perf(git): replace per-request token decryption with indexed hash lookup

[jaredglaser]

Summary

Git HTTP auth (src/routes/api/git.$.ts) loaded every git_tokens row and JWE-decrypted each one on every request before the timing-safe compare, making auth O(n) in token count with a JWE decrypt per row.

• Migration 024_git_token_hash.sql adds a token_hash column (SHA-256 hex of the raw token) with a unique index.
• createGitToken now writes the hash at creation (hashGitToken in src/lib/git/git-token-auth.ts).
• Auth is now a single indexed lookup by token_hash plus timingSafeEqual, mirroring the sessions pattern in src/lib/auth/session-manager.ts. A length guard prevents timingSafeEqual from throwing on a malformed stored hash.
• Rows created before the migration have a NULL hash. Those fall back to the legacy decrypt-and-compare scan (now scoped to WHERE token_hash IS NULL), and the hash is backfilled on a successful match so the next request takes the fast path. Keyring and JWE decrypt load lazily, so the fast path never touches them.
• Token matching was extracted to src/lib/git/git-token-auth.ts with injected repo and decrypt dependencies so it is unit-testable outside the route file.
• Repository: findAllEncrypted (sole caller was the route) became findLegacyEncrypted; added findByTokenHash and setTokenHash.

Migration numbering note: open PRs #276 and #278 also claim 024, so renumbering this migration on rebase is expected.

Testing

• bun run typecheck clean.
• bun test --isolate src/lib/git/__tests__/git-token-auth.test.ts (8 pass): fast path skips legacy scan and decryption, legacy match backfills the hash, malformed stored hash falls through without throwing, all-decrypt-failure logging, fire-and-forget backfill failure does not throw.
• bun test --isolate src/lib/database/repositories/__tests__/git-token-repository.test.ts (17 pass): create inserts token_hash, findByTokenHash, findLegacyEncrypted filters NULL-hash rows, setTokenHash.
• bun test --isolate src/data/__tests__/git-tokens.functions.test.ts (8 pass): created token stores the SHA-256 hash of the raw token.

Closes #243

🤖 Generated with Claude Code

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ℹ️ Review info

⚙️ Run configuration

Configuration used: Organization UI

Review profile: ASSERTIVE

Plan: Pro

Run ID: 4460f34e-d2eb-4f8c-be00-442ba7b31e3f

📥 Commits

Reviewing files that changed from the base of the PR and between 5d66d9f and a3450f9.

📒 Files selected for processing (8)

• migrations/024_git_token_hash.sql
• src/data/__tests__/git-tokens.functions.test.ts
• src/data/git-tokens.functions.tsx
• src/lib/database/repositories/__tests__/git-token-repository.test.ts
• src/lib/database/repositories/git-token-repository.ts
• src/lib/git/__tests__/git-token-auth.test.ts
• src/lib/git/git-token-auth.ts
• src/routes/api/git.$.ts

✨ Finishing Touches

🧪 Generate unit tests (beta)

• Create PR with unit tests
• Commit unit tests in branch perf/f18-git-token-hash-lookup

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