fix(windows): desktop backend spawn (#531) + model-aware engine selection (#532)

Two runtime bugs found during end-to-end testing on a clean Windows 11
24H2 Azure VM.

#531 - Desktop "Failed to get response": run_jarvis_command spawned the
backend with .output(), which waits for the process to exit. `jarvis
serve` never exits, so the Tauri command hung forever (the Start button
never resolved); and it ran `uv run jarvis` with no cwd, so in a packaged
install -- where the cwd isn't the checkout -- `jarvis` wasn't found and
the server never started. Now: run from find_project_root(), and for
`serve` spawn detached (.spawn()), drain stderr, and poll /health for
readiness (mirrors start_backend); short commands keep .output().

The server layer itself was verified healthy on Windows (/health and
/v1/chat/completions both 200, localhost included) -- the fault was the
Tauri spawn path.

#532 - "OpenAI client not available" after reboot: when the local engine
is down, get_engine's fallback selected CloudEngine because health() is
True if ANY provider client exists -- without checking the resolved
model's provider has a client. A user with e.g. OPENROUTER_API_KEY and a
gpt-* model then hit the OpenAI path with no client. Add
CloudEngine.can_serve(model) (checks the specific provider client via the
same routing generate()/stream() use) + a default can_serve->True on the
base engine, and make get_engine model-aware so it skips an engine that
can't serve the model -- the user falls through to the helpful "no engine
available / start ollama" message instead.

Tests: engine discovery/cloud/model-matrix + cli serve/ask suites pass
(the one ask_e2e failure is a pre-existing version-banner flake, fails
identically on main). The Tauri crate couldn't be compiled locally (no
GTK/webkit sys-libs in this env); relies on CI.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

frontend/src-tauri/src/lib.rs

@@ -1540,19 +1540,89 @@ async fn fetch_models(api_url: String) -> Result<serde_json::Value, String> {
 
 #[tauri::command]
 async fn run_jarvis_command(args: Vec<String>) -> Result<String, String> {
-    let mut cmd_args = vec!["run".to_string(), "jarvis".to_string()];
-    cmd_args.extend(args);
     let uv_bin = resolve_bin("uv");
-    let output = tokio::process::Command::new(&uv_bin)
-        .args(&cmd_args)
-        .output()
-        .await
-        .map_err(|e| format!("Failed to launch jarvis: {}", e))?;
 
-    if output.status.success() {
-        Ok(String::from_utf8_lossy(&output.stdout).to_string())
-    } else {
-        Err(String::from_utf8_lossy(&output.stderr).to_string())
+    let mut cmd_args = vec!["run".to_string(), "jarvis".to_string()];
+    cmd_args.extend(args.iter().cloned());
+
+    let mut cmd = tokio::process::Command::new(&uv_bin);
+    cmd.args(&cmd_args);
+    // Run from the project root so `uv run jarvis` resolves the OpenJarvis
+    // project regardless of the app's launch cwd. In a packaged install the
+    // cwd isn't the checkout, so without this `jarvis` isn't found and the
+    // backend never starts — the UI then shows "Failed to get response"
+    // (see #531).
+    if let Some(ref root) = find_project_root() {
+        cmd.current_dir(root);
+    }
+
+    let is_serve = args.first().map(|a| a.as_str() == "serve").unwrap_or(false);
+
+    if !is_serve {
+        // Short-lived command (e.g. `stop`, `status`): wait for it and return
+        // its captured output.
+        let output = cmd
+            .output()
+            .await
+            .map_err(|e| format!("Failed to launch jarvis: {}", e))?;
+        return if output.status.success() {
+            Ok(String::from_utf8_lossy(&output.stdout).to_string())
+        } else {
+            Err(String::from_utf8_lossy(&output.stderr).to_string())
+        };
+    }
+
+    // `jarvis serve` is a long-running server that never exits. The old code
+    // used `.output()`, which waits for the process to exit and so hung this
+    // command forever — the "Start" button never resolved (#531). Spawn it
+    // detached instead, drain stderr (a full 4 KB Windows pipe can otherwise
+    // stall the child mid-startup, #309), and poll /health for readiness.
+    cmd.stdout(std::process::Stdio::null())
+        .stderr(std::process::Stdio::piped());
+    let mut child = cmd
+        .spawn()
+        .map_err(|e| format!("Failed to launch jarvis serve: {}", e))?;
+
+    let tail: StderrTail = Arc::new(Mutex::new(Vec::new()));
+    if let Some(stderr) = child.stderr.take() {
+        spawn_jarvis_stderr_drainer(stderr, tail.clone());
+    }
+
+    let client = reqwest::Client::builder()
+        .timeout(Duration::from_secs(2))
+        .build()
+        .map_err(|e| format!("Failed to build HTTP client: {}", e))?;
+    let url = format!("http://127.0.0.1:{}/health", JARVIS_PORT);
+    let deadline = tokio::time::Instant::now() + Duration::from_secs(120);
+
+    loop {
+        // Surface an early crash (bad venv, missing Rust ext, etc.) right away
+        // instead of waiting out the full readiness timeout.
+        if let Ok(Some(status)) = child.try_wait() {
+            let stderr = String::from_utf8_lossy(tail.lock().await.as_slice()).into_owned();
+            return Err(format!(
+                "jarvis serve exited (code {:?}) before becoming healthy:\n{}",
+                status.code(),
+                stderr.trim()
+            ));
+        }
+        if let Ok(resp) = client.get(&url).send().await {
+            if resp.status().is_success() {
+                // Leave the server running (the Child is detached on drop —
+                // kill_on_drop defaults to false); `stop` tears it down.
+                return Ok(format!(
+                    "jarvis serve is ready on http://127.0.0.1:{}",
+                    JARVIS_PORT
+                ));
+            }
+        }
+        if tokio::time::Instant::now() >= deadline {
+            return Err(format!(
+                "jarvis serve did not become healthy on port {} within 120s.",
+                JARVIS_PORT
+            ));
+        }
+        tokio::time::sleep(Duration::from_millis(500)).await;
     }
 }
 

