FN-8414: fix mission interview thinking-level binding

Fix mission interviews that omit a thinking level while preserving project and plugin bindings.

- Remove the ambiguous session positional overload.
- Resolve omitted thinking levels from planning settings and display the configured default.
- Cover omitted and explicit thinking-level session starts with regression tests.
- Add a patch changeset for the crash fix.

Files changed:
 ...n-8414-mission-interview-thinking-level-bind.md |   7 ++
 .../app/components/MissionInterviewModal.tsx       |  25 ++++-
 .../__tests__/MissionInterviewModal.test.tsx       |  13 +++
 .../mission-interview-thinking-level-bind.test.ts  | 108 +++++++++++++++++++++
 packages/dashboard/src/mission-interview.ts        |  19 ++--
 packages/dashboard/src/mission-routes.ts           |  21 +++-
 6 files changed, 178 insertions(+), 15 deletions(-)

Fusion-Task-Id: FN-8414

Fusion-Task-Lineage: d3be2cd6-9221-4e1d-a27a-c5fbe04f9200

Co-authored-by: Fusion (runfusion.ai) <noreply@runfusion.ai>

.changeset/fn-8414-mission-interview-thinking-level-bind.md

@@ -0,0 +1,7 @@
+---
+"@runfusion/fusion": patch
+---
+
+summary: Fix mission interview start crashing when thinking level is left at Default.
+category: fix
+dev: Retire createMissionInterviewSession positional overload; resolve planning thinkingLevel from settings when body omits it; preserve projectId/pluginRunner binding (GitHub #2356 / FN-8414).

packages/dashboard/app/components/MissionInterviewModal.tsx

@@ -1,6 +1,6 @@
 import { useState, useCallback, useEffect, useRef } from "react";
 import { useTranslation } from "react-i18next";
-import type { PlanningQuestion, ThinkingLevel } from "@fusion/core";
+import type { PlanningQuestion, Settings, ThinkingLevel } from "@fusion/core";
 import { getErrorMessage, THINKING_LEVELS } from "@fusion/core";
 import {
   startMissionInterview,
@@ -11,6 +11,7 @@ import {
   fetchAiSession,
   parseConversationHistory,
   fetchModels,
+  fetchSettings,
   updateGlobalSettings,
   type MissionPlanSummary,
   type ConversationHistoryEntry,
@@ -154,9 +155,29 @@ export function MissionInterviewModal({
   const [modelsError, setModelsError] = useState<string | null>(null);
   const [favoriteProviders, setFavoriteProviders] = useState<string[]>([]);
   const [favoriteModels, setFavoriteModels] = useState<string[]>([]);
+  const [settings, setSettings] = useState<Pick<Settings, "defaultThinkingLevel">>();
 
   const modelSelectionValue = getModelSelectionValue(modelProvider, modelId);
 
+  /*
+  FNXC:MissionInterview 2026-07-19-20:46:
+  FN-8414 / GitHub #2356 requires the untouched mission interview picker to show
+  the configured thinking default instead of a hardcoded "off" placeholder.
+  Server-side planning resolution remains authoritative when the request omits it.
+  */
+  useEffect(() => {
+    let cancelled = false;
+    setSettings(undefined);
+    void fetchSettings(projectId)
+      .then((loadedSettings) => {
+        if (!cancelled) setSettings(loadedSettings);
+      })
+      .catch(() => undefined);
+    return () => {
+      cancelled = true;
+    };
+  }, [projectId]);
+
   // Load models on mount
   useEffect(() => {
     const load = async () => {
@@ -892,7 +913,7 @@ export function MissionInterviewModal({
                     showThinkingLevel
                     thinkingLevel={thinkingLevel}
                     onThinkingLevelChange={(level) => setThinkingLevel(THINKING_LEVELS.includes(level as ThinkingLevel) ? (level as ThinkingLevel) : "")}
-                    defaultThinkingLevel="off"
+                    defaultThinkingLevel={settings?.defaultThinkingLevel ?? "off"}
                   />
                   {modelsError && (
                     <div className="form-hint form-hint-error">

packages/dashboard/app/components/__tests__/MissionInterviewModal.test.tsx

@@ -18,6 +18,7 @@ const mockAcquireSessionLock = vi.fn();
 const mockReleaseSessionLock = vi.fn();
 const mockForceAcquireSessionLock = vi.fn();
 const mockFetchModels = vi.fn();
+const mockFetchSettings = vi.fn();
 
 vi.mock("../../api", () => ({
   startMissionInterview: (...args: any[]) => mockStartMissionInterview(...args),
@@ -32,6 +33,7 @@ vi.mock("../../api", () => ({
   releaseSessionLock: (...args: any[]) => mockReleaseSessionLock(...args),
   forceAcquireSessionLock: (...args: any[]) => mockForceAcquireSessionLock(...args),
   fetchModels: (...args: any[]) => mockFetchModels(...args),
+  fetchSettings: (...args: any[]) => mockFetchSettings(...args),
 }));
 
 const mockGetMissionGoal = vi.fn(() => "");
@@ -149,6 +151,7 @@ describe("MissionInterviewModal", () => {
     mockReleaseSessionLock.mockResolvedValue(undefined);
     mockForceAcquireSessionLock.mockResolvedValue({ acquired: true, currentHolder: null });
     mockFetchModels.mockResolvedValue({ models: [], favoriteProviders: [], favoriteModels: [] });
+    mockFetchSettings.mockResolvedValue({ defaultThinkingLevel: "off" });
     localStorage.removeItem("floating-window:mission-interview");
     vi.spyOn(window, "requestAnimationFrame").mockImplementation((callback: FrameRequestCallback) => {
       callback(0);
@@ -183,6 +186,16 @@ describe("MissionInterviewModal", () => {
     Object.defineProperty(element, "releasePointerCapture", { configurable: true, value: vi.fn() });
   }
 
