Phases 16.2 + L2 + 17 VRAM gate + MySQL + 18 Lance hybrid milestone

Five threads of work landing as one milestone — all individually
verified end-to-end against real data, full release build clean,
46 unit tests pass.

## Phase 16.2 / 16.5 — autotune agent + ingest triggers

`vectord::agent` is a long-running tokio task that watches the trial
journal and autonomously proposes + runs new HNSW configs. Distinct
from `autotune::run_autotune` (synchronous one-shot grid). Triggered
on POST /vectors/agent/enqueue/{idx} or by the periodic wake; ingest
paths now push DatasetAppended events when an index's source dataset
gets re-ingested. Rate-limited (max_trials_per_hour) and cooldown-
gated so it can't saturate Ollama under live load.

The proposer is ε-greedy around the current champion: with prob 0.25
sample random from full bounds, otherwise perturb champion ± small
delta on both axes. Dedup against history. Deterministic — RNG seeded
from history.len() so the same journal state proposes the same next
config (helps offline replay debugging).

`[agent]` config section in lakehouse.toml; opt-in via enabled=true.

## Federation Layer 2 — runtime bucket lifecycle + per-index scoping

`BucketRegistry.buckets` moved to `std::sync::RwLock<HashMap>` so
buckets can be added/removed after startup. POST /storage/buckets
provisions at runtime; DELETE /storage/buckets/{name} unregisters
(refuses primary/rescue with 403). Local-backend buckets get their
root directory auto-created.

`IndexMeta.bucket` (default "primary" via serde) records each index's
home bucket. `TrialJournal` and `PromotionRegistry` now hold
Arc<BucketRegistry> + IndexRegistry; they resolve target store per-
index via IndexMeta.bucket. PromotionRegistry::list_all scans every
bucket and dedups by index_name. Pre-federation indexes keep working
unchanged — they just default to primary.

`ModelProfile.bucket: Option<String>` declares per-profile artifact
home. POST /vectors/profile/{id}/activate auto-provisions the
profile's bucket under storage.profile_root if not yet registered.

EvalSets stay primary-only for now — noted gap, low-risk to extend
later with the same resolver pattern.

## Phase 17 — VRAM-aware two-profile gate

Sidecar gains POST /admin/unload (Ollama keep_alive=0 trick — forces
immediate VRAM release), POST /admin/preload (keep_alive=5m with
empty prompt, takes the slot warm), and GET /admin/vram (combines
nvidia-smi snapshot with Ollama /api/ps). Exposed via aibridge as
unload_model / preload_model / vram_snapshot.

`VectorState.active_profile` is the GPU-slot singleton —
Arc<RwLock<Option<ActiveProfileSlot>>>. activate_profile checks for
a previous profile with a different ollama_name and unloads it
before preloading the new one; same-model reactivations skip the
unload (Ollama no-ops). New routes: POST /vectors/profile/{id}/
deactivate (unload + clear slot), GET /vectors/profile/active.

Verified live: staffing-recruiter (qwen2.5) → docs-assistant
(mistral) swap freed qwen2.5 from VRAM and loaded mistral. nomic-
embed-text persists across swaps because both profiles use it —
free optimization that fell out of the design. Scoped search
correctly 403s cross-profile in both directions.

## MySQL streaming connector

`crates/ingestd/src/my_stream.rs` mirrors pg_stream.rs for MySQL.
Pure-rust `mysql_async` driver (default-features=false to avoid C
deps). Same OFFSET pagination, same Parquet-streaming write shape.
Type mapping per ADR-010: int/bigint → Int32/Int64, decimal/float
→ Float64, tinyint(1)/bool → Boolean, everything else → Utf8 with
fallback parsers for date/time/json/uuid via Display.

POST /ingest/mysql parallel to /ingest/db. Same PII auto-detection,
same lineage capture (source_system="mysql"), same agent-trigger
hook. `redact_dsn` generalized — was hardcoded to "postgresql://"
length, now works for any scheme://user:pass@host/path URL (latent
PII leak fix for MySQL DSNs).

Verified live against MariaDB on localhost: 10 rows × 9 columns of
test data round-tripped through datatypes int/varchar/decimal/
tinyint/datetime/text. PII detection auto-flagged name + email.
Aggregation queries through DataFusion match the source values
exactly.

