Parent design: MemoryVault — see Detailed Design §3 (Recall hooks — SessionStart + UserPromptSubmit) and §4 (Recall engine — sqlite-vec + grep+frontmatter merge) for full architectural context.

This part ships the read loop — the two hooks that inject MemoryVault content into the agent's context + the recall engine they call. Together these make the vault actually usable: without recall, save is theater.

Two-hook recall pattern:

• SessionStart hook — fires once on session boot. Globs MemoryVault/personal-private/_always-load/*.md, reads each, formats as a single markdown block, injects into session context. Outputs a "Loaded N MemoryVault always-load entries" transparency line. Hard time budget 500ms; degraded-graceful on overrun.
• UserPromptSubmit hook — fires on every user message. Takes the prompt as the recall query and calls the recall engine for top-K (K=5 default) relevant entries. Dedups against the already-loaded _always-load entries (by file path), then injects the remaining matches as a system message before the agent processes the prompt. Outputs a "Loaded N relevant entries: " transparency line so the user can see what memory shaped the response. Hard time budget 300ms; degraded-graceful on overrun.

Recall engine (called by both hooks; also exposable as /memory search for manual semantic queries):

1. Embed the query — local sentence-transformers (BGE-large default; ~1.3GB checkpoint cached at ~/.cache/crickets/sentence-transformers/; PyTorch MPS on Apple Silicon for acceleration) as of v0.9.2 (see local-only embeddings decision, 2026-05-20 — crickets-hld). Synchronous call; on time-budget overrun, fall back to grep-only.
2. Vec search — query sqlite-vec for top-K nearest entries by cosine similarity. Returns (path, similarity_score).
3. Grep + frontmatter search in parallel — scan entry titles + tags + first-line content for keyword matches; filter by frontmatter (status: active only by default; respect group filter if query specifies; respect --include-inbox flag for _inbox/ access).
4. Merge — union the two result sets; rank by similarity_score × 0.7 + keyword_match_count × 0.3; dedup.
5. Return top-K — default K=5.

Filtering invariants: recall never surfaces status: superseded entries by default; _inbox/ excluded unless --include-inbox flag set; _archive/ always excluded.

Local-only as of v0.9.2 (local-only embeddings decision, 2026-05-20 — crickets-hld) — no API path remains. sentence-transformers + BGE-large is the production mode; AGENT_TOOLKIT_EMBEDDING_MODEL env var swaps in a smaller model for low-spec hosts. If sentence-transformers is unavailable (not installed, or PyTorch MPS issue), recall degrades to grep+frontmatter-only.

• write-primitives — recall reads entries written by /memory save. Without entries, recall returns empty; with entries, recall validates that save's frontmatter + vec-indexing actually work end-to-end. This dependency is the natural sequencing gate: save must ship first.

1. SessionStart hook fires on session start — install the hook at the 2 host destinations; start a Claude Code session against a scratch vault with seeded _always-load/; verify the hook runs + injects entries + outputs the transparency line.
2. UserPromptSubmit hook fires on every user message — same scratch session; submit multiple prompts; verify the hook fires per prompt + recall returns relevant matches + dedups against already-loaded entries.
3. Recall returns top-K relevant entries — seed a fixture vault with ~20 entries on varied topics; submit queries with both keyword-match and paraphrase semantics; verify top-K returns the expected matches per the rubric (semantic queries should pull paraphrase matches that grep alone would miss).
4. Time budgets respected — SessionStart completes in <500ms; UserPromptSubmit completes in <300ms; on overrun, hook logs warning + proceeds with partial results rather than blocking.
5. status: superseded filtered by default — create an entry, evolve it; verify recall returns only the new entry (not the superseded one).
6. Offline-capable recall works — verify recall succeeds with network disconnected once BGE-large model is cached locally (v0.9.2 is local-only by default — see local-only embeddings decision, 2026-05-20 — crickets-hld; no API path exists to fall back to).
7. Local-embedding failure → grep fallback — simulate sentence-transformers missing; verify recall degrades to grep+frontmatter-only rather than failing entirely.
8. Smoke install verifies hooks land — smoke-install-bash.sh + .ps1 extended to verify both hook scripts install at the 2 host destinations.
9. All 3 OS CI workflows green on the commit that lands this part.

• The recall engine is shared between SessionStart, UserPromptSubmit, and (eventually) /memory search. Build it as a single Python module (memory/recall_engine.py or similar) callable from each hook script + the skill's search sub-command.
• The 300ms UserPromptSubmit budget is tight. Consider an embedding cache: tokenize the prompt → check a small LRU cache of recent embeddings → cache hit avoids the API/local call entirely. Defer caching to a follow-up if v1 hits the budget without it.
• The merge formula (sim × 0.7 + keyword × 0.3) is a guess per Tech Debt #7. Ship instrumented — every recall logs its components so the user can validate via /memory inspect and tune from real use.
• _always-load/ is just a path convention; the SessionStart hook doesn't filter by frontmatter always_load: true — it just loads everything in that subdir. The always_load: true frontmatter is informational only in v1 (might be used by /memory inspect to surface always-load entries differently).