diff --git a/agent/message_sanitization.py b/agent/message_sanitization.py
index 4956c1749e..080c4009e9 100644
--- a/agent/message_sanitization.py
+++ b/agent/message_sanitization.py
@@ -466,7 +466,8 @@ __all__ = [
     "close_interrupted_tool_sequence", "coalesce_tool_call_id", "coerce_tool_name",
     "deterministic_call_id", "matches_reasoning_echo_family", "needs_reasoning_echo",
     "normalize_provider_tool_call_ids", "reapply_reasoning_echo", "reasoning_echo_family",
-    "reasoning_replay_route", "record_reasoning_field_rejection", "route_reasoning_carriers",
+    "reasoning_replay_route", "record_reasoning_field_rejection", "rejected_reasoning_carriers",
+    "route_reasoning_carriers",
     "sanitize_outbound_kwargs", "stale_thinking_reaches_wire", "strip_images_for_rejecting_model",
     "tool_call_id_variants", "tool_result_id_variants", "uniquify_tool_call_ids",
 ]
@@ -946,6 +947,27 @@ def reasoning_route_key(agent: Any) -> tuple[str, str, str]:
     )
 
 
+_REJECTION_MODEL_CONFIG_KEY = "reasoning_rejected_carriers"
+
+
+def rejected_reasoning_carriers(agent: Any) -> frozenset:
+    """Reasoning keys the active (provider, host, model) rejected in this session.
+
+    Persisted in the session's ``model_config`` so a resumed process (``--resume``, a gateway
+    restart) never re-learns a rejection with another 400. Loaded once per ``session_id``.
+    """
+    routes = agent.__dict__.setdefault("_reasoning_rejecting_routes", {})
+    session_id = getattr(agent, "session_id", None)
+    if session_id and getattr(agent, "_reasoning_rejections_loaded_for", None) != session_id:
+        agent._reasoning_rejections_loaded_for = session_id
+        getter = getattr(getattr(agent, "_session_db", None), "get_session_model_config_value", None)
+        stored = getter(session_id, _REJECTION_MODEL_CONFIG_KEY, []) if callable(getter) else []
+        for entry in stored if isinstance(stored, list) else ():
+            if isinstance(entry, list) and len(entry) == 4 and isinstance(entry[3], list):
+                routes.setdefault(tuple(entry[:3]), set()).update(k for k in entry[3] if k in _ALL_CARRIERS)
+    return frozenset(routes.get(reasoning_route_key(agent), ()))
+
+
 def record_reasoning_field_rejection(agent: Any, error_body: Any, sent_messages: Any) -> frozenset:
     """Remember the reasoning keys this route rejected; returns the NEW ones (empty = no retry).
 
@@ -956,9 +978,14 @@ def record_reasoning_field_rejection(agent: Any, error_body: Any, sent_messages:
     fields = rejected_reasoning_fields(error_body, sent_messages)
     if not fields:
         return frozenset()
-    known = agent._reasoning_rejecting_routes.setdefault(reasoning_route_key(agent), set())
-    new = fields - known
-    known.update(new)
+    new = fields - rejected_reasoning_carriers(agent)
+    if not new:
+        return frozenset()
+    routes = agent._reasoning_rejecting_routes
+    routes.setdefault(reasoning_route_key(agent), set()).update(new)
+    patcher = getattr(getattr(agent, "_session_db", None), "patch_session_model_config", None)
+    if callable(patcher) and getattr(agent, "session_id", None) and not getattr(agent, "_persist_disabled", False):
+        patcher(agent.session_id, {_REJECTION_MODEL_CONFIG_KEY: [[*key, sorted(v)] for key, v in sorted(routes.items())]})
     return frozenset(new)
 
 
diff --git a/agent/reasoning_params.py b/agent/reasoning_params.py
index 0a20144d7f..cdb57a8d58 100644
--- a/agent/reasoning_params.py
+++ b/agent/reasoning_params.py
@@ -161,9 +161,9 @@ class ReasoningParamsMixin:
         per turn — and recomputed after ``switch_model()`` / fallback activation or a recorded
         field rejection, the only events allowed to change the replayed bytes mid-session.
         """
-        from agent.message_sanitization import reasoning_replay_route, reasoning_route_key
+        from agent.message_sanitization import reasoning_replay_route, rejected_reasoning_carriers
 
