perf(server): derive complete checkpoint summaries from numstat

[rynfar]

Automatic checkpoint summaries generated full patches solely to count changed lines. Large patches could hit the output cap and save incomplete totals. Use NUL-delimited Git numstat for those summaries; on-demand diffs still request full patches.

Adapts upstream #9694, c163d502dd32b993c03d8c20a5fae55b159bd8dc. Preserves Pylon rollback anchors, missing-baseline handling, assistant-message linkage, completion receipts, and Sigstore dependencies. The server no longer imports Pierre’s parser, so its direct dependency is removed.

Validation: all 63 focused checkpoint, reactor, Git-driver, and process tests pass. Coverage includes a 25,000-line summary before completion receipts, rename/copy destinations, unusual filenames, binary files, whitespace modes, unchanged user index, and output-limit errors. Server typecheck and scoped lint pass.

Model: GPT-6 Astra. Harness: Codex.

---

^{Need help on this PR? Tag @codesmith-bot with what you need. Autofix is disabled.}

[github-actions]

Thread transfer impact

✅ Thread transfer remains within every enforced ceiling.

Provider	Metric	Main baseline	This PR	Impact	PR ceiling
Codex	Total thread wire	13.8 KiB	13.8 KiB	−40 B (−0.3%)	15.1 KiB	✅
Codex	Thread snapshot wire	7.1 KiB	7.1 KiB	−4 B (−0.1%)	7.3 KiB	✅
Codex	Live turn WebSocket wire	6.7 KiB	6.7 KiB	−36 B (−0.5%)	7.8 KiB	✅
Codex	Live turn WebSocket decoded	57.4 KiB	57.3 KiB	−44 B (−0.1%)	66.4 KiB	✅
Codex	Live turn messages	10	9	−1 (−10.0%)	21	✅
Claude	Total thread wire	13.8 KiB	13.8 KiB	+64 B (+0.5%)	15.1 KiB	✅
Claude	Thread snapshot wire	7.1 KiB	7.1 KiB	+7 B (+0.1%)	7.3 KiB	✅
Claude	Live turn WebSocket wire	6.7 KiB	6.7 KiB	+57 B (+0.8%)	7.8 KiB	✅
Claude	Live turn WebSocket decoded	58.1 KiB	58.2 KiB	+88 B (+0.1%)	66.4 KiB	✅
Claude	Live turn messages	8	10	+2 (+25.0%)	21	✅

Baseline: 16c999a · PR result: 688491f · Source CI: success

Scenario and decoded snapshot size

10 historical turns, 5 command tools per turn, 878.9 KiB retained MCP result per historical turn, and a 1.05 MiB retained result in the measured turn.

• Codex decoded thread snapshot: 111.2 KiB
• Claude decoded thread snapshot: 111.9 KiB

Updated in place by a trusted workflow. PR artifacts are strictly validated and never executed.