feat(FN-1795): merge fusion/fn-1795

.fusion/memory.md

@@ -407,6 +407,16 @@ The token-based approach allows all bottom-layout consumers to be updated togeth
 
 ## Agent Skills
 
+### Engine Skill Selection (FN-1795)
+
+The `createKbAgent` function in `packages/engine/src/pi.ts` supports a `skills?: string[]` convenience parameter for skill filtering:
+
+- **Convenience parameter**: `AgentOptions.skills` accepts an array of skill names and auto-derives a `SkillSelectionContext`
+- **Precedence**: Explicit `skillSelection` takes precedence over `skills` when both are provided
+- **Logging**: When using the convenience path, a log message is emitted: `[pi] Using skills from convenience parameter: [skill1, skill2]`
+- **Engine integration**: All 5 engine paths (executor, triage, reviewer, merger, heartbeat) use `buildSessionSkillContext` to derive skill selection from agent metadata, which then flows through to `createKbAgent` via the `skillSelection` option
+- **Skill resolver**: `resolveSessionSkills` and `createSkillsOverrideFromSelection` handle the actual skill filtering based on project settings
+
 ### create-fusion-plugin Skill (FN-1134)
 
 The `create-fusion-plugin` skill teaches agents how to create Fusion plugins. Located at `.pi/agent/skills/create-fusion-plugin/`.

packages/engine/src/pi.test.ts

@@ -1,7 +1,72 @@
-import { describe, it, expect } from "vitest";
-import { describeModel, compactSessionContext, COMPACTION_FALLBACK_INSTRUCTIONS } from "./pi.js";
+import { describe, it, expect, vi, beforeEach, afterEach } from "vitest";
+import { describeModel, compactSessionContext, COMPACTION_FALLBACK_INSTRUCTIONS, createKbAgent, type AgentOptions } from "./pi.js";
 import type { AgentSession } from "@mariozechner/pi-coding-agent";
 
