refactor: architecture revision — modular monolith, auth-commit, event protobuf, privacy-from-day-0

- ADR-0003: modular monolith for Phase 0 with documented extraction triggers
- ADR-0004: Auth.js + OIDC-shaped boundary; dedicated provider when mobile ships
- ADR-0005: protobuf for events, OpenAPI for HTTP, schema-registry CI gate
- New architecture docs: data-model, metrics (magic proxies), privacy (Phase-0 feature)
- Prime directives updated: privacy-as-feature, modular-by-package-deployable-by-stage
- Roadmap revised: Apple OAuth deferred to M1; web push in M1; k3s intermediate; tip-kind-aware UI
- PLAN updated: Phase-0 deletion endpoint, metrics baseline, compose profiles, import-boundary lint
- License decision in README (ARR with OSS plan in Phase 5)

services/recommender/README.md

@@ -16,12 +16,14 @@ POST /feedback
 ## Internals (stable seams)
 
 - **Candidate sources** — pluggable async generators. v0: Todoist tasks via `integrations`. Later: advice library, calendar nudges, health prompts.
-- **Context assembler** — merges request context with features (inline now, feature-store later).
-- **Policy** — `Policy.pick(candidates, context) → tip`. Registered by name:
+- **Feature assembler** — fills the `context` blob (inline in Phase 0; calls feature store from M1). Never inlined into policy code.
+- **Policy registry** — `Policy.pick(candidates, context) → tip`. Named entries:
   - `random` — v0 (Phase 0).
-  - `bandit.linucb` — v1 (Phase 1).
+  - `bandit.linucb.pooled` — v1 (Phase 1). **Global-then-personalize**: pooled features shared across users; per-user residual once data allows.
   - `remote` — delegates to `ml/serving` FastAPI scorer (Phase 1+).
+- **Shadow hook** — every request optionally runs N shadow policies in parallel and logs their picks + estimated rewards. Promotion from shadow → A/B → launch is a separate, deliberate step (ADR-0002).
+- **TipInstance persistence** — every decision writes `context_snapshot` (features seen at decision time). This is what makes offline replay honest.
 
 ## Phase 0 goal
 
-`RandomPolicy` only. The service, contract, and seams exist; the brain does not yet.
+`RandomPolicy` only. The service, contract, registry, shadow hook, and tip-instance persistence all exist; no ML yet.