feat(merger): scope pnpm verification to changed packages in monorepo

When a pnpm workspace is detected and git context is available,
inferDefaultTestCommand now derives the set of packages touched by the
branch diff (git diff --name-only <base>...HEAD) and emits:

  pnpm --filter "<pkg>...^" test

instead of the broad `pnpm test`. The `...^` suffix includes dependents
so packages that import the changed one are also exercised. Falls back
to unscoped `pnpm test` when git context is missing, the workspace has
no package roots, or all changed files are at the root (e.g. config).

New exports: parsePnpmWorkspaceGlobs, resolveWorkspacePackageRoots,
mapChangedFilesToPackageNames, deriveScopedPnpmTestCommand.
testSource is now "inferred-scoped" for the scoped path.

Tests added: parsePnpmWorkspaceGlobs (7), resolveWorkspacePackageRoots
(4), mapChangedFilesToPackageNames (4), inferDefaultTestCommand scoping
(6). All 466 merger test files pass.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

packages/engine/src/__tests__/merger-verification.test.ts

@@ -111,6 +111,7 @@ vi.mock("node:child_process", async () => {
 vi.mock("node:fs", () => ({
   existsSync: vi.fn().mockReturnValue(true),
   readFileSync: vi.fn(),
+  readdirSync: vi.fn().mockReturnValue([]),
 }));
 
 vi.mock("../rate-limit-retry.js", () => ({
@@ -145,6 +146,10 @@ import {
   resolveTaskDiffBaseRef,
   commitOrAmendMergeWithFixes,
   MergeAbortedError,
+  parsePnpmWorkspaceGlobs,
+  resolveWorkspacePackageRoots,
+  mapChangedFilesToPackageNames,
+  deriveScopedPnpmTestCommand,
   type ConflictCategory,
 } from "../merger.js";
 import { mergerLog } from "../logger.js";
@@ -156,9 +161,10 @@ import { type TaskStore, type Task, type MergeResult, DEFAULT_SETTINGS } from "@
 const mockedCreateFnAgent = vi.mocked(createFnAgent);
 const mockedExecSync = vi.mocked(execSync);
 const mockedExec = vi.mocked(exec);
-const { existsSync: mockedExistsSyncRaw, readFileSync: mockedReadFileSyncRaw } = await import("node:fs");
+const { existsSync: mockedExistsSyncRaw, readFileSync: mockedReadFileSyncRaw, readdirSync: mockedReaddirSyncRaw } = await import("node:fs");
 const mockedExistsSync = vi.mocked(mockedExistsSyncRaw);
 const mockedReadFileSync = vi.mocked(mockedReadFileSyncRaw);
+const mockedReaddirSync = vi.mocked(mockedReaddirSyncRaw);
 
 function createMockStore(taskOverrides: Partial<Task> = {}, allTasks: Task[] = []) {
   const baseTask: Task = {
@@ -2670,4 +2676,282 @@ describe("aiMergeTask — in-merge verification fix", () => {
   });
 });
 