+  it("renders the configured thinking level as the mission interview default", async () => {
+    mockFetchSettings.mockResolvedValue({ defaultThinkingLevel: "high" });
+
+    renderModal();
+
+    await waitFor(() => {
+      expect(screen.getByTestId("custom-model-dropdown-thinking-badge")).toHaveTextContent("Default (high)");
+    });
+  });
+
   it("renders mission interview inside a floating desktop workspace", () => {
     setViewport(1200, 900);
 

packages/dashboard/src/__tests__/mission-interview-thinking-level-bind.test.ts

@@ -0,0 +1,108 @@
+// @vitest-environment node
+
+import { afterEach, beforeEach, describe, expect, it, vi } from "vitest";
+import { THINKING_LEVELS, type ThinkingLevel } from "@fusion/core";
+
+const { buildSessionSkillContextSyncMock } = vi.hoisted(() => ({
+  buildSessionSkillContextSyncMock: vi.fn(() => ({ skillSelectionContext: undefined })),
+}));
+
+vi.mock("@fusion/engine", async (importOriginal) => {
+  const actual = await importOriginal<typeof import("@fusion/engine")>();
+  return {
+    ...actual,
+    buildSessionSkillContextSync: buildSessionSkillContextSyncMock,
+    resolveMcpServersForStore: vi.fn(async () => ({ servers: [] })),
+    createFnAgent: vi.fn(async () => ({
+      session: {
+        state: { messages: [] as Array<{ role: string; content: string }> },
+        prompt: vi.fn(async function (this: { state: { messages: Array<{ role: string; content: string }> } }) {
+          this.state.messages.push({
+            role: "assistant",
+            content: JSON.stringify({
+              type: "question",
+              data: { id: "scope", type: "text", question: "What should this mission accomplish?" },
+            }),
+          });
+        }),
+        dispose: vi.fn(),
+      },
+    })),
+  };
+});
+
+vi.mock("../planning-board-tools.js", () => ({
+  createPlanningBoardTools: vi.fn(() => []),
+}));
+
+import {
+  __resetMissionInterviewState,
+  createMissionInterviewSession,
+  getMissionInterviewSession,
+} from "../mission-interview.js";
+import { resolveMissionInterviewThinkingLevel } from "../mission-routes.js";
+
+const store = {} as never;
+const pluginRunner = { getPluginSkills: vi.fn(() => []) };
+
+async function createSession(thinkingLevel: ThinkingLevel | undefined, projectId: string | null) {
+  const sessionId = await createMissionInterviewSession(
+    "127.0.0.1",
+    "Plan reliable interviews",
+    "/tmp/fusion-dashboard-test",
+    store,
+    undefined,
+    undefined,
+    undefined,
+    thinkingLevel,
+    projectId,
+    pluginRunner,
+  );
+  await vi.waitFor(() => expect(buildSessionSkillContextSyncMock).toHaveBeenCalled());
+  return getMissionInterviewSession(sessionId);
+}
+
+describe("mission interview thinking-level argument binding", () => {
+  beforeEach(() => {
+    __resetMissionInterviewState();
+    buildSessionSkillContextSyncMock.mockClear();
+    pluginRunner.getPluginSkills.mockClear();
+  });
+
+  afterEach(() => {
+    __resetMissionInterviewState();
+  });
+
+  it("preserves the plugin runner and project scope when thinkingLevel is omitted", async () => {
+    const session = await createSession(undefined, "proj-1");
+
+    expect(session?.projectId).toBe("proj-1");
+    expect(session?.pluginRunner).toBe(pluginRunner);
+    expect(session?.error).toBeUndefined();
+    expect(buildSessionSkillContextSyncMock).toHaveBeenCalledWith(null, "executor", "/tmp/fusion-dashboard-test", pluginRunner);
+    expect(session?.error).not.toBe("pluginRunner.getPluginSkills is not a function");
+  });
+
+  it("does not silently discard a real plugin runner for an unscoped omitted-thinking start", async () => {
+    const session = await createSession(undefined, null);
+
+    expect(session?.projectId).toBeNull();
+    expect(session?.pluginRunner).toBe(pluginRunner);
+    expect(session?.error).toBeUndefined();
+    expect(buildSessionSkillContextSyncMock).toHaveBeenCalledWith(null, "executor", "/tmp/fusion-dashboard-test", pluginRunner);
+  });
+
+  it.each(THINKING_LEVELS)("keeps plugin runner and project scope bound for %s", async (thinkingLevel) => {
+    const session = await createSession(thinkingLevel, "proj-1");
+
+    expect(session?.thinkingLevel).toBe(thinkingLevel);
+    expect(session?.projectId).toBe("proj-1");
+    expect(session?.pluginRunner).toBe(pluginRunner);
+    expect(buildSessionSkillContextSyncMock).toHaveBeenCalledWith(null, "executor", "/tmp/fusion-dashboard-test", pluginRunner);
+  });
+
+  it("uses planning settings only when the request omits thinkingLevel", () => {
+    expect(resolveMissionInterviewThinkingLevel({ planningThinkingLevel: "high", defaultThinkingLevel: "low" }, undefined)).toBe("high");
+    expect(resolveMissionInterviewThinkingLevel({ planningThinkingLevel: "high" }, "minimal")).toBe("minimal");
+  });
+});