src/openjarvis/cli/ask.py

@@ -714,7 +714,13 @@ def ask(
     register_builtin_models()
 
     effective_engine_key = engine_key or config.intelligence.preferred_engine or None
-    resolved = get_engine(config, effective_engine_key)
+    # Pass the model we intend to run so engine selection can skip an engine
+    # that can't actually serve it (e.g. the cloud fallback when the local
+    # engine is down but only a non-OpenAI key is set — see #532). This is the
+    # -m flag or the configured default; when neither is set we leave it None
+    # and a model is chosen per-engine below.
+    selection_model = model_name or config.intelligence.default_model or None
+    resolved = get_engine(config, effective_engine_key, model=selection_model)
     if resolved is None:
         console.print(
             "[red bold]No inference engine available.[/red bold]\n\n"

src/openjarvis/cli/serve.py

@@ -146,7 +146,13 @@ def serve(
         except Exception as exc:
             logger.debug("Telemetry store init failed: %s", exc)
 
-    resolved = get_engine(config, engine_key)
+    # Select with the model we'll actually serve so an engine that can't
+    # serve it (e.g. the cloud fallback without the matching provider key) is
+    # skipped rather than chosen and failing per-request later (see #532).
+    selection_model = (
+        model_name or config.server.model or config.intelligence.default_model or None
+    )
+    resolved = get_engine(config, engine_key, model=selection_model)
     if resolved is None:
         console.print(
             "[red bold]No inference engine available.[/red bold]\n\n"

src/openjarvis/engine/_discovery.py

@@ -156,12 +156,26 @@ def discover_models(
 
 
 def get_engine(
-    config: JarvisConfig, engine_key: str | None = None
+    config: JarvisConfig,
+    engine_key: str | None = None,
+    model: str | None = None,
 ) -> Tuple[str, InferenceEngine] | None:
     """Get a specific engine by key, or the default with fallback.
 
+    When *model* is given, an engine is selected only if it can actually
+    serve that model (``engine.can_serve(model)``). This stops the cloud
+    fallback from being chosen — when the local engine is down — for a model
+    whose provider client is missing, which otherwise surfaces as a confusing
+    "OpenAI client not available" instead of a helpful "start your local
+    engine" message (see #532). When *model* is ``None`` selection stays
+    model-agnostic (unchanged behaviour).
+
     Returns ``(key, engine_instance)`` or ``None`` if no engine is available.
     """
+
+    def _usable(engine: InferenceEngine) -> bool:
+        return engine.health() and (model is None or engine.can_serve(model))
+
     # Build an ordered list of keys to try, then fall back to full discovery.
     keys_to_try: list[str] = []
     if engine_key:
@@ -176,14 +190,16 @@ def get_engine(
             continue
         try:
             engine = _make_engine(key, config)
-            if engine.health():
+            if _usable(engine):
                 return (key, engine)
         except Exception as exc:
             logger.debug("Engine %r health check failed: %s", key, exc)
 
-    # Fallback to any healthy engine
-    healthy = discover_engines(config)
-    return healthy[0] if healthy else None
+    # Fallback to the first healthy engine that can serve the model.
+    for key, engine in discover_engines(config):
+        if model is None or engine.can_serve(model):
+            return (key, engine)
+    return None
 
 
 __all__ = ["discover_engines", "discover_models", "get_engine"]

src/openjarvis/engine/_stubs.py

@@ -119,6 +119,17 @@ class InferenceEngine(ABC):
     def health(self) -> bool:
         """Return ``True`` when the engine is reachable and healthy."""
 
+    def can_serve(self, model: str) -> bool:
+        """Return ``True`` if this engine can serve *model*.
+
+        Defaults to ``True``: local engines accept any model id (whether a
+        specific model is *installed* is a separate concern from engine
+        selection). Engines that multiplex provider-specific clients (e.g.
+        the cloud engine) override this so selection can skip an engine whose
+        client for the model's provider isn't configured (see #532).
+        """
+        return True
+
     def close(self) -> None:
         """Release resources (HTTP clients, connections, threads, etc.)."""
 

src/openjarvis/engine/cloud.py

@@ -1477,6 +1477,34 @@ class CloudEngine(InferenceEngine):
             models.extend(_CODEX_MODELS)
         return models
 
+    def _client_for_model(self, model: str) -> Any:
+        """Return the provider client ``generate``/``stream`` will dispatch to
+        for *model* (mirrors the routing in those methods)."""
+        if _is_codex_model(model):
+            return self._codex_client
+        if _is_openrouter_model(model):
+            return self._openrouter_client
+        if _is_minimax_model(model):
+            return self._minimax_client
+        if _is_anthropic_model(model):
+            return self._anthropic_client
+        if _is_google_model(model):
+            return self._google_client
+        return self._openai_client
+
+    def can_serve(self, model: str) -> bool:
+        """Return ``True`` only if the provider client for *model* exists.
+
+        ``health()`` is ``True`` whenever *any* provider client is configured,
+        but a request for, say, a ``gpt-*`` model still needs the OpenAI
+        client specifically. Without this check the cloud engine gets picked
+        as a fallback (when the local engine is down) for a model it can't
+        serve, then dies at call time with "<provider> client not available"
+        instead of the user getting a helpful "start your local engine"
+        message (see #532).
+        """
+        return self._client_for_model(model) is not None
+
     def health(self) -> bool:
         return (
             self._openai_client is not None