refactor(cli): simplify use-activity-query.ts (Commit 2.6)

Extract activity query hook into modular pieces:
- query-cache.ts: Cache entries, listeners, ref counts, snapshots
- query-executor.ts: Query execution with retries, deduplication
- query-invalidation.ts: Invalidation strategies, fullDeleteCacheEntry

Critical fixes applied:
- Fix infinite retry loop: scheduleRetry uses clearRetryTimeout (not clearRetryState)
- Fix memory leak: fullDeleteCacheEntry clears all state for GC
- Fix incomplete deps: Added refs for refetchOnMount/staleTime/enabled

Additional fixes:
- Remove redundant bumpGeneration call in fullDeleteCacheEntry
- Add isEnabled callback to cancel retries when disabled
- Remove dead exports (getInFlightPromise, setInFlightPromise)

Reduces use-activity-query.ts from ~480 to ~316 lines (-34%).
All 1,911 CLI tests pass. 9 e2e tests pass.
Reviewed by 4 CLI agents (Codebuff, Codex, Claude Code, Gemini).

Author: brandonkachen

REFACTORING_PLAN.md

@@ -36,7 +36,7 @@ This document outlines a prioritized refactoring plan for the 51 issues identifi
 | 2.4 | Consolidate billing duplication | ✅ Complete | Codex CLI |
 | 2.5a | Extract multiline keyboard navigation | ✅ Complete | Codebuff |
 | 2.5b | Extract multiline editing handlers | ✅ Complete | Codebuff |
-| 2.6 | Simplify use-activity-query.ts | ⬜ Not Started | - |
+| 2.6 | Simplify use-activity-query.ts | 🔄 In Progress | Codex CLI |
 | 2.7 | Consolidate XML parsing | ⬜ Not Started | - |
 | 2.8 | Consolidate analytics | ⬜ Not Started | - |
 | 2.9 | Refactor doStream | ⬜ Not Started | - |
@@ -557,18 +557,71 @@ After initial commit, 4 CLI agents reviewed and identified warnings. All were fi
 
 ---
 
-### Commit 2.6: Simplify `use-activity-query.ts`
+### Commit 2.6: Simplify `use-activity-query.ts` 🔄 IN PROGRESS
 **Files:** `cli/src/hooks/use-activity-query.ts`  
 **Est. Time:** 4-5 hours  
-**Est. LOC Changed:** ~500-600
+**Est. LOC Changed:** ~500-600  
+**Actual LOC Changed:** ~794 insertions (new files), ~480 lines refactored
 
-| Task | Description |
-|------|-------------|
-| Evaluate external caching library | Consider `react-query` or similar |
-| If keeping custom: Extract `QueryCache` class | Cache management |
-| Extract `QueryExecutor` | Query execution logic |
-| Extract `QueryInvalidation` | Invalidation strategies |
-| Simplify main hook | Compose extracted pieces |
+| Task | Description | Status |
+|------|-------------|--------|
+| Evaluate external caching library | Kept custom (react-query overkill for this use case) | ✅ |
+| Extract `query-cache.ts` module | Cache entries, listeners, ref counts, snapshots | ✅ |
+| Extract `query-executor.ts` module | Query execution with retries, deduplication | ✅ |
+| Extract `query-invalidation.ts` module | Invalidation strategies, removeQuery, setQueryData | ✅ |
+| Simplify main hook | Compose extracted pieces | ✅ |
+| Fix critical issues from review | See below | ✅ |
+
+**New Files Created:**
+- `cli/src/utils/query-cache.ts` (~224 lines) - Cache management:
+  - `CacheEntry`, `KeySnapshot` types
+  - `serializeQueryKey`, `subscribeToKey`, `getKeySnapshot`
+  - `setCacheEntry`, `getCacheEntry`, `isEntryStale`
+  - `setQueryFetching`, `isQueryFetching`
+  - `incrementRefCount`, `decrementRefCount`, `getRefCount`
+  - `bumpGeneration`, `getGeneration`, `deleteCacheEntry`
+  - `resetCache` (for testing)
+- `cli/src/utils/query-executor.ts` (~187 lines) - Query execution:
+  - `createQueryExecutor` - factory for fetch functions with retry/dedup
+  - `clearRetryState`, `clearRetryTimeout` - retry management
+  - `scheduleRetry` - exponential backoff scheduling
+  - `getRetryCount`, `setRetryCount` - retry state
+  - `resetExecutorState` (for testing)
+- `cli/src/utils/query-invalidation.ts` (~67 lines) - Invalidation:
+  - `invalidateQuery` - mark query as stale
+  - `removeQuery` - full removal with cleanup
+  - `getQueryData`, `setQueryData` - direct cache access
+  - `fullDeleteCacheEntry` - comprehensive cleanup for GC
+
+**Component Size Reduction:**
+- `use-activity-query.ts`: ~480 → ~316 lines (-34%)
+
+**Critical Issues Fixed (from 4-agent review):**
+
+| Issue | Problem | Fix Applied |
+|-------|---------|-------------|
+| **Infinite Retry Loop** | `scheduleRetry` called `clearRetryState` which deleted the retry count that was just set, so retry count never accumulated | Created `clearRetryTimeout()` that only clears the timeout (not count). `scheduleRetry` now uses this. |
+| **Memory Leak in deleteCacheEntry** | `deleteCacheEntry` didn't clear in-flight promises or retry state when GC runs | Created `fullDeleteCacheEntry()` in query-invalidation.ts that clears all state. GC effect now uses this. |
+| **Incomplete useEffect deps** | Initial fetch effect missing deps (refetchOnMount, staleTime, doFetch) - hidden by eslint-disable | Added `refetchOnMountRef` and `staleTimeRef` refs. Deps are now `[enabled, serializedKey, doFetch]`. |
+
+**Review Findings (from 4 CLI agents):**
+- ✅ All 3 critical issues correctly fixed
+- ✅ Extraction boundaries well-chosen with clear responsibilities
+- ✅ Backwards compatibility maintained via re-exports
+- ⚠️ Suggestion: Double bumpGeneration call in fullDeleteCacheEntry (harmless but redundant)
+- ⚠️ Suggestion: enabled:false doesn't cancel pending retries (edge case, non-blocking)
+- ⚠️ Suggestion: Dead exports (getInFlightPromise, setInFlightPromise) - future API surface
+
+**E2E Test Results (Codebuff Local CLI):**
+- ✅ Basic CLI startup and usage display
+- ✅ Activity detection and refetch
+- ✅ Query caching behavior
+- ✅ Error recovery and stability
+
+**Test Results:**
+- 1,911 CLI tests pass
+- 52 use-activity-query tests pass
+- TypeScript compiles cleanly
 
 **Dependencies:** None  
 **Risk:** Medium