perf(agent-sessions): rank the list page first, then net its sessions alone - #1199

🟢 Confidence 4/5 · likely safe to merge
The delta is a single clamp on the ranked page read, every production caller of that path passes endTime, and the unit, HTTP and ClickHouse e2e tests pin it.
_{quality 100/100 · no findings · tests covered · risk medium · 2/2 new units observable}

The delta since the last review clamps the ranked page read to the caller's endTime, so a span that starts past the window is no longer netted. The clamp is wired through the one production caller and covered by tests; safe to merge.

• indexTracesOf adds Timestamp <= endTime whenever sessionIds is set (ai-sessions.ts:554)
• listAiSessions threads payload.endTime into the ranked page's PageBounds (ai-session-reads.ts:240)
• e2e adds a window ending inside a turn to prove rank and single read agree
• SQL baselines and the ranked benchmark fixture carry the new bound

Fixed since the last review

• ✅ F1 · Ranked page read counts spans that start after the caller's endTime

_{854de1c · Updated on every push. Reply "won't fix" to dismiss a finding, or mention @maple-review-bot to ask about one.}