feat(diagram-engine): open shape vocabulary — catalog + pass-through, structured style merge

The expressiveness gap traced to vocabulary: draw.io has hundreds of shapes,
the declarative layer allowed six. Opening it, with the failure modes from
design review handled:

- shapes.ts: a ~20-entry curated catalog (full style fragment incl. the
  matching perimeter — required or edges connect to the bounding box; a
  text-scale factor verified in the real editor — the same sentence overflows
  a 1.0x rhombus and fits a 1.5x one; labelOutside+glyph for umlActor-style
  figures). Any other token passes through verbatim: draw.io degrades unknown
  shapes to rectangles safely (verified). Injection-capable tokens (;/=) are
  rejected outright.
- Pass-through emits a WARNING with a nearest-catalog hint (bounded edit
  distance), so a typo'd 'cyclinder' is a one-turn fix instead of a silently
  rectangular node forever. set_shape/set_role/set_group operations make the
  fix possible without remove+re-add (which would drop links).
- mergeStyle(): style fragments merge per-key (later wins, bare shape classes
  displace each other) instead of string concatenation. This is what makes
  shape and theme composable by rule — shape owns geometry keys, theme owns
  colour/type keys, and an overlap resolves by order instead of emitting
  contradictory duplicates.
- dai_shape marker carries the declared token through the round trip:
  appearance-based reverse mapping cannot distinguish aliases (diamond vs
  decision) or a rotated queue from a cylinder.
- dai_auto marker separates engine-measured size from user-fixed size: parsed
  boxes no longer freeze the first layout's numbers, so changing a label
  re-measures. Pinned nodes keep everything, as before.
- draw_graph's closed shape enum opened to match (first instance of the
  schema-drift problem the review predicted).

14 new tests: merge ownership, injection rejection, near-match hints,
alias-preserving round trip, re-measure on label change, mxgraph.* tokens
staying boxes with role/group intact. 556 unit tests green; acceptance
diagram (person/hexagon/cylinder/queue/cloud/decision/callout) verified in
the real editor.

lib/diagram-engine/operations.ts

@@ -86,17 +86,10 @@ export const OperationSchema = z.discriminatedUnion("op", [
             .optional()
             .describe("Border colour; pair it with fill"),
         shape: z
-            .enum([
-                "box",
-                "decision",
-                "terminator",
-                "round",
-                "data",
-                "document",
-            ])
+            .string()
             .optional()
             .describe(
-                "Flowchart outline: decision=diamond, terminator=start/end, data=input/output, document=report. Omit for a plain rectangle",
+                "What the node IS, drawn as its conventional outline. Catalog: decision/diamond, terminator (start/end), round, data (input/output), document, cylinder (database), queue, person (actor/user), cloud (external system), hexagon (service), ellipse (concept), callout (note), step (pipeline stage), note, card, process, tape, cube. Any other draw.io shape token also works verbatim. Omit for a plain rectangle",
             ),
         grow: z
             .number()
@@ -261,6 +254,36 @@ export const OperationSchema = z.discriminatedUnion("op", [
         id: z.string(),
         label: z.string(),
     }),
+    z.object({
+        op: z.literal("set_shape"),
+        id: z.string(),
+        shape: z
+            .string()
+            .describe("New shape token; 'box' resets to a plain rectangle"),
+    }),
+    z.object({
+        op: z.literal("set_role"),
+        id: z.string(),
+        role: z
+            .enum([
+                "banner",
+                "heading",
+                "body",
+                "callout",
+                "good",
+                "bad",
+                "metric",
+                "muted",
+            ])
+            .describe("New information role; 'body' resets to the default"),
+    }),
+    z.object({
+        op: z.literal("set_group"),
+        id: z.string(),
+        group: z
+            .string()
+            .describe("New semantic zone; empty string removes the zone"),
+    }),
     z.object({
         op: z.literal("set_dir"),
         id: z.string().describe("Container to re-orient"),
@@ -579,6 +602,50 @@ export function applyOperations(
                 break
             }
 
+            case "set_shape": {
+                const node = findNode(tree, op.id)
+                if (!node || node.kind !== "box") {
+                    errors.push(`set_shape: "${op.id}" is not a box`)
+                    break
+                }
+                // The verbatim style is last render's composition with the OLD shape
+                // baked in; keeping it would override the new declaration entirely.
+                if (op.shape === "box") delete node.shape
+                else node.shape = op.shape
+                delete node.style
+                delete node.w
+                delete node.h
+                break
+            }
+
+            case "set_role": {
+                const node = findNode(tree, op.id)
+                if (!node || (node.kind !== "box" && node.kind !== "group")) {
+                    errors.push(
+                        `set_role: "${op.id}" is not a box or container`,
+                    )
+                    break
+                }
+                if (op.role === "body") delete node.role
+                else node.role = op.role
+                delete node.style
+                break
+            }
+
+            case "set_group": {
+                const node = findNode(tree, op.id)
+                if (!node || (node.kind !== "box" && node.kind !== "group")) {
+                    errors.push(
+                        `set_group: "${op.id}" is not a box or container`,
+                    )
+                    break
+                }
+                if (op.group === "") delete node.group
+                else node.group = op.group
+                delete node.style
+                break
+            }
+
             case "set_dir": {
                 const node = findNode(tree, op.id)
                 if (!node || !isContainer(node)) {