fix(schedule): close absolute-time review gaps

packages/context/time-context/tests/invariant.spec.ts

@@ -141,7 +141,30 @@ describe('time-context invariants', () => {
         `2026-07-14T00:00:00+00:00[${timeZone}]`,
         policy,
       )))
-    }).toThrow(/browser zone cannot format/)
+    }).toThrow(/browser time zone is unsupported/)
+  })
+
+  it('rejects one corrupt zone even when another zone would classify the turn as mixed', async () => {
+    const ctx = await setup()
+    const session = preparing(1, 1, 'Asia/Shanghai')
+    session.append('user/message', createUserMessage({
+      content: [{ type: 'text', text: 'second browser prompt' }],
+      source: {
+        kind: 'user',
+        rpcId: 'turn-1-invalid',
+        clientTimeZone: 'Not/A_Real_Zone',
+      } as never,
+    }), { surfaceOp: 'append' })
+    expect(() => {
+      ctx.emit('session/event', session, event(reading(
+        '1',
+        '1',
+        'model-visible message',
+        '2026-07-14T00:00:00+00:00[UTC]',
+        'Browser time zone for this request: mixed ["Asia/Shanghai","Not/A_Real_Zone"]. '
+        + 'Ask the user to clarify otherwise-unqualified dates and times.',
+      )))
+    }).toThrow(/browser time zone is unsupported/)
   })
 
   it('validates each existing reading against its preceding durable prefix', async () => {

packages/context/time-context/tests/request-zone.spec.ts

@@ -33,6 +33,19 @@ describe('browser request-zone context', () => {
     })
   })
 
+  it('validates every browser zone before classifying a mixed turn', () => {
+    expect(() => deriveBrowserTimeZoneContext([
+      browserMessage('+08:00'),
+    ])).toThrow(/canonical UTC or IANA Area\/Location/)
+    expect(() => deriveBrowserTimeZoneContext([
+      browserMessage('Asia/Shanghai'),
+      browserMessage('Not/A_Real_Zone'),
+    ])).toThrow(/browser time zone is unsupported/)
+    expect(() => deriveBrowserTimeZoneContext([
+      browserMessage('Etc/UTC'),
+    ])).toThrow(/browser time zone must be canonical/)
+  })
+
   it('renders one explicit model policy for every context', () => {
     expect(renderBrowserTimeZoneContext({ kind: 'resolved', timeZone: 'Asia/Shanghai' }))
       .toContain('Interpret otherwise-unqualified dates and times in this zone.')