+// ── parsePnpmWorkspaceGlobs ───────────────────────────────────────────────
+
+describe("parsePnpmWorkspaceGlobs", () => {
+  it("parses a simple packages list", () => {
+    const content = `packages:\n  - "packages/*"\n  - "plugins/*"\n`;
+    expect(parsePnpmWorkspaceGlobs(content)).toEqual(["packages/*", "plugins/*"]);
+  });
+
+  it("handles single-quoted entries", () => {
+    const content = `packages:\n  - 'packages/*'\n`;
+    expect(parsePnpmWorkspaceGlobs(content)).toEqual(["packages/*"]);
+  });
+
+  it("handles unquoted entries", () => {
+    const content = `packages:\n  - packages/*\n`;
+    expect(parsePnpmWorkspaceGlobs(content)).toEqual(["packages/*"]);
+  });
+
+  it("stops at next top-level key", () => {
+    const content = `packages:\n  - packages/*\ncatalog:\n  react: ^18\n`;
+    expect(parsePnpmWorkspaceGlobs(content)).toEqual(["packages/*"]);
+  });
+
+  it("returns empty array for empty content", () => {
+    expect(parsePnpmWorkspaceGlobs("")).toEqual([]);
+  });
+
+  it("returns empty array when no packages key", () => {
+    expect(parsePnpmWorkspaceGlobs("name: root\n")).toEqual([]);
+  });
+
+  it("parses literal (non-glob) package paths", () => {
+    const content = `packages:\n  - "plugins/fusion-plugin-foo"\n`;
+    expect(parsePnpmWorkspaceGlobs(content)).toEqual(["plugins/fusion-plugin-foo"]);
+  });
+});
+
+// ── resolveWorkspacePackageRoots ──────────────────────────────────────────
+
+describe("resolveWorkspacePackageRoots", () => {
+  beforeEach(() => {
+    vi.clearAllMocks();
+  });
+
+  it("resolves glob pattern to subdirectories with package.json", () => {
+    mockedReaddirSync.mockReturnValue([
+      { name: "dashboard", isDirectory: () => true },
+      { name: "engine", isDirectory: () => true },
+    ] as any);
+    mockedExistsSync.mockImplementation((p: any) => String(p).endsWith("package.json"));
+
+    const roots = resolveWorkspacePackageRoots("/repo", ["packages/*"]);
+    expect(roots).toEqual(["packages/dashboard", "packages/engine"]);
+  });
+
+  it("skips directories without package.json", () => {
+    mockedReaddirSync.mockReturnValue([
+      { name: "dashboard", isDirectory: () => true },
+      { name: ".cache", isDirectory: () => true },
+    ] as any);
+    mockedExistsSync.mockImplementation((p: any) => String(p).includes("dashboard/package.json"));
+
+    const roots = resolveWorkspacePackageRoots("/repo", ["packages/*"]);
+    expect(roots).toEqual(["packages/dashboard"]);
+  });
+
+  it("handles literal (non-glob) paths", () => {
+    mockedExistsSync.mockImplementation((p: any) => String(p).endsWith("package.json"));
+    const roots = resolveWorkspacePackageRoots("/repo", ["plugins/fusion-plugin-foo"]);
+    expect(roots).toEqual(["plugins/fusion-plugin-foo"]);
+  });
+
+  it("returns empty when readdirSync throws", () => {
+    mockedReaddirSync.mockImplementation(() => { throw new Error("ENOENT"); });
+    const roots = resolveWorkspacePackageRoots("/repo", ["packages/*"]);
+    expect(roots).toEqual([]);
+  });
+});
+
+// ── mapChangedFilesToPackageNames ─────────────────────────────────────────
+
+describe("mapChangedFilesToPackageNames", () => {
+  beforeEach(() => {
+    vi.clearAllMocks();
+  });
+
+  it("maps a changed file to the correct package name", () => {
+    mockedReadFileSync.mockReturnValue(JSON.stringify({ name: "@fusion/dashboard" }));
+    mockedExistsSync.mockReturnValue(true);
+
+    const names = mapChangedFilesToPackageNames(
+      ["packages/dashboard/src/index.ts"],
+      ["packages/dashboard", "packages/engine"],
+      "/repo",
+    );
+    expect(names).toEqual(["@fusion/dashboard"]);
+  });
