[codex] Add session lane and lock diagnostics

[brian-chenyang]

Summary

Adds production-safe diagnostics on top of the current v2026.3.9-fix-by-kevin-20260403 OpenClaw branch.

• Extends lane snapshots from main-only to include active session:* lanes, with laneType, active, queued, peakActiveLast30s, depth, and oldestQueuedMs.
• Adds session file lock diagnostics for slow acquisition, timeout, and long-held lock release.
• Adds focused tests for session lane snapshots and lock diagnostic events.

Why

OpenMAI incidents showed main lane was not saturated, while user-facing failures correlated with long session-lane waits, provider timeouts, and containers.json.lock contention. The previous logs could not distinguish whether the lock was held too long, waited on too long, or merely failed at the end of a long task.

Validation

• pnpm exec vitest run --config vitest.unit.config.ts src/process/command-queue.test.ts
• pnpm exec vitest run src/agents/session-write-lock.test.ts
• pnpm format:check src/process/command-queue.ts src/process/command-queue.test.ts src/logging/diagnostic.ts src/infra/diagnostic-events.ts src/agents/session-write-lock.ts src/agents/session-write-lock.test.ts
• pnpm exec oxlint --type-aware src/process/command-queue.ts src/process/command-queue.test.ts src/logging/diagnostic.ts src/infra/diagnostic-events.ts src/agents/session-write-lock.ts src/agents/session-write-lock.test.ts
• pnpm build