session-memory Phase 0: end-to-end verification + docs (T07)

- verified full sweep over 85 real local Claude transcripts: 63 sessions
  ingested+analyzed, eviction under tiny cap freed 26MB with zero data loss,
  digest-preservation invariant holds, idempotent re-run
- session_memory/README.md: usage, scheduling, retention knobs
- design doc: OQ4 resolved (median ~49KB/session), OQ6 (multi-file sessions)
- workplan AGENTIC-WP-0002 finished

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

docs/DESIGN-session-memory.md

@@ -356,8 +356,16 @@ hub indexes).
   human-intervention markers), refine in Detect phase.
 - **OQ3** `task_ref` resolution — can we always map a session to a workplan task
   (via cwd + branch + state-hub), or only sometimes?
-- **OQ4** Right default for `raw_soft_cap_bytes` — measure real per-session sizes
-  first (Grok dirs are heavier than Claude single-files).
+- ~~**OQ4** Right default for `raw_soft_cap_bytes`.~~ **Measured** (Phase 0, 85
+  real local Claude files / 63 distinct sessions): source bytes per session
+  min 396 · **median ~49 KB** · max 48 MB (one outlier) · ~103 MB total. Claude
+  defaults (4 GiB soft / 6 GiB hard) leave ample headroom; revisit once Grok dirs
+  (heavier, multi-file) are ingested in Phase 1.
+- **OQ6 (new, found in Phase 0)** Multi-file sessions: ~84 transcript files mapped
+  to ~63 `session_uid`s — some sessions span multiple files (resume/sidechain
+  sharing a `sessionId`). Current behavior upserts (last file wins per
+  `(session_uid, seq)`); a future refinement is to *merge* events across files of
+  one session rather than overwrite. Acceptable for Phase 0.
 - **OQ5** Should push-hooks be opt-in per machine to avoid surprising the agents?
 
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