test(FN-4956): complete Step 4 — add layer3 file-scope regressions

Fusion-Task-Id: FN-4956
Fusion-Task-Lineage: 7105cd5e-27f4-4e84-b2ae-e811a183803f

packages/engine/src/__tests__/reliability-interactions/layer3-ai-arbiter-file-scope.real-git.test.ts

@@ -0,0 +1,129 @@
+import { afterEach, describe, expect, it } from "vitest";
+import { mkdir, mkdtemp, rm, writeFile } from "node:fs/promises";
+import { tmpdir } from "node:os";
+import { join } from "node:path";
+import { execSync, spawnSync } from "node:child_process";
+import { assertSquashOverlapsFileScope, applyLayer3ConflictScopePartition, getConflictedFiles } from "../../merger.js";
+
+const hasGit = spawnSync("git", ["--version"], { stdio: "pipe" }).status === 0;
+const describeIfGit = hasGit ? describe : describe.skip;
+
+function git(cwd: string, cmd: string): string {
+  return execSync(cmd, { cwd, encoding: "utf-8", stdio: ["pipe", "pipe", "pipe"] }).trim();
+}
+
+async function setupConflictRepo() {
+  const rootDir = await mkdtemp(join(tmpdir(), "fn-4956-ri-"));
+  git(rootDir, "git init -b main");
+  git(rootDir, 'git config user.email "test@example.com"');
+  git(rootDir, 'git config user.name "Test User"');
+
+  await mkdir(join(rootDir, "packages/desktop/src"), { recursive: true });
+  await writeFile(join(rootDir, "AGENTS.md"), "line\nshared\n", "utf-8");
+  await writeFile(join(rootDir, "packages/desktop/src/foo.ts"), "export const value = 'base';\n", "utf-8");
+  git(rootDir, "git add AGENTS.md packages/desktop/src/foo.ts");
+  git(rootDir, "git commit -m 'chore: base'");
+
+  git(rootDir, "git checkout -b fusion/fn-4956");
+  await writeFile(join(rootDir, "AGENTS.md"), "line\nbranch\n", "utf-8");
+  await writeFile(join(rootDir, "packages/desktop/src/foo.ts"), "export const value = 'branch';\n", "utf-8");
+  git(rootDir, "git add AGENTS.md packages/desktop/src/foo.ts");
+  git(rootDir, "git commit -m 'feat: branch edits'");
+
+  git(rootDir, "git checkout main");
+  await writeFile(join(rootDir, "AGENTS.md"), "line\nmain\n", "utf-8");
+  await writeFile(join(rootDir, "packages/desktop/src/foo.ts"), "export const value = 'main';\n", "utf-8");
+  git(rootDir, "git add AGENTS.md packages/desktop/src/foo.ts");
+  git(rootDir, "git commit -m 'feat: main edits'");
+
+  git(rootDir, "git merge --squash fusion/fn-4956 || true");
+  return rootDir;
+}
+
+describeIfGit("reliability interactions: layer3 ai arbiter file scope", () => {
+  const roots: string[] = [];
+  afterEach(async () => {
+    while (roots.length > 0) {
+      await rm(roots.pop()!, { recursive: true, force: true });
+    }
+  });
+
+  it("skips foreign conflicted files and keeps squash in scope", async () => {
+    const rootDir = await setupConflictRepo();
+    roots.push(rootDir);
+
+    const auditEvents: Array<{ type: string; metadata: any }> = [];
+    const task = { id: "FN-4956", scopeOverride: false } as any;
+    const store = {
+      parseFileScopeFromPrompt: async () => ["packages/desktop/src/**"],
+      appendAgentLog: async () => undefined,
+      logEntry: async () => undefined,
+    } as any;
+
+    const conflicted = await getConflictedFiles(rootDir);
+    expect(conflicted.sort()).toEqual(["AGENTS.md", "packages/desktop/src/foo.ts"].sort());
+
+    const partitioned = await applyLayer3ConflictScopePartition({
+      store,
+      task,
+      taskId: "FN-4956",
+      rootDir,
+      branch: "fusion/fn-4956",
+      conflictFiles: conflicted,
+      auditor: {
+        git: async (event: any) => {
+          auditEvents.push({ type: event.type, metadata: event.metadata });
+        },
+      } as any,
+    });
+
+    expect(partitioned.inScopeConflicts).toEqual(["packages/desktop/src/foo.ts"]);
+    expect(partitioned.skippedFiles).toEqual(["AGENTS.md"]);
+
+    const staged = git(rootDir, "git diff --cached --name-only").split("\n").filter(Boolean);
+    expect(staged).toContain("packages/desktop/src/foo.ts");
+    expect(staged).not.toContain("AGENTS.md");
+
+    await expect(assertSquashOverlapsFileScope({
+      store,
+      taskId: "FN-4956",
+      rootDir,
+      task,
+    } as any)).resolves.toBeUndefined();
+
+    expect(auditEvents.some((event) => event.type === "merge:layer3:foreign-file-skipped" && event.metadata.skippedFiles.includes("AGENTS.md"))).toBe(true);
+  });
+
+  it("emits scope-override bypass and does not skip foreign files", async () => {
+    const rootDir = await setupConflictRepo();
+    roots.push(rootDir);
+
+    const auditEvents: Array<{ type: string; metadata: any }> = [];
+    const task = { id: "FN-4956", scopeOverride: true, scopeOverrideReason: "interaction-test" } as any;
+    const store = {
+      parseFileScopeFromPrompt: async () => ["packages/desktop/src/**"],
+      appendAgentLog: async () => undefined,
+      logEntry: async () => undefined,
+    } as any;
+
+    const conflicted = await getConflictedFiles(rootDir);
+    const partitioned = await applyLayer3ConflictScopePartition({
+      store,
+      task,
+      taskId: "FN-4956",
+      rootDir,
+      branch: "fusion/fn-4956",
+      conflictFiles: conflicted,
+      auditor: {
+        git: async (event: any) => {
+          auditEvents.push({ type: event.type, metadata: event.metadata });
+        },
+      } as any,
+    });
+
+    expect(partitioned.inScopeConflicts.sort()).toEqual(conflicted.sort());
+    expect(partitioned.skippedFiles).toEqual([]);
+    expect(auditEvents.some((event) => event.type === "merge:layer3:scope-override-bypass")).toBe(true);
+    expect(auditEvents.some((event) => event.type === "merge:layer3:foreign-file-skipped")).toBe(false);
+  });
+});