+
+  it("assigns to the longest matching prefix", () => {
+    mockedReadFileSync.mockImplementation((p: any) => {
+      const path = String(p);
+      if (path.includes("plugins/examples/foo")) return JSON.stringify({ name: "@fusion/example-foo" });
+      if (path.includes("plugins")) return JSON.stringify({ name: "@fusion/plugins" });
+      return JSON.stringify({ name: "unknown" });
+    });
+    mockedExistsSync.mockReturnValue(true);
+
+    const names = mapChangedFilesToPackageNames(
+      ["plugins/examples/foo/index.ts"],
+      ["plugins", "plugins/examples/foo"],
+      "/repo",
+    );
+    expect(names).toEqual(["@fusion/example-foo"]);
+  });
+
+  it("returns empty array for files not in any package root", () => {
+    const names = mapChangedFilesToPackageNames(
+      ["root-file.ts"],
+      ["packages/dashboard"],
+      "/repo",
+    );
+    expect(names).toEqual([]);
+  });
+
+  it("deduplicates package names when multiple files touch same package", () => {
+    mockedReadFileSync.mockReturnValue(JSON.stringify({ name: "@fusion/dashboard" }));
+    mockedExistsSync.mockReturnValue(true);
+
+    const names = mapChangedFilesToPackageNames(
+      ["packages/dashboard/a.ts", "packages/dashboard/b.ts"],
+      ["packages/dashboard"],
+      "/repo",
+    );
+    expect(names).toEqual(["@fusion/dashboard"]);
+  });
+});
+
+// ── inferDefaultTestCommand — scoped pnpm workspace ──────────────────────
+
+describe("inferDefaultTestCommand — pnpm workspace scoping", () => {
+  beforeEach(() => {
+    vi.clearAllMocks();
+    mockedExistsSync.mockReturnValue(false);
+  });
+
+  it("returns pnpm test (unscoped/inferred) when no git context provided", () => {
+    mockedExistsSync.mockImplementation((p: any) => {
+      const path = String(p);
+      return path.includes("pnpm-lock.yaml") || path.includes("pnpm-workspace.yaml");
+    });
+
+    const result = inferDefaultTestCommand("/tmp/root");
+    expect(result?.command).toBe("pnpm test");
+    expect(result?.testSource).toBe("inferred");
+  });
+
+  it("returns scoped command (inferred-scoped) when monorepo + git context + 1 changed package", () => {
+    mockedExistsSync.mockImplementation((p: any) => {
+      const path = String(p);
+      // workspace files exist; package.json for dashboard exists
+      if (path.includes("pnpm-lock.yaml")) return true;
+      if (path.includes("pnpm-workspace.yaml")) return true;
+      if (path.includes("package.json")) return true;
+      return false;
+    });
+    mockedReadFileSync.mockImplementation((p: any) => {
+      const path = String(p);
+      if (path.includes("pnpm-workspace.yaml")) {
+        return `packages:\n  - "packages/*"\n`;
+      }
+      if (path.includes("dashboard/package.json")) {
+        return JSON.stringify({ name: "@fusion/dashboard" });
+      }
+      return JSON.stringify({ name: "unknown" });
+    });
+    mockedReaddirSync.mockReturnValue([
+      { name: "dashboard", isDirectory: () => true },
+    ] as any);
+    mockedExecSync.mockImplementation((cmd: any) => {
+      const cmdStr = String(cmd);
+      if (cmdStr.includes("git diff --name-only")) {
+        return "packages/dashboard/src/index.ts\n";
+      }
+      return "";
+    });
+
+    const result = inferDefaultTestCommand("/tmp/root", undefined, undefined, "main", "fusion/fn-123");
+    expect(result?.command).toBe(`pnpm --filter "@fusion/dashboard...^" test`);
+    expect(result?.testSource).toBe("inferred-scoped");
+  });
+
+  it("returns command with 2 filters when 2 packages are changed", () => {
+    mockedExistsSync.mockImplementation((p: any) => {
+      const path = String(p);
