refactor(apps): address review on the accessor-consolidation parity harness

- parityHarness: deep-snapshot recorded params at emit time so a later
  accessor mutation of a shared object cannot rewrite an already-recorded
  call; fix the stale migration-doc reference.
- parityHarness test: assert the emitted params (id + APP_ID sentinel on
  lookup, mutated message + APP_ID sentinel on write), not just the ordered
  method names.
- docs: give the AppResourceBridge fenced block an explicit language.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

Author: d-gubert

docs/proposals/apps-accessor-consolidation/README.md

@@ -258,7 +258,7 @@ manager / the app's own storage item"*. Rather than keeping a residual `accessor
 them, add one internal bridge so they ride the existing, permission-checked, appId-substituting
 `bridges:*` channel:
 
-```
+```text
 AppResourceBridge (host-side, internal — not part of the app-facing definition surface)
 ├── doProvideSetting(setting, appId)            → ProxiedApp.getStorageItem() mutation (SettingsExtend semantics)
 ├── doGetAppSetting(id, appId)                  → app.getStorageItem().settings[id] (SettingRead semantics)

packages/apps/base-runtime/src/lib/accessors/tests/helpers/parityHarness.test.ts

@@ -44,7 +44,7 @@ describe('parityHarness', () => {
 	});
 
 	it('pins the host-bound traffic a MOVE-style accessor emits (worked example: ModifyExtender.extendMessage + finish)', async () => {
-		const { sender, methods } = createRecordingSender({
+		const { sender, emitted } = createRecordingSender({
 			'bridges:getMessageBridge:doGetById': { id: 'message-id', text: 'original' },
 		});
 
@@ -55,7 +55,23 @@ describe('parityHarness', () => {
 		await extender.finish(messageExtender);
 
 		// This is the parity assertion a Phase 1-2 port must keep satisfying: the
-		// exact ordered bridge traffic, normalized to the APP_ID sentinel.
-		assert.deepStrictEqual(methods(), ['bridges:getMessageBridge:doGetById', 'bridges:getMessageBridge:doUpdate']);
+		// exact ordered bridge traffic *and* its params, normalized to the APP_ID
+		// sentinel.
+		const calls = emitted();
+		assert.deepStrictEqual(
+			calls.map((c) => c.method),
+			['bridges:getMessageBridge:doGetById', 'bridges:getMessageBridge:doUpdate'],
+		);
+
+		// extendMessage looks the message up by id; the caller identity is the APP_ID sentinel.
+		assert.deepStrictEqual(calls[0].params, ['message-id', 'APP_ID']);
+
+		// finish writes the mutated message back, again trailed by the APP_ID sentinel.
+		// (editedAt is a fresh Date, so we assert the fields the accessor is responsible for.)
+		const [updatedMessage, appId] = calls[1].params as [Record<string, unknown>, string];
+		assert.strictEqual(appId, 'APP_ID');
+		assert.strictEqual(updatedMessage.id, 'message-id');
+		assert.deepStrictEqual(updatedMessage.editor, { id: 'user-id' });
+		assert.deepStrictEqual(updatedMessage.customFields, { key: 'value' });
 	});
 });

packages/apps/base-runtime/src/lib/accessors/tests/helpers/parityHarness.ts

@@ -3,7 +3,7 @@ import type * as Messenger from '../../../messenger';
 /**
  * Transitional parity harness for the accessor-consolidation migration.
  *
- * MOVE accessors (see docs/base-runtime-accessor-consolidation.md) are *live in
+ * MOVE accessors (see docs/proposals/apps-accessor-consolidation/README.md) are *live in
  * production today* via the host proxy path, so a subtly wrong port - a dropped
  * default, an off-by-one on a cap, a renamed sort field - is an immediate
  * observable regression. Ordinary ported unit tests only prove the new local
@@ -62,7 +62,10 @@ export function createRecordingSender(responses: CannedResponses = {}): Recordin
 	const calls: RecordedCall[] = [];
 
 	const sender = ((requestDescriptor: { method: string; params?: unknown }) => {
-		const params = Array.isArray(requestDescriptor.params) ? requestDescriptor.params : [];
+		// Deep-snapshot the params at emit time (including nested objects/arrays) so a
+		// later accessor mutation of a shared object cannot rewrite a call we already
+		// recorded - the recorded sequence must reflect the wire traffic as it was sent.
+		const params = structuredClone(Array.isArray(requestDescriptor.params) ? requestDescriptor.params : []);
 		const call: RecordedCall = { method: requestDescriptor.method, params };
 		calls.push(call);