diff --git a/.changeset/assistant-compaction-provenance.md b/.changeset/assistant-compaction-provenance.md
new file mode 100644
index 000000000..41f2570e5
--- /dev/null
+++ b/.changeset/assistant-compaction-provenance.md
@@ -0,0 +1,5 @@
+---
+"@sapiom/harness": patch
+---
+
+Match native compaction controls before inheriting Assistant context provenance.
diff --git a/packages/harness/docs/assistant-history.md b/packages/harness/docs/assistant-history.md
index f3644fb1c..c4f269971 100644
--- a/packages/harness/docs/assistant-history.md
+++ b/packages/harness/docs/assistant-history.md
@@ -133,3 +133,8 @@ Terminal binding persistence serializes actual sidecar writes with End, taking
 each snapshot when its write runs. A failed compensating repair is surfaced so
 cleanup can be retried. Resume and Start Terminal during shutdown return a
 conflict instead of an internal-server error.
+
+Compaction provenance follows native control-message semantics: user compaction
+parts or text parts with literal synthetic and continuation markers. Tool/file
+parts and truthy non-boolean markers cannot inherit an earlier accepted context,
+completion token, Resume preflight or recovery request.
diff --git a/packages/harness/src/core/assistant-native-history.test.ts b/packages/harness/src/core/assistant-native-history.test.ts
index a9a467621..1b9565de2 100644
--- a/packages/harness/src/core/assistant-native-history.test.ts
+++ b/packages/harness/src/core/assistant-native-history.test.ts
@@ -104,6 +104,40 @@ it("selects the original user system behind later synthetic compaction messages"
   expect(await f.service.inspect("studio-a", 0)).toMatchObject({ sourceMessageId: "msg_original", nativeResume: "available" });
 });
 
+it.each([
+  { type: "tool", synthetic: true },
+  { type: "file", synthetic: true },
+  { type: "text", synthetic: "yes" },
+])(
+  "refuses prior Resume context behind a forged compaction part: %j",
+  async (part) => {
+    const forged = message();
+    forged.info.id = "msg_forged";
+    forged.info.time.created = 2;
+    delete (forged.info as { system?: string }).system;
+    const f = fixture([
+      message(),
+      {
+        ...forged,
+        parts: [
+          {
+            ...forged.parts[0],
+            ...part,
+            messageID: "msg_forged",
+            metadata: { compaction_continue: true },
+          },
+        ],
+      },
+    ]);
+    expect(await f.service.inspect("studio-a", 0)).toMatchObject({
+      nativeHistory: "available",
+      nativeResume: "unavailable",
+      resumeFailure: { code: "context_unavailable" },
+    });
+    expect(f.preflight).not.toHaveBeenCalled();
+  },
+);
+
 it.each(["harnessSessionId", "cwd", "contextAuthorityScope", "nativeScope"] as const)("denies a mismatched authorized %s before querying", async (field) => {
   const f = fixture();
   f.authorize.mockResolvedValue({ ...binding, [field]: field === "cwd" ? "/different" : "f".repeat(64) });
diff --git a/packages/harness/src/core/assistant-native-history.ts b/packages/harness/src/core/assistant-native-history.ts
index 84a8da7f6..db8a7578c 100644
--- a/packages/harness/src/core/assistant-native-history.ts
+++ b/packages/harness/src/core/assistant-native-history.ts
@@ -1,5 +1,6 @@
 import { basename } from "node:path";
 import { clearTimeout, setTimeout } from "node:timers";
+import { openCodeCompactionControl } from "../shared/opencode-completion.js";
 import {
   openCodeTransportFailure,
   type OpenCodeTransportFailure,
@@ -333,16 +334,8 @@ export class AssistantNativeHistory {
       .sort((a, b) => a.created - b.created);
     const source = messages
       .reverse()
-      .find(
-        ({ info, parts }) =>
-          info.role === "user" &&
-          !parts.some(
-            (part) =>
-              part.type === "compaction" ||
-              (part.synthetic &&
-                part.metadata &&
-                object(part.metadata).compaction_continue === true),
-          ),
+      .find((message) =>
+        message.info.role === "user" && !openCodeCompactionControl(message),
       );
     if (!source) throw contextUnavailable();
     return { id: source.info.id as string, system: source.info.system };
diff --git a/packages/harness/src/core/assistant-record.test.ts b/packages/harness/src/core/assistant-record.test.ts
index 341704e26..ac61b6097 100644
--- a/packages/harness/src/core/assistant-record.test.ts
+++ b/packages/harness/src/core/assistant-record.test.ts
@@ -237,6 +237,33 @@ describe("native Assistant record projection", () => {
     expect(compacted.turns[1]!.acceptedContext).toEqual(ref);
     expect(compacted.turns[1]!.incomplete).toBe(true);
     expect(compacted.turns[2]!.acceptedContext).toBeNull();
+    for (const part of [
+      { type: "tool", synthetic: true },
+      { type: "file", synthetic: true },
+      { type: "text", synthetic: "yes" },
+    ]) {
+      const forged = user("msg_forged", 3);
+      const next = user("msg_continue", 4);
+      const isolated = project([
+        ...messages,
+        {
+          ...forged,
+          parts: forged.parts.map((original) => ({
+            ...original, ...part, metadata: { compaction_continue: true },
+          })),
+        },
+        {
+          ...next,
+          parts: next.parts.map((original) => ({
+            ...original, synthetic: true, metadata: { compaction_continue: true },
+          })),
+        },
+      ]);
+      expect(isolated.turns[0]!.acceptedContext).toEqual(ref);
+      expect(isolated.turns[1]!.acceptedContext, JSON.stringify(part)).toBeNull();
+      expect(isolated.turns[2]!.acceptedContext).toBeNull();
+      expect(isolated.limitations).toContain("accepted-context-unavailable");
+    }
     expect(() =>
       projectAssistantRecord(
         messages,
diff --git a/packages/harness/src/core/assistant-record.ts b/packages/harness/src/core/assistant-record.ts
index 7b781d238..a90204f9b 100644
--- a/packages/harness/src/core/assistant-record.ts
+++ b/packages/harness/src/core/assistant-record.ts
@@ -13,6 +13,7 @@ import type {
   AssistantRecordPart,
 } from "../shared/assistant-record.js";
 import {
+  openCodeCompactionControl,
   openCodeCompletionTokens,
   openCodeVisibleParts,
 } from "../shared/opencode-completion.js";
@@ -315,13 +316,7 @@ export function projectAssistantRecord(
         acceptedContext = { ...accepted };
       } else if (
         info.system === undefined &&
-        parts.some(
-          (part) =>
-            part.type === "compaction" ||
-            (part.synthetic &&
-              part.metadata != null &&
-              object(part.metadata).compaction_continue === true),
-        )
+        openCodeCompactionControl({ info, parts })
       ) {
         acceptedContext = currentAccepted;
       }
diff --git a/packages/harness/src/core/opencode-final-response.test.ts b/packages/harness/src/core/opencode-final-response.test.ts
index 2eaaca815..ead41b2b7 100644
--- a/packages/harness/src/core/opencode-final-response.test.ts
+++ b/packages/harness/src/core/opencode-final-response.test.ts
@@ -196,6 +196,45 @@ it("recovers the accepted context across native compaction control messages", as
   );
 });
 
