 'PEER_DENIED', 'RECORDER_UNAVAILABLE', 'RECORDING_ACTIVE', 'RECORDING_FAILED', 'RECORDING_NOT_ACTIVE', 'REGION_NOT_FOUND', 'RESPONSE_TOO_LARGE', 'SENSITIVE_DIAGNOSTICS_DISABLED', 'SESSION_EXISTS', 'SESSION_NOT_FOUND', 'TIMEOUT', 'UNSAFE_NAVIGATION', 'UNSAFE_RESOURCE_TYPE', 'UNSUPPORTED_CAPABILITY', 'USER_PRESENCE_DENIED', 'USER_PRESENCE_UNAVAILABLE', 'VAULT_LOCKED', 'VAULT_OPERATION_FAILED', 'VAULT_RESPONSE_INVALID', 'VAULT_UNAVAILABLE']
@@ -113,7 +113,8 @@ class ScreenshotParameters(TypedDict):
     name: NotRequired[str]
     fullPage: NotRequired[bool]
     output: NotRequired[str]
-    series: NotRequired[Literal['viewport', 'section']]
+    series: NotRequired[Literal['viewport', 'section', 'region']]
+    region: NotRequired[str]
     outputPrefix: NotRequired[str]
     format: NotRequired[str]
     clipboard: NotRequired[bool]
@@ -318,7 +319,12 @@ class Screenshot(TypedDict, total=False):
     bytes: NotRequired[int | float]
     createdAt: NotRequired[int | float]
     artifacts: NotRequired[list[JsonValue]]
+    series: NotRequired[Literal['viewport', 'section', 'region']]
+    count: NotRequired[int | float]
+    positions: NotRequired[list[JsonValue]]
     truncated: NotRequired[bool]
+    totalPoints: NotRequired[int | float]
+    untrustedContent: NotRequired[bool]
 
 class ArtifactList(TypedDict, total=False):
     directory: Required[str]
@@ -1315,6 +1321,8 @@ class AuthenticationRequired(TypedDict, total=False):
                    'timeout': {'defaultMilliseconds': 15000, 'parameterPresentOverrides': {}}},
  'screenshot': {'capabilityNegotiated': True,
                 'constraints': ['target, full-page, and series modes are mutually constrained',
+                                'region is required only for region series and must be an @rN '
+                                'reference',
                                 'PDF requires full-page mode and no clipboard'],
                 'parameters': [{'maximumBytes': 16,
                                 'name': 'target',
@@ -1345,7 +1353,12 @@ class AuthenticationRequired(TypedDict, total=False):
                                 'required': False,
                                 'sensitive': False,
                                 'type': 'string',
-                                'values': ['viewport', 'section']},
+                                'values': ['viewport', 'section', 'region']},
+                               {'maximumBytes': 16,
+                                'name': 'region',
+                                'required': False,
+                                'sensitive': False,
+                                'type': 'string'},
                                {'maximumBytes': 80,
                                 'name': 'outputPrefix',
                                 'required': False,
@@ -1382,7 +1395,23 @@ class AuthenticationRequired(TypedDict, total=False):
                                                  {'name': 'artifacts',
                                                   'required': False,
                                                   'type': 'array'},
+                                                 {'name': 'series',
+                                                  'required': False,
+                                                  'type': 'string',
+                                                  'values': ['viewport', 'section', 'region']},
+                                                 {'name': 'count',
+                                                  'required': False,
+                                                  'type': 'number'},
+                                                 {'name': 'positions',
+                                                  'required': False,
+                                                  'type': 'array'},
                                                  {'name': 'truncated',
+                                                  'required': False,
+                                                  'type': 'boolean'},
+                                                 {'name': 'totalPoints',
+                                                  'required': False,
+                                                  'type': 'number'},
