fix(router-core): reset oldest pointer when evicting the sole LRU cache entry

[FrancoKaddour]

What

When set() evicts the only entry in the LRU cache (oldest === newest), the node has no next pointer, so the branch that updated oldest was never taken. oldest kept a stale reference to the deleted node while newest was correctly set to undefined.

On the next set() call the stale oldest caused cache.delete() to run against a key that no longer existed — leaving the new entry untracked by oldest. Subsequent insertions then grew the cache silently beyond its max capacity.

Root cause

// Before (buggy)
if (toDelete.next) {
  oldest = toDelete.next      // ← only set when a successor exists
  toDelete.next.prev = undefined
}
if (toDelete === newest) {
  newest = undefined          // ← correctly cleared
}
// When oldest === newest, toDelete.next is undefined → oldest is never cleared

Fix

// After
oldest = toDelete.next        // always update oldest (undefined when no successor)
if (toDelete.next) {
  toDelete.next.prev = undefined
}
if (toDelete === newest) {
  newest = undefined
}

Test

Added a test case respects max=1 across multiple replacements to lru.test.ts that reproduces the bug and passes with the fix.

Summary by CodeRabbit

• Bug Fixes

  • Improved least-recently-used cache eviction so the oldest entry is updated correctly when items are removed.
  • Fixed behavior for single-item caches to ensure older entries are evicted as new values are added.

• Tests

  • Added coverage for repeated replacements in a cache with a maximum size of 1.

[coderabbitai]

No actionable comments were generated in the recent review. 🎉

ℹ️ Recent review info

⚙️ Run configuration

Configuration used: defaults

Review profile: CHILL

Plan: Pro

Run ID: 0a68a162-a90b-42ff-b659-bca118c50fe9

📥 Commits

Reviewing files that changed from the base of the PR and between 208100b and 1fcf45e.

📒 Files selected for processing (2)

• packages/router-core/src/lru-cache.ts
• packages/router-core/tests/lru.test.ts

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📝 Walkthrough

Walkthrough

The eviction logic in the LRU cache's set method was modified so that oldest is assigned from toDelete.next unconditionally, rather than only within the conditional block. A test was added verifying correct behavior when max=1 across multiple replacements.

Changes

LRU eviction fix

Layer / File(s)	Summary
Eviction pointer fix and test coverage packages/router-core/src/lru-cache.ts, packages/router-core/tests/lru.test.ts	oldest is now assigned from toDelete.next before the conditional cleanup, ensuring it becomes undefined when there is no successor; a new test verifies max=1 correctly evicts prior keys across multiple replacements.

Estimated code review effort: 1 (Trivial) | ~5 minutes

🚥 Pre-merge checks | ✅ 5

✅ Passed checks (5 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 core fix to LRU eviction when removing the sole cache entry.
Docstring Coverage	✅ Passed	No functions found in the changed files to evaluate docstring coverage. Skipping docstring coverage check.
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 unit tests (beta)

• Create PR with unit tests

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