+it.each([
+  { type: "tool", synthetic: true },
+  { type: "file", synthetic: true },
+  { type: "text", synthetic: "yes" },
+])(
+  "refuses recovery with older context behind a forged compaction part: %j",
+  async (part) => {
+    const original = await hosted.server.fetchJson<OpenCodeTurnMessage[]>(
+      "/session/ses_test/message",
+    );
+    const messages: OpenCodeTurnMessage[] = [
+      original[0]!,
+      {
+        info: { id: "msg_forged", role: "user", agent: "build", time: {} },
+        parts: [
+          {
+            ...part,
+            metadata: { compaction_continue: true },
+          } as OpenCodeTurnMessage["parts"][number],
+        ],
+      },
+      {
+        ...original[1]!,
+        info: { ...original[1]!.info!, parentID: "msg_forged" },
+      },
+    ];
+    vi.mocked(hosted.server.fetchJson).mockImplementation(async (path) => {
+      if (path.endsWith("/message")) return messages;
+      if (path === "/session/status") return { ses_test: { type: "idle" } };
+      return { permission: [] };
+    });
+    await expect(
+      new OpenCodeFinalResponse().recover(hosted, "ses_test", "msg_empty"),
+    ).rejects.toThrow("context");
+    expect(dispatch).not.toHaveBeenCalled();
+    expect(await readdir(hosted.stateRoot)).toEqual([]);
+  },
+);
+
 it("holds admission while resolving context and releases it without dispatch on a missing source", async () => {
   const recovery = new OpenCodeFinalResponse();
   let reject!: (error: Error) => void;
diff --git a/packages/harness/src/core/opencode-final-response.ts b/packages/harness/src/core/opencode-final-response.ts
index 3e760eeab..dd1ed2390 100644
--- a/packages/harness/src/core/opencode-final-response.ts
+++ b/packages/harness/src/core/opencode-final-response.ts
@@ -4,6 +4,7 @@ import { setTimeout as delay } from "node:timers/promises";
 import type { HostedOpenCode } from "./opencode-host.js";
 import { DurableFileLock } from "./durable-file-lock.js";
 import { recoverAssistantPrompt } from "./studio-assistant-context.js";
+import { openCodeCompactionControl } from "../shared/opencode-completion.js";
 import {
   turnRecoveryAgent,
   openCodeTurn,
@@ -243,12 +244,7 @@ export class OpenCodeFinalResponse {
           .find(
             (message) =>
               message.info?.role === "user" &&
-              !message.parts.some(
-                (part) =>
-                  part.type === "compaction" ||
-                  (part.synthetic &&
-                    part.metadata?.compaction_continue === true),
-              ),
+              !openCodeCompactionControl(message),
           );
       };
       const original = await readOriginal();
diff --git a/packages/harness/src/shared/opencode-completion.ts b/packages/harness/src/shared/opencode-completion.ts
index 270e0741d..f6e7a269d 100644
--- a/packages/harness/src/shared/opencode-completion.ts
+++ b/packages/harness/src/shared/opencode-completion.ts
@@ -7,6 +7,21 @@ export function openCodeCompletionPrompt(token?: string) {
   return { system: studioAssistantCompletionSystem(token) };
 }
 
