feat: validate continuity config and extract receipt contract

plugins/continuity/README.md

@@ -6,7 +6,10 @@ This package is the skeleton for extracting the current approved-plan continuity
 
 - Task 2: package skeleton created
 - Task 3: config schema contract scaffolded
-- Plugin logic intentionally not implemented yet
+- Task 4: config validation tests added
+- Task 5: minimal config validator implemented
+- Task 6: receipt validator contract extracted
+- Plugin evaluator / adapter logic intentionally not implemented yet
 
 ## Layout
 
@@ -34,6 +37,25 @@ plugins/continuity/
 
 See `examples/openclaw.continuity.example.json`.
 
+## Receipt validator contract
+
+The MVP receipt validator currently defines this minimum shape:
+
+- `planId`
+- `currentTask`
+- `nextDerivedAction`
+- `dispatchedAt`
+- `dispatchRunId`
+- `childSessionKey`
+- `replyClosureState`
+
+API surface:
+
+- `validateReceipt(receipt)`
+- `isValidReceipt(receipt)`
+
+See `src/continuity/types.md` for the extracted contract note.
+
 ## Notes
 
 - Current terminal states preserved by default: `waiting_user`, `blocked`, `pending_verification`