fix: honor bridge default backend when model is omitted

- derive request model from the configured default backend
- add regression coverage for omitted-model requests against the HTTP server

Author: OdinBot33

examples/subscription_bridge/server.py

@@ -43,6 +43,19 @@ def resolve_backend(model: str | None, default_backend: str = "codex") -> str:
     return default_backend
 
 
+def default_model_for_backend(backend: str) -> str:
+    if backend == "claude":
+        return "claude/claude-sonnet-4-6"
+    return "codex/gpt-5.4"
+
+
+def resolve_request_model(payload: dict[str, Any], *, default_backend: str) -> str:
+    raw_model = payload.get("model")
+    if isinstance(raw_model, str) and raw_model.strip():
+        return raw_model.strip()
+    return default_model_for_backend(default_backend)
+
+
 def _model_flag_value(model: str | None) -> str | None:
     if not model:
         return None
@@ -686,8 +699,9 @@ def do_GET(self) -> None:  # noqa: N802
     def do_POST(self) -> None:  # noqa: N802
         try:
             payload = self._read_json()
-            model = str(payload.get("model") or "codex/gpt-5.4")
-            backend = resolve_backend(model, default_backend=self.server.default_backend)  # type: ignore[attr-defined]
+            default_backend = self.server.default_backend  # type: ignore[attr-defined]
+            model = resolve_request_model(payload, default_backend=default_backend)
+            backend = resolve_backend(model, default_backend=default_backend)
             workdir = Path(self.server.workdir)  # type: ignore[attr-defined]
             request_id = f"bridge_{uuid.uuid4().hex}"
 

tests/examples/test_subscription_bridge.py

@@ -2,6 +2,9 @@
 
 import json
 import subprocess
+import threading
+import time
+import urllib.request
 from pathlib import Path
 from typing import Any, cast
 
@@ -16,6 +19,46 @@ def test_resolve_backend_prefers_model_prefix() -> None:
     assert server.resolve_backend("gpt-5.4", default_backend="codex") == "codex"
 
 
+def test_resolve_request_model_uses_backend_default_when_model_is_omitted() -> None:
+    assert server.resolve_request_model({}, default_backend="codex") == "codex/gpt-5.4"
+    assert server.resolve_request_model({}, default_backend="claude") == "claude/claude-sonnet-4-6"
+    assert (
+        server.resolve_request_model({"model": "claude/claude-sonnet-4-6"}, default_backend="codex")
+        == "claude/claude-sonnet-4-6"
+    )
+
+
+def test_http_server_uses_backend_default_model_when_request_omits_model(
+    monkeypatch: pytest.MonkeyPatch, tmp_path: Path
+) -> None:
+    def fake_run_backend(*, backend: str, prompt: str, model: str | None, workdir: Path) -> str:
+        return f"backend={backend};model={model};workdir={workdir.name}"
+
+    monkeypatch.setattr(server, "run_backend", fake_run_backend)
+
+    httpd = server.make_server("127.0.0.1", 0, default_backend="claude", workdir=tmp_path)
+    thread = threading.Thread(target=httpd.serve_forever, daemon=True)
+    thread.start()
+    time.sleep(0.05)
+    try:
+        req = urllib.request.Request(
+            f"http://127.0.0.1:{httpd.server_address[1]}/v1/chat/completions",
+            data=json.dumps({"messages": [{"role": "user", "content": "Say hi."}]}).encode("utf-8"),
+            headers={"Content-Type": "application/json"},
+        )
+        with urllib.request.urlopen(req) as resp:
+            payload = json.loads(resp.read().decode("utf-8"))
+    finally:
+        httpd.shutdown()
+        httpd.server_close()
+        thread.join(timeout=2)
+
+    assert payload["model"] == "claude/claude-sonnet-4-6"
+    assert payload["choices"][0]["message"]["content"].startswith(
+        "backend=claude;model=claude/claude-sonnet-4-6"
+    )
+
+
 def test_build_chat_prompt_from_messages_preserves_roles() -> None:
     payload = {
         "messages": [