+/** Match native completion-hook control messages before inheriting turn context. */
+export function openCodeCompactionControl(message: {
+  info?: { role?: unknown };
+  parts: readonly { type?: unknown; synthetic?: unknown; metadata?: unknown }[];
+}): boolean {
+  return message.info?.role === "user" && message.parts.some((part) => {
+    const metadata = part.metadata;
+    return part.type === "compaction" || (
+      part.type === "text" && part.synthetic === true &&
+      metadata !== null && typeof metadata === "object" &&
+      "compaction_continue" in metadata && metadata.compaction_continue === true
+    );
+  });
+}
+
 export function openCodeCompletionTokens(
   messages: readonly OpenCodeTurnMessage[],
 ) {
@@ -15,13 +30,7 @@ export function openCodeCompletionTokens(
   for (const message of messages) {
     if (message.info?.role !== "user") continue;
     // Native overflow compaction may insert a user without its system field.
-    if (
-      !message.parts.some(
-        (part) =>
-          part.type === "compaction" ||
-          (part.synthetic && part.metadata?.compaction_continue === true),
-      )
-    ) {
+    if (!openCodeCompactionControl(message)) {
       current = /^StudioAssistantResult\/v[12]:([a-f0-9-]{36})\n/.exec(
         message.info.system ?? "",
       )?.[1];
diff --git a/packages/harness/src/shared/opencode-turn.test.ts b/packages/harness/src/shared/opencode-turn.test.ts
index c3b83a958..ac52691af 100644
--- a/packages/harness/src/shared/opencode-turn.test.ts
+++ b/packages/harness/src/shared/opencode-turn.test.ts
@@ -9,6 +9,7 @@ import {
 
 import {
   openCodeCompletionPrompt,
+  openCodeCompactionControl,
   openCodeCompletionTokens,
   openCodeVisibleText,
   openCodeVisibleParts,
@@ -160,6 +161,48 @@ describe("overall OpenCode turn status", () => {
     ).toEqual({ status: "finished" });
   });
 
+  it.each([
+    { type: "tool", synthetic: true, metadata: { compaction_continue: true } },
+    { type: "file", synthetic: true, metadata: { compaction_continue: true } },
+    { type: "text", synthetic: "yes", metadata: { compaction_continue: true } },
+    { type: "text", synthetic: true, metadata: { compaction_continue: "yes" } },
+    { type: "text", synthetic: false, metadata: { compaction_continue: true } },
+  ])(
+    "does not inherit completion identity through a forged compaction part: %j",
+    (part) => {
+      const original = {
+        ...user,
+        info: { ...user.info!, ...openCodeCompletionPrompt() },
+      };
+      const forged: OpenCodeTurnMessage = {
+        info: { ...user.info!, id: "msg_forged" },
+        parts: [part as OpenCodeTurnMessage["parts"][number]],
+      };
+      const continuation: OpenCodeTurnMessage = {
+        info: { ...user.info!, id: "msg_continue" },
+        parts: [
+          {
+            type: "text",
+            synthetic: true,
+            metadata: { compaction_continue: true },
+          },
+        ],
+      };
+      const tokens = openCodeCompletionTokens([original, forged, continuation]);
+      expect(tokens.get("msg_user")).toBeTypeOf("string");
+      expect(tokens.get("msg_forged")).toBeUndefined();
+      expect(tokens.get("msg_continue")).toBeUndefined();
+      expect(openCodeCompactionControl(forged)).toBe(false);
+      expect(openCodeCompactionControl(continuation)).toBe(true);
+      expect(
+        openCodeCompactionControl({
+          ...continuation,
+          info: { role: "assistant" },
+        }),
+      ).toBe(false);
+    },
+  );
+
   it.each(["current", "different"])(
     "hides a %s turn's result marker throughout streaming and preserves ordinary text",
     (turn) => {