fix: canonicalize the upstream key, not just the repository path [patch]

[matt-edmondson]

Fixes #37.

BranchStateHandler.Resolve canonicalized one half of the MirrorKey and passed the other through verbatim:

MirrorKey key = new(route.Upstream, Canonicalize(route.RepositoryPath));

route.Upstream comes straight off the URL segment. Both checks immediately above it key their dictionaries with StringComparer.OrdinalIgnoreCase — verified in UpstreamRegistry and RepositoryAllowList — so GitHub and github are accepted as the same configured upstream. Everything derived from the key afterwards compares ordinally.

The result is the duplication issue #24 removed for repository-path casing, still reachable through the sibling field. Measured, not assumed: with the fix reverted, TwoSpellingsOfOneUpstream_ShareOneMirrorFetchDiffAndAdmission reports clone running 2 times where it expects 1, and a second mirror.git appears on the volume.

The change

One line — both halves of the key now go through Canonicalize:

MirrorKey key = new(Canonicalize(route.Upstream), Canonicalize(route.RepositoryPath));

Canonicalize's doc comment is rewritten to match: it had spelled out at length exactly why the path must be canonicalized while describing only the path, which is what made the omission easy to miss. It now names the upstream key as the other half and says why the same argument covers it.

Nothing reaching the forge changes

Worth stating explicitly, because canonicalizing something a caller sent could look like rewriting a request:

• The upstream base URL comes from registry.TryResolve, i.e. from configuration — never from the caller's segment. The canonical key is only this service's own bookkeeping.
• The repository URL is still built with UpstreamUrl.TryCombine(upstreamBase, route.RepositoryPath, …) — the caller's spelling of the path, untouched, per the existing note that the forge is the authority on how it spells its own names.
• registry.TryResolve and allowList.IsAllowed still receive route.Upstream, and EndpointLog.UnknownUpstream still logs the literal spelling the caller used.

What the canonical key now feeds consistently: MirrorStore's on-disk directory, MirrorKey.ToFlightKey() for SingleFlight coalescing, DiffKey, the admission key, and the metric labels.

Tests

Added to RepositoryIdentityTests, the class #24's fix created, mirroring its four cases with upstream casing varying instead of path casing. Verified by stashing the BranchStateHandler.cs change and re-running: three of the four fail against the old implementation.

Test	Old implementation
TwoSpellingsOfOneUpstream_ShareOneMirrorFetchDiffAndAdmission	fails — clone count is 2, expected 1
TwoSpellingsOfOneUpstream_ProduceOneMirrorDirectory	fails — two mirror.git directories on the volume
ARequestWithTheUpstreamSpelledDifferently_MirrorsUnderTheCanonicalUpstream	fails — nothing under <root>/github/…
TwoSpellingsOfOneUpstream_AreBothServed	passes — this one is the premise (both spellings are served), not the bug

The class <remarks> is widened from "the path" to "the key", since it is now documenting both fields.

Full suite: 203 passed, 0 failed, 0 skipped. Whole solution builds with 0 warnings, 0 errors.

🤖 Generated with Claude Code

https://claude.ai/code/session_018VSTy8Ye7JXqeFqvhrmnRt

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[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

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