documentation updates

docs/services/summarization.md

@@ -12,7 +12,21 @@ the full context window with raw episodes.
 
 ## Trigger Conditions
 
-`triggerSummary(session, allEpisodes)` calls `maybeSummarize` fire-and-forget.
+`triggerSummary(session)` calls `maybeSummarize` fire-and-forget. It takes only
+the `session` — it no longer receives the full episode list. Instead
+`maybeSummarize` fetches exactly what it needs:
+
+1. `GET /sessions/:id/episode-stats` — a cheap aggregate (`COUNT`, `SUM(token_count)`,
+   `MAX(id)`) that gates the token threshold **without** pulling every episode row
+2. Only if over threshold: `GET /sessions/:id/episodes/since/:afterId` — the
+   un-summarized tail (episodes newer than the last summary's range), fetched in
+   full for the summary prompt
+
+This replaced an earlier approach where `chat/index.js` fetched the entire
+session (`getRecentEpisodes(session.id, 9999)`) on every message just to hand it
+over — an O(session length) cost per turn. The stats query now runs on every
+message; full episode text is fetched only when a summary actually fires.
+
 `maybeSummarize` proceeds only when both conditions are met:
 
 1. Total session token count exceeds `SUMMARIES.THRESHOLD_TOKENS` (default 200)