fix(first-run): découple busy de la détection des CLI (#28)

Même backend réparé, le wizard restait à la merci d'une détection qui ne
répond pas : `reload()` et `detect()` awaitaient `detectProfiles` sous le
même drapeau `busy` qui grise « Save and continue » et « Detect installed
CLIs ». Une promesse IPC jamais résolue laissait donc les deux boutons
grisés à vie — sans issue pour l'utilisateur.

La détection redevient ce qu'elle est : une étape best-effort, jamais
bloquante.

- `busy` ne garde plus que ce dont le wizard ne peut pas se passer
  (`firstRunState`) ou qui mute l'état (`configureProfiles`). Il ne dépend
  plus jamais de `detectProfiles`. L'invariant est documenté en tête de
  module.
- Un drapeau `detecting` distinct suit la sonde et n'inhibe aucune action.
  Il est relâché par un timer (`DETECT_TIMEOUT_MS`), jamais par la seule
  promesse : celle-ci peut rester pendante indéfiniment.
- Un identifiant de tour monotone (`detectRun`) invalide les tours périmés
  et ceux qui survivent au démontage, évitant un `setState` hors montage.
- `reload()` rend les lignes immédiatement puis lance la détection en tâche
  détachée. Si elle échoue, les lignes restent cochables à la main ; seul le
  bouton explicite remonte l'erreur.

Tests: vitest 59 fichiers / 569 tests verts, tsc --noEmit exit 0.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

frontend/src/features/first-run/FirstRunWizard.test.tsx

@@ -6,6 +6,7 @@
  */
 import { describe, it, expect, vi } from "vitest";
 import {
+  act,
   render,
   screen,
   waitFor,
@@ -13,9 +14,11 @@ import {
 } from "@testing-library/react";
 
 import { MockProfileGateway } from "@/adapters/mock";
+import type { ProfileAvailability } from "@/domain";
 import type { Gateways } from "@/ports";
 import { DIProvider } from "@/app/di";
 import { FirstRunWizard } from "./FirstRunWizard";
+import { DETECT_TIMEOUT_MS } from "./useFirstRun";
 
 function renderWizard(
   profile: MockProfileGateway = new MockProfileGateway(),
@@ -301,6 +304,69 @@ describe("FirstRunWizard — OpenAI-compatible local/LAN profile (ticket #14)",
   });
 });
 
+// Ticket #28 — the wizard must survive a detection that never answers. When the
+// backend `detect_profiles` command panics, the `invoke` promise is neither
+// resolved nor rejected: nothing after `await detectProfiles(...)` ever runs.
+// `busy` must therefore never be tied to detection, or both buttons stay greyed
+// out for good and the first run cannot be completed.
+describe("FirstRunWizard — detection that never answers (ticket #28)", () => {
+  /** A gateway whose `detectProfiles` promise stays pending forever. */
+  class HangingDetectGateway extends MockProfileGateway {
+    override detectProfiles(): Promise<ProfileAvailability[]> {
+      return new Promise<ProfileAvailability[]>(() => {});
+    }
+  }
+
+  it("keeps Save and Detect enabled once firstRunState answered", async () => {
+    renderWizard(new HangingDetectGateway());
+    await waitForLoaded();
+
+    // The rows are rendered, so the blocking load is over: both actions are live.
+    const save = screen.getByRole("button", { name: "Save and continue" });
+    const detect = screen.getByRole("button", { name: "Detect installed CLIs" });
+    expect((save as HTMLButtonElement).disabled).toBe(false);
+    expect((detect as HTMLButtonElement).disabled).toBe(false);
+
+    // Detection is merely reported as in flight, never as a blocking state.
+    expect(screen.getByRole("status").textContent).toMatch(/detecting/i);
+
+    // Re-probing by hand must not freeze them either.
+    fireEvent.click(detect);
+    expect((save as HTMLButtonElement).disabled).toBe(false);
+    expect((detect as HTMLButtonElement).disabled).toBe(false);
+  });
+
+  it("still finishes the first run while detection hangs", async () => {
+    const profile = new HangingDetectGateway();
+    const { onDone } = renderWizard(profile, vi.fn());
+    await waitForLoaded();
+
+    // Nothing got pre-checked (detection never answered): tick a profile by hand.
+    fireEvent.click(screen.getByLabelText("use Claude Code"));
+    fireEvent.click(screen.getByRole("button", { name: "Save and continue" }));
+
+    await waitFor(() => expect(onDone).toHaveBeenCalled());
+    const saved = await profile.listProfiles();
+    expect(saved.map((p) => p.command)).toEqual(["claude"]);
+  });
+
+  it("drops the detecting flag on timeout even if the promise never settles", async () => {
+    vi.useFakeTimers({ shouldAdvanceTime: true });
+    try {
+      renderWizard(new HangingDetectGateway());
+      await waitForLoaded();
+      expect(screen.getByRole("status").textContent).toMatch(/detecting/i);
+
+      await act(async () => {
+        vi.advanceTimersByTime(DETECT_TIMEOUT_MS + 1);
+      });
+      expect(screen.queryByRole("status")).toBeNull();
+    } finally {
+      vi.useRealTimers();
+    }
+  });
+});
+
 describe("FirstRunWizard reopening after the first run (forceOpen)", () => {
   /** A gateway whose first run is already done (profiles configured). */
   async function configuredGateway() {

