refactor(web): test file cache identity through its public helpers

[juliusmarminge]

The file-content hash was exported only for a unit test, although the file preview uses the cache-key functions that wrap it.

Keep the hash private and check same-length edits through projectFileCacheKey. Remove the redundant identical-call assertion and retain the editor identity tests for local edits, external edits, and environment changes.

Verification: all 3 focused tests pass, web typecheck passes, and focused lint/format checks pass. Runtime behavior and rendered UI are unchanged, so screenshots do not apply.

Model: gpt-6 astra. Harness: Codex in T3 Code.

Note

Make fileContentRevision private and test cache identity via projectFileCacheKey

• Removes the module export of fileContentRevision in fileContentRevision.ts, making the hash helper private to its module
• Reworks the test suite in fileContentRevision.test.ts to assert cache identity through the public projectFileCacheKey helper instead of the now-private function
• Behavioral Change: out-of-tree consumers importing fileContentRevision directly will no longer find the export; the hashing algorithm and revision format are unchanged

^{Macroscope summarized 9fce39c.}

[macroscopeapp]

Approvability

Verdict: Approved at 9fce39c

Macroscope's review found this PR approvable — This is a narrowly scoped encapsulation refactor: the hashing behavior and production cache-key helpers remain unchanged, while the test now exercises those public helpers directly. The only production-file change removes an unused internal export, with no repository consumers or customer-facing behavior affected.

^{You can add or adjust custom eligibility rules. Learn more.}

[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	13.5 KiB	13.6 KiB	+55 B (+0.4%)	15.1 KiB	✅
Codex	Thread snapshot wire	7.0 KiB	7.0 KiB	0 B (0.0%)	7.3 KiB	✅
Codex	Live turn WebSocket wire	6.5 KiB	6.6 KiB	+55 B (+0.8%)	7.8 KiB	✅
Codex	Live turn WebSocket decoded	57.0 KiB	57.1 KiB	+88 B (+0.2%)	66.4 KiB	✅
Codex	Live turn messages	8	10	+2 (+25.0%)	21	✅
Claude	Total thread wire	13.5 KiB	13.5 KiB	+2 B (+0.0%)	15.1 KiB	✅
Claude	Thread snapshot wire	7.0 KiB	7.0 KiB	+2 B (+0.0%)	7.3 KiB	✅
Claude	Live turn WebSocket wire	6.5 KiB	6.5 KiB	0 B (0.0%)	7.8 KiB	✅
Claude	Live turn WebSocket decoded	57.8 KiB	57.8 KiB	0 B (0.0%)	66.4 KiB	✅
Claude	Live turn messages	8	8	0 (0.0%)	21	✅

Baseline: c2cfe59 · PR result: 9fce39c · 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: 113.8 KiB
• Claude decoded thread snapshot: 114.5 KiB

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