docs: define continuity receipt linkage fields

docs/runbooks/approved-plan-continuity.md

@@ -17,3 +17,21 @@
 ### `dispatchedAt`
 - The timestamp indicating when the next derived action was actually dispatched.
 - Use this field to record when the continuity handoff occurred.
+
+## Continuity receipt linkage fields
+
+### `dispatchRunId`
+- The unique identifier for the dispatch run that produced or recorded the next-step continuity handoff.
+- Use this field to link the receipt to one concrete dispatch execution, not just a planned action.
+- This field is for receipt linkage and traceability only; it does not by itself define continuity-gate pass/fail behavior.
+
+### `childSessionKey`
+- The session linkage key for the child session or spawned execution context that receives the dispatched next action.
+- Use this field to connect the continuity receipt to the specific downstream session that should carry the workflow forward.
+- This field records linkage identity only; it does not by itself imply hook integration or dispatch binding logic.
+
+### `replyClosureState`
+- The closure state recorded at the point the current reply is being closed.
+- Use this field to state whether the reply closed under a dispatch-linked continuation path or some separately defined terminal closure state.
+- This field is defined here as a receipt field only; legal closure states and gate enforcement are defined in later tasks.
+