fix(run-engine): fix queue cache memory leak and replace MemoryStore with LRU cache

[ericallam]

• Fix memory leak in RunAttemptSystem queue cache - was keying by runId instead of queue identifier
• Replace @unkey/cache MemoryStore with new LRUMemoryStore for O(1) operations and better memory bounds

Problem

Cache Key Bug

The queue cache in #resolveTaskRunExecutionQueue was keyed by runId, creating one cache entry per run instead of per queue. With 1-2 hour TTLs and 5000 entry soft cap, these accumulated causing memory growth.

MemoryStore Performance

The @unkey/cache MemoryStore uses O(n) synchronous iteration for eviction, blocking the event loop at high throughput.

Solution

Cache Key Fix

Changed cache key from params.runId to queue identifier:

const cacheKey = params.lockedQueueId ?? `${params.runtimeEnvironmentId}:${params.queueName}`;

LRU Cache

Created LRUMemoryStore adapter using lru-cache package:

• O(1) get/set/delete operations
• Strict memory bounds (hard max vs soft cap)
• No event loop blocking

Test Results:

Metric	Before Fix	After Fix
Queue cache entries (per 1000 runs)	~1000	1
Old space growth	32.27 MB	5.45 MB
Heap growth	7.21 MB (3.9%)	4.81 MB (2.6%)

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Latest commit: f1be5b3

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Walkthrough

Introduces a new LRU-backed in-memory cache implementation (LRUMemoryStore, createLRUMemoryStore) and exports it from internal-packages/cache, adds the lru-cache dependency and Vitest config, and adds comprehensive tests for the LRUMemoryStore. Replaces many in-process MemoryStore usages across the codebase with createLRUMemoryStore(...) calls (webapp services, run-engine, queues, rate-limiting, idempotency, etc.). Also updates one private method signature in runAttemptSystem to change how queue cache keys are derived and used.

Estimated code review effort

🎯 4 (Complex) | ⏱️ ~45 minutes

🚥 Pre-merge checks | ✅ 1 | ❌ 2

❌ Failed checks (2 warnings)

Check name	Status	Explanation	Resolution
Description check	⚠️ Warning	The description is largely incomplete. It lacks the required checklist section, testing section details, and screenshots section, missing most of the template structure despite containing substantial technical content.	Add the missing checklist (with contributor guide confirmation), a dedicated Testing section explaining validation steps, and follow the provided template structure more closely.
Docstring Coverage	⚠️ Warning	Docstring coverage is 33.33% which is insufficient. The required threshold is 80.00%.	Write docstrings for the functions missing them to satisfy the coverage threshold.

✅ Passed checks (1 passed)

Check name	Status	Explanation
Title check	✅ Passed	The title clearly describes the main changes: fixing a queue cache memory leak and replacing MemoryStore with LRU cache, both primary objectives of this PR.

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