test: close per-file coverage gaps opened by the message-machine refactor

Downstream packages lost the tests that exercised their agent-loop-facing
edges when the loop was rewritten. Restore 100% per-file coverage with
behavior tests through public seams: llm-retry config validation and
cancellation races, goal replay drift/staleness/teardown edges, plan-mode
disposed-flush, workspace-context empty-change commits, api-proxy
synchronous send failures, acp-snapshot spill-path extraction and refresh
write-back, ACP injection-triggered turns, cli-demo and tui inbox
lifecycle edges, and agent-loop retry/settlement/lifecycle branches.
The only source changes are narrowly-justified v8 ignore annotations on
invariant guards and one redundant-guard removal (workspace-context).

packages/support/acp-snapshot/tests/normalize.spec.ts

@@ -1,6 +1,7 @@
 import { describe, expect, it } from 'vitest'
 import {
   type NormalizeContext,
+  extractSnapshotSpillPaths,
   normalizeSessionLog,
   normalizeStdout,
   scrubRequestHeaders,
@@ -319,6 +320,24 @@ describe('normalizeSessionLog', () => {
   })
 })
 
+describe('extractSnapshotSpillPaths', () => {
+  it('maps each spill filename to its full matched path, last match wins per name', () => {
+    const log = [
+      'Full formatted result stored at: /tmp/dsh-acp-snapshot-spill/session-c22bc3f1d2af/8a7b6c5d4e3f-bash.txt. Use read with offset/limit, or grep this path to search within it.',
+      'stale copy at /tmp/dsh-acp-snap-012345678/session-aaaaaaaaaaaa/bbbbbbbbbbbb-grep.txt then',
+      'fresh copy at /tmp/dsh-acp-snap-012345678/session-cccccccccccc/dddddddddddd-grep.txt then',
+    ].join('\n')
+    expect(extractSnapshotSpillPaths(log)).toEqual(new Map([
+      ['bash.txt', '/tmp/dsh-acp-snapshot-spill/session-c22bc3f1d2af/8a7b6c5d4e3f-bash.txt'],
+      ['grep.txt', '/tmp/dsh-acp-snap-012345678/session-cccccccccccc/dddddddddddd-grep.txt'],
+    ]))
+  })
+
+  it('returns an empty map when the log carries no snapshot spill paths', () => {
+    expect(extractSnapshotSpillPaths('no spill paths here, only /tmp/other.txt\n')).toEqual(new Map())
+  })
+})
+
 describe('scrubRequestHeaders', () => {
   const headerLine = JSON.stringify({ type: 'session', version: 0, id: 's', createdAt: 1, cwd: '/w' })
   const headerEvent = (header: object) =>