fix(pi): repair MLflow SSE stream termination safely

src/ucode/agents/__init__.py

@@ -369,6 +369,7 @@ def check_gateway_endpoint(state: dict, tool: str) -> bool:
             bool(state.get("claude_models"))
             or bool(state.get("codex_models"))
             or bool(state.get("gemini_models"))
+            or bool(state.get("oss_models"))
         )
     return False
 
@@ -379,7 +380,7 @@ def check_gateway_endpoint(state: dict, tool: str) -> bool:
     "codex": ("codex",),
     "gemini": ("gemini",),
     "copilot": ("claude", "codex"),
-    "pi": ("claude", "codex", "gemini"),
+    "pi": ("claude", "codex", "gemini", "oss"),
 }
 
 

src/ucode/agents/_mlflow_proxy.py

@@ -0,0 +1,277 @@
+"""Loopback SSE-repair proxy for Pi's MLflow chat-completions provider.
+
+Some MLflow-served models omit the terminal OpenAI ``finish_reason``. Pi's
+strict ``openai-completions`` parser rejects those streams. This loopback-only
+proxy forwards requests without logging credentials or bodies and repairs only
+successful SSE responses that have already produced data. Healthy SSE and all
+non-streaming/error responses pass through unchanged.
+"""
+
+from __future__ import annotations
+
+import json
+from email.message import Message
+from http.client import IncompleteRead
+from http.server import BaseHTTPRequestHandler, ThreadingHTTPServer
+from typing import IO
+from urllib import error as urllib_error
+from urllib import request as urllib_request
+from urllib.parse import urlsplit
+
+from ucode.gateway_proxy import _HOP_BY_HOP
+from ucode.ui import print_warning
+
+_STREAM_CHUNK = 8192
+_CHAT_COMPLETIONS_PATH = "/ai-gateway/mlflow/v1/chat/completions"
+_SKIP_REQUEST_HEADERS = _HOP_BY_HOP | {"accept-encoding"}
+_ERROR_BODY = b'{"error":"MLflow proxy upstream unavailable"}\n'
+
+
+class _NoRedirect(urllib_request.HTTPRedirectHandler):
+    """Keep authenticated requests pinned to the configured workspace origin."""
+
+    def redirect_request(self, req, fp, code, msg, headers, newurl):
+        return None
+
+
+def _finish_chunk(chunk_id: str | None) -> bytes:
+    payload: dict = {
+        "object": "chat.completion.chunk",
+        "choices": [{"delta": {}, "index": 0, "finish_reason": "stop"}],
+    }
+    if chunk_id is not None:
+        payload["id"] = chunk_id
+    return json.dumps(payload, separators=(",", ":")).encode("utf-8")
+
+
+def _data_payload(raw_line: bytes) -> bytes | None:
+    """Return an SSE data field's payload, accepting the optional one space."""
+    stripped = raw_line.rstrip(b"\r\n")
+    if not stripped.startswith(b"data:"):
+        return None
+    payload = stripped[5:]
+    return payload[1:] if payload.startswith(b" ") else payload
+
+
+def _forwarded_request_headers(handler: BaseHTTPRequestHandler) -> dict[str, str]:
+    return {
+        key: value
+        for key, value in handler.headers.items()
+        if key.lower() not in _SKIP_REQUEST_HEADERS
+    }
+
+
+def _safe_response_headers(headers: Message, *, streaming: bool) -> list[tuple[str, str]]:
+    safe: list[tuple[str, str]] = []
+    for key, value in headers.items():
+        lowered = key.lower()
+        if lowered in _HOP_BY_HOP:
+            # A non-streaming body is unchanged, so preserving Content-Length
+            # avoids relying on EOF framing. Repaired streams can change size.
+            if lowered == "content-length" and not streaming:
+                safe.append((key, value))
+            continue
+        safe.append((key, value))
+    return safe
+
+
+class _ProxyHandler(BaseHTTPRequestHandler):
+    protocol_version = "HTTP/1.1"
+    upstream_origin: str
+
+    def log_message(self, format: str, *args: object) -> None:
+        return
+
+    def do_POST(self) -> None:  # noqa: N802 (stdlib handler API)
+        raw_length = self.headers.get("Content-Length", "0")
+        try:
+            length = int(raw_length)
+            if length < 0:
+                raise ValueError
+        except (TypeError, ValueError):
+            self._fixed_response(400, b'{"error":"invalid Content-Length"}\n')
+            return
+
+        try:
+            body = self.rfile.read(length) if length else b""
+        except OSError:
+            return
+        parsed_target = urlsplit(self.path)
+        if (
+            parsed_target.scheme
+            or parsed_target.netloc
+            or parsed_target.fragment
+            or parsed_target.path != _CHAT_COMPLETIONS_PATH
+        ):
+            self._fixed_response(400, b'{"error":"invalid MLflow proxy request target"}\n')
+            return
+        target = self.upstream_origin.rstrip("/") + parsed_target.path
+        if parsed_target.query:
+            target += f"?{parsed_target.query}"
+        request = urllib_request.Request(
+            target,
+            data=body,
+            method="POST",
+            headers=_forwarded_request_headers(self),
+        )
+        try:
+            opener = urllib_request.build_opener(_NoRedirect)
+            with opener.open(request, timeout=600) as response:  # noqa: S310
+                content_type = response.headers.get_content_type().lower()
+                if content_type == "text/event-stream":
+                    self._relay_sse(response.status, response.headers, response)
+                else:
+                    self._relay_verbatim(response.status, response.headers, response)
+        except urllib_error.HTTPError as exc:
+            # Relay upstream status, headers, and bytes verbatim. Never turn an
+            # upstream rejection into a successful repaired stream.
+            self._relay_verbatim(exc.code, exc.headers, exc)
+        except (urllib_error.URLError, OSError):
+            self._fixed_response(502, _ERROR_BODY)
+
+    def _send_headers(self, status: int, headers: Message, *, streaming: bool) -> bool:
+        try:
+            self.send_response(status)
+            for key, value in _safe_response_headers(headers, streaming=streaming):
+                self.send_header(key, value)
