fix(continual-learning): harden wasRealCollision verifier (Codex review)

Addresses the P1 brittleness in the Step 3 verifier so learned_from edges
(graph/live.ts:413) can't be silently zeroed on stage.

- Capture overlap AT detection time as Collision.gitOverlap (podman.ts), while
  engineer_states are still fresh, instead of re-deriving from possibly-stale
  state when the user clicks. deriveWasRealCollision() now prefers this stored
  evidence and only falls back to a live re-derivation for older collisions.
- Canonicalize engineer names (trim + lowercase) on both the capture and the
  fallback path, so "Karti" vs "karti" no longer misses the git state.
- conflictKey now reuses the shared comparableBasename() helper (dedupe).

shared/src/collision.ts gains optional `gitOverlap?: boolean` (additive).
shared rebuilt; backend+frontend typecheck + eslint pass. PLAN.md rung 3 updated.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

docs/PLAN.md

@@ -510,14 +510,19 @@ no schema change. Owner: RSI track. Independent of the MongoDB-cleanup handoff.
      kind), `plan.md:66` (second similar event behaves differently).
 
 3. **Step 3 - derive `wasRealCollision` from git overlap (backend-authoritative)** ✅
-   - `backend/src/memory/store.ts` `recordOutcome` now overrides the
-     client-supplied `wasRealCollision` with `deriveWasRealCollision()`: a
-     collision is real only if BOTH named engineers currently have the collided
-     file in their git `changedFiles` (`getGitStates`, 120s freshness TTL).
-     Conservative `false` when orphaned/stale. `frontend/.../useInterventions.ts`
-     stops sending a hardcoded `true` (now a backend-overridden placeholder).
-   - Restores the (accepted × wasReal) 2×2 the spec assumes.
+   - Overlap is captured AT detection time as `Collision.gitOverlap`
+     (`backend/src/agent/podman.ts`), while `engineer_states` are still fresh —
+     true only if ALL involved engineers have the collided file in their git
+     `changedFiles`, matched on case/whitespace-canonical names.
+   - `backend/src/memory/store.ts` `recordOutcome` overrides the client value
+     with `deriveWasRealCollision()`, which prefers the stored `gitOverlap`
+     (immune to late clicks / stale sidecars / the 120s TTL) and only falls back
+     to a live canonical-name re-derivation for pre-existing collisions.
+     `frontend/.../useInterventions.ts` stops sending hardcoded `true`.
+   - Restores the (accepted × wasReal) 2×2 the spec assumes; keeps `learned_from`
+     edges (`graph/live.ts:413`) from being silently zeroed on stage.
    - Spec: `docs/continual-learning/spec.md:98-108`, `policy.md:35-42`.
+   - Hardened per Codex review (name canonicalization + detection-time capture).
 
 Follow-ups (separate rungs, not in this change): Step 4-5 `strategy_versions` +
 Gemini-proposed `LearningProposal` slice; Step 6 durable `owns` write; seed a