[jferrl]

Description

Almost every Token() call returns a cached token, and nothing measured that path. A
change that reintroduced work there — an allocation per call, or a lost cache — would not
fail any existing test, because they all assert behaviour rather than cost.

Baseline on an 18-core M-series machine:

BenchmarkInstallationTokenSource_CacheHit-18
    31613367    34.90 ns/op    0 B/op    0 allocs/op

The benchmark asserts the test server saw exactly one request after the loop. Without that
check it would still print a number if caching broke — it would just be timing HTTP round
trips and calling them cache hits. Verified against a build with the cache removed:

benchmark made 30813 installation-token requests, want 1: the loop was not measuring cache hits

What is deliberately not here

No concurrency tests. I wrote a set that counted HTTP requests under 200 concurrent
callers, then checked whether they earned their place by mutating the source:

Mutation	Caught by the existing suite
Caching disabled entirely	Yes — TestReuseTokenSourceWithSkew
Cache kept, lock dropped across the refresh	Yes — TestReuseTokenSourceWithSkew
Wrapper correct but not wired into NewInstallationTokenSource	Yes — Test_WithInstallationExpirySkew_Wiring

All three were already covered, so the new tests were redundant and were dropped. The
existing collapse test is also the stronger assertion: it checks every goroutine receives
the same token, not just that one request was made.

Type of Change

• 🔧 Chore (dependency updates, tooling, etc.)

Testing

• New and existing unit tests pass locally with my changes
• I have tested this change manually

go test ./... passes and golangci-lint run ./... reports 0 issues. The benchmark does
not run during go test, so CI time is unchanged.

Documentation

• I have updated the documentation accordingly
• I have updated the CHANGELOG.md file
• I have added/updated code comments where necessary

CHANGELOG.md is untouched: this adds no library behaviour for a consumer to act on.

Checklist

• My code follows the style guidelines of this project
• I have performed a self-review of my own code
• My changes generate no new warnings
• I have checked my code and corrected any misspellings
• My changes are compatible with the Go versions in go.mod and the CI matrix

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 98.88%. Comparing base (69b5dd9) to head (487cbe9).

Additional details and impacted files

@@           Coverage Diff           @@
##             main      #71   +/-   ##
=======================================
  Coverage   98.88%   98.88%           
=======================================
  Files           5        5           
  Lines         447      447           
=======================================
  Hits          442      442           
  Misses          5        5           

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