+      if (path.includes("pnpm-lock.yaml")) return true;
+      if (path.includes("pnpm-workspace.yaml")) return true;
+      if (path.includes("package.json")) return true;
+      return false;
+    });
+    mockedReadFileSync.mockImplementation((p: any) => {
+      const path = String(p);
+      if (path.includes("pnpm-workspace.yaml")) return `packages:\n  - "packages/*"\n`;
+      if (path.includes("dashboard/package.json")) return JSON.stringify({ name: "@fusion/dashboard" });
+      if (path.includes("engine/package.json")) return JSON.stringify({ name: "@fusion/engine" });
+      return JSON.stringify({ name: "unknown" });
+    });
+    mockedReaddirSync.mockReturnValue([
+      { name: "dashboard", isDirectory: () => true },
+      { name: "engine", isDirectory: () => true },
+    ] as any);
+    mockedExecSync.mockImplementation((cmd: any) => {
+      const cmdStr = String(cmd);
+      if (cmdStr.includes("git diff --name-only")) {
+        return "packages/dashboard/src/index.ts\npackages/engine/src/merger.ts\n";
+      }
+      return "";
+    });
+
+    const result = inferDefaultTestCommand("/tmp/root", undefined, undefined, "main", "fusion/fn-123");
+    expect(result?.command).toContain("--filter");
+    expect(result?.command).toContain("@fusion/dashboard");
+    expect(result?.command).toContain("@fusion/engine");
+    expect(result?.testSource).toBe("inferred-scoped");
+  });
+
+  it("falls back to pnpm test (inferred) when all changes are root-only files", () => {
+    mockedExistsSync.mockImplementation((p: any) => {
+      const path = String(p);
+      if (path.includes("pnpm-lock.yaml")) return true;
+      if (path.includes("pnpm-workspace.yaml")) return true;
+      if (path.includes("package.json")) return true;
+      return false;
+    });
+    mockedReadFileSync.mockImplementation((p: any) => {
+      const path = String(p);
+      if (path.includes("pnpm-workspace.yaml")) return `packages:\n  - "packages/*"\n`;
+      return JSON.stringify({ name: "unknown" });
+    });
+    mockedReaddirSync.mockReturnValue([
+      { name: "dashboard", isDirectory: () => true },
+    ] as any);
+    // Changed file is at root (pnpm-workspace.yaml) — no package prefix match
+    mockedExecSync.mockImplementation((cmd: any) => {
+      const cmdStr = String(cmd);
+      if (cmdStr.includes("git diff --name-only")) {
+        return "pnpm-workspace.yaml\n";
+      }
+      return "";
+    });
+
+    const result = inferDefaultTestCommand("/tmp/root", undefined, undefined, "main", "fusion/fn-123");
+    expect(result?.command).toBe("pnpm test");
+    expect(result?.testSource).toBe("inferred");
+  });
+
+  it("falls back to pnpm test (inferred) when no git context", () => {
+    mockedExistsSync.mockImplementation((p: any) => {
+      const path = String(p);
+      return path.includes("pnpm-lock.yaml") || path.includes("pnpm-workspace.yaml");
+    });
+
+    // No baseBranch or branch passed
+    const result = inferDefaultTestCommand("/tmp/root", undefined, undefined, undefined, undefined);
+    expect(result?.command).toBe("pnpm test");
+    expect(result?.testSource).toBe("inferred");
+  });
+
+  it("explicit testCommand always wins over scoping", () => {
+    mockedExistsSync.mockImplementation((p: any) => {
+      const path = String(p);
+      return path.includes("pnpm-lock.yaml") || path.includes("pnpm-workspace.yaml");
+    });
+
+    const result = inferDefaultTestCommand("/tmp/root", "vitest run --reporter=verbose", undefined, "main", "fusion/fn-123");
+    expect(result?.command).toBe("vitest run --reporter=verbose");
+    expect(result?.testSource).toBe("explicit");
+  });
+});
 