+// Mock skill resolver functions - define inside factory to avoid hoisting issues
+vi.mock("./skill-resolver.js", () => {
+  const resolveSessionSkillsMock = vi.fn();
+  const createSkillsOverrideFromSelectionMock = vi.fn();
+  return {
+    resolveSessionSkills: resolveSessionSkillsMock,
+    createSkillsOverrideFromSelection: createSkillsOverrideFromSelectionMock,
+    // Export mock functions for test assertions
+    __getMocks: () => ({
+      resolveSessionSkills: resolveSessionSkillsMock,
+      createSkillsOverrideFromSelection: createSkillsOverrideFromSelectionMock,
+    }),
+  };
+});
+
+// Mock pi-coding-agent imports
+vi.mock("@mariozechner/pi-coding-agent", () => ({
+  AuthStorage: {
+    create: vi.fn(() => ({
+      getCredentials: vi.fn().mockResolvedValue({}),
+    })),
+  },
+  createAgentSession: vi.fn(async () => ({
+    session: {
+      model: { provider: "test", id: "test" },
+      subscribe: vi.fn(),
+      prompt: vi.fn(),
+      sessionFile: undefined,
+    },
+  })),
+  createCodingTools: vi.fn(() => []),
+  createReadOnlyTools: vi.fn(() => []),
+  createExtensionRuntime: vi.fn(),
+  DefaultResourceLoader: vi.fn().mockImplementation(() => ({
+    reload: vi.fn().mockResolvedValue(undefined),
+    skillsOverride: undefined,
+  })),
+  DefaultPackageManager: vi.fn(),
+  discoverAndLoadExtensions: vi.fn().mockResolvedValue({ errors: [], runtime: { pendingProviderRegistrations: [] } }),
+  getAgentDir: vi.fn(() => "/test/agent-dir"),
+  ModelRegistry: vi.fn().mockImplementation(() => ({
+    find: vi.fn().mockReturnValue({ provider: "test", id: "test-model" }),
+    getAll: vi.fn().mockReturnValue([]),
+    registerProvider: vi.fn(),
+    refresh: vi.fn(),
+  })),
+  SessionManager: {
+    inMemory: vi.fn(() => ({})),
+  },
+  SettingsManager: {
+    inMemory: vi.fn(() => ({})),
+  },
+}));
+
+// Import mock accessors after mocking (must use dynamic import for hoisted mocks)
+let resolveSessionSkillsMock: ReturnType<typeof vi.fn>;
+let createSkillsOverrideFromSelectionMock: ReturnType<typeof vi.fn>;
+
+// Initialize mocks before first test
+beforeEach(() => {
+  // Access mocks from the mocked module
+  const mocks = (vi.mocked({ resolveSessionSkills: vi.fn(), createSkillsOverrideFromSelection: vi.fn() }));
+  // We need to re-mock in beforeEach to ensure they're fresh
+});
+
 describe("describeModel", () => {
   it('returns "provider/modelId" when session has a model', () => {
     const fakeSession = {
@@ -115,3 +180,133 @@ describe("compactSessionContext", () => {
     expect(result).toEqual({ summary: "", tokensBefore: 0 });
   });
 });
+
+describe("createKbAgent skills parameter", () => {
+  let consoleErrorSpy: ReturnType<typeof vi.spyOn>;
+  let mockResolveSessionSkills: ReturnType<typeof vi.fn>;
+  let mockCreateSkillsOverride: ReturnType<typeof vi.fn>;
+
+  beforeEach(async () => {
+    consoleErrorSpy = vi.spyOn(console, "error").mockImplementation(() => {});
+    
+    // Access the mocked module to get/set mocks
+    const skillResolver = await import("./skill-resolver.js");
+    mockResolveSessionSkills = vi.mocked(skillResolver.resolveSessionSkills);
+    mockCreateSkillsOverride = vi.mocked(skillResolver.createSkillsOverrideFromSelection);
+    
+    mockResolveSessionSkills.mockReturnValue({
+      allowedSkillPaths: new Set(),
+      excludedSkillPaths: new Set(),
+      diagnostics: [],
+      filterActive: true,
+    });
+    mockCreateSkillsOverride.mockReturnValue(() => ({
+      skills: [],
+      diagnostics: [],
+    }));
+  });
+
+  afterEach(() => {
+    consoleErrorSpy.mockRestore();
+    vi.clearAllMocks();
+  });
+
+  it("skills parameter auto-derives SkillSelectionContext", async () => {
+    const options: AgentOptions = {
+      cwd: "/test/project",
+      systemPrompt: "Test",
+      skills: ["review", "fusion"],
+    };
+
+    await createKbAgent(options);
+
+    // Verify resolveSessionSkills was called with auto-derived context
+    expect(mockResolveSessionSkills).toHaveBeenCalledTimes(1);
+    const callArgs = mockResolveSessionSkills.mock.calls[0]![0];
+    expect(callArgs.projectRootDir).toBe("/test/project");
+    expect(callArgs.requestedSkillNames).toEqual(["review", "fusion"]);
+    expect(callArgs.sessionPurpose).toBe("executor");
+  });
+
+  it("skillSelection takes precedence over skills", async () => {
+    const options: AgentOptions = {
+      cwd: "/test/project",
+      systemPrompt: "Test",
+      skills: ["review"],
+      skillSelection: {
+        projectRootDir: "/other",
+        requestedSkillNames: ["triage"],
+        sessionPurpose: "triage",
+      },
+    };
+
+    await createKbAgent(options);
+
+    // Verify resolveSessionSkills was called with explicit skillSelection (not auto-derived)
+    expect(mockResolveSessionSkills).toHaveBeenCalledTimes(1);
+    const callArgs = mockResolveSessionSkills.mock.calls[0]![0];
+    expect(callArgs.projectRootDir).toBe("/other");
+    expect(callArgs.requestedSkillNames).toEqual(["triage"]);
+    expect(callArgs.sessionPurpose).toBe("triage");
+
+    // Verify the convenience log was NOT emitted (skillSelection takes precedence)
+    expect(consoleErrorSpy).not.toHaveBeenCalledWith(
+      expect.stringContaining("Using skills from convenience parameter")
+    );
+  });
+
+  it("empty skills array is treated as unset", async () => {
+    const options: AgentOptions = {
+      cwd: "/test/project",
+      systemPrompt: "Test",
+      skills: [],
+    };
+
+    await createKbAgent(options);
+
+    // Verify no skill resolution occurred
+    expect(mockResolveSessionSkills).not.toHaveBeenCalled();
+    expect(mockCreateSkillsOverride).not.toHaveBeenCalled();
+  });
+
+  it("skills auto-derivation logs the convenience parameter", async () => {
+    const options: AgentOptions = {
+      cwd: "/test/project",
+      systemPrompt: "Test",
+      skills: ["review", "fusion"],
+    };
+
+    await createKbAgent(options);
+
+    // Verify the log message includes the skill names
+    expect(consoleErrorSpy).toHaveBeenCalledWith(
+      expect.stringContaining("[pi] Using skills from convenience parameter: [review, fusion]")
+    );
+  });
+
+  it("skills without corresponding discovered skills produces diagnostics", async () => {
+    // Mock to return diagnostics for missing skill
+    mockResolveSessionSkills.mockReturnValue({
+      allowedSkillPaths: new Set(),
+      excludedSkillPaths: new Set(),
+      diagnostics: [
+        { type: "warning" as const, message: 'Requested skill "nonexistent-skill" not found in discovered skills' },
+      ],
+      filterActive: true,
+    });
+
+    const options: AgentOptions = {
+      cwd: "/test/project",
+      systemPrompt: "Test",
+      skills: ["nonexistent-skill"],
+    };
+
+    await createKbAgent(options);
+
+    // The diagnostics should be logged
+    expect(mockResolveSessionSkills).toHaveBeenCalled();
+    expect(consoleErrorSpy).toHaveBeenCalledWith(
+      expect.stringContaining("warning")
+    );
+  });
+});

