feat(HAI-102): thread model settings through reviewer and merger

- Add defaultProvider and defaultModelId to ReviewOptions interface
- Forward model settings from store to createHaiAgent in reviewer
- Forward model settings from store to createHaiAgent in merger
- Pass settings from executor to reviewStep call
- Add tests for model settings threading in both reviewer and merger

packages/engine/src/executor.ts

@@ -533,10 +533,15 @@ export class TaskExecutor {
         await store.logEntry(taskId, `${reviewType} review requested for Step ${step} (${step_name})`);
 
         try {
+          const settings = await store.getSettings();
           const result = await reviewStep(
             worktreePath, taskId, step, step_name,
             reviewType, promptContent, baseline,
-            { onText: (delta) => options.onAgentText?.(taskId, delta) },
+            {
+              onText: (delta) => options.onAgentText?.(taskId, delta),
+              defaultProvider: settings.defaultProvider,
+              defaultModelId: settings.defaultModelId,
+            },
           );
 
           await store.logEntry(

packages/engine/src/merger.test.ts

@@ -292,6 +292,52 @@ describe("aiMergeTask — includeTaskIdInCommit setting", () => {
   });
 });
 
+describe("aiMergeTask — model settings threading", () => {
+  beforeEach(() => {
+    vi.clearAllMocks();
+    mockedExistsSync.mockReturnValue(true);
+    setupHappyPathExecSync();
+    mockedCreateHaiAgent.mockResolvedValue({
+      session: {
+        prompt: vi.fn().mockResolvedValue(undefined),
+        dispose: vi.fn(),
+      },
+    } as any);
+  });
+
+  it("passes defaultProvider and defaultModelId from settings to createHaiAgent", async () => {
+    const store = createMockStore(
+      { id: "HAI-050", worktree: "/tmp/root/.worktrees/HAI-050" },
+      [{ id: "HAI-050", worktree: "/tmp/root/.worktrees/HAI-050", column: "in-review" } as Task],
+    );
+    (store.getSettings as ReturnType<typeof vi.fn>).mockResolvedValue({
+      ...DEFAULT_SETTINGS,
+      defaultProvider: "openai",
+      defaultModelId: "gpt-4o",
+    });
+
+    await aiMergeTask(store, "/tmp/root", "HAI-050");
+
+    expect(mockedCreateHaiAgent).toHaveBeenCalledTimes(1);
+    const opts = mockedCreateHaiAgent.mock.calls[0][0] as any;
+    expect(opts.defaultProvider).toBe("openai");
+    expect(opts.defaultModelId).toBe("gpt-4o");
+  });
+
+  it("does not set model fields when settings omit them", async () => {
+    const store = createMockStore(
+      { id: "HAI-050", worktree: "/tmp/root/.worktrees/HAI-050" },
+      [{ id: "HAI-050", worktree: "/tmp/root/.worktrees/HAI-050", column: "in-review" } as Task],
+    );
+
+    await aiMergeTask(store, "/tmp/root", "HAI-050");
+
+    const opts = mockedCreateHaiAgent.mock.calls[0][0] as any;
+    expect(opts.defaultProvider).toBeUndefined();
+    expect(opts.defaultModelId).toBeUndefined();
+  });
+});
+
 describe("aiMergeTask — agent log persistence", () => {
   beforeEach(() => {
     vi.clearAllMocks();

packages/engine/src/merger.ts

@@ -231,12 +231,15 @@ export async function aiMergeTask(
       : undefined,
   });
 