packages/engine/src/merger.ts

@@ -43,7 +43,7 @@ export {
   type VerificationResult,
 } from "./verification-utils.js";
 
-import { existsSync, readFileSync, writeFileSync, unlinkSync, renameSync } from "node:fs";
+import { existsSync, readFileSync, readdirSync, writeFileSync, unlinkSync, renameSync } from "node:fs";
 import { createHash } from "node:crypto";
 import { join } from "node:path";
 import { resolveTaskWorktreePath } from "./worktree-paths.js";
@@ -461,7 +461,7 @@ async function syncDependenciesForMerge(
 interface InferredTestCommand {
   command: string;
   /** Source indicates whether this was explicitly configured or inferred from project files */
-  testSource: "explicit" | "inferred";
+  testSource: "explicit" | "inferred" | "inferred-scoped";
   buildSource?: "explicit" | "inferred";
 }
 
@@ -745,22 +745,209 @@ export async function classifyOwnedLandedEvidence(
   };
 }
 
+/**
+ * Parse a pnpm-workspace.yaml file and return the list of package glob patterns.
+ * Handles only the `packages:` list format used in pnpm workspace configs.
+ * Returns an empty array on any parse failure (best-effort).
+ *
+ * @internal Exported for testing only.
+ */
+export function parsePnpmWorkspaceGlobs(workspaceYamlContent: string): string[] {
+  const globs: string[] = [];
+  let inPackages = false;
+  for (const rawLine of workspaceYamlContent.split("\n")) {
+    const line = rawLine.trimEnd();
+    if (/^packages\s*:/.test(line)) {
+      inPackages = true;
+      continue;
+    }
+    if (inPackages) {
+      // A new top-level key ends the packages block
+      if (/^\S/.test(line) && line.trim() !== "") {
+        break;
+      }
+      // List item: "  - 'some/glob'" or `  - "some/glob"` or `  - some/glob`
+      const match = line.match(/^\s+-\s+['"]?([^'"#\s]+)['"]?/);
+      if (match && match[1]) {
+        globs.push(match[1]);
+      }
+    }
+  }
+  return globs;
+}
+
+/**
+ * Given a list of workspace package globs (e.g. "packages/*") and a rootDir,
+ * return all package root directories (dirs that contain a package.json) that
+ * match at least one glob.
+ *
+ * Glob matching: only simple single-star patterns at the last path segment are
+ * supported (covering the `packages/*` and `plugins/examples/*` patterns used
+ * in practice). Literal paths (no glob) are treated as direct package roots.
+ *
+ * @internal Exported for testing only.
+ */
+export function resolveWorkspacePackageRoots(
+  rootDir: string,
+  globs: string[],
+): string[] {
+  const roots: string[] = [];
+  for (const glob of globs) {
+    const starIdx = glob.indexOf("*");
+    if (starIdx === -1) {
+      // Literal path — treat the glob itself as a package root
+      const candidate = join(rootDir, glob);
+      if (existsSync(join(candidate, "package.json"))) {
+        roots.push(glob); // Store relative to rootDir
+      }
+      continue;
+    }
+    // Pattern like "packages/*" or "plugins/examples/*"
+    // The prefix is everything before the last slash before the star
+    const prefix = glob.slice(0, starIdx);
+    const parentDir = join(rootDir, prefix.replace(/\/$/, ""));
+    let entries: string[];
+    try {
+      entries = readdirSync(parentDir, { withFileTypes: true })
+        .filter((e) => e.isDirectory())
+        .map((e) => e.name);
+    } catch {
+      continue;
+    }
+    for (const entry of entries) {
+      const relPath = `${prefix.replace(/\/$/, "")}/${entry}`;
+      const absPath = join(rootDir, relPath);
+      if (existsSync(join(absPath, "package.json"))) {
+        roots.push(relPath); // Store relative to rootDir
+      }
+    }
+  }
+  return roots;
+}
+
+/**
+ * Given a list of changed files (relative to rootDir) and a list of package
+ * root paths (relative to rootDir), return the unique package names (from each
+ * package.json's "name" field) whose root is the longest prefix-match for at
+ * least one changed file.
+ *
+ * @internal Exported for testing only.
+ */
+export function mapChangedFilesToPackageNames(
+  changedFiles: string[],
+  packageRoots: string[],
