Code quality: address review findings to reach 9.5/10

[thymikee]

Context

A bulk code review of all changes since v0.11.3 (15 commits, 102 files, +6,324/-660 lines) rated the codebase 7.5/10. This issue tracks the concrete fixes needed to reach 9.5/10.

Findings & Execution Plan

1. Magic Numbers & Undocumented Thresholds (recurring across files)

Scattered heuristic constants with no rationale. Makes maintenance and tuning harder.

Files & constants to document:

• src/daemon/android-snapshot-freshness.ts — ANDROID_FRESHNESS_WINDOW_MS = 2_500
• src/daemon/handlers/snapshot-capture.ts — retry delays, empty interactive thresholds
• src/daemon/handlers/snapshot.ts — 2,000ms stale detection window
• src/daemon/handlers/find.ts — 750ms snapshot cache window
• src/daemon/handlers/interaction-scroll.ts — stall count threshold (2)
• src/daemon/handlers/interaction-targeting.ts — 0.5px rect tolerance, 85-95% viewport overly-broad thresholds
• src/daemon/scroll-planner.ts — 25% safe-band zones, 10%/8px lane padding
• src/utils/output.ts — 20-node minimum / 8+ duplicates for nav subtree detection
• src/utils/scroll-indicator.ts — 1%/99% boundary thresholds

2. Operator Precedence Bug in scrollable.ts

Line 11: role || '' + subrole || '' — + binds tighter than ||, producing incorrect concatenation.

3. Long Functions Need Decomposition

• src/core/dispatch.ts — dispatchCommand() ~786 lines
• src/daemon/request-router.ts — 560+ lines, heavy RequestRouterDeps
• src/daemon/handlers/session-observability.ts — three major commands in one function

4. Test Gaps: Missing Edge Cases

• src/utils/__tests__/mobile-snapshot-semantics.test.ts — zero-width viewports, exact boundary nodes, negative coordinates
• src/daemon/handlers/__tests__/snapshot-handler.test.ts — malformed snapshot data
• src/utils/__tests__/output.test.ts — boundary conditions for nav subtree detection

5. Minor Issues

• src/platforms/ios/devices.ts:339 — whichCmd('xcrun') result unused
• src/platforms/android/app-lifecycle.ts:495 — global cachedBundletoolInvocation not safe for concurrent multi-device
• src/platforms/android/ui-hierarchy.ts:322 — BFS uses shift() on array (O(n) per pop)

Scope

Items 1, 2, 4, and 5 are in scope for this issue. Item 3 (function decomposition) is intentionally deferred — it's a larger refactor that should be a separate PR.