fix: close peer socket listener handoff window

CodeRabbit and Claude review found that documenting caller-owned raw socket errors still left a Promise handoff window and a stale timeout-listener risk. The peer connection API now requires a caller error handler and installs it before resolving, while cleanup removes internal error and timeout listeners on every path.

Constraint: Keep the fix precise to PR #375 review feedback and avoid warning suppression or fallback behavior.
Rejected: Leave the behavior documented only | still permits an unhandled socket error window between resolve and caller listener attachment.
Rejected: Keep a no-op internal error listener | would silently swallow caller-owned socket errors.
Confidence: high
Scope-risk: narrow
Directive: Do not add raw connectToPeer callers without providing a real onSocketError handler and capability handshake.
Tested: bun test src/utils/__tests__/udsMessaging.test.ts src/services/AgentSummary/__tests__/agentSummary.test.ts
Tested: bunx tsc --noEmit --pretty false
Tested: bun run lint
Tested: bun run test:all
Tested: bun test --coverage --coverage-reporter lcov --coverage-dir coverage
Tested: bun run build
Tested: bun run build:vite
Tested: bun audit
Not-tested: Manual external ACP peer runtime beyond repository tests.

src/services/AgentSummary/__tests__/agentSummary.test.ts

@@ -161,7 +161,9 @@ describe('startAgentSummarization', () => {
 
     expect(forkCalls).toEqual([])
     expect(updateCalls).toEqual([])
-    expectDebugLogContaining('no bounded context available')
+    expectDebugLogContaining(
+      '[AgentSummary] Skipping summary for task-1: no bounded context available',
+    )
   })
 
   test('skips summarization before building context when transcript is too short', async () => {
@@ -173,7 +175,9 @@ describe('startAgentSummarization', () => {
 
     expect(forkCalls).toEqual([])
     expect(updateCalls).toEqual([])
-    expectDebugLogContaining('not enough messages (2)')
+    expectDebugLogContaining(
+      '[AgentSummary] Skipping summary for task-1: not enough messages (2)',
+    )
   })
 
   test('skips and reschedules while poor mode is active', async () => {
@@ -188,7 +192,7 @@ describe('startAgentSummarization', () => {
 
     expect(forkCalls).toEqual([])
     expect(updateCalls).toEqual([])
-    expectDebugLogContaining('poor mode active')
+    expectDebugLogContaining('[AgentSummary] Skipping summary — poor mode active')
     expect(scheduledCount).toBe(initialScheduledCount + 1)
     expect(lastTimerHandle).not.toBe(initialTimerHandle)
   })
@@ -218,7 +222,7 @@ describe('startAgentSummarization', () => {
 
     handle.stop()
 
-    expectDebugLogContaining('Stopping summarization for task-1')
+    expectDebugLogContaining('[AgentSummary] Stopping summarization for task-1')
     expect(clearedHandles).toEqual([pendingHandle])
   })
 })

src/utils/__tests__/udsMessaging.test.ts

@@ -307,7 +307,9 @@ describe('UDS inbox retention', () => {
       '../udsClient.js'
     )
 
-    const error = await connectToPeer(path).then(
+    const error = await connectToPeer(path, () => {
+      throw new Error('Unexpected post-connect socket error')
+    }).then(
       () => undefined,
       err => err,
     )
@@ -338,13 +340,25 @@ describe('UDS inbox retention', () => {
     })
 
     let client: Socket | undefined
+    const socketErrors: Error[] = []
     try {
       const { connectToPeer } = await import('../udsClient.js')
-      client = await connectToPeer(path, 1000)
+      client = await connectToPeer(
+        path,
+        error => {
+          socketErrors.push(error)
+        },
+        1000,
+      )
       await new Promise(resolve => setTimeout(resolve, 100))
 
       expect(client.destroyed).toBe(false)
-      expect(client.listenerCount('error')).toBe(0)
+      expect(client.listenerCount('error')).toBe(1)
+      expect(client.listenerCount('timeout')).toBe(0)
+
+      const socketError = new Error('post-connect failure')
+      client.emit('error', socketError)
+      expect(socketErrors).toEqual([socketError])
     } finally {
       client?.destroy()
       for (const socket of sockets) {

src/utils/udsClient.ts

@@ -266,36 +266,49 @@ export async function sendToUdsSocket(
 
 /**
  * Connect to a peer and return the raw socket for bidirectional communication.
- * The caller is responsible for managing the connection lifecycle, including
- * attaching an 'error' listener immediately after the Promise resolves. This
- * function detaches its internal error listener on successful connect so
- * caller-owned socket errors are not silently swallowed.
+ * The caller owns the post-connect lifecycle through onSocketError, which is
+ * attached before the Promise resolves so peer socket errors cannot be
+ * swallowed or surface through a listener handoff window.
+ * Pre-connect failures reject with UdsPeerConnectionError.
+ * This only opens the transport; callers still own any capability handshake.
  */
 export function connectToPeer(
   socketPath: string,
+  onSocketError: (error: Error) => void,
   timeoutMs = 5000,
 ): Promise<Socket> {
   return new Promise<Socket>((resolve, reject) => {
     const conn = createConnection(socketPath)
     let settled = false
-    const fail = (cause: unknown) => {
+    const onTimeout = () => {
+      fail(new Error('Connection timed out'))
+    }
+    function cleanupListeners(): void {
+      conn.setTimeout(0)
+      conn.off('error', fail)
+      conn.off('timeout', onTimeout)
+    }
+    function fail(cause: unknown): void {
       if (settled) {
         return
       }
       settled = true
+      cleanupListeners()
       conn.destroy()
       reject(new UdsPeerConnectionError(socketPath, cause))
     }
     conn.once('connect', () => {
+      if (settled) {
+        return
+      }
       settled = true
-      conn.setTimeout(0)
-      conn.off('error', fail)
+      cleanupListeners()
+      conn.on('error', onSocketError)
       resolve(conn)
     })
     conn.on('error', fail)
-    conn.setTimeout(timeoutMs, () => {
-      fail(new Error('Connection timed out'))
-    })
+    conn.once('timeout', onTimeout)
+    conn.setTimeout(timeoutMs)
   })
 }