docs: record AI Design outcome integration

.project-docs/60-reflection/cases/20260903-design-message-send-client-integration-6f3a8c21__adopt-source-record-before-commit.md

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+# Adopt source task records before committing an Integration
+
+## Trigger
+
+Integration task `20260903-design-message-send-client-integration-6f3a8c21`
+cherry-picked a reviewed source commit with the default auto-commit behavior. The
+product patch was clean, but that commit also introduced the source task record.
+`check_doc_drift.py` correctly blocked because the Integration ownership record had
+not captured that foreign task-owned document as an unchanged source.
+
+## Recovery
+
+No product or user file was lost. After explicit user approval, the task soft-reset
+only its newly created, unpushed commit, preserving both index and worktree. It then
+resumed the same Integration ownership with `--adopt-existing` while the exact source
+record was staged, verified the staged patch, and recommitted the identical source
+change.
+
+## Reusable Rule
+
+When a source commit adds or updates its own task record, do not let cherry-pick
+auto-commit it inside an already-owned Integration worktree. Use
+`git cherry-pick --no-commit <source>` (or pause an ordinary merge before commit),
+then resume the same Integration task with `task_context.py start ...
+--adopt-existing`. Confirm the source record is byte-for-byte unchanged, commit the
+source patch, and run the task-aware drift check. Never edit the source task record
+to make the gate pass.
+
+## Evidence
+
+- Source: `83f3f134a6779251aaa18f3290308cd9221b038f`.
+- Integrated product commit:
+  `a16dfd0d6f48b99899ba84ac63bde4dcd661d067`.
+- The source-path comparison and final task-aware drift check verify that the
+  source record and product files were integrated unchanged.