feat: add learner memory ingestion

.planning/phases/003-learner-memory/003-RESEARCH.md

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+# Phase 3 Research
+
+## Question
+
+How should learner memory be added without turning the diagnostic session store
+into durable product truth?
+
+## Findings
+
+### Keep memory separate from interview sessions
+
+Diagnostic sessions contain raw interaction records. Learner memory should be a
+separate derived state built from graded evidence. This preserves the boundary
+between temporary/session context and durable learning claims.
+
+### Apply only evidenced updates
+
+The memory service should ignore update candidates that do not include evidence.
+This directly enforces the OpenSpec rule that inferred memory requires evidence.
+
+### In-memory is still enough
+
+The current product does not yet need restart durability. A store interface plus
+tests gives the shape of persistence without adding database complexity early.
+
+## Recommendation
+
+1. Add `internal/learnermemory` with profile, mastery, misconception,
+   intervention, and review schedule records.
+2. Extend workflow runner memory extraction to return evidenced candidates.
+3. Wire diagnostic answer submission to memory ingestion.
+4. Add HTTP read endpoint for learner memory snapshot.
+5. Verify with tests and live smoke.