test: keep review assertions tied to real failure paths

CodeRabbit flagged three non-blocking but valid review gaps: platform-specific mailbox errno checks, brittle UDS connection-failure message assertions, and missing AgentSummary reschedule proof after fork errors. This keeps the fixes narrow by tightening the affected assertions and adding a structured UDS connection error for tests to assert behavior instead of prose.

Constraint: PR #374 is a review follow-up and must not hide warnings, skip tests, or merge the PR.

Rejected: Matching the UDS failure message literal | preserves the brittle coupling CodeRabbit flagged.

Rejected: Asserting only that mailbox writes throw | would allow unrelated pre-path failures to pass.

Confidence: high

Scope-risk: narrow

Directive: Keep UDS connection-failure tests on structured error data, not display wording.

Tested: bun test src/services/AgentSummary/__tests__/agentSummary.test.ts src/utils/__tests__/teammateMailbox.test.ts src/utils/__tests__/udsMessaging.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

Not-tested: GitHub-hosted CodeRabbit refresh until pushed.

src/utils/udsClient.ts

@@ -36,6 +36,18 @@ export type PeerSession = {
   alive: boolean
 }
 
+export class UdsPeerConnectionError extends Error {
+  readonly socketPath: string
+  readonly cause: unknown
+
+  constructor(socketPath: string, cause: unknown) {
+    super(`Failed to connect to peer at ${socketPath}: ${errorMessage(cause)}`)
+    this.name = 'UdsPeerConnectionError'
+    this.socketPath = socketPath
+    this.cause = cause
+  }
+}
+
 // ---------------------------------------------------------------------------
 // Session directory
 // ---------------------------------------------------------------------------
@@ -237,9 +249,7 @@ export async function sendToUdsSocket(
       maxFrameBytes: MAX_UDS_FRAME_BYTES,
       onSettled: finish,
       formatSocketError: err =>
-        new Error(
-          `Failed to connect to peer at ${target.socketPath}: ${errorMessage(err)}`,
-        ),
+        new UdsPeerConnectionError(target.socketPath, err),
     })
     conn.setTimeout(5000, () => {
       finish(new Error('Connection timed out'))