Problem

sessions.list RPC takes 5-8s per call in our environment, causing Gateway backpressure under normal polling load.

Root Cause

1. Full row build before filter/limit: listSessionsFromStore() builds the full gateway session row for all 253 sessions before applying limit. Even limit=20 doesn't reduce work.

2. N+1 transcript fallback: buildGatewaySessionRow() calls resolveTranscriptUsageFallback() for ~122/253 sessions that lack totalTokens/contextTokens/estimatedCostUsd fields. Each fallback reads the transcript file from disk.

3. O(N²) child session resolution: resolveChildSessionKeys() scans the full store for every row.

Evidence

• sessions.json deserialization is fast (~15ms total)
• 44% of sessions.list calls exceed 8s under concurrent polling
• Peak: 234 slow calls at 18:00 when multiple cron jobs trigger
• limit parameter has near-zero effect on latency

Suggested Fix

In src/gateway/session-utils.ts - listSessionsFromStore():

1. Reorder: filter/sort/limit using cheap entry fields BEFORE buildGatewaySessionRow()
2. Pre-compute child index at list level instead of per-row scan
3. Consider TTL cache for repeated calls with no store changes

Environment

• OpenClaw: v2026.3.x
• Sessions: ~253 total across 5 agents
• OS: Darwin/arm64