+            # The proxy never reuses downstream connections. EOF framing is
+            # therefore safe for responses without Content-Length (including
+            # 204s and repaired SSE), and shutdown cannot leave a keep-alive
+            # client waiting on an otherwise complete response.
+            self.send_header("Connection", "close")
+            self.close_connection = True
+            self.end_headers()
+            return True
+        except (BrokenPipeError, ConnectionResetError, OSError):
+            return False
+
+    def _relay_verbatim(self, status: int, headers: Message, stream: IO[bytes]) -> None:
+        if not self._send_headers(status, headers, streaming=False):
+            return
+        try:
+            while chunk := stream.read(_STREAM_CHUNK):
+                self.wfile.write(chunk)
+            self.wfile.flush()
+        except (BrokenPipeError, ConnectionResetError, OSError, IncompleteRead):
+            return
+
+    def _relay_sse(self, status: int, headers: Message, stream: IO[bytes]) -> None:
+        if not self._send_headers(status, headers, streaming=True):
+            return
+        saw_data = False
+        saw_finish = False
+        saw_done = False
+        saw_error = False
+        last_id: str | None = None
+        event_data: list[bytes] = []
+
+        def inspect_event() -> None:
+            nonlocal saw_error, saw_finish, last_id
+            if not event_data:
+                return
+            payload = b"\n".join(event_data)
+            event_data.clear()
+            try:
+                event = json.loads(payload)
+            except (UnicodeDecodeError, json.JSONDecodeError):
+                return
+            if not isinstance(event, dict):
+                return
+            if "error" in event:
+                saw_error = True
+            event_id = event.get("id")
+            if isinstance(event_id, str):
+                last_id = event_id
+            choices = event.get("choices")
+            if isinstance(choices, list) and any(
+                isinstance(choice, dict) and choice.get("finish_reason") is not None
+                for choice in choices
+            ):
+                saw_finish = True
+
+        try:
+            for raw_line in stream:
+                payload = _data_payload(raw_line)
+                event_line = raw_line.rstrip(b"\r\n")
+                if not event_line:
+                    inspect_event()
+                elif event_line.lower().startswith(b"event:"):
+                    event_name = event_line[6:]
+                    if event_name.startswith(b" "):
+                        event_name = event_name[1:]
+                    if event_name.lower() == b"error":
+                        saw_error = True
+                if payload == b"[DONE]":
+                    inspect_event()
+                    if saw_data and not saw_finish and not saw_error:
+                        self._write(b"data: " + _finish_chunk(last_id) + b"\n\n")
+                        saw_finish = True
+                    self._write(raw_line)
+                    saw_done = True
+                    continue
+                if payload is not None and payload:
+                    saw_data = True
+                    event_data.append(payload)
+                self._write(raw_line)
+        except (BrokenPipeError, ConnectionResetError, OSError, IncompleteRead):
+            # Never turn a transport-failed partial stream into a successful
+            # synthetic completion. EOF without a transport exception remains
+            # repairable below because affected gateways can end cleanly after
+            # their final data event.
+            return
+
+        # ``HTTPResponse`` line iteration can end without raising even when a
+        # declared Content-Length was not satisfied. A positive remainder is
+        # still a transport truncation, not a clean finish-reason omission.
+        remaining = getattr(stream, "length", None)
+        if isinstance(remaining, int) and remaining > 0:
+            return
+
+        inspect_event()
+        if saw_data and not saw_error:
+            try:
+                if not saw_finish:
+                    self._write(b"data: " + _finish_chunk(last_id) + b"\n\n")
+                if not saw_done:
+                    self._write(b"data: [DONE]\n\n")
+            except (BrokenPipeError, ConnectionResetError, OSError):
+                return
+
+    def _write(self, data: bytes) -> None:
+        self.wfile.write(data)
+        self.wfile.flush()
+
+    def _fixed_response(self, status: int, body: bytes) -> None:
+        try:
+            self.send_response(status)
+            self.send_header("Content-Type", "application/json")
+            self.send_header("Content-Length", str(len(body)))
+            self.end_headers()
+            self.wfile.write(body)
+            self.wfile.flush()
+        except (BrokenPipeError, ConnectionResetError, OSError):
+            return
+
+
+class _Server(ThreadingHTTPServer):
+    daemon_threads = True
+    allow_reuse_address = True
+
+
+def start(upstream_origin: str) -> tuple[ThreadingHTTPServer, str] | None:
+    """Bind a repair proxy to a fresh loopback port; the caller owns its lifecycle."""
+    if not isinstance(upstream_origin, str) or not upstream_origin:
+        print_warning("MLflow stream repair proxy was not started: invalid upstream URL.")
+        return None
+    parsed_origin = urlsplit(upstream_origin)
+    if parsed_origin.scheme not in {"http", "https"} or not parsed_origin.netloc:
+        print_warning("MLflow stream repair proxy was not started: invalid upstream URL.")
+        return None
+    handler = type("_BoundProxyHandler", (_ProxyHandler,), {"upstream_origin": upstream_origin})
+    try:
+        server = _Server(("127.0.0.1", 0), handler)
+    except OSError as exc:
+        print_warning(f"MLflow stream repair proxy was not started ({exc}).")
+        return None
+    port = int(server.server_address[1])
+    return server, f"http://127.0.0.1:{port}"

