perf(icons): coalesce file icon IPC

[JustYannicc]

What changed

• Added path-keyed in-flight coalescing around Raycast file icon IPC requests so concurrent identical file icons share one getFileIconDataUrl call.
• Replaced the unbounded renderer fileIconCache with a 1024-entry LRU cache for successful data URLs and resolved null fallbacks.
• Kept rejected IPC failures retryable by avoiding permanent negative cache writes on rejection.
• Added a self-contained node:test harness for concurrent duplicate icons, rejection recovery, LRU eviction, and non-file image icon behavior.

Why

The file icon runtime lived on a hot render path for Raycast list/grid items. Before this change, duplicate mounted file icons could all observe a cache miss before the first IPC call resolved, so identical icons fanned out into repeated getFileIconDataUrl IPC calls. The cache was also a module-level Map with no cap, so browsing or rendering many unique paths retained every icon result for the life of the renderer.

Baseline mock-render harness for the pre-fix request/cache logic reported sameMountedIcons=100, sameIpcCalls=100, uniqueMountedIcons=5000, uniqueIpcCalls=5000, and uniqueCacheEntries=5000.

Compatibility impact

Raycast icon rendering semantics are preserved. File icons still render the same data URL image when available, and still fall back to the existing document/folder glyph while loading or after unavailable icons. Cached file icons may remain stale, matching the existing tolerance. Non-file icon paths continue through the existing remote/image/Phosphor handling. No user-facing strings or locale files changed.

How tested

• Baseline before fix: node -e <mock old FileIcon request/cache harness> -> {"sameMountedIcons":100,"sameIpcCalls":100,"uniqueMountedIcons":5000,"uniqueIpcCalls":5000,"uniqueCacheEntries":5000}.
• After fix on scoped branch: node --test scripts/test-icon-runtime-file-icon-cache.mjs -> pass; asserts 100 concurrent identical mounts call IPC once, rejected IPC retries later, 5,000 unique paths stay capped at 1,024 cache entries with LRU eviction, and non-file image icons do not call file icon IPC.
• Scoped diff check: git diff --check origin/main...HEAD -> pass.
• Renderer typecheck on scoped origin/main branch: ./node_modules/.bin/tsc -p tsconfig.renderer.json --noEmit was attempted and is blocked by existing unrelated origin/main errors, including src/renderer/src/App.tsx, src/renderer/src/CameraExtension.tsx, src/renderer/src/components/LiquidGlassSurface.tsx, and other pre-existing renderer type issues outside this PR diff.

Stack validation

The runtime fix was developed and validated from codex/perf-integration-stack, which contains the active performance stack. Before creating this scoped origin/main PR branch, the stack-based worker branch passed:

• node --test scripts/test-icon-runtime-file-icon-cache.mjs
• node --test scripts/test-icon-asset-cache.mjs scripts/test-icon-runtime-phosphor-cache.mjs
• ./node_modules/.bin/tsc -p tsconfig.renderer.json --noEmit
• git diff --check

The upstream PR branch codex/perf-file-icon-cache-coalesce-pr was created from origin/main and contains only the file-icon runtime/test diff.

[JustYannicc]

Superseded by the consolidated renderer performance PR #533: #533. Closing this scoped source PR so review stays centralized there.