fix(tui_gateway): restore openrouter provider on session resume

tests/test_tui_gateway_server.py

@@ -1233,18 +1233,19 @@ def update_session_cwd(self, *_args):
 
 
 def test_stored_session_runtime_overrides_skips_bare_billing_provider():
-    """A bare billing bucket ("custom"/"auto"/"openrouter") must not be restored as the
-    provider identity on resume. A custom endpoint that never used `/model` persists only
+    """A bare billing bucket ("custom"/"auto") must not be restored as the provider
+    identity on resume. A custom endpoint that never used `/model` persists only
     `billing_provider="custom"`; restoring that broke `session.resume` with "No LLM provider
-    configured" (agent_init treats it as non-routable). A real provider, or an explicit
+    configured" (agent_init treats it as non-routable). ``"openrouter"`` is NOT a bare bucket
+    — it is a fully routable provider; see #57588. A real provider, or an explicit
     `model_config.provider`, is still restored.
     """
     # Bare "custom" bucket, no explicit model_config.provider: no provider override restored.
     ov = server._stored_session_runtime_overrides({"model": "my-model", "billing_provider": "custom"})
     assert "provider_override" not in ov
     assert ov["model_override"]["provider"] is None
 
-    for bare in ("auto", "openrouter", "custom"):
+    for bare in ("auto", "custom"):
         ov = server._stored_session_runtime_overrides({"model": "m", "billing_provider": bare})
         assert "provider_override" not in ov
 
@@ -1261,6 +1262,33 @@ def test_stored_session_runtime_overrides_skips_bare_billing_provider():
     assert ov["model_override"]["provider"] == "custom:myendpoint"
 
 
+def test_openrouter_session_resume_restores_provider():
+    """OpenRouter is a fully routable provider — sessions that used OpenRouter must
+    restore the "openrouter" provider override on resume, not fall through to whatever
+    the current global model is.  (#57588)
+    """
+    # OpenRouter session with no explicit model_config.provider (the common case
+    # for sessions that never used /model): billing_provider="openrouter" should
+    # be restored as the provider override.
+    ov = server._stored_session_runtime_overrides(
+        {"model": "anthropic/claude-opus-4.8", "billing_provider": "openrouter"}
+    )
+    assert ov["provider_override"] == "openrouter"
+    assert ov["model_override"]["provider"] == "openrouter"
+    assert ov["model_override"]["model"] == "anthropic/claude-opus-4.8"
+
+    # When an explicit model_config.provider exists, it takes precedence over
+    # billing_provider (this path was already correct).
+    ov = server._stored_session_runtime_overrides(
+        {
+            "model": "anthropic/claude-opus-4.8",
+            "billing_provider": "openrouter",
+            "model_config": {"provider": "openrouter", "base_url": "https://openrouter.ai/api/v1"},
+        }
+    )
+    assert ov["provider_override"] == "openrouter"
+
+
 def test_persist_live_session_runtime_preserves_resume_metadata(monkeypatch):
     updates = {}
 

tui_gateway/server.py

@@ -2008,7 +2008,12 @@ def _resolve_startup_runtime() -> tuple[str, str | None]:
 
 # Bare billing buckets are not routable provider identities (kept in parity with the
 # provider gate in agent_init). Restoring one as a session provider override breaks resume.
-_BARE_BILLING_PROVIDERS = {"auto", "openrouter", "custom"}
+# ``openrouter`` is deliberately excluded — it is a fully routable provider with its own
+# API key and base_url.  Sessions that used OpenRouter store
+# ``billing_provider="openrouter"``; dropping it forces resume to the current global
+# model (e.g. a custom endpoint), which is the wrong provider for the stored model.
+#  See #57588.
+_BARE_BILLING_PROVIDERS = {"auto", "custom"}
 
 
 def _stored_session_runtime_overrides(row: dict | None) -> dict: