test(acp-snapshot): wait for the durable goal pause before disposal

The goal scenario asserted a paused revision-2 goal, but the pause is
appended only after cancellation reaches idle — after turn/end. Under
parallel snapshot files the subprocess could dispose before the pause
record persisted, folding the log to an active revision-1 goal.

Add a waitForEventAfterTurnEnd input step (the turn-end/title waiters'
shape, parameterized by event type) and use it in the goal scenario to
hold the subprocess open until the goal-state record lands.

examples/acp-agent/tests/goal-snapshots/goal-session/input.json

@@ -2,13 +2,10 @@
   "steps": [
     { "op": "initialize" },
     { "op": "newSession" },
-    {
-      "op": "promptAndWaitForAgentMessage",
-      "text": "Create a durable two-round goal for the ACP snapshot, inspect it, then report readiness.",
-      "waitForText": "GOAL ROUND ONE"
-    },
+    { "op": "promptAndWaitForAgentMessage", "text": "Create a durable two-round goal for the ACP snapshot, inspect it, then report readiness.", "waitForText": "GOAL ROUND ONE" },
     { "op": "waitForTurnStart", "minimumTurn": 3 },
     { "op": "cancel", "waitForFile": { "path": ".dsh-snapshot-goal-cancel-ready" } },
-    { "op": "waitForTurnEnd" }
+    { "op": "waitForTurnEnd" },
+    { "op": "waitForEventAfterTurnEnd", "type": "user/message" }
   ]
 }