diff --git a/scripts/agent_exec_adapters.py b/scripts/agent_exec_adapters.py
index dee9f352..26aac68f 100644
--- a/scripts/agent_exec_adapters.py
+++ b/scripts/agent_exec_adapters.py
@@ -429,22 +429,39 @@ def _build_bounded_unit_prompt(packet_text: str) -> str:
 
 
 def extract_terminal_record(text: str | None) -> dict[str, Any] | None:
-    """Return the last valid terminal record embedded in one final message."""
+    """Return the sole terminal record that ends one final message.
+
+    Only whitespace may follow the record, and no other valid record may
+    precede it; anything else fails closed.
+    """
     if not isinstance(text, str) or not text:
         return None
-    text = text[-_MAX_TERMINAL_TEXT_CHARS:]
+    text = text[-_MAX_TERMINAL_TEXT_CHARS:].rstrip()
     decoder = json.JSONDecoder()
+
+    def decode_at(pos: int) -> tuple[object, int]:
+        try:
+            return decoder.raw_decode(text, pos)
+        except json.JSONDecodeError:
+            return None, -1
+
     pos = text.rfind("{")
     while pos != -1:
-        try:
-            candidate, _ = decoder.raw_decode(text, pos)
-        except json.JSONDecodeError:
-            candidate = None
-        record = _valid_terminal_record(candidate)
-        if record is not None:
-            return record
+        candidate, end = decode_at(pos)
+        if end == len(text) and isinstance(candidate, dict):
+            break
         pos = text.rfind("{", 0, pos)
-    return None
+    else:
+        return None
+    record = _valid_terminal_record(candidate)
+    if record is None:
+        return None
+    earlier = text.rfind("{", 0, pos)
+    while earlier != -1:
+        if _valid_terminal_record(decode_at(earlier)[0]) is not None:
+            return None
+        earlier = text.rfind("{", 0, earlier)
+    return record
 
 
 def _valid_terminal_record(obj: object) -> dict[str, Any] | None:
diff --git a/tests/test_agent_exec.py b/tests/test_agent_exec.py
index 029375d9..0981c541 100644
--- a/tests/test_agent_exec.py
+++ b/tests/test_agent_exec.py
@@ -2325,7 +2325,7 @@ class AgentExecControllerTests(unittest.TestCase):
                 "pi",
                 _pi_help(),
                 _pi_json_events(
-                    "ok\n```json\n" + _terminal_json() + "\n```",
+                    "ok\n" + _terminal_json() + "\n",
                     agent_end_padding=2 * agent_exec.TERMINAL_LINE_MAX_BYTES,
                 ),
                 "success",
@@ -2411,12 +2411,35 @@ class TerminalRecordDecodingTests(unittest.TestCase):
         )
 
     def test_cursor_stream_json_result_is_decoded(self) -> None:
-        lines = _cursor_stream_events("Done.\n" + _terminal_json() + "\nThanks.")
+        lines = _cursor_stream_events("Done.\n" + _terminal_json() + "\n  \n")
         record = self._decode("cursor", lines)
         assert record is not None
         self.assertEqual(record["terminal_status"], "completed")
         self.assertEqual(record["changed_files"], ["src/marker.txt"])
 
+    def test_terminal_record_must_be_sole_final_content(self) -> None:
+        invalid = json.dumps({"terminal_status": "done", "summary": "x"})
+        texts = {
+            "trailing-prose": "Done.\n" + _terminal_json() + "\nThanks.",
+            "trailing-invalid-object": _terminal_json() + "\n" + invalid,
+            "trailing-non-terminal-object": _terminal_json() + ' {"note":"x"}',
+            "truncated-terminal-object": _terminal_json() + '\n{"terminal_status":',
+            "two-records": _terminal_json() + "\n" + _terminal_json(),
+            "conflicting-records": _terminal_json() + "\n" + _terminal_json("blocked"),
+        }
+        for name, text in texts.items():
+            for adapter, lines in (
+                ("cursor", _cursor_stream_events(text)),
+                ("antigravity", _agy_stream_events(text)),
+                ("pi", _pi_json_events(text)),
+            ):
+                with self.subTest(case=name, adapter=adapter):
+                    self.assertIsNone(self._decode(adapter, lines))
+            with self.subTest(case=name, adapter="custom"):
+                self.assertIsNone(
+                    self._decode("custom", [], stdout_tail="", result_text=text)
+                )
+
     def test_cursor_user_echo_and_error_result_are_not_records(self) -> None:
         lines = _cursor_stream_events("prose only")
         echo = json.loads(lines[1])