-        rejected = frozenset(getattr(self, "_reasoning_rejecting_routes", {}).get(reasoning_route_key(self), ()))
+        rejected = rejected_reasoning_carriers(self)
         key = (getattr(self, "api_mode", None), self.provider, self.model, getattr(self, "_base_url_lower", self.base_url),
                self._reasoning_echo_opt_in(), rejected)
         cached = getattr(self, "_reasoning_route_cache", None)
diff --git a/tests/agent/test_reasoning_replay_routes.py b/tests/agent/test_reasoning_replay_routes.py
index 75fe290279..e8182b7259 100644
--- a/tests/agent/test_reasoning_replay_routes.py
+++ b/tests/agent/test_reasoning_replay_routes.py
@@ -8,7 +8,7 @@ from types import SimpleNamespace
 import pytest
 
 from agent.message_sanitization import (
-    apply_reasoning_content_policy, reapply_reasoning_echo, reasoning_replay_route,
+    apply_reasoning_content_policy, reapply_reasoning_echo, reasoning_replay_route, rejected_reasoning_carriers,
 )
 from agent.transports.chat_completions import ChatCompletionsTransport
 
@@ -74,11 +74,11 @@ class _Rejection(Exception):
         self.body = body
 
 
-def _agent(model):
+def _agent(model, db=None):
     return SimpleNamespace(
         provider="nous", model=model, base_url="https://inference-api.nousresearch.com/v1",
         api_mode="chat_completions", _force_ascii_payload=False, _image_rejecting_models=set(),
-        _reasoning_rejecting_routes={}, log_prefix="", _vprint=lambda *a, **k: None,
+        log_prefix="", _vprint=lambda *a, **k: None, session_id="s1" if db else None, _session_db=db,
     )
 
 
@@ -91,14 +91,18 @@ def _recover(agent, body, sent):
     )[0]
 
 
-def test_named_field_rejection_strips_once_per_model_and_never_loops():
-    lane = _agent("z-ai/glm-5.3-flash:US")
+def test_named_field_rejection_strips_once_per_model_and_never_loops(tmp_path):
+    from hermes_state import SessionDB
+
+    db = SessionDB(db_path=tmp_path / "state.db")
+    db.create_session("s1", source="cli", model="z-ai/glm-5.3-flash:US")
+    lane = _agent("z-ai/glm-5.3-flash:US", db)
     sent = [{"role": "user", "content": "hi"}, deepcopy(_TURN)]
     sent[1].pop("tool_calls")
     body = "Extra inputs are not permitted, field: 'messages[1].reasoning_details'"
     # A generic upstream error (content filter behind "Provider returned error") is not a rejection.
     assert _recover(lane, "Provider returned error", sent) is False
-    assert lane._reasoning_rejecting_routes == {}
+    assert not rejected_reasoning_carriers(lane)
 
     assert _recover(lane, body, sent) is True
     rejected = lane._reasoning_rejecting_routes[("nous", "inference-api.nousresearch.com", "z-ai/glm-5.3-flash:US")]
@@ -110,6 +114,8 @@ def test_named_field_rejection_strips_once_per_model_and_never_loops():
     assert "reasoning" not in sent[1] and "reasoning_details" not in sent[1]
     # Same rejection again: nothing new to strip -> normal error path, no loop.
     assert _recover(lane, body, [{"role": "assistant", "reasoning_details": _DETAILS}]) is False
+    # A resumed process (fresh agent, same session) never re-learns it with another 400.
+    assert rejected_reasoning_carriers(_agent(lane.model, db)) == {"reasoning", "reasoning_details"}
     # A sibling model on the same gateway keeps every carrier.
     sibling = reasoning_replay_route("chat_completions", "nous", "moonshotai/kimi-k3", lane.base_url)
     assert "reasoning_details" in sibling.carriers