fix(router): consolidated config-reload memory-leak fix (#3006–#3009 bundle)

[asoorm]

What

Consolidated bundle of the four root-cause fixes for memory retention on router config hot-reload, combined onto one branch so the leak can be validated end-to-end in a single checkout.

ℹ️ Not a replacement. These commits are the originals authored in #3006, #3007, #3008, #3009. This PR exists purely to validate them together (and against the regression test in #3019). Review/merge the individual PRs as the source of truth.

Commits (cherry-picked, in merge order)

Commit	Original PR
clear slowplancache entries on Close	#3006
stop pinning schema AST in cached plan entries	#3007
call OnRouterConfigReload before CDN/manifest hot-reload	#3008
skip plan cache OnEvict during graphMux shutdown	#3009

Root cause

On reload, graphMux.Shutdown() → planCache.Close() triggers ristretto's Clear(), which fires the plan cache OnEvict for every entry, demoting the whole cache into planFallbackCache. That fallback is held by the long-lived reloadPersistentState (core/graph_server.go:1609), and slowplancache.Close() didn't clear its map — so the old plan cache + schema AST survived every reload. The fix set stops the demote-on-shutdown, clears the fallback on close, releases stale refs in the hot-reload path, and drops the unused schema-AST field.

Validation

• Builds clean (go build ./...).
• Regression test test(router): reproduce config-reload plan-cache retention leak #3019 (TestReloadConfig_PlanCacheRetentionLeak) is red on main and green on this branch.

Why draft

Coordination/validation branch for #3006–#3009 — not intended to merge on its own.

Summary by CodeRabbit

• Bug Fixes

  • Improved shutdown behavior so cached plans are released cleanly and no longer trigger delayed cache work during reload or shutdown.
  • Reduced the risk of stale cache entries lingering after a router configuration refresh.

• Tests

  • Added coverage to verify cache shutdown fully clears stored entries and resets cache state.

[coderabbitai]

No actionable comments were generated in the recent review. 🎉

ℹ️ Recent review info

⚙️ Run configuration

Configuration used: Organization UI

Review profile: CHILL

Plan: Pro

Run ID: 2fd2f7a9-4cb4-470f-a2e5-ef56c609dd45

📥 Commits

Reviewing files that changed from the base of the PR and between 2226f3f and 38c42fc.

📒 Files selected for processing (5)

• router/core/graph_server.go
• router/core/operation_planner.go
• router/core/router.go
• router/pkg/slowplancache/slow_plan_cache.go
• router/pkg/slowplancache/slow_plan_cache_test.go

---

Walkthrough

The router updates internal plan metadata, reload timing, eviction handling during shutdown, and slow plan cache teardown. A new test covers the cache close behavior.

Changes

Plan cache lifecycle updates

Layer / File(s)	Summary
Internal plan metadata shape router/core/operation_planner.go	planWithMetaData stores preparedPlan and operationDocument, and planOperation stops populating the removed schema-related field.
Config reload and plan-cache shutdown sequencing router/core/router.go, router/core/graph_server.go	Router.newServer calls OnRouterConfigReload() before replacing the graph server, and graphMux gates plan-cache eviction writes during shutdown before waiting on planFallbackCache.
Slow plan cache teardown router/pkg/slowplancache/slow_plan_cache.go, router/pkg/slowplancache/slow_plan_cache_test.go	Cache.Close() deletes all cached entries, resets size to 0, and the new test checks that close empties the cache state.

Estimated code review effort

🎯 3 (Moderate) | ⏱️ ~20 minutes

🚥 Pre-merge checks | ✅ 4 | ❌ 1

❌ Failed checks (1 warning)

Check name	Status	Explanation	Resolution
Docstring Coverage	⚠️ Warning	Docstring coverage is 0.00% which is insufficient. The required threshold is 80.00%.	Write docstrings for the functions missing them to satisfy the coverage threshold.

✅ Passed checks (4 passed)

Check name	Status	Explanation
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
Title check	✅ Passed	The title accurately summarizes the bundled router config-reload memory-leak fixes and reflects the main change set.
Linked Issues check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check	✅ Passed	Check skipped because no linked issues were found for this pull request.

✨ Finishing Touches

📝 Generate docstrings

• Create stacked PR
• Commit on current branch

Warning

There were issues while running some tools. Please review the errors and either fix the tool's configuration or disable the tool if it's a critical failure.

🔧 golangci-lint (2.12.2)

level=error msg="[linters_context] typechecking error: pattern ./...: directory prefix . does not contain main module or its selected dependencies"

---

_{Comment @coderabbitai help to get the list of available commands.}

[github-actions]

Router image scan passed

✅ No security vulnerabilities found in image:

ghcr.io/wundergraph/cosmo/router:sha-9b52b259e567185dfdb5c1c0491b385c641b41d5

[codecov]

Codecov Report

❌ Patch coverage is 16.66667% with 10 lines in your changes missing coverage. Please review.
✅ Project coverage is 51.03%. Comparing base (5efb3c2) to head (38c42fc).
⚠️ Report is 1 commits behind head on main.

Files with missing lines	Patch %	Lines
router/core/graph_server.go	16.66%	4 Missing and 1 partial ⚠️
router/pkg/slowplancache/slow_plan_cache.go	0.00%	5 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #3020      +/-   ##
==========================================
- Coverage   60.27%   51.03%   -9.25%     
==========================================
  Files         477      243     -234     
  Lines       62471    29475   -32996     
  Branches     6131        0    -6131     
==========================================
- Hits        37656    15042   -22614     
+ Misses      24787    12903   -11884     
- Partials       28     1530    +1502     

Files with missing lines	Coverage Δ
router/core/operation_planner.go	57.77% <ø> (ø)
router/core/router.go	63.98% <100.00%> (ø)
router/core/graph_server.go	76.25% <16.66%> (ø)
router/pkg/slowplancache/slow_plan_cache.go	5.76% <0.00%> (ø)

... and 716 files with indirect coverage changes

🚀 New features to boost your workflow:

• ❄️ Test Analytics: Detect flaky tests, report on failures, and find test suite problems.
• 📦 JS Bundle Analysis: Save yourself from yourself by tracking and limiting bundle sizes in JS merges.