diff --git a/agent/codex_responses_adapter.py b/agent/codex_responses_adapter.py
index ee75f4190e6d..edff776536e7 100644
--- a/agent/codex_responses_adapter.py
+++ b/agent/codex_responses_adapter.py
@@ -191,6 +191,28 @@ def _deterministic_call_id(fn_name: str, arguments: str, index: int = 0) -> str:
     return f"call_{digest}"
 
 
+def _clamp_responses_call_id(call_id: str) -> str:
+    """Keep a ``call_id`` within the Responses API's 64-char limit (#73492).
+
+    The codex app-server namespaces MCP tool call ids as
+    ``codex_mcp__<server>__<tool>_<codex_call_id>``; with an ``exec-<uuid>``
+    component the built-in ``hermes-tools`` server already overflows 64 chars,
+    and the Responses API rejects the whole payload with a non-retryable HTTP
+    400 that then replays every turn — permanently bricking the session.
+
+    Sibling defect to #10788 (which clamped ``input[*].id``), applied here to
+    ``call_id``. The surrogate is a pure, deterministic function of the
+    original, so the ``function_call`` and its matching ``function_call_output``
+    — which carry the same original id — map to the same surrogate and stay
+    paired without correlating the two items. Short ids pass through unchanged,
+    preserving prompt-cache prefixes.
+    """
+    if len(call_id) <= _MAX_RESPONSES_ITEM_ID_LENGTH:
+        return call_id
+    digest = hashlib.sha256(call_id.encode("utf-8", errors="replace")).hexdigest()[:32]
+    return f"call_{digest}"
+
+
 def _split_responses_tool_id(raw_id: Any) -> tuple[Optional[str], Optional[str]]:
     """Split a stored tool id into (call_id, response_item_id)."""
     if not isinstance(raw_id, str):
@@ -546,7 +568,7 @@ def _chat_messages_to_responses_input(
 
                         items.append({
                             "type": "function_call",
-                            "call_id": call_id,
+                            "call_id": _clamp_responses_call_id(call_id),
                             "name": fn_name,
                             "arguments": arguments,
                         })
@@ -589,7 +611,7 @@ def _chat_messages_to_responses_input(
 
             items.append({
                 "type": "function_call_output",
-                "call_id": call_id,
+                "call_id": _clamp_responses_call_id(call_id),
                 "output": output_value,
             })
 
diff --git a/tests/agent/test_codex_responses_adapter.py b/tests/agent/test_codex_responses_adapter.py
index eb690a9e3b82..a7c7ea25e8f1 100644
--- a/tests/agent/test_codex_responses_adapter.py
+++ b/tests/agent/test_codex_responses_adapter.py
@@ -227,6 +227,72 @@ def test_chat_messages_to_responses_input_keeps_short_message_id():
     assert message_item["id"] == _VALID_ITEM_ID
 
 
+# The codex app-server overflows the Responses 64-char call_id limit for
+# MCP-routed tools, e.g. codex_mcp__hermes-tools__web_search_exec-<uuid> (#73492).
+_OVERSIZED_CALL_ID = "codex_mcp__hermes-tools__web_search_exec-" + "0" * 43
+
+
+def test_chat_messages_to_responses_input_clamps_oversized_call_id():
+    """An oversized call_id must be clamped to <=64 chars on BOTH the
+    function_call and its matching function_call_output, to the same surrogate,
+    so the pairing survives (#73492)."""
+    messages = [
+        {
+            "role": "assistant",
+            "content": "",
+            "tool_calls": [
+                {
+                    "call_id": _OVERSIZED_CALL_ID,
+                    "function": {"name": "web_search", "arguments": "{}"},
+                }
+            ],
+        },
+        {
+            "role": "tool",
+            "tool_call_id": _OVERSIZED_CALL_ID,
+            "content": "some result",
+        },
+    ]
+
+    items = _chat_messages_to_responses_input(messages)
+
+    call = next(i for i in items if i.get("type") == "function_call")
+    output = next(i for i in items if i.get("type") == "function_call_output")
+
+    assert len(call["call_id"]) <= 64
+    assert call["call_id"] != _OVERSIZED_CALL_ID
+    # Deterministic surrogate — the pair must still reference the same id.
+    assert call["call_id"] == output["call_id"]
+
+
+def test_chat_messages_to_responses_input_keeps_short_call_id():
+    """A call_id already within the limit passes through unchanged (#73492)."""
+    messages = [
+        {
+            "role": "assistant",
+            "content": "",
+            "tool_calls": [
+                {
+                    "call_id": "call_abc123",
+                    "function": {"name": "web_search", "arguments": "{}"},
+                }
+            ],
+        },
+        {
+            "role": "tool",
+            "tool_call_id": "call_abc123",
+            "content": "some result",
+        },
+    ]
+
+    items = _chat_messages_to_responses_input(messages)
+
+    call = next(i for i in items if i.get("type") == "function_call")
+    output = next(i for i in items if i.get("type") == "function_call_output")
+    assert call["call_id"] == "call_abc123"
+    assert output["call_id"] == "call_abc123"
+
+
 def test_preflight_codex_input_items_drops_oversized_message_id():
     items = _preflight_codex_input_items(
         [