feat(superdeck): replace flutter_mermaid with mermaid_core

.agents/skills/superdeck-presentations/references/runtime-customization.md

@@ -403,7 +403,10 @@ SuperDeckApp(
 ```
 
 Mermaid diagrams render directly from fenced `mermaid` blocks. They do not
-require a plugin, custom runner, browser, generated image, or cache:
+require a plugin, custom runner, browser, generated image, or cache. The native
+port includes flowchart, sequence, class, state, ER, journey, chart, timeline
+and Git-graph families; syntax outside the port's supported subset can differ
+from mermaid.js, and a rejected diagram shows the failing line on the slide:
 
 ````markdown
 ```mermaid

demo/.superdeck/build_status.json

@@ -1,5 +1,5 @@
 {
   "status": "success",
-  "timestamp": "2026-08-25T18:24:50.927825Z",
-  "slideCount": 34
+  "timestamp": "2026-09-21T17:21:10.714812Z",
+  "slideCount": 35
 }

demo/.superdeck/superdeck.json

@@ -1088,6 +1088,47 @@
     ],
     "comments": []
   },
+  {
+    "key": "7iMG66ab",
+    "options": {
+      "title": "Mermaid diagrams"
+    },
+    "sections": [
+      {
+        "blocks": [
+          {
+            "type": "block",
+            "flex": 1,
+            "scrollable": false,
+            "content": "## Diagrams render on the slide\n"
+          }
+        ],
+        "flex": 1,
+        "spacing": 0.0,
+        "type": "section"
+      },
+      {
+        "blocks": [
+          {
+            "type": "block",
+            "flex": 1,
+            "scrollable": false,
+            "content": "\n\n```mermaid\nflowchart LR\n  Draft[Draft slides] --> Review{Ready?}\n  Review -->|Yes| Present[Present]\n  Review -->|No| Draft\n```\n"
+          },
+          {
+            "type": "block",
+            "flex": 1,
+            "scrollable": false,
+            "content": "```mermaid\nclassDiagram\n  Deck \"1\" o-- \"many\" Slide\n  Slide : +String key\n  Slide : +render()\n```"
+          }
+        ],
+        "flex": 1,
+        "spacing": 0.0,
+        "type": "section"
+      }
+    ],
+    "comments": []
+  },
   {
     "key": "MKokn2KA",
     "options": {},

demo/.superdeck/superdeck_full.json

@@ -2947,6 +2947,117 @@
     ],
     "comments": []
   },
+  {
+    "key": "7iMG66ab",
+    "options": {
+      "title": "Mermaid diagrams"
+    },
+    "sections": [
+      {
+        "blocks": [
+          {
+            "type": "block",
+            "flex": 1,
+            "scrollable": false,
+            "content": {
+              "type": "document",
+              "children": [
+                {
+                  "type": "element",
+                  "tag": "h2",
+                  "children": [
+                    {
+                      "type": "text",
+                      "text": "Diagrams render on the slide"
+                    }
+                  ],
+                  "generatedId": "diagrams-render-on-the-slide"
+                }
+              ],
+              "linkReferences": {},
+              "footnoteLabels": [],
+              "footnoteReferences": {}
+            }
+          }
+        ],
+        "flex": 1,
+        "spacing": 0.0,
+        "type": "section"
+      },
+      {
+        "blocks": [
+          {
+            "type": "block",
+            "flex": 1,
+            "scrollable": false,
+            "content": {
+              "type": "document",
+              "children": [
+                {
+                  "type": "element",
+                  "tag": "pre",
+                  "children": [
+                    {
+                      "type": "element",
+                      "tag": "code",
+                      "attributes": {
+                        "class": "language-mermaid"
+                      },
+                      "children": [
+                        {
+                          "type": "text",
+                          "text": "flowchart LR\n  Draft[Draft slides] --> Review{Ready?}\n  Review -->|Yes| Present[Present]\n  Review -->|No| Draft\n"
+                        }
+                      ]
+                    }
+                  ]
+                }
+              ],
+              "linkReferences": {},
+              "footnoteLabels": [],
+              "footnoteReferences": {}
+            }
+          },
+          {
+            "type": "block",
+            "flex": 1,
+            "scrollable": false,
+            "content": {
+              "type": "document",
+              "children": [
+                {
+                  "type": "element",
+                  "tag": "pre",
+                  "children": [
+                    {
+                      "type": "element",
+                      "tag": "code",
+                      "attributes": {
+                        "class": "language-mermaid"
+                      },
+                      "children": [
+                        {
+                          "type": "text",
+                          "text": "classDiagram\n  Deck "1" o-- "many" Slide\n  Slide : +String key\n  Slide : +render()\n"
+                        }
+                      ]
+                    }
+                  ]
+                }
+              ],
+              "linkReferences": {},
+              "footnoteLabels": [],
+              "footnoteReferences": {}
+            }
+          }
+        ],
+        "flex": 1,
+        "spacing": 0.0,
+        "type": "section"
+      }
+    ],
+    "comments": []
+  },
   {
     "key": "MKokn2KA",
     "options": {},

demo/slides.md

@@ -555,6 +555,32 @@ layout: fullscreen
   cacheKey: "fluttermix-fullscreen"
 }
 
+---
+title: Mermaid diagrams
+---
+
+## Diagrams render on the slide
+
+@section
+
+@block
+
+```mermaid
+flowchart LR
+  Draft[Draft slides] --> Review{Ready?}
+  Review -->|Yes| Present[Present]
+  Review -->|No| Draft
+```
+
+@block
+
+```mermaid
+classDiagram
+  Deck "1" o-- "many" Slide
+  Slide : +String key
+  Slide : +render()
+```
+
 ---
 
 @section{

docs/guides/mermaid-diagrams.mdx

@@ -24,19 +24,21 @@ of the Flutter widget tree for thumbnails, screenshots, and PDF export.
 
 ## Supported diagram types
 
-SuperDeck supports:
-
-- flowcharts
-- sequence diagrams
-- pie charts
-- Gantt charts
-- timelines
-- Kanban boards
-- radar charts
-- XY charts
-
-Class, state, journey, entity-relationship, mind map, Git graph, and other
-Mermaid diagram families are not supported.
+SuperDeck renders every diagram family the Dart Mermaid port supports,
+including:
+
+- flowcharts and sequence diagrams
+- class, state, entity-relationship and user-journey diagrams
+- pie, Gantt, XY, radar and quadrant charts
+- timelines, Kanban boards, mind maps and Git graphs
+- C4, architecture, requirement, packet, sankey, block and treemap diagrams
+
+Diagram families are ported by hand from Mermaid's own grammars, so a diagram
+that renders on mermaid.js can still be rejected here, and layout is not
+pixel-identical. Rejected input says so on the slide with the failing line.
+SuperDeck also guards the two known flowchart cases where version 0.3.0 would
+otherwise accept invalid syntax and draw an incomplete diagram, but this is not
+a claim of full mermaid.js conformance.
 
 ## Flowcharts
 
@@ -128,26 +130,54 @@ xychart-beta
   line [70, 82, 95]
 ```
 