src/ucode/agents/claude.py

@@ -27,6 +27,7 @@
 from ucode.databricks import (
     build_auth_shell_command,
     build_tool_base_url,
+    claude_model_supports_1m,
     get_databricks_token,
 )
 from ucode.launcher import exec_or_spawn
@@ -82,11 +83,6 @@ def _resolve_web_search_model(state: dict) -> str | None:
 
 
 WEB_SEARCH_MCP_NAME = "web_search"
-# Matches both the AI Gateway form (`databricks-claude-opus-4-8`) and the UC
-# model-services form (`system.ai.claude-opus-4-8`).
-_CLAUDE_MODEL_RE = re.compile(
-    r"^(?:system\.ai\.)?(?:databricks-)?claude-(opus|sonnet)-(\d+)-(\d+)(.*)$"
-)
 
 # Env keys the MLflow Stop hook reads to route traces. Written into the
 # settings `env` block alongside the hook itself.
@@ -375,19 +371,9 @@ def render_overlay(
 
 
 def _maybe_add_1m_suffix(model: str) -> str:
-    if model.endswith("[1m]"):
-        return model
-    match = _CLAUDE_MODEL_RE.match(model)
-    if not match:
+    if model.endswith("[1m]") or not claude_model_supports_1m(model):
         return model
-
-    family, major_raw, minor_raw, _ = match.groups()
-    major = int(major_raw)
-    minor = int(minor_raw)
-    should_suffix = (family == "opus" and (major, minor) >= (4, 6)) or (
-        family == "sonnet" and (major, minor) >= (4, 6)
-    )
-    return f"{model}[1m]" if should_suffix else model
+    return f"{model}[1m]"
 
 
 def _register_web_search_mcp(workspace: str, search_model: str, profile: str | None = None) -> bool: