chore(simplify): share FALLBACK_POLL_MS as the tombstone TTL + trim verbose comments

Simplify pass on top of #2069 fix:

- Export FALLBACK_POLL_MS from canvas/src/store/socket.ts and import
  it as TOMBSTONE_TTL_MS in deleteTombstones.ts. Single source of
  truth — tuning one without the other would silently re-open the
  hydrate-races-delete window. Required-fix per simplify reviewer.
- Compress deleteTombstones.ts docstring from 30 lines to 10 — keep
  the "what + why module-level"; drop the long-form problem
  description (issue #2069 carries it).
- Compress canvas.ts call-site comments at removeSubtree (4 lines →
  2) and hydrate (2 lines → 2 but tighter).
- Don't reassign the workspaces parameter inside hydrate — use a
  const `live` and thread it through the two downstream calls
  (computeAutoLayout, buildNodesAndEdges). Same effect, no lint
  smell.
- Trim the canvas.test.ts integration-test preamble.

No behaviour change.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

canvas/src/store/__tests__/canvas.test.ts

@@ -552,11 +552,7 @@ describe("removeSubtree", () => {
     }
   });
 
-  // #2069: a `GET /workspaces` that was IN-FLIGHT before the DELETE
-  // completed can land AFTER removeSubtree, hydrate the store with a
-  // stale snapshot, and resurrect deleted nodes. The tombstone path
-  // (deleteTombstones.ts) makes hydrate skip ids deleted within the
-  // last 10s. Lock the contract end-to-end.
+  // #2069: lock the tombstone path end-to-end at the store level.
   it("hydrate cannot resurrect ids that removeSubtree just dropped (#2069)", () => {
     useCanvasStore.getState().removeSubtree("root");
     expect(useCanvasStore.getState().nodes.map((n) => n.id).sort())

canvas/src/store/canvas.ts

@@ -833,10 +833,8 @@ export const useCanvasStore = create<CanvasState>((set, get) => ({
         }
       }
     }
-    // Mark every removed id with a tombstone so an in-flight GET
-    // /workspaces response that lands AFTER this can't resurrect them
-    // via hydrate (#2069). Tombstones expire after the WS-fallback
-    // poll cadence so legitimate re-imports flow normally.
+    // Tombstone removed ids so an in-flight GET /workspaces can't
+    // resurrect them via hydrate (#2069).
     markDeleted(removed);
     set({
       nodes: nodes.filter((n) => !removed.has(n.id)),
@@ -849,10 +847,10 @@ export const useCanvasStore = create<CanvasState>((set, get) => ({
   },
 
   hydrate: (workspaces: WorkspaceData[]) => {
-    // Filter out workspaces whose ids match a fresh tombstone — they
-    // were just deleted locally and this snapshot is stale (#2069).
-    workspaces = workspaces.filter((w) => !wasRecentlyDeleted(w.id));
-    const layoutOverrides = computeAutoLayout(workspaces);
+    // Drop ids tombstoned by a recent removeSubtree (#2069 — stale
+    // in-flight GET /workspaces).
+    const live = workspaces.filter((w) => !wasRecentlyDeleted(w.id));
+    const layoutOverrides = computeAutoLayout(live);
     // Carry the live measured/grown parent sizes from the existing
     // store into the rebuild. buildNodesAndEdges runs an auto-rescue
     // pass on each child to detach orphans whose stored relative
@@ -873,7 +871,7 @@ export const useCanvasStore = create<CanvasState>((set, get) => ({
       }
     }
     const { nodes, edges } = buildNodesAndEdges(
-      workspaces,
+      live,
       layoutOverrides,
       currentParentSizes,
     );

canvas/src/store/deleteTombstones.ts

@@ -1,34 +1,19 @@
 /**
- * Transient "recently deleted" map used by canvas.ts to short-circuit
- * the hydrate-races-cascade-delete window described in #2069.
+ * Transient "recently deleted" map keyed by workspace id.
  *
- * Problem
- * -------
- * `removeSubtree(rootId)` drops a parent + descendants locally after
- * `DELETE /workspaces/:id?confirm=true` returns 200. `hydrate()` is
- * server-authoritative and rebuilds the entire node array from whatever
- * `/workspaces` returns. If a `GET /workspaces` was IN-FLIGHT before the
- * DELETE completed, its response (still containing the deleted subtree)
- * can land AFTER our local `removeSubtree`, hydrate the store with the
- * stale snapshot, and re-introduce the deleted nodes on the canvas.
+ * `removeSubtree` calls `markDeleted(ids)` on every removal; `hydrate`
+ * calls `wasRecentlyDeleted(id)` to filter out incoming workspaces
+ * whose ids match a fresh tombstone — prevents an in-flight
+ * GET /workspaces from resurrecting just-deleted nodes via hydrate.
  *
- * Fix
- * ---
- * `removeSubtree` calls `markDeleted(ids)` to record a tombstone for every
- * removed id. `hydrate` calls `wasRecentlyDeleted(id)` to filter out any
- * incoming workspace whose id matches a fresh tombstone. After
- * `TOMBSTONE_TTL_MS`, the entry expires and a legitimately-recreated id
- * (template re-import, undo, manual recreate) flows through normally.
- *
- * GC happens lazily at every read AND at write time so the map stays
- * bounded — no separate timer / interval / unmount plumbing.
- *
- * Module-level (not store state) so it doesn't trigger React Flow
- * re-renders and isn't part of the public store surface. The store is a
- * singleton, so module identity ≡ store identity for this purpose.
+ * TTL is shared with the WS-fallback poll cadence so a single
+ * round-trip is covered. Module-level (not store state) so it doesn't
+ * trigger React Flow re-renders. (#2069)
  */
 
-const TOMBSTONE_TTL_MS = 10_000; // matches the 10s WS-fallback poll cadence
+import { FALLBACK_POLL_MS } from "./socket";
+
+const TOMBSTONE_TTL_MS = FALLBACK_POLL_MS;
 
 const tombstones = new Map<string, number>();
 

canvas/src/store/socket.ts

@@ -63,7 +63,7 @@ export class RehydrateDedup {
  *  network truly is down. The dedup gate inside rehydrate() collapses
  *  this against the post-onopen rehydrate, so reconnect doesn't pay
  *  for a duplicate fetch. */
-const FALLBACK_POLL_MS = 10_000;
+export const FALLBACK_POLL_MS = 10_000;
 
 class ReconnectingSocket {
   private ws: WebSocket | null = null;