+  rootDir: string,
+): string[] {
+  const nameSet = new Set<string>();
+  for (const file of changedFiles) {
+    // Find the longest package root that is a prefix of this file
+    let bestRoot: string | null = null;
+    let bestLen = -1;
+    for (const pkgRoot of packageRoots) {
+      const prefix = pkgRoot.endsWith("/") ? pkgRoot : `${pkgRoot}/`;
+      if (file === pkgRoot || file.startsWith(prefix)) {
+        if (pkgRoot.length > bestLen) {
+          bestLen = pkgRoot.length;
+          bestRoot = pkgRoot;
+        }
+      }
+    }
+    if (bestRoot !== null) {
+      // Read the package name from package.json
+      try {
+        const pkgJsonPath = join(rootDir, bestRoot, "package.json");
+        const raw = readFileSync(pkgJsonPath, "utf-8");
+        const parsed = JSON.parse(raw) as { name?: string };
+        if (parsed.name) {
+          nameSet.add(parsed.name);
+        }
+      } catch {
+        // If we can't read the package name, use the relative root path
+        nameSet.add(bestRoot);
+      }
+    }
+  }
+  return Array.from(nameSet);
+}
+
+/**
+ * Attempt to derive the set of pnpm package names touched by the branch.
+ * Returns null when scoping cannot be determined (missing git context, no
+ * workspace file, root-only changes, etc.) — callers fall back to `pnpm test`.
+ *
+ * @internal Exported for testing only.
+ */
+export function deriveScopedPnpmTestCommand(
+  rootDir: string,
+  baseBranch: string,
+  branch: string,
+): string | null {
+  // 1. Read and parse pnpm-workspace.yaml
+  const workspacePath = join(rootDir, "pnpm-workspace.yaml");
+  let workspaceContent: string;
+  try {
+    workspaceContent = readFileSync(workspacePath, "utf-8");
+  } catch {
+    return null;
+  }
+  const globs = parsePnpmWorkspaceGlobs(workspaceContent);
+  if (globs.length === 0) return null;
+
+  // 2. Resolve actual package roots
+  const packageRoots = resolveWorkspacePackageRoots(rootDir, globs);
+  if (packageRoots.length === 0) return null;
+
+  // 3. Get the changed files between base and branch tip
+  let changedFilesOutput: string;
+  try {
+    changedFilesOutput = execSync(
+      `git diff --name-only ${quoteArg(baseBranch)}...HEAD`,
+      { cwd: rootDir, stdio: "pipe", encoding: "utf-8" },
+    ).toString();
+  } catch {
+    return null;
+  }
+  const changedFiles = changedFilesOutput
+    .split("\n")
+    .map((f) => f.trim())
+    .filter(Boolean);
+  if (changedFiles.length === 0) return null;
+
+  // 4. Map changed files to package names
+  const packageNames = mapChangedFilesToPackageNames(changedFiles, packageRoots, rootDir);
+  if (packageNames.length === 0) {
+    // All changes are at the root (e.g. workspace config) — fall back to full suite
+    return null;
+  }
+
+  // 5. Compose the scoped pnpm command
+  // `...^` includes dependents (packages that import the changed packages)
+  const filters = packageNames.map((name) => `--filter "${name}...^"`).join(" ");
+  return `pnpm ${filters} test`;
+}
+
 /**
  * Infer a default test command based on project files.
  * Returns the command and whether it was explicitly configured or inferred.
  *
  * Inference rules:
- * - pnpm-lock.yaml → "pnpm test"
+ * - pnpm-lock.yaml → "pnpm test" (or scoped when monorepo + git context available)
  * - yarn.lock → "yarn test"
  * - bun.lock/bun.lockb → "bun test"
  * - package-lock.json → "npm test"
  *
+ * When a pnpm workspace is detected and git context (baseBranch + branch) is
+ * provided, the command is automatically scoped to the packages touched by the
+ * branch diff. testSource will be "inferred-scoped" in that case.
+ *
  * Returns null if no test command can be inferred.
  */
 export function inferDefaultTestCommand(
   rootDir: string,
   explicitTestCommand?: string,
   explicitBuildCommand?: string,
+  baseBranch?: string,
+  branch?: string,
 ): InferredTestCommand | null {
   // If explicit test command is set, use it (no inference needed)
   if (explicitTestCommand?.trim()) {
@@ -771,49 +958,46 @@ export function inferDefaultTestCommand(
     };
   }
 
