Memory leak: Unbounded caches grow without limit

[sauerdaniel]

Problem

Several internal caches in OpenCode use standard Map objects without size limits. Over long-running sessions, these caches can grow without bound, contributing to memory issues like those reported in #5363.

Affected Caches

1. Instance cache (project/instance.ts) - Caches project instances by directory
2. Provider SDK cache (provider/provider.ts) - Caches loaded SDK instances
3. LSP spawning cache (lsp/index.ts) - Tracks LSP server spawn promises

Code Example

// Current: unbounded Map that grows forever
const cache = new Map<string, Context>()

// No eviction when cache gets large
cache.set(directory, context)

Impact

• Memory usage grows continuously over time
• Long-running sessions can consume excessive RAM (70GB+ reported in #5363)
• No mechanism to evict stale entries
• Opening many directories causes unbounded growth

Relates to #5363

Expected Behavior

Caches should have bounded size with LRU eviction:

const cache = createLruCache<string, Context>({
  maxEntries: 20,
  onEvict: (key, value) => {
    // Clean up evicted entry
    value.dispose()
  }
})

Proposed Solution

Create a bounded LRU (Least Recently Used) cache utility that:

• Limits maximum entries with configurable maxEntries
• Automatically evicts least-recently-used entries when limit is reached
• Provides onEvict callback for cleanup when entries are removed
• Maintains Map-like interface for drop-in replacement

[github-actions[bot]]

This issue might be a duplicate of or closely related to existing issues. Please check:

• #5363: "opencode eating 70gb of memory?" - Direct memory exhaustion report that this issue addresses
• #8947: "[FEATURE]: TUI whole and LSP memory limits as part of configuration" - Requests memory limiting capabilities to contain memory growth
• #8887: "[BUG] Snapshot module ignores 'watcher.ignore' config, causing excessive disk usage and performance degradation" - Related performance issue where unbounded tracking causes resource exhaustion
• #8577: "Snapshot feature needs safeguards for large directories" - Another snapshot-related resource exhaustion issue
• #9136: "fix(test): prevent memory and resource leaks in test infrastructure" - Addresses similar unbounded resource accumulation pattern in tests

The unbounded cache pattern described in this issue is a root cause of the memory issues mentioned in #5363 and #8947, and similar patterns appear in the snapshot and test infrastructure.