+                                                 {'name': 'untrustedContent',
                                                   'required': False,
                                                   'type': 'boolean'}],
                                       'name': 'Screenshot',
@@ -2208,7 +2237,8 @@ def screenshot(
         name: str | None = None,
         full_page: bool | None = None,
         output: str | None = None,
-        series: Literal['viewport', 'section'] | None = None,
+        series: Literal['viewport', 'section', 'region'] | None = None,
+        region: str | None = None,
         output_prefix: str | None = None,
         format: str | None = None,
         clipboard: bool | None = None,
@@ -2229,6 +2259,8 @@ def screenshot(
             parameters['output'] = cast(JsonValue, output)
         if series is not None:
             parameters['series'] = cast(JsonValue, series)
+        if region is not None:
+            parameters['region'] = cast(JsonValue, region)
         if output_prefix is not None:
             parameters['outputPrefix'] = cast(JsonValue, output_prefix)
         if format is not None:
@@ -2881,7 +2913,8 @@ async def screenshot(
         name: str | None = None,
         full_page: bool | None = None,
         output: str | None = None,
-        series: Literal['viewport', 'section'] | None = None,
+        series: Literal['viewport', 'section', 'region'] | None = None,
+        region: str | None = None,
         output_prefix: str | None = None,
         format: str | None = None,
         clipboard: bool | None = None,
@@ -2902,6 +2935,8 @@ async def screenshot(
             parameters['output'] = cast(JsonValue, output)
         if series is not None:
             parameters['series'] = cast(JsonValue, series)
+        if region is not None:
+            parameters['region'] = cast(JsonValue, region)
         if output_prefix is not None:
             parameters['outputPrefix'] = cast(JsonValue, output_prefix)
         if format is not None:
diff --git a/packages/headless-python/tests/test_protocol.py b/packages/headless-python/tests/test_protocol.py
index 7fbbbd0..7614396 100644
--- a/packages/headless-python/tests/test_protocol.py
+++ b/packages/headless-python/tests/test_protocol.py
@@ -95,6 +95,18 @@ def test_schema_driven_validation_matches_swift_bounds() -> None:
             "auth.login",
             {"challenge": "id", "account": "work", "password": "secret"},
         )
+    create_request(
+        "screenshot",
+        {"series": "region", "region": "@r4", "outputPrefix": "checkout", "format": "png"},
+    )
+    with pytest.raises(ValidationError, match="requires exactly one region reference"):
+        create_request("screenshot", {"series": "region"})
+    with pytest.raises(ValidationError, match="requires exactly one region reference"):
+        create_request("screenshot", {"series": "viewport", "region": "@r4"})
+    with pytest.raises(ValidationError, match="does not support PDF or clipboard"):
+        create_request("screenshot", {"series": "region", "region": "@r4", "clipboard": True})
+    with pytest.raises(ValidationError, match="mutually exclusive"):
+        create_request("screenshot", {"fullPage": True, "target": "@e1"})
     with pytest.raises(ValidationError, match="finite number"):
         create_request("wait", {"timeoutMs": 10**1000})
     with pytest.raises(ValidationError, match="request id is invalid"):
diff --git a/sdk/protocol-fixtures.json b/sdk/protocol-fixtures.json
index 86d4ce7..2769b74 100644
--- a/sdk/protocol-fixtures.json
+++ b/sdk/protocol-fixtures.json
@@ -76,6 +76,36 @@
           "originalActionReplayed": false
         }
       }
+    },
+    {
+      "name": "region screenshot series",
+      "argv": ["screenshot", "--by-region", "@r4", "--output", "checkout"],
+      "request": {
+        "id": "fixture-region-screenshot",
+        "version": "0.5",
+        "command": "screenshot",
+        "parameters": {
+          "fullPage": false,
+          "series": "region",
+          "region": "@r4",
+          "format": "png",
+          "outputPrefix": "checkout"
+        }
+      },
+      "response": {
+        "id": "fixture-region-screenshot",
+        "version": "0.5",
+        "ok": true,
+        "result": {
+          "series": "region",
+          "count": 1,
+          "artifacts": [],
+          "positions": [{"index": 1, "kind": "region"}],
+          "truncated": false,
+          "totalPoints": 1,
+          "untrustedContent": true
+        }
+      }
     }
   ],
   "directRequests": [
diff --git a/sdk/protocol-schema.json b/sdk/protocol-schema.json
index 65fa928..0ad10b6 100644
--- a/sdk/protocol-schema.json
+++ b/sdk/protocol-schema.json
@@ -1 +1 @@
-{"cancellation":{"afterSend":"close the client connection; command outcome is unknown until state is inspected","beforeSend":"request is not written","ownedHost":"terminate, await, and reap only a host process launched by that SDK instance","sharedHost":"never stop the host implicitly"},"commands":[{"capabilityNegotiated":false,"constraints":[],"name":"ping","parameters":[],"result":{"mayContainUntrustedContent":false,"schema":{"additionalProperties":true,"fields":[{"name":"ready","required":true,"type":"boolean"},{"name":"pid","required":true,"type":"number"},{"name":"engine","required":true,"type":"string"},{"name":"platform","required":true,"type":"string"},{"name":"productVersion","required":true,"type":"string"},{"name":"protocolVersion","required":true,"type":"string"},{"name":"capabilities","required":true,"type":"object"},{"name":"recordingAvailable","required":true,"type":"boolean"},{"name":"artifactDirectory","required":true,"type":"string"},{"name":"navigationAllowlist","required":true,"type":"array"}],"name":"HostStatus","type":"object"}},"scope":"host","timeout":{"defaultMilliseconds":15000,"parameterPresentOverrides":{}}},{"capabilityNegotiated":false,"constraints":[],"name":"shutdown","parameters":[],"result":{"mayContainUntrustedContent":false,"schema":{"additionalProperties":true,"fields":[{"name":"stopping","required":true,"type":"boolean"}],"name":"Shutdown","type":"object"}},"scope":"host","timeout":{"defaultMilliseconds":15000,"parameterPresentOverrides":{}}},{"capabilityNegotiated":false,"constraints":[],"name":"profile.clear","parameters":[],"result":{"mayContainUntrustedContent":false,"schema":{"additionalProperties":true,"fields":[{"name":"cleared","required":true,"type":"boolean"},{"name":"session","required":true,"type":"string"}],"name":"ProfileClear","type":"object"}},"scope":"host","timeout":{"defaultMilliseconds":15000,"parameterPresentOverrides":{}}},{"capabilityNegotiated":false,"constraints":[],"name":"session.create","parameters":[{"maximumBytes":64,"name":"name","required":true,"sensitive":false,"type":"string"},{"name":"isolated","required":false,"sensitive":false,"type":"boolean"}],"result":{"mayContainUntrustedContent":false,"schema":{"additionalProperties":true,"fields":[{"name":"session","required":true,"type":"string"},{"name":"isolated","required":true,"type":"boolean"}],"name":"SessionCreate","type":"object"}},"scope":"host","timeout":{"defaultMilliseconds":15000,"parameterPresentOverrides":{}}},{"capabilityNegotiated":false,"constraints":[],"name":"session.list","parameters":[],"result":{"mayContainUntrustedContent":false,"schema":{"additionalProperties":true,"fields":[{"items":{"type":"string"},"name":"sessions","required":true,"type":"array"},{"items":{"additionalProperties":true,"fields":[{"name":"name","required":true,"type":"string"},{"name":"isolated","required":true,"type":"boolean"},{"name":"ageMs","required":true,"type":"number"},{"name":"status","required":true,"type":"string","values":["available","navigating","unavailable"]},{"name":"url","required":true,"type":"string-or-null"},{"name":"title","required":true,"type":"string-or-null"},{"name":"urlTruncated","required":true,"type":"boolean"},{"name":"titleTruncated","required":true,"type":"boolean"},{"name":"untrustedContent","required":true,"type":"boolean"}],"name":"SessionDetail","type":"object"},"name":"details","required":true,"type":"array"}],"name":"SessionList","type":"object"}},"scope":"host","timeout":{"defaultMilliseconds":15000,"parameterPresentOverrides":{}}},{"capabilityNegotiated":false,"constraints":[],"name":"session.close","parameters":[],"result":{"mayContainUntrustedContent":false,"schema":{"additionalProperties":true,"fields":[{"name":"closed","required":true,"type":"string