feat: add receive message reconciliation helper

docs/superpowers/plans/2026-07-10-r6f-r14-continuous-execution-plan.md

@@ -857,19 +857,19 @@ git push gitea main
 - Produces: `func ReconcileMessageSources(left, right []MessageReconciliationCandidate) MessageReconciliationSummary`.
 - Summary fields: `strong_matches`, `medium_matches`, `unmatched_left`, `unmatched_right`, `auto_merge_recommended`.
 
-- [ ] **Step 1: Write reconciliation tests**
+- [x] **Step 1: Write reconciliation tests**
 
 Add `TestReconcileMessageSourcesStrongAndMediumMatches`: same message id is strong; same conversation/sender and timestamp within 3000ms is medium; auto merge remains false until a strong-ratio threshold is met.
 
-- [ ] **Step 2: Implement pure Go helper**
+- [x] **Step 2: Implement pure Go helper**
 
 No DB/log IO in the helper. It only compares sanitized candidates.
 
-- [ ] **Step 3: Add script wrapper**
+- [x] **Step 3: Add script wrapper**
 
 Script runs against fixture JSON first; optional real evidence mode prints counts and booleans only.
 
-- [ ] **Step 4: Verify and commit**
+- [x] **Step 4: Verify and commit**
 
 ```powershell
 git diff --check
@@ -885,6 +885,14 @@ git push gitea main
 
 **Acceptance gate:** 对账能力存在，但默认 receive routing 不改变。
 
+
+**R12 Result:**
+
+- Added pure Go reconciliation helper and tests.
+- Added `scripts/verify-receive-source-reconciliation.ps1 -UseFixture`.
+- Fixture output is sanitized and keeps `default_receive_routing_changed=false`.
+- Default receive routing remains PacketReader/log-backed; no `auto` merge was enabled.
+
 ---
 
 ### R13: End-to-end business goals smoke