fix(coding-agent): restore compaction preflight events

[minpeter]

Summary

• restore observable auto-compaction lifecycle events for auth/preparation preflight failures
• emit a matching non-error terminal event when an owned preflight attempt cannot proceed
• preserve PR fix(coding-agent): stabilize compaction lifecycle #310 stale-controller protection, including synchronous compaction_start listener supersession
• strengthen the existing overflow characterization and add no-preparation/reentrant-listener coverage

Root cause and attribution

Current main inherited the regression from PR #310 commit b3f643e915: _runAutoCompaction() moved compaction_start below auth/preparation validation and removed early terminal events. The existing no-auth characterization consequently observed zero starts instead of two.

The exact owner boundary was reproduced before this change:

• 10a82f30d (parent of owner commit): PASS
• b3f643e915 (PR fix(coding-agent): stabilize compaction lifecycle #310 head): FAIL, expected 2 / received 0
• 38bd3a3cf (merged main baseline): identical FAIL
• PRs fix(coding-agent): bound compaction status width #328, fix(codemode): bound eval status history on current main #334, and fix(coding-agent): isolate Inspector import crashes #336: identical inherited failure with byte-identical relevant source/test blobs

This repair is isolated from PR #328 and contains only the three compaction lifecycle files shown in the diff.

Verification

• Existing focused RED: reproduced expected [] to have a length of 2 but got +0
• Focused GREEN: 1/1 passed
• Final compaction domain: 45 files, 366 tests passed
• Full workspace after build:
  • coding-agent: 558 files passed / 4 skipped
  • 4,602 tests passed / 32 skipped
  • all remaining workspace suites passed
• Root npm run build: passed
• Root npm run check: passed, including Biome, dependency/import/lock checks, tsgo, browser smoke, web UI, and Neo build/vet/tests
• Real source CLI isolation/auth self-check: 9/9 passed
• Real source CLI RPC with localhost OpenAI Responses mock: passed
• Real source CLI deterministic mock loop with localhost OpenAI Completions mock: passed
• Independent final read-only review: PASS - no actionable findings

Evidence

Local evidence index:

local-ignore/qa-evidence/20260724-compaction-preflight-lifecycle/EVIDENCE.md

Supporting source-CLI artifacts:

• local-ignore/qa-evidence/20260725-compaction-preflight-rpc/
• local-ignore/qa-evidence/20260725-compaction-preflight-mock/

Original CI attribution:

local-ignore/qa-evidence/20260724-compaction-progress-live-cdp-final/ci-current-main-attribution/attribution.md

---

Summary by cubic

Restores auto-compaction preflight lifecycle events and balances start/end signals around auth/preparation checks. Prevents stale terminal events when a start listener supersedes controller ownership.

• Bug Fixes
  • Emit compaction_start before auth/prep; on preflight reject, emit a matching non-error compaction_end; recheck ownership after start to avoid stale ends.
  • Preserve overflow recovery and controller-ownership safeguards; add tests for no-prep and listener-abort cases; update changes.md.

^{Written for commit d027216. Summary will update on new commits.}

[minpeter]

Superseded by the current-main ownership fix at minpeter@e1d0c4d on fix/compaction-preflight-ownership-current-main. Live main already restored balanced preflight start/end events; that commit isolates the remaining synchronous-listener ownership hole so an aborted or superseded attempt cannot emit a stale terminal event. Draft PR creation is currently blocked by GitHub’s critical “Incident with Pull Requests” outage (GraphQL request 966C:2882C:1FB40D:262C04:6A63C18F; REST request D97A:2882C:1FD2CD:2651DE:6A63C1CA).