Verify each finding against the current code and only fix it if needed.

Inline comments:
In `@pkg/auth/manager_chain.go`:
- Around line 45-47: The current chainCacheKey (manager.chainCacheKey) builds a
key by concatenating m.realm.Value and strings.Join(m.chain, "->"), which can
collide when values contain ":" or "->"; replace this with an unambiguous
encoding (e.g., JSON-encode a small struct {Realm string; Chain []string} or
base64 of a deterministic encoding) so realm and chain elements are uniquely
separated; update chainCacheKey to return that encoded string (and handle any
encoding error deterministically) instead of the current simple concatenation.

---

Outside diff comments:
In `@pkg/auth/manager_chain.go`:
- Around line 55-87: The current cache miss path (using chainCacheKey +
processCredentialCache) is race-safe but allows duplicate authentication because
concurrent goroutines can both miss at the initial Load and both call
authenticateFromIndex, causing duplicate AssumeRole calls; fix by adding per-key
in-flight coordination (e.g., use singleflight.Group or a per-key mutex map)
around the miss path: when Load misses, enter the singleflight call keyed by
chainCacheKey, inside the singleflight function re-check
processCredentialCache.Load (or call findFirstValidCachedCredentials) to avoid a
lost-race, then call authenticateFromIndex only once and Store the resulting
processCachedCreds to processCredentialCache before returning; ensure the public
path around cache load -> singleflight -> re-check -> authenticateFromIndex ->
Store uses chainCacheKey and references processCredentialCache,
authenticateFromIndex, findFirstValidCachedCredentials, processCachedCreds and
m.chainCacheKey.

---

Nitpick comments:
In `@pkg/auth/manager_chain.go`:
- Around line 36-42: The exported ResetProcessCredentialCache helper is
test-only and should be hidden from the production API: rename the function
ResetProcessCredentialCache to an unexported resetProcessCredentialCache and
keep its logic operating on processCredentialCache.Range/Delete; if
external-package tests need access, move or duplicate an exported wrapper into
an export_test.go test-only file instead of keeping this in the runtime package
API.

Verify each finding against the current code and only fix it if needed.

Nitpick comments:
In `@pkg/auth/manager_chain.go`:
- Around line 51-89: Add performance tracking to authenticateChain by invoking
perf.Track at function entry: in the method manager.authenticateChain,
immediately after the function begins, add a deferred call using defer
perf.Track(nil, "auth.Manager.authenticateChain")() so the function's latency is
recorded; ensure the perf package is imported if not already. This keeps the hot
path aligned with repo tracking conventions and measures cache hit/miss latency
for authenticateChain.

Verify each finding against the current code and only fix it if needed.

Inline comments:
In `@pkg/auth/manager_chain_process_cache_test.go`:
- Around line 17-46: Remove the manual countingIdentity test double and replace
it with a mock generated via go.uber.org/mock/mockgen: add a //go:generate
directive in the pkg/auth package referencing the types.Identity interface, run
mockgen to produce a mock (e.g., mock_types_identity.go with
mock.NewMockIdentity), then update tests that referenced countingIdentity
(including uses of Authenticate, PrepareEnvironment, GetProviderName, etc.) to
construct the generated mock, configure expectations/Return values for
Authenticate and other methods, and assert call counts via gomock's EXPECT()
instead of countingIdentity.callCount.

In `@pkg/auth/manager_chain.go`:
- Around line 56-58: The current unchecked type assertion
entry.(*processCachedCreds) can panic if a malformed value is in
processCredentialCache; change it to a safe assertion (e.g., cached, ok :=
entry.(*processCachedCreds)) and skip/evict the entry when ok is false before
calling m.isCredentialValid("process-cache", cached.credentials); ensure you
reference processCredentialCache, cacheKey, processCachedCreds, and
m.isCredentialValid when making the check so the code either continues safely or
clears the bad cache entry instead of panicking.

---

Nitpick comments:
In `@pkg/auth/manager_chain_process_cache_test.go`:
- Around line 47-242: These four near-duplicate tests should be combined into a
single table-driven test (e.g. TestProcessCredentialCache_TableDriven) that
iterates over cases; for each case call resetProcessCredentialCache(),
optionally pre-seed processCredentialCache with the case's seed key/value,
construct a manager with the case's
chain/realm/identities/providers/credentialStore (reusing the existing test
helper types testProvider, countingIdentity, testCreds, testStore), call
m.authenticateChain(ctx, role), then assert the returned creds and the
identity.callCount matches the case's expected count; use t.Run(case.name,
func(t *testing.T){ ... }) to isolate cases and require/assert as in the
originals. Ensure you reference and reuse authenticateChain,
resetProcessCredentialCache, processCredentialCache, manager.chain,
manager.realm.Value, and countingIdentity.callCount to implement the checks.