fix: canonicalise the repository path so one repository is one mirror [patch]

[matt-edmondson]

Fixes #24

What was wrong

The allow-list matches case insensitively on purpose — RepositoryPattern.Translate compiles with RegexOptions.IgnoreCase, and its remarks say why. But every identity derived from the same repositoryPath afterwards compares ordinally:

• MirrorStore.TryResolve Path.Combines the segments verbatim, so on the Linux container this ships as, Studio/Game.git and studio/game.git are two different mirror.git directories.
• MirrorKey.ToFlightKey() backs both the SingleFlight clone/fetch coalescing in MirrorFetcher and the Repository component of DiffKey, so the two spellings share neither fetch coalescing nor a DiffCache entry.
• CredentialAdmission.Key hashes the path ordinally, so each spelling is probed with its own git ls-remote.

Two callers addressing one repository with different casing therefore both pass the allow-list and then cost two bare mirrors on disk, two fetches per polling heartbeat, two computed diffs and two admission probes — the duplication this service exists to remove.

The change

BranchStateHandler.Resolve reduces the repository path to lower case once, immediately after the allow-list accepts it and before it becomes the mirror directory, the flight key, the DiffKey or the admission key. The new Canonicalize helper carries a remark explaining that the allow-list's case-insensitivity is what makes it necessary, so it does not get "simplified" away later, as the triage comment asked.

What is sent to the forge keeps the caller's spelling: the canonical form exists for this service's own bookkeeping, and the forge is the authority on how it spells its own repository names. That also means a deployment against a case-sensitive forge keeps working.

The README gains a short paragraph on this, since the on-disk layout is operator-visible.

Tests

New GitBranchStateCache.Tests/Integration/RepositoryIdentityTests.cs, driving the real handler through the existing ServiceFixture (mock filesystem, scripted git):

• both spellings are still served (the premise the rest rests on)
• two spellings share one clone, one ls-remote and one diff-tree
• two spellings leave one mirror.git directory on the volume
• a request spelled differently from the allow-list mirrors under the canonical lower-case path

Three of the four fail against main (2 clones, 2 mirror directories, no canonical directory) and pass with the change; verified in both directions by temporarily reverting Canonicalize to the identity function and re-running.

Full suite: 197 passed, 0 failed, in both Debug and Release. Release build is clean, 0 warnings.

Noted, not changed

The upstream key has the same shape of problem — UpstreamRegistry and RepositoryAllowList both look it up OrdinalIgnoreCase, so github and GitHub would split identity the same way. It is left alone here to keep this change to what the issue scopes; worth its own issue if it is judged worth fixing.

🤖 Generated with Claude Code

https://claude.ai/code/session_019AADb2wQHKruFMAnTyzCfv

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Generated by Claude Code

[sonarqubecloud]

Quality Gate passed

Issues
7 New issues
0 Accepted issues

Measures
0 Security Hotspots
100.0% Coverage on New Code
0.0% Duplication on New Code

See analysis details on SonarQube Cloud