feat(lab): claude-p auto-compact detection + coding-arm authoring parity

The coding_markdown_v1 acq pilot exposed two run-killing gaps. First,
claude -p auto-compacted twice (preTokens 207,948 and 179,180) after the
model batch-whole-read all 31 docs, silently replacing served documents
with lossy summaries - invisible to the runner, and it voids the typed
context_overflow mechanism whole-read control rows depend on. Second,
the CC Write prior captured generate_docx ({filename, content}, ten
straight rejections) and the conjunctive terse refusal defeated the
model's one-key-at-a-time debugging.

- claudeP: parse system/compact_boundary stream events (real fixtures
  from the pilot session; snake_case variants covered); receipts ride
  the existing StreamChatResult.compactions rail with usage zeroed (the
  spend is already in turn envelopes) and triggerReason "provider_auto";
  system events now count as watchdog liveness (the pilot's second
  compaction ran 377s, past the 240s inactivity limit).
- lab-beaver-arm: top-level context_compaction_count/context_compactions
  metrics + loud warn on nonzero.
- localAssistantTools (CODING_PARITY only): generate_docx accepts
  'content' as the body and derives 'title' from filename/first heading,
  teaching the schema via a receipt note; the refusal now states the
  full expected contract plus received keys. Frozen arms byte-identical
  (probe: v1 keeps the terse refusal).
- upstreamMikeBenchmarkSurface: CODING_GENERATE_DOCX_TOOL names its keys
  in prose against the Write prior ("this is not a file Write"); same
  name, same schema.

Probes: compaction fixtures 7/7; plane probe parity 12/12, md 5/5,
plain 3/3; served-surface coding2/coding/v2 preflights green; suites
57/57; tsc clean.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_011pfUVhNFTRvhYGXBwoKNj6