perf(app): better memory management

specs/15-file-content-cache-bounds.md

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+## File content cache bounds
+
+Add explicit caps for loaded file contents in `FileProvider`
+
+---
+
+### Summary
+
+`packages/app/src/context/file.tsx` caches file contents in-memory (`store.file[path].content`) for every loaded file within the current directory scope. Over a long session (reviewing many diffs/files), this can grow without bound.
+
+This spec adds an in-module LRU + size cap for file _contents_ only, keeping metadata entries while evicting the heavy payload.
+
+---
+
+### Scoped files (parallel-safe)
+
+- `packages/app/src/context/file.tsx`
+
+---
+
+### Goals
+
+- Cap the number of in-memory file contents retained per directory
+- Optionally cap total approximate bytes across loaded contents
+- Avoid evicting content that is actively being used/rendered
+- Keep changes localized to `file.tsx`
+
+---
+
+### Non-goals
+
+- Changing persisted file-view state (`file-view`) limits (already pruned separately)
+- Introducing a shared cache utility used elsewhere
+
+---
+
+### Proposed approach
+
+1. Track content entries in an LRU Map
+
+- `const contentLru = new Map<string, number>()` where value is approximate bytes.
+- On successful `load(path)` completion, call `touchContent(path, bytes)`.
+- In `get(path)`, if the file has `content`, call `touchContent(path)` to keep active files hot.
+
+2. Evict least-recently-used contents when over cap
+
+- Add constants:
+  - `MAX_FILE_CONTENT_ENTRIES` (e.g. 30-50)
+  - `MAX_FILE_CONTENT_BYTES` (optional; e.g. 10-25MB)
+- When evicting a path:
+  - remove it from `contentLru`
+  - clear `store.file[path].content`
+  - set `store.file[path].loaded = false` (or keep loaded but ensure UI can reload)
+
+3. Reset LRU on directory scope change
+
+- The existing scope reset already clears `store.file`; also clear the LRU map.
+
+---
+
+### Implementation steps
+
+1. Add LRU state + helper functions
+
+- `approxBytes(fileContent)` (prefer `content.length * 2`)
+- `touchContent(path, bytes?)`
+- `evictContent(keep?: Set<string>)`
+
+2. Touch on content load
+
+- After setting `draft.content = x.data`, compute bytes and touch
+
+3. Touch on `get()` usage
+
+- If `store.file[path]?.content` exists, touch
+
+4. Evict on every content set
+
+- After `touchContent`, run eviction until within caps
+
+---
+
+### Acceptance criteria
+
+- Loading hundreds of files does not grow memory linearly; content retention plateaus
+- Actively viewed file content is not evicted under normal use
+- Evicted files can be reloaded correctly when accessed again
+
+---
+
+### Validation plan
+
+- Manual:
+  - Load many distinct files (e.g. via review tab)
+  - Confirm only the latest N files retain `content`
+  - Switch back to an older file; confirm it reloads without UI errors