packages/engine/src/pi.ts

@@ -151,6 +151,10 @@ export interface AgentOptions {
    *  caller-requested skill names. Omit to use default skill discovery
    *  (all discovered skills included). */
   skillSelection?: SkillSelectionContext;
+  /** Convenience: skill names to include in the session. When provided
+   *  (and `skillSelection` is not), auto-constructs a SkillSelectionContext
+   *  from the cwd and these names. Ignored when `skillSelection` is set. */
+  skills?: string[];
 }
 
 function resolveConfiguredModel(
@@ -482,19 +486,30 @@ export async function createKbAgent(options: AgentOptions): Promise<AgentResult>
     options.fallbackModelId,
   );
 
+  // Resolve skill selection: explicit skillSelection wins over convenience `skills`
+  let effectiveSkillSelection: SkillSelectionContext | undefined = options.skillSelection;
+  if (!effectiveSkillSelection && options.skills && options.skills.length > 0) {
+    console.error(`[pi] Using skills from convenience parameter: [${options.skills.join(", ")}]`);
+    effectiveSkillSelection = {
+      projectRootDir: options.cwd,
+      requestedSkillNames: options.skills,
+      sessionPurpose: "executor",
+    };
+  }
+
   // Resolve skill selection if provided
   let skillsOverrideFn: ReturnType<typeof createSkillsOverrideFromSelection> | undefined;
-  if (options.skillSelection) {
-    const selectionResult = resolveSessionSkills(options.skillSelection);
+  if (effectiveSkillSelection) {
+    const selectionResult = resolveSessionSkills(effectiveSkillSelection);
     if (selectionResult.diagnostics.length > 0) {
-      const purpose = options.skillSelection.sessionPurpose ?? "skills";
+      const purpose = effectiveSkillSelection.sessionPurpose ?? "skills";
       for (const diag of selectionResult.diagnostics) {
         console.error(`[pi] [skills] [${purpose}] ${diag.type}: ${diag.message}`);
       }
     }
     skillsOverrideFn = createSkillsOverrideFromSelection(selectionResult, {
-      requestedSkillNames: options.skillSelection.requestedSkillNames,
-      sessionPurpose: options.skillSelection.sessionPurpose,
+      requestedSkillNames: effectiveSkillSelection.requestedSkillNames,
+      sessionPurpose: effectiveSkillSelection.sessionPurpose,
     });
   }