21 lines
1.1 KiB
Markdown
21 lines
1.1 KiB
Markdown
# ADR-0002: Recommender as the stable contract, policy as a plugin
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## Status
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Accepted — 2026-04-13
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## Context
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v0 picks a random Todoist task. v1+ will use a contextual bandit, then learned rankers, then collaborative signals. If the HTTP contract and the candidate-generation path are coupled to today's "random", every change is a migration.
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## Decision
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`recommender` exposes `POST /recommend` as the one stable contract. Internally it has three seams:
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1. **Candidate sources** — async functions that yield `TipCandidate`s from integrations, advice libraries, etc.
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2. **Context assembler** — pulls features (today: inline; later: feature store).
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3. **Policy** — `Policy.pick(candidates, context) → tip`. Registered by name; selected per-request by the experiments framework (Phase 4) or a static config (now).
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Swapping a policy never changes the contract or the client.
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## Consequences
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- v0 policy is `RandomPolicy`, trivially 50 lines.
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- v1 moves scoring to `ml/serving` behind the same `Policy` interface (`RemotePolicy` wrapper).
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- A/B is introduced without touching clients.
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