"}],"name":"SessionClose","type":"object"}},"scope":"session","timeout":{"defaultMilliseconds":15000,"parameterPresentOverrides":{}}},{"capabilityNegotiated":false,"constraints":[],"name":"visit","parameters":[{"maximumBytes":8192,"name":"url","required":true,"sensitive":false,"type":"string"}],"result":{"mayContainUntrustedContent":true,"schema":{"additionalProperties":true,"fields":[{"name":"url","required":true,"type":"string"},{"name":"title","required":true,"type":"string"},{"name":"readyState","required":true,"type":"string"},{"name":"text","required":true,"type":"string"},{"name":"runningAnimations","required":true,"type":"number"},{"name":"mutationQuietMs","required":true,"type":"number"},{"name":"scrollY","required":true,"type":"number"},{"name":"contentHeight","required":true,"type":"number"}],"name":"PageState","type":"object"}},"scope":"session","timeout":{"defaultMilliseconds":15000,"parameterPresentOverrides":{}}},{"capabilityNegotiated":false,"constraints":[],"name":"inspect","parameters":[{"name":"interactive","required":false,"sensitive":false,"type":"boolean"},{"name":"text","required":false,"sensitive":false,"type":"boolean"},{"maximumBytes":16,"name":"context","required":false,"sensitive":false,"type":"string","values":["summary","outline","text","actions","full"]},{"maximumBytes":512,"name":"task","required":false,"sensitive":false,"type":"string"},{"maximumBytes":16,"name":"within","required":false,"sensitive":false,"type":"string"},{"maximum":250,"minimum":1,"name":"limit","required":false,"sensitive":false,"type":"integer"},{"maximum":16000,"minimum":256,"name":"budget","required":false,"sensitive":false,"type":"integer"},{"maximum":8,"minimum":0,"name":"depth","required":false,"sensitive":false,"type":"integer"}],"result":{"mayContainUntrustedContent":true,"schema":{"additionalProperties":true,"fields":[{"name":"url","required":true,"type":"string"},{"name":"title","required":true,"type":"string"},{"name":"contextMode","required":true,"type":"string"},{"name":"viewport","required":true,"type":"object"},{"name":"untrustedContent","required":true,"type":"boolean"},{"name":"elements","required":false,"type":"array"},{"name":"regions","required":false,"type":"array"},{"name":"snippets","required":false,"type":"array"},{"name":"text","required":false,"type":"string"}],"name":"Inspection","type":"object"}},"scope":"session","timeout":{"defaultMilliseconds":15000,"parameterPresentOverrides":{}}},{"capabilityNegotiated":false,"constraints":["exactly one target reference or semantic role/name target"],"name":"click","parameters":[{"maximumBytes":16,"name":"target","required":false,"sensitive":false,"type":"string"},{"maximumBytes":128,"name":"role","required":false,"sensitive":false,"type":"string"},{"maximumBytes":1000,"name":"name","required":false,"sensitive":false,"type":"string"}],"result":{"mayContainUntrustedContent":true,"schema":{"additionalProperties":true,"fields":[{"name":"clicked","required":true,"type":"string"},{"name":"role","required":true,"type":"string"},{"name":"name","required":true,"type":"string"}],"name":"Click","type":"object"}},"scope":"session","timeout":{"defaultMilliseconds":15000,"parameterPresentOverrides":{}}},{"capabilityNegotiated":false,"constraints":["exactly one target reference or semantic role/name target"],"name":"fill","parameters":[{"maximumBytes":16,"name":"target","required":false,"sensitive":false,"type":"string"},{"maximumBytes":128,"name":"role","required":false,"sensitive":false,"type":"string"},{"maximumBytes":1000,"name":"name","required":false,"sensitive":false,"type":"string"},{"maximumBytes":900000,"name":"value","required":true,"sensitive":true,"type":"string"}],"result":{"mayContainUntrustedContent":true,"schema":{"additionalProperties":true,"fields":[{"name":"filled","required":true,"type":"string"},{"name":"valueLength","required":true,"type":"number"}],"name":"Fill","type":"object"}},"scope":"session","timeout":{"defaultMilliseconds":15000,"parameterPresentOverrides":{}}},{"capabilityNegotiated":false,"constraints":["exactly one target reference or semantic role/name target","exactly one option label or value","native single-selection HTML select controls 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