frontend/src/features/first-run/FirstRunWizard.tsx

@@ -78,6 +78,8 @@ export function FirstRunWizard({
         )}
 
         <Toolbar>
+          {/* `detecting` deliberately does NOT disable this button (ticket #28):
+              detection is best-effort and may never answer. */}
           <Button
             onClick={() => void vm.detect()}
             disabled={vm.busy}
@@ -85,6 +87,11 @@ export function FirstRunWizard({
           >
             Detect installed CLIs
           </Button>
+          {vm.detecting && (
+            <span role="status" className="text-xs text-muted">
+              Detecting…
+            </span>
+          )}
         </Toolbar>
 
         <ul className="flex list-none flex-col gap-3 p-0">

frontend/src/features/first-run/useFirstRun.ts

@@ -3,9 +3,17 @@
  * (L5). Owns the wizard state (selectable reference candidates + selection +
  * availability) and the actions. Consumes the {@link ProfileGateway}
  * exclusively — never `invoke()` — so the feature is testable with a mock.
+ *
+ * **Invariant (ticket #28)**: `busy` gates only the requests the wizard cannot
+ * render without (`firstRunState`) or that mutate state (`configureProfiles`).
+ * It NEVER depends on `detectProfiles`: CLI detection is a detached, best-effort
+ * step tracked by the separate {@link FirstRunViewModel.detecting} flag, bounded
+ * by {@link DETECT_TIMEOUT_MS}. A detection that panics backend-side (leaving the
+ * `invoke` promise forever pending) must not freeze "Save and continue" /
+ * "Detect installed CLIs".
  */
 
-import { useCallback, useEffect, useState } from "react";
+import { useCallback, useEffect, useRef, useState } from "react";
 
 import type {
   AgentProfile,
@@ -15,6 +23,9 @@ import type {
 } from "@/domain";
 import { useGateways } from "@/app/di";
 
+/** How long the UI waits for a detection round before giving up on it. */
+export const DETECT_TIMEOUT_MS = 3_000;
+
 /** One row in the wizard: a candidate profile, selected state, availability. */
 export interface WizardEntry {
   profile: AgentProfile;
@@ -31,8 +42,10 @@ export interface FirstRunViewModel {
   entries: WizardEntry[];
   /** Last error message, or null. */
   error: string | null;
-  /** Whether a request is in flight. */
+  /** Whether a blocking request is in flight (load / save). Never detection. */
   busy: boolean;
+  /** Whether a best-effort detection round is in flight. Never disables actions. */
+  detecting: boolean;
   /** Toggles selection of a candidate by id. */
   toggle: (id: string) => void;
   /** Replaces a candidate's profile (edited command/args/injection). */
@@ -60,41 +73,101 @@ export function useFirstRun(): FirstRunViewModel {
   const [entries, setEntries] = useState<WizardEntry[]>([]);
   const [error, setError] = useState<string | null>(null);
   const [busy, setBusy] = useState(false);
+  const [detecting, setDetecting] = useState(false);
+
+  /** Monotonic id of the latest detection round; older rounds are ignored. */
+  const detectRun = useRef(0);
+  const detectTimer = useRef<ReturnType<typeof setTimeout> | null>(null);
+
+  useEffect(
+    () => () => {
+      // Unmount: invalidate any in-flight round (its promise may never settle).
+      detectRun.current += 1;
+      if (detectTimer.current !== null) clearTimeout(detectTimer.current);
+    },
+    [],
+  );
+
+  /**
+   * Best-effort detection round, detached from `busy`. A round is abandoned
+   * after {@link DETECT_TIMEOUT_MS} — the underlying promise may stay pending
+   * forever (backend panic ⇒ no IPC response), so `detecting` is released by a
+   * timer, never by the promise alone. `preselect` ticks the installed CLIs (the
+   * auto-detection on open); the manual button only refreshes availability.
+   */
+  const runDetection = useCallback(
+    async (
+      candidates: AgentProfile[],
+      opts: { preselect: boolean; reportError: boolean },
+    ) => {
+      const run = detectRun.current + 1;
+      detectRun.current = run;
+      const stale = () => detectRun.current !== run;
+
+      setDetecting(true);
+      if (detectTimer.current !== null) clearTimeout(detectTimer.current);
+      detectTimer.current = setTimeout(() => {
+        if (!stale()) setDetecting(false);
+      }, DETECT_TIMEOUT_MS);
+
+      try {
+        const results: ProfileAvailability[] =
+          await profile.detectProfiles(candidates);
+        if (stale()) return;
+        const byId = new Map(results.map((r) => [r.profile.id, r.available]));
+        setEntries((prev) =>
+          prev.map((e) => {
+            const available = byId.get(e.profile.id) ?? e.available;
+            return {
+              ...e,
+              available,
+              selected: opts.preselect ? available === true : e.selected,
+            };
+          }),
+        );
+      } catch (e) {
+        // Detection unavailable: rows stay as they are (the user can tick them
+        // by hand and re-run). Only the explicit button surfaces the failure.
+        if (stale()) return;
+        if (opts.reportError) setError(describe(e));
+      } finally {
+        if (!stale()) {
+          if (detectTimer.current !== null) clearTimeout(detectTimer.current);
+          detectTimer.current = null;
+          setDetecting(false);
+        }
+      }
+    },
+    [profile],
+  );
 
