feat(cache): add L2CacheKeyInterceptor for custom cache key transformation

[jensneuse]

Summary

Add L2CacheKeyInterceptor function type to CachingOptions, enabling library users (like Cosmo Router) to customize L2 cache keys per-request without modifying graphql-go-tools internals. The interceptor receives SubgraphName and CacheName metadata for conditional customization, and is applied after the existing subgraph header prefix.

Key Changes

• Added L2CacheKeyInterceptor function type and L2CacheKeyInterceptorInfo struct to v2/pkg/engine/resolve/context.go
• Applied interceptor in prepareCacheKeys() and buildMutationEntityCacheKey() in v2/pkg/engine/resolve/loader_cache.go
• Added comprehensive test suite with 4 subtests covering transformation, L1 isolation, metadata passing, and nil behavior

Test Plan

• All 4 new interceptor tests pass
• All existing L1/L2 cache tests pass (no regressions)
• Race detector passes
• Federation caching tests pass

🤖 Generated with Claude Code

Summary by CodeRabbit

• New Features
  • Added optional L2 cache key interception feature, enabling custom transformation of cache keys during lookups, writes, and deletions. Interceptor receives contextual metadata including subgraph and cache names. L1 cache behavior remains unaffected.
  • Includes comprehensive test coverage validating interceptor behavior across multiple caching scenarios.

[coderabbitai]

📝 Walkthrough

Walkthrough

The changes introduce a new public API for L2 cache key interception in the resolve layer, allowing optional transformation of L2 cache keys before lookups, writes, and deletions. The interceptor is applied in two code paths (prepareCacheKeys and buildMutationEntityCacheKey) while L1 caching remains unaffected. Comprehensive tests verify behavior across multiple scenarios including transformation, L1 isolation, and nil-case handling.

Changes

Cohort / File(s)	Summary
L2 Cache Key Interceptor API v2/pkg/engine/resolve/context.go	Adds new public types L2CacheKeyInterceptorInfo and L2CacheKeyInterceptor, and extends CachingOptions with a new optional L2CacheKeyInterceptor field for transforming L2 cache keys before lookup/write/delete operations.
L2 Cache Key Interceptor Implementation v2/pkg/engine/resolve/loader_cache.go	Applies the L2 cache key interceptor (if provided) in two functions: prepareCacheKeys transforms keys in the L2 cache key collection, and buildMutationEntityCacheKey transforms the final mutation entity cache key.
L2 Cache Key Interceptor Tests v2/pkg/engine/resolve/l2_cache_key_interceptor_test.go	Adds comprehensive test suite with helpers and test cases verifying interceptor transforms L2 keys with tenant prefix, does not affect L1 keys, captures interceptor info payload (SubgraphName and CacheName), and handles nil interceptor case correctly.

Estimated code review effort

🎯 3 (Moderate) | ⏱️ ~20 minutes

🚥 Pre-merge checks | ✅ 2

✅ Passed checks (2 passed)

Check name	Status	Explanation
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
Title check	✅ Passed	The title 'feat(cache): add L2CacheKeyInterceptor for custom cache key transformation' directly and specifically describes the main change in the pull request—introducing a new L2 cache key interceptor feature for custom cache key transformation.

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✨ Finishing Touches

• 📝 Generate docstrings (stacked PR)
• 📝 Generate docstrings (commit on current branch)

🧪 Generate unit tests (beta)

• Create PR with unit tests
• Post copyable unit tests in a comment
• Commit unit tests in branch jensneuse/custom-cache-keys

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[coderabbitai]

🧹 Nitpick comments (1)

v2/pkg/engine/resolve/loader_cache.go (1)

1094-1101: Please add a mutation-path interceptor test for key symmetry.

This path now transforms mutation entity keys too. A dedicated test through detectMutationEntityImpact would protect delete/get symmetry from regressions.

🤖 Prompt for AI Agents

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

In `@v2/pkg/engine/resolve/loader_cache.go` around lines 1094 - 1101, Add a
dedicated unit test that uses detectMutationEntityImpact to verify key symmetry
for mutation-path transformations: simulate an
ExecutionOptions.Caching.L2CacheKeyInterceptor (the same interceptor type used
in loader_cache.go) that mutates keys via L2CacheKeyInterceptorInfo
(SubgraphName/CacheName) and assert that mutation-path operations (delete) and
retrieval (get) produce symmetric cache keys; ensure the test registers the
interceptor on l.ctx.ExecutionOptions.Caching.L2CacheKeyInterceptor and fails if
detectMutationEntityImpact reports any asymmetry so future changes to
L2CacheKeyInterceptor application to mutation entity keys are caught.

🤖 Prompt for all review comments with AI agents

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

Nitpick comments:
In `@v2/pkg/engine/resolve/loader_cache.go`:
- Around line 1094-1101: Add a dedicated unit test that uses
detectMutationEntityImpact to verify key symmetry for mutation-path
transformations: simulate an ExecutionOptions.Caching.L2CacheKeyInterceptor (the
same interceptor type used in loader_cache.go) that mutates keys via
L2CacheKeyInterceptorInfo (SubgraphName/CacheName) and assert that mutation-path
operations (delete) and retrieval (get) produce symmetric cache keys; ensure the
test registers the interceptor on
l.ctx.ExecutionOptions.Caching.L2CacheKeyInterceptor and fails if
detectMutationEntityImpact reports any asymmetry so future changes to
L2CacheKeyInterceptor application to mutation entity keys are caught.

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ℹ️ Review info

⚙️ Run configuration

Configuration used: Path: .coderabbit.yaml

Review profile: CHILL

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Run ID: c359189a-0bfc-413d-b6a6-c104f1c4d1ca

📥 Commits

Reviewing files that changed from the base of the PR and between ae8725d and 0378c5c.

📒 Files selected for processing (3)

• v2/pkg/engine/resolve/context.go
• v2/pkg/engine/resolve/l2_cache_key_interceptor_test.go
• v2/pkg/engine/resolve/loader_cache.go