packages/dashboard/src/mission-interview.ts

@@ -1293,17 +1293,16 @@ export async function createMissionInterviewSession(
   promptOverrides?: PromptOverrideMap,
   modelProvider?: string,
   modelId?: string,
-  thinkingLevelOrProjectId?: ThinkingLevel | string | null,
-  projectIdOrPluginRunner?: string | null | SkillPluginRunner,
-  pluginRunnerMaybe?: SkillPluginRunner,
+  thinkingLevel?: ThinkingLevel,
+  projectId?: string | null,
+  pluginRunner?: SkillPluginRunner,
 ): Promise<string> {
-  const thinkingLevel = THINKING_LEVELS.includes(thinkingLevelOrProjectId as ThinkingLevel)
-    ? (thinkingLevelOrProjectId as ThinkingLevel)
-    : undefined;
-  const projectId = thinkingLevel
-    ? (projectIdOrPluginRunner as string | null | undefined)
-    : (thinkingLevelOrProjectId as string | null | undefined);
-  const pluginRunner = (thinkingLevel ? pluginRunnerMaybe : projectIdOrPluginRunner) as SkillPluginRunner | undefined;
+  /*
+  FNXC:MissionInterview 2026-07-19-20:46:
+  FN-8414 / GitHub #2356 removed the legacy positional overload because an omitted
+  thinkingLevel shifted projectId into pluginRunner. Keep this fixed tail so TypeScript
+  rejects a project-id string where a SkillPluginRunner is required.
+  */
   if (!checkRateLimit(ip)) {
     const resetTime = getRateLimitResetTime(ip);
     throw new RateLimitError(

packages/dashboard/src/mission-routes.ts

@@ -15,8 +15,8 @@
 import { Router, type Request, type Response, type NextFunction } from "express";
 import { AsyncLocalStorage } from "node:async_hooks";
 import { TaskStore, resolvePlanningSettingsModel, AgentStore, THINKING_LEVELS } from "@fusion/core";
-import type { Goal, ThinkingLevel } from "@fusion/core";
-import { listEligibleExecutorAgents } from "@fusion/engine";
+import type { Goal, Settings, ThinkingLevel } from "@fusion/core";
+import { listEligibleExecutorAgents, resolvePlanningThinkingLevel } from "@fusion/engine";
 import {
   getScopedStore as resolveScopedRequestStore,
   getProjectContext as resolveSharedProjectContext,
@@ -64,6 +64,14 @@ import {
 import type { AiSessionStore } from "./ai-session-store.js";
 import { resolveBranchAssignmentContext, resolveBranchSelection } from "./routes/branch-selection.js";
 
+/** Resolve the mission-start override through the planning settings hierarchy. */
+export function resolveMissionInterviewThinkingLevel(
+  settings: Partial<Settings> | undefined,
+  thinkingLevel: ThinkingLevel | undefined,
+): ThinkingLevel | undefined {
+  return resolvePlanningThinkingLevel(settings, thinkingLevel) as ThinkingLevel | undefined;
+}
+
 // ── Validation Utilities ────────────────────────────────────────────────────
 
 function validateMissionId(id: string): boolean {
@@ -558,6 +566,13 @@ export function createMissionRouter(
         const effectiveModel = resolvePlanningSettingsModel(settings);
         const resolvedProvider = modelProvider ?? effectiveModel.provider;
         const resolvedModelId = modelId ?? effectiveModel.modelId;
+        /*
+        FNXC:MissionInterview 2026-07-19-20:46:
+        FN-8414 / GitHub #2356 makes omitted request thinkingLevel inherit the planning
+        settings hierarchy, matching model resolution above. The fixed session signature
+        then preserves projectId and pluginRunner instead of shifting positional arguments.
+        */
+        const resolvedThinkingLevel = resolveMissionInterviewThinkingLevel(settings, validatedThinkingLevel);
 
         const sessionId = await createMissionInterviewSession(
           ip,
@@ -567,7 +582,7 @@ export function createMissionRouter(
           settings.promptOverrides,
           resolvedProvider,
           resolvedModelId,
-          validatedThinkingLevel,
+          resolvedThinkingLevel,
           projectId ?? null,
           pluginRunner,
         );