Implement AGENTIC-WP-0011 kaizen correlation follow-up

Add bidirectional doc links (PRD §9.1, README, DESIGN §11), session-close
HELIX_* env convention, stable digest JSON contract, and digest_lookup CLI
for read-only correlate lookups. All tasks done; 163 tests green.

docs/DESIGN-session-memory.md

@@ -394,10 +394,65 @@ into Helix Forge.
 **Related kaizen-agentic docs:** [ADR-004 project metrics convention](https://gitea.coulomb.social/coulomb/kaizen-agentic/src/branch/main/docs/adr/ADR-004-project-metrics-convention.md),
 [wiki/EcosystemIntegration.md](https://gitea.coulomb.social/coulomb/kaizen-agentic/src/branch/main/wiki/EcosystemIntegration.md).
 
+### 11.1 Session-close env export (dual-layer agents)
+
+Agents that run **both** Helix Forge capture and kaizen `metrics record` should
+export the following **after** the ingest sweep has written the session digest
+(`python -m session_memory.ingest` or an equivalent Stop/SessionEnd hook). Names
+match kaizen-agentic ADR-004 — do not invent parallel aliases.
+
+| Variable | Source in Helix Forge | Purpose |
+|----------|----------------------|---------|
+| `HELIX_SESSION_UID` | `Session.session_uid` | Primary correlation key → `helix_session_uid` |
+| `HELIX_REPO` | `digest.repo` | Project/repo scoping |
+| `HELIX_FLAVOR` | `digest.flavor` | Agent runtime (`claude` / `codex` / `grok`) |
+| `HELIX_TOKENS` | `digest.cost.input_tokens + digest.cost.output_tokens` | Token rollup → `tokens` |
+| `HELIX_INFRA_OVERHEAD_SHARE` | infra bucket share over `tool_histogram` (see `measure.metrics.session_metrics`) | MCP/plumbing overhead → `infra_overhead_share` |
+
+Example (after digest exists):
+
+```bash
+export HELIX_SESSION_UID="claude:abc-123"
+export HELIX_REPO="agentic-resources"
+export HELIX_FLAVOR="claude"
+export HELIX_TOKENS=125000
+export HELIX_INFRA_OVERHEAD_SHARE=0.117
+# optional — lets kaizen correlate without guessing the store location:
+export HELIX_STORE_DB="$(pwd)/session_memory/.store/mem.db"
+kaizen-agentic metrics record   # merges HELIX_* when present
+```
+
+### 11.2 Digest store location and read API
+
+- **`HELIX_STORE_DB`** — absolute path to the SQLite file holding Tier 2 digests.
+  Defaults to `config.toml` `[store].db_path` (`session_memory/.store/mem.db` relative
+  to the repo root). Export as an absolute path when setting the variable on session
+  close so `metrics correlate` works across hosts and working directories.
+- **Thin CLI** — `python -m session_memory.digest_lookup <session_uid> [--json]`
+  prints one digest without running ingest. Exit `0` on hit, `1` when missing.
+- **Programmatic** — `Store.get_digest(session_uid)` returns the JSON blob written
+  by `build_digest` / `analyze`.
+
+**Stable digest JSON shape** (fields consumers may rely on):
+
+| Field | Type | Notes |
+|-------|------|-------|
+| `session_uid` | string | Normalized uid (`<flavor>:<native-id>`) |
+| `flavor`, `repo`, `domain` | string | Session attribution |
+| `model` | string | Model id when known |
+| `started_at`, `ended_at` | string | ISO timestamps |
+| `outcome` | string | `success` / `fail` / `abandoned` / `unknown` |
+| `cost` | object | `input_tokens`, `output_tokens`, `cache_tokens`, `wall_clock_s`, `turns`, `retries` |
+| `tool_histogram` | object | Tool name → call count |
+| `event_count`, `kind_counts`, `markers` | object/int | Compact activity summary |
+| `first_prompt`, `last_assistant` | string | Short text snippets |
+| `error_snippets` | array | `{fingerprint, sample, count, tool}` entries |
+| `schema_version` | int | Digest schema version |
+
 ---
 
-*Next step: [AGENTIC-WP-0002] implements Phase 0 — the schema, the Claude
-collector, the Tier1/Tier2 store, and the budget-based eviction sweep.*
+*Implemented:* Phases 0–4, weekly retro ([AGENTIC-WP-0002]–[AGENTIC-WP-0010]);
+kaizen correlation follow-up ([AGENTIC-WP-0011]).
 
 ## Sources