+## Class, state, ER and journey diagrams
+
+````markdown
+```mermaid
+classDiagram
+  Deck "1" o-- "many" Slide
+  Slide : +String key
+  Slide : +render()
+```
+````
+
+```mermaid
+stateDiagram-v2
+  [*] --> Draft
+  Draft --> Review: submit
+  Review --> Draft: changes
+  Review --> [*]: approve
+```
+
 ## Layout and appearance
 
-Diagrams adapt to the width assigned to their Markdown block and keep their
-natural calculated height. SuperDeck makes the renderer background transparent
-so the slide background remains visible. Diagram colors follow the app's light
-or dark Flutter theme.
+Diagrams scale down to the width assigned to their Markdown block and keep
+their natural aspect ratio. SuperDeck makes the renderer background
+transparent so the slide background remains visible, and derives diagram
+colours from the app's Material colour scheme, so a diagram follows the deck's
+light or dark theme.
+
+Diagram nodes are exposed to screen readers and browser automation, so a slide
+with a diagram is not an unlabelled picture.
+
+`%%{init: ...}%%` directives and YAML frontmatter configuration are read, so
+per-diagram theme and layout options work, including `look: handDrawn` and the
+ELK layout engine.
 
 For dense diagrams, give the block more horizontal space or simplify the
 source. A diagram inside a narrow multi-column section has less room than the
 same diagram in a full-width section.
 
-The previous JavaScript configuration map, browser launch options, Mermaid
-`init` directives, custom CSS, and PNG viewport settings do not apply to the
-runtime renderer.
+The build plugin's JavaScript configuration map, browser launch options,
+custom CSS, and PNG viewport settings have no runtime counterpart.
 
 ## Errors and troubleshooting
 
-Mermaid parsing now happens in the Flutter app rather than during
-`superdeck build`. Invalid syntax or an unsupported diagram type displays an
-inline error card on the slide and in static exports.
+Mermaid parsing happens in the Flutter app rather than during
+`superdeck build`. Invalid syntax or an unknown diagram type displays an
+inline error card on the slide naming the line that failed, and the same
+failure stops a PDF export rather than writing a page with the diagram
+missing.
 
 When a diagram shows an error:
 
@@ -156,6 +186,8 @@ When a diagram shows an error:
 3. Compare the syntax with the examples on this page.
 4. Check the presentation at the same block size used by the final slide.
 
-The official Mermaid live editor supports more syntax than SuperDeck's runtime
-renderer, so success there does not guarantee that a diagram works in
-SuperDeck.
+The official Mermaid live editor is the reference implementation. A diagram
+that works there usually works here, but the Dart port is a hand-written
+re-implementation. Keep diagrams within the documented subset and treat a
+renderer disagreement as a compatibility issue to report, even if neither
+renderer returns an error.