Route GVFS endpoints to dedicated cache servers

[Derrick Stolee (derrickstolee)]

Why This Matters

The microsoft/git GVFS helper can route protocol endpoints to dedicated cache servers, but VFS for Git previously sent every protocol request to one global cache URL. Supporting the same endpoint-specific preferences lets cache infrastructure migrate incrementally without making a dedicated endpoint a hard dependency.

The /gvfs/sizes endpoint is unique to VFS for Git, so this change adds the corresponding gvfs.sizes.cache-server setting alongside the prefetch, GET, and POST settings used by Scalar.

Commit Narrative

1. Route GVFS endpoints to dedicated cache servers: load, persist, and validate endpoint overrides; add matching gvfs clone options; preserve overrides during mount-time cache resolution.
2. Fall back safely from dedicated cache endpoints: retry failed endpoint requests through the global cache, preserve circuit-breaker budgets, distinguish network body failures from local processing errors, propagate cancellation unchanged, and emit authority-only telemetry.
3. Explain endpoint-specific cache routing: document configuration, precedence, fallback order, and troubleshooting.
4. Cover prefetch failure telemetry redaction: exercise terminal prefetch failures at the production entry point and ensure diagnostics retain only URI authority.

Routing and Fallback Behavior

• gvfs.prefetch.cache-server routes /gvfs/prefetch.
• gvfs.get.cache-server routes object GET requests.
• gvfs.post.cache-server routes object POST requests.
• gvfs.sizes.cache-server routes /gvfs/sizes.
• If an endpoint-specific route is absent or fails, the request uses gvfs.cache-server.
• Sizes requests can additionally fall back from the global cache to origin.
• Existing repositories without endpoint overrides retain their previous behavior.

Endpoint-to-global transitions do not consume the process-wide circuit-breaker budget. Response-body transport failures can trigger fallback, while local processing failures remain on the current route. OperationCanceledException propagates without retry or fallback. Fallback and terminal prefetch diagnostics include only URI authority, excluding credentials, paths, queries, and fragments.

Clone and Configuration Surface

gvfs clone accepts --prefetch-cache-server-url, --get-cache-server-url, --post-cache-server-url, and --sizes-cache-server-url. Values are stored in local Git config and malformed absolute URLs are rejected.

gvfs cache-server --get and --set continue to operate only on the global cache setting. Endpoint-specific values can be inspected or changed with git config --local.

Related microsoft/git Changes

• microsoft/git#836: gvfs-helper: add config to incrementally replace cache servers
• microsoft/git#849: scalar: add endpoint cache-server clone options

Tests

Coverage includes configuration precedence and persistence, mount-time resolution, clone option parsing and URL validation, endpoint/global/origin routing, HTTP and transport failures, response-body failures, local handler failures, cancellation propagation, telemetry redaction, terminal endpoint reporting, and circuit-breaker accounting.

[Derrick Stolee (derrickstolee)]

This PR has not yet been vetted by the author.

It has now been vetted.

[tyrielv]

InProcessMount.cs looks like it needs a call to WithEndpointOverridesFrom

[Derrick Stolee (derrickstolee)]

🤖 Agreed - I am tracing this cache resolution path and will preserve the endpoint-specific overrides here as well.

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_{AI response generated by rocket}

[Derrick Stolee (derrickstolee)]

🤖 Fixed in 072c1690: mount-time global cache resolution now reapplies the endpoint-specific overrides from local config, matching the existing clone, prefetch, and verb resolution paths.

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_{AI response generated by rocket}

[tyrielv]

Machine-drafted review (Review Swarm), reviewed and approved by me before posting. Five inline notes below; the circuit-breaker one is the load-bearing item.