## Phase 18 — Hybrid Parquet+HNSW ⊕ Lance backend (ADR-019)

`vectord-lance` is a new firewall crate. Lance pulls Arrow 57 and
DataFusion 52 — incompatible with the rest of the workspace's
Arrow 55 / DataFusion 47. The firewall isolates that dep tree:
public API uses only std types (Vec<f32>, Vec<String>, Hit, Row,
*Stats), so no Arrow types cross the crate boundary and nothing
propagates to vectord. The ADR-019 path that didn't ship until now.

`vectord::lance_backend::LanceRegistry` lazy-creates a
LanceVectorStore per index, resolving bucket → URI via the
conventional local-bucket layout. `IndexMeta.vector_backend` and
`ModelProfile.vector_backend` carry the choice (default Parquet so
existing indexes unchanged).

Six routes under /vectors/lance/*:
- migrate/{idx}: convert binary-blob Parquet → Lance FixedSizeList
- index/{idx}: build IVF_PQ
- search/{idx}: vector search (embed via sidecar)
- doc/{idx}/{doc_id}: random row fetch
- append/{idx}: native fragment append
- stats/{idx}: row count + index presence

Verified live on the real resumes_100k_v2 corpus (100K × 768d):
- Migrate: 0.57s
- Build IVF_PQ index: 16.2s (matches ADR-019 bench; 14× faster than
  HNSW's 230s for the same data)
- Search end-to-end (Ollama embed + Lance scan): 23-53ms
- Random doc_id fetch: 5-7ms (filter scan; faster than Parquet's
  ~35ms full-file scan, slower than the bench's 311us positional
  take — would close that gap with a scalar btree on doc_id)
- Append 100 rows: 3.3ms / +320KB on disk vs Parquet's required
  full ~330MB rewrite — the structural win
- Index survives append; both backends coexist cleanly

## Known follow-ups not in this milestone

- ModelProfile.vector_backend doesn't yet auto-route /vectors/profile/
  {id}/search to Lance; callers go through /vectors/lance/* directly
- Scalar btree on doc_id (closes the 5-7ms → ~300us gap)
- vectord-lance built default-features=false → no S3 yet
- IVF_PQ recall not measured (ADR-019 caveat) — needs a Lance-aware
  variant of the eval harness
- Watcher-path ingest doesn't push agent triggers (HTTP paths do)
- EvalSets still primary-only (federation gap)
- No PATCH endpoint to move an existing index between buckets
- The pre-existing storaged::append_log doctest fails to compile
  (malformed `{prefix}/` parses as code fence) — pre-existing bug,
  left for a focused fix

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

crates/shared/src/config.rs

@@ -16,8 +16,46 @@ pub struct Config {
     pub auth: AuthConfig,
     #[serde(default)]
     pub observability: ObservabilityConfig,
+    #[serde(default)]
+    pub agent: AgentSettings,
 }
 
+/// Phase 16.2 — background autotune agent settings.
+///
+/// Duplicated from `vectord::agent::AgentConfig` because `shared` can't
+/// depend on `vectord` (vectord already depends on shared). The gateway
+/// copies these into the vectord config at startup.
+#[derive(Debug, Clone, Deserialize)]
+pub struct AgentSettings {
+    #[serde(default)]
+    pub enabled: bool,
+    #[serde(default = "default_cycle_interval_secs")]
+    pub cycle_interval_secs: u64,
+    #[serde(default = "default_cooldown_secs")]
+    pub cooldown_between_trials_secs: u64,
+    #[serde(default = "default_min_recall")]
+    pub min_recall: f32,
+    #[serde(default = "default_max_trials_per_hour")]
+    pub max_trials_per_hour: u32,
+}
+
+impl Default for AgentSettings {
+    fn default() -> Self {
+        Self {
+            enabled: false,
+            cycle_interval_secs: default_cycle_interval_secs(),
+            cooldown_between_trials_secs: default_cooldown_secs(),
+            min_recall: default_min_recall(),
+            max_trials_per_hour: default_max_trials_per_hour(),
+        }
+    }
+}
+
+fn default_cycle_interval_secs() -> u64 { 60 }
+fn default_cooldown_secs() -> u64 { 30 }
+fn default_min_recall() -> f32 { 0.9 }
+fn default_max_trials_per_hour() -> u32 { 30 }
+
 #[derive(Debug, Clone, Deserialize)]
 pub struct GatewayConfig {
     #[serde(default = "default_host")]
@@ -159,6 +197,7 @@ impl Default for Config {
             ai: AiConfig::default(),
             auth: AuthConfig::default(),
             observability: ObservabilityConfig::default(),
+            agent: AgentSettings::default(),
         }
     }
 }