+  const buildSource = explicitBuildCommand?.trim() ? "explicit" : undefined;
+
   // Infer test command from lock files
   if (existsSync(join(rootDir, "pnpm-lock.yaml"))) {
-    // Monorepo heuristic: a pnpm-workspace.yaml means `pnpm test` will fan out
+    // Monorepo heuristic: if pnpm-workspace.yaml exists and we have git context,
-    // across every workspace package on every merge, which is usually far slower
+    // scope the command to only the packages touched by this branch's diff.
-    // than necessary. Warn so the user sets an explicit scoped testCommand
-    // (e.g. `pnpm -r --filter "...[main]" test`). We don't auto-scope because
-    // the default branch name isn't guaranteed and git context may be unavailable.
     if (existsSync(join(rootDir, "pnpm-workspace.yaml"))) {
+      if (baseBranch?.trim() && branch?.trim()) {
+        try {
+          const scoped = deriveScopedPnpmTestCommand(rootDir, baseBranch.trim(), branch.trim());
+          if (scoped) {
+            mergerLog.log(
+              `Scoped inferred test command to changed packages: ${scoped}`,
+            );
+            return { command: scoped, testSource: "inferred-scoped", buildSource };
+          }
+        } catch {
+          // Fall through to unscoped fallback
+        }
+      }
+      // No git context or scoping failed — warn and use unscoped
       mergerLog.warn(
         `Inferred test command "pnpm test" in a pnpm workspace (${rootDir}). ` +
         `This runs the full monorepo suite on every merge. Consider setting an explicit ` +
         `scoped testCommand in project settings, e.g. \`pnpm -r --filter "...[main]" test\`.`,
       );
     }
-    return {
+    return { command: "pnpm test", testSource: "inferred", buildSource };
-      command: "pnpm test",
-      testSource: "inferred",
-      buildSource: explicitBuildCommand?.trim() ? "explicit" : undefined,
-    };
   }
 
   if (existsSync(join(rootDir, "yarn.lock"))) {
-    return {
+    return { command: "yarn test", testSource: "inferred", buildSource };
-      command: "yarn test",
-      testSource: "inferred",
-      buildSource: explicitBuildCommand?.trim() ? "explicit" : undefined,
-    };
   }
 
   if (existsSync(join(rootDir, "bun.lock")) || existsSync(join(rootDir, "bun.lockb"))) {
-    return {
+    return { command: "bun test", testSource: "inferred", buildSource };
-      command: "bun test",
-      testSource: "inferred",
-      buildSource: explicitBuildCommand?.trim() ? "explicit" : undefined,
-    };
   }
 
   if (existsSync(join(rootDir, "package-lock.json"))) {
-    return {
+    return { command: "npm test", testSource: "inferred", buildSource };
-      command: "npm test",
-      testSource: "inferred",
-      buildSource: explicitBuildCommand?.trim() ? "explicit" : undefined,
-    };
   }
 
   // No inference possible — return null, letting the caller decide what to do
@@ -974,7 +1158,7 @@ async function runDeterministicVerification(
   taskId: string,
   testCommand?: string,
   buildCommand?: string,
-  testSource?: "explicit" | "inferred",
+  testSource?: "explicit" | "inferred" | "inferred-scoped",
   buildSource?: "explicit" | "inferred",
   signal?: AbortSignal,
 ): Promise<VerificationResult> {
@@ -1027,7 +1211,7 @@ async function runDeterministicVerification(
   // ── End cache lookup ───────────────────────────────────────────────────
 