   const reload = useCallback(async () => {
     setBusy(true);
     setError(null);
+    let refs: AgentProfile[] | null = null;
     try {
       const state: FirstRunState = await profile.firstRunState();
       setIsFirstRun(state.isFirstRun);
-      const refs = state.referenceProfiles;
+      refs = state.referenceProfiles;
       // Show the rows immediately (nothing pre-checked yet).
       setEntries(
         refs.map((p) => ({ profile: p, selected: false, available: null })),
       );
-      // Auto-detect once on open: only the CLIs actually installed end up
-      // pre-checked. The manual "Detect installed CLIs" button stays available to
-      // re-probe. If detection is unavailable, rows stay unchecked (the user can
-      // still tick them by hand and re-run detection).
-      try {
-        const results = await profile.detectProfiles(refs);
-        const byId = new Map(results.map((r) => [r.profile.id, r.available]));
-        setEntries(
-          refs.map((p) => {
-            const available = byId.get(p.id) ?? null;
-            return { profile: p, selected: available === true, available };
-          }),
-        );
-      } catch {
-        /* detection unavailable: leave rows unchecked */
-      }
     } catch (e) {
       setError(describe(e));
       setIsFirstRun(false);
     } finally {
+      // Released as soon as the rows are rendered — detection is not awaited.
       setBusy(false);
     }
-  }, [profile]);
+
+    // Auto-detect once on open, detached: only the CLIs actually installed end
+    // up pre-checked. The manual "Detect installed CLIs" button stays available
+    // to re-probe, whatever happens to this round.
+    if (refs !== null) {
+      void runDetection(refs, { preselect: true, reportError: false });
+    }
+  }, [profile, runDetection]);
 
   useEffect(() => {
     void reload();
@@ -119,25 +192,12 @@ export function useFirstRun(): FirstRunViewModel {
   }, []);
 
   const detect = useCallback(async () => {
-    setBusy(true);
     setError(null);
-    try {
+    await runDetection(
-      const candidates = entries.map((e) => e.profile);
+      entries.map((e) => e.profile),
-      const results: ProfileAvailability[] =
+      { preselect: false, reportError: true },
-        await profile.detectProfiles(candidates);
-      const byId = new Map(results.map((r) => [r.profile.id, r.available]));
-      setEntries((prev) =>
-        prev.map((e) => ({
-          ...e,
-          available: byId.get(e.profile.id) ?? e.available,
-        })),
     );
-    } catch (e) {
+  }, [runDetection, entries]);
-      setError(describe(e));
-    } finally {
-      setBusy(false);
-    }
-  }, [profile, entries]);
 
   const finish = useCallback(async () => {
     setBusy(true);
@@ -158,6 +218,7 @@ export function useFirstRun(): FirstRunViewModel {
     entries,
     error,
     busy,
+    detecting,
     toggle,
     updateProfile,
     remove,