fix(review): detect working tree renames without changing the index

[rynfar]

Review diffs presented a moved tracked file and its new untracked path as a deletion and addition. Use a temporary copy of the Git index to detect renames across the complete working tree while preserving the user's real index, staged deletions and split-index state. Fall back to separate diffs when the combined read is unavailable.

Adopts 26894dda7b6d78c5863ccec6581caf0ec7f4843b (#8086), fully, from cycle #497 bounded by 4a4c6dd2adc350a68ba18bb28b24b5a7e4660dab. Pylon's existing Git command execution and review response contracts remain in place.

Validation: GitVcsDriverCore focused suite passed (part of 247 tests across five affected server files); server/shared typechecks and scoped lint passed. Independent adversarial review found no actionable issues, including temporary index cleanup, literal NUL pathspecs, split indexes, staged deletions and fallback behavior. CI must pass on the final head before merge.

Implemented with GPT-6 in Codex.

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Project	Deployment	Actions	Updated
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Thread transfer impact

✅ Thread transfer remains within every enforced ceiling.

Provider	Metric	Main baseline	This PR	Impact	PR ceiling
Codex	Total thread wire	14.1 KiB	14.1 KiB	−9 B (−0.1%)	15.1 KiB	✅
Codex	Thread snapshot wire	7.2 KiB	7.2 KiB	−5 B (−0.1%)	7.3 KiB	✅
Codex	Live turn WebSocket wire	6.9 KiB	6.8 KiB	−4 B (−0.1%)	7.8 KiB	✅
Codex	Live turn WebSocket decoded	58.8 KiB	58.8 KiB	0 B (0.0%)	66.4 KiB	✅
Codex	Live turn messages	10	10	0 (0.0%)	21	✅
Claude	Total thread wire	14.1 KiB	14.1 KiB	−7 B (−0.0%)	15.1 KiB	✅
Claude	Thread snapshot wire	7.2 KiB	7.2 KiB	−1 B (−0.0%)	7.3 KiB	✅
Claude	Live turn WebSocket wire	6.9 KiB	6.9 KiB	−6 B (−0.1%)	7.8 KiB	✅
Claude	Live turn WebSocket decoded	59.7 KiB	59.7 KiB	0 B (0.0%)	66.4 KiB	✅
Claude	Live turn messages	10	10	0 (0.0%)	21	✅

Baseline: f3402be · PR result: 884fc77 · 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: 115.6 KiB
• Claude decoded thread snapshot: 116.3 KiB

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