feat: reconcile exempts pinned agent terminals

M3 of pinned terminals (v0.17.0):
- reconcileAgentTerminals skips removal of agent tabs with pin !== undefined
  (the agent closed them / pty exited, but the user pinned them)
- The xterm reconnect-failure banner is the user-visible 'disconnected'
  signal (design M3 convergence: no title suffix, no meta write)
- A later push reviving the same uuid is a no-op (id already exists)
- Unpinned agent tabs still remove as before; toAdd path unaffected

src/client/state.ts

@@ -1002,7 +1002,13 @@ export function reconcileAgentTerminals(
   const existingUuids = new Set(existingAgentTabs.map(tab => agentUuidOf(tab.id)))
   const serverUuids = new Set(agentTerminals.map(t => t.uuid))
   const toAdd = agentTerminals.filter(t => !existingUuids.has(t.uuid))
-  const toRemove = existingAgentTabs.filter(tab => !serverUuids.has(agentUuidOf(tab.id)))
+  // Pinned agent terminals (v0.17.0+) are EXEMPT from removal: the agent
+  // closed them or the pty exited, but the user pinned them so the tab
+  // stays as a disconnected surface. The xterm view's reconnect-failure
+  // banner is the user-visible "disconnected" signal (the design's M3
+  // convergence: no title suffix, no meta write — the tab keeps its uuid
+  // so a later reconcile push revives it if the agent reopens the same one).
+  const toRemove = existingAgentTabs.filter(tab => !serverUuids.has(agentUuidOf(tab.id)) && tab.pin === undefined)
   if (toAdd.length === 0 && toRemove.length === 0) return state
   // Remove tabs whose uuids vanished from the server list (the agent closed
   // them, or the pty exited and was reaped). Reuse closeTab's leaf cleanup;

tests/agent-terminal-reconcile.spec.ts

@@ -1,7 +1,7 @@
 import { describe, expect, it } from 'vitest'
 import {
   allLeaves, makeDefaultState, openTabInActivePane, reconcileAgentTerminals,
-  tabOpenIn, toggleBottomPanel,
+  setTabPin, tabOpenIn, toggleBottomPanel,
 } from '../src/client/state.ts'
 
 describe('agent terminal reconciliation', () => {
@@ -69,4 +69,61 @@ describe('agent terminal reconciliation', () => {
     expect(allLeaves(s.bottomSplits).flatMap(l => l.tabs).some(t => t.id === 'agent:aaa-111')).toBe(true)
     expect(allLeaves(s.splits).flatMap(l => l.tabs).some(t => t.id === 'agent:aaa-111')).toBe(false)
   })
+
+  describe('pinned agent terminal exemption (v0.17.0)', () => {
+    it('keeps a pinned agent tab when its uuid vanishes from the server list', () => {
+      let s = makeDefaultState(400, true)
+      s = reconcileAgentTerminals(s, [
+        { uuid: 'aaa-111', title: 'keep' },
+        { uuid: 'bbb-222', title: 'pinned' },
+      ])
+      // Pin bbb-222, then drop it from the server list.
+      s = setTabPin(s, 'agent:bbb-222', { scope: 'global' })
+      s = reconcileAgentTerminals(s, [{ uuid: 'aaa-111', title: 'keep' }])
+      // aaa-111 (unpinned) survived; bbb-222 (pinned) survived too.
+      expect(tabOpenIn(s, 'agent:aaa-111')).toBe(true)
+      expect(tabOpenIn(s, 'agent:bbb-222')).toBe(true)
+      // The pin marker is intact.
+      const tabs = allLeaves(s.splits).flatMap(l => l.tabs)
+      const pinned = tabs.find(t => t.id === 'agent:bbb-222')!
+      expect(pinned.pin).toEqual({ scope: 'global' })
+    })
+
+    it('still removes an unpinned agent tab when the uuid vanishes', () => {
+      let s = makeDefaultState(400, true)
+      s = reconcileAgentTerminals(s, [
+        { uuid: 'aaa-111', title: 'pinned' },
+        { uuid: 'bbb-222', title: 'unpinned' },
+      ])
+      s = setTabPin(s, 'agent:aaa-111', { scope: 'workspace', homeCwd: '/p' })
+      s = reconcileAgentTerminals(s, []) // both vanish
+      // Pinned stays, unpinned goes.
+      expect(tabOpenIn(s, 'agent:aaa-111')).toBe(true)
+      expect(tabOpenIn(s, 'agent:bbb-222')).toBe(false)
+    })
+
+    it('a pinned tab whose uuid RETURNS in a later push is a no-op (already exists)', () => {
+      let s = makeDefaultState(400, true)
+      s = reconcileAgentTerminals(s, [{ uuid: 'aaa-111', title: 'gone' }])
+      s = setTabPin(s, 'agent:aaa-111', { scope: 'global' })
+      // First push without it: exempted, stays.
+      s = reconcileAgentTerminals(s, [])
+      expect(tabOpenIn(s, 'agent:aaa-111')).toBe(true)
+      // Later push brings it back: reconcile sees the uuid already exists,
+      // does not re-add, does not touch the pin.
+      const before = s
+      s = reconcileAgentTerminals(s, [{ uuid: 'aaa-111', title: 'gone' }])
+      expect(s).toBe(before)
+    })
+
+    it('exemption does not block the toAdd path (new uuids still land)', () => {
+      let s = makeDefaultState(400, true)
+      s = reconcileAgentTerminals(s, [{ uuid: 'aaa-111', title: 'first' }])
+      s = setTabPin(s, 'agent:aaa-111', { scope: 'global' })
+      // aaa-111 vanishes (exempted), bbb-222 is brand-new.
+      s = reconcileAgentTerminals(s, [{ uuid: 'bbb-222', title: 'second' }])
+      expect(tabOpenIn(s, 'agent:aaa-111')).toBe(true) // pinned, kept
+      expect(tabOpenIn(s, 'agent:bbb-222')).toBe(true) // new, added
+    })
+  })
 })