   // Build source indicator for logging
-  const testSourceLabel = testSource === "inferred" ? " [inferred]" : "";
+  const testSourceLabel = (testSource === "inferred" || testSource === "inferred-scoped") ? ` [${testSource}]` : "";
   const buildSourceLabel = buildSource === "inferred" ? " [inferred]" : "";
 
   mergerLog.log(
@@ -1035,9 +1219,10 @@ async function runDeterministicVerification(
     (hasTestCommand ? ` [test:${testSourceLabel} ${normalizedTestCommand}]` : "") +
     (hasBuildCommand ? ` [build:${buildSourceLabel} ${normalizedBuildCommand}]` : ""),
   );
+  const testSourceDisplayLabel = (testSource === "inferred" || testSource === "inferred-scoped") ? ` [${testSource}]` : "";
   const deterministicVerificationMessage =
     "Running deterministic merge verification" +
-    (hasTestCommand ? ` (test${testSource === "inferred" ? " [inferred]" : ""}: ${normalizedTestCommand})` : "") +
+    (hasTestCommand ? ` (test${testSourceDisplayLabel}: ${normalizedTestCommand})` : "") +
     (hasBuildCommand ? ` (build${buildSource === "inferred" ? " [inferred]" : ""}: ${normalizedBuildCommand})` : "");
   await store.logEntry(taskId, deterministicVerificationMessage);
   await store.appendAgentLog(taskId, deterministicVerificationMessage, "text", undefined, "merger");
@@ -1283,7 +1468,7 @@ async function attemptInMergeVerificationFix(
   fixAttemptNumber?: number,
   testCommand?: string,
   buildCommand?: string,
-  testSource?: "explicit" | "inferred",
+  testSource?: "explicit" | "inferred" | "inferred-scoped",
   buildSource?: "explicit" | "inferred",
   fixModifiedFiles?: Set<string>,
 ): Promise<boolean> {
@@ -5019,7 +5204,7 @@ async function applyBranchCommitsPreservingHistory(params: {
   result: MergeResult;
   testCommand?: string;
   buildCommand?: string;
-  testSource?: "explicit" | "inferred";
+  testSource?: "explicit" | "inferred" | "inferred-scoped";
   buildSource?: "explicit" | "inferred";
   signal?: AbortSignal;
 }): Promise<{ landedCommitCount: number; landedCommitShas: string[]; baseSha: string; fullySubsumedByMain: boolean; skippedEmptyCount: number }> {
@@ -8281,8 +8466,15 @@ export async function aiMergeTask(
   const explicitBuildCommand = settings.buildCommand?.trim() || undefined;
 
   // Infer default test command if explicit testCommand is not set
-  // This ensures merge verification runs even when settings.testCommand is not configured
+  // This ensures merge verification runs even when settings.testCommand is not configured.
-  const inferredTest = inferDefaultTestCommand(rootDir, explicitTestCommand, explicitBuildCommand);
+  // Thread baseBranch + branch so pnpm workspaces can be scoped to changed packages.
+  const inferredTest = inferDefaultTestCommand(
+    rootDir,
+    explicitTestCommand,
+    explicitBuildCommand,
+    mergeTarget.branch,
+    branch,
+  );
   const effectiveTestCommand = inferredTest?.command || explicitTestCommand;
   const effectiveTestSource = inferredTest?.testSource;
   const effectiveBuildCommand = explicitBuildCommand;
@@ -9632,8 +9824,8 @@ interface MergeAttemptParams {
   mergeTargetBranch?: string;
   testCommand?: string;
   buildCommand?: string;
-  /** Source of the test command: 'explicit' from settings or 'inferred' from project files */
+  /** Source of the test command: 'explicit' from settings or 'inferred'/'inferred-scoped' from project files */
-  testSource?: "explicit" | "inferred";
+  testSource?: "explicit" | "inferred" | "inferred-scoped";
   /** Source of the build command: 'explicit' from settings or 'inferred' (future use) */
   buildSource?: "explicit" | "inferred";
   /** Set when the pre-merge rebase recovery cascade (Layers 1–2) failed and