feat: SignalSource abstraction — generalize signal ingestion beyond Todoist (#78)

- Add Signal + SignalSource interfaces to packages/shared-types
- TipCandidate.features widened to Record<string,number|boolean> to match Signal
- TodoistSignalSource: encapsulates fetch, cache, 401 handling, bus events, and act()
- SignalAggregator: parallel fan-out across sources with per-source failure isolation
- Recommender refactored to consume Signal[] via aggregator; source action dispatch via aggregator.act()
- ADR-0009: signal normalization strategy

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

packages/shared-types/src/http/signal.ts

@@ -0,0 +1,18 @@
+/** A normalized signal from any connected source */
+export interface Signal {
+  id: string;
+  source: string;                             // e.g. 'todoist', 'google-calendar', 'manual'
+  kind: 'task' | 'event' | 'habit' | 'insight';
+  content: string;
+  metadata: Record<string, unknown>;          // source-specific raw fields
+  features: Record<string, number | boolean>; // bandit-ready numeric/boolean features
+  timestamp: string;                          // ISO 8601
+}
+
+/** A pluggable data source that produces normalized signals */
+export interface SignalSource {
+  readonly id: string;
+  fetchSignals(userId: string): Promise<Signal[]>;
+  /** Optional: perform an action on the originating system (e.g. mark task done) */
+  act?(userId: string, signalId: string, action: string): Promise<void>;
+}

packages/shared-types/src/http/tip.ts

@@ -18,13 +18,11 @@ export interface Tip {
 /**
  * A scored tip candidate flowing through the bandit pipeline.
  * Extends Tip with features needed for scoring.
+ * features is a flexible map so new signal sources can contribute without
+ * schema changes — the bandit serialises them as-is.
  */
 export interface TipCandidate extends Tip {
-  features: {
-    is_overdue: boolean;
-    task_age_days: number;
-    priority: number;
-  };
+  features: Record<string, number | boolean>;
 }
 
 /** POST /recommend response */

packages/shared-types/src/index.ts

@@ -2,3 +2,4 @@ export * from './http/tip.js';
 export * from './http/auth.js';
 export * from './http/integrations.js';
 export * from './http/user.js';
+export * from './http/signal.js';