+  // Forward model settings from store so the merger honours the user's model choice
   const { session } = await createHaiAgent({
     cwd: rootDir,
     systemPrompt: buildMergeSystemPrompt(includeTaskId),
     tools: "coding",
     onText: agentLogger.onText,
     onToolStart: agentLogger.onToolStart,
+    defaultProvider: settings.defaultProvider,
+    defaultModelId: settings.defaultModelId,
   });
 
   try {

packages/engine/src/reviewer.test.ts

@@ -0,0 +1,81 @@
+import { describe, it, expect, vi, beforeEach } from "vitest";
+
+vi.mock("./pi.js", () => ({
+  createHaiAgent: vi.fn(),
+}));
+
+import { reviewStep } from "./reviewer.js";
+import { createHaiAgent } from "./pi.js";
+
+const mockedCreateHaiAgent = vi.mocked(createHaiAgent);
+
+function createMockSession(reviewText: string) {
+  return {
+    session: {
+      prompt: vi.fn().mockResolvedValue(undefined),
+      subscribe: vi.fn().mockImplementation((cb: any) => {
+        // Simulate the reviewer producing text
+        cb({
+          type: "message_update",
+          assistantMessageEvent: { type: "text_delta", delta: reviewText },
+        });
+      }),
+      dispose: vi.fn(),
+    },
+  } as any;
+}
+
+describe("reviewStep — model settings threading", () => {
+  beforeEach(() => {
+    vi.clearAllMocks();
+  });
+
+  it("passes defaultProvider and defaultModelId to createHaiAgent when provided", async () => {
+    mockedCreateHaiAgent.mockResolvedValue(
+      createMockSession("### Verdict: APPROVE\n### Summary\nLooks good."),
+    );
+
+    await reviewStep(
+      "/tmp/worktree", "HAI-100", 1, "Test Step", "plan", "# prompt",
+      undefined,
+      {
+        defaultProvider: "anthropic",
+        defaultModelId: "claude-sonnet-4-5",
+      },
+    );
+
+    expect(mockedCreateHaiAgent).toHaveBeenCalledTimes(1);
+    const opts = mockedCreateHaiAgent.mock.calls[0][0];
+    expect(opts.defaultProvider).toBe("anthropic");
+    expect(opts.defaultModelId).toBe("claude-sonnet-4-5");
+  });
+
+  it("does not set model fields when ReviewOptions omits them", async () => {
+    mockedCreateHaiAgent.mockResolvedValue(
+      createMockSession("### Verdict: APPROVE\n### Summary\nAll good."),
+    );
+
+    await reviewStep(
+      "/tmp/worktree", "HAI-100", 1, "Test Step", "plan", "# prompt",
+      undefined,
+      {},
+    );
+
+    expect(mockedCreateHaiAgent).toHaveBeenCalledTimes(1);
+    const opts = mockedCreateHaiAgent.mock.calls[0][0];
+    expect(opts.defaultProvider).toBeUndefined();
+    expect(opts.defaultModelId).toBeUndefined();
+  });
+
+  it("extracts APPROVE verdict correctly", async () => {
+    mockedCreateHaiAgent.mockResolvedValue(
+      createMockSession("### Verdict: APPROVE\n### Summary\nLooks good."),
+    );
+
+    const result = await reviewStep(
+      "/tmp/worktree", "HAI-100", 1, "Test Step", "plan", "# prompt",
+    );
+
+    expect(result.verdict).toBe("APPROVE");
+  });
+});

packages/engine/src/reviewer.ts

@@ -111,6 +111,10 @@ export interface ReviewResult {
 
 export interface ReviewOptions {
   onText?: (delta: string) => void;
+  /** Default model provider (e.g. "anthropic"). When set with `defaultModelId`, overrides the reviewer's model selection. */
+  defaultProvider?: string;
+  /** Default model ID within the provider (e.g. "claude-sonnet-4-5"). When set with `defaultProvider`, overrides the reviewer's model selection. */
+  defaultModelId?: string;
 }
 
 /**
@@ -137,6 +141,8 @@ export async function reviewStep(
     systemPrompt: REVIEWER_SYSTEM_PROMPT,
     tools: "readonly",
     onText: (delta) => options.onText?.(delta),
+    defaultProvider: options.defaultProvider,
+    defaultModelId: options.defaultModelId,
   });
 
   let reviewText = "";