diff --git a/packages/pi-coding-agent/src/core/package-manager.ts b/packages/pi-coding-agent/src/core/package-manager.ts
index da19d3d94..44209e04f 100644
--- a/packages/pi-coding-agent/src/core/package-manager.ts
+++ b/packages/pi-coding-agent/src/core/package-manager.ts
@@ -414,7 +414,13 @@ function resolveExtensionEntries(dir: string): string[] | null {
 	const packageJsonPath = join(dir, "package.json");
 	if (existsSync(packageJsonPath)) {
 		const manifest = readPiManifestFile(packageJsonPath);
-		if (manifest?.extensions?.length) {
+		if (manifest) {
+			// When a pi manifest exists, it is authoritative — don't fall through
+			// to index.ts/index.js auto-detection. This allows library directories
+			// (like cmux) to opt out by declaring "pi": {} with no extensions.
+			if (!manifest.extensions?.length) {
+				return null;
+			}
 			const entries: string[] = [];
 			for (const extPath of manifest.extensions) {
 				const resolvedExtPath = resolve(dir, extPath);
@@ -422,9 +428,7 @@ function resolveExtensionEntries(dir: string): string[] | null {
 					entries.push(resolvedExtPath);
 				}
 			}
-			if (entries.length > 0) {
-				return entries;
-			}
+			return entries.length > 0 ? entries : null;
 		}
 	}
 
diff --git a/scripts/copy-resources.cjs b/scripts/copy-resources.cjs
index 56d728a40..4ff932917 100644
--- a/scripts/copy-resources.cjs
+++ b/scripts/copy-resources.cjs
@@ -18,6 +18,23 @@ function copyNonTsFiles(srcDir, destDir) {
     }
 
     mkdirSync(dirname(destPath), { recursive: true });
+
+    // Rewrite pi.extensions paths from .ts to .js in package.json files
+    // so they match the compiled output (tsc compiles index.ts → index.js
+    // but package.json is copied as-is).
+    if (entry.name === 'package.json') {
+      try {
+        const pkg = JSON.parse(require('fs').readFileSync(srcPath, 'utf-8'));
+        if (Array.isArray(pkg?.pi?.extensions)) {
+          pkg.pi.extensions = pkg.pi.extensions.map(ext =>
+            ext.replace(/\.ts$/, '.js').replace(/\.tsx$/, '.js')
+          );
+          require('fs').writeFileSync(destPath, JSON.stringify(pkg, null, 2) + '\n');
+          continue;
+        }
+      } catch { /* fall through to plain copy */ }
+    }
+
     copyFileSync(srcPath, destPath);
   }
 }
diff --git a/src/extension-discovery.ts b/src/extension-discovery.ts
index 8e586a052..23a52ec0d 100644
--- a/src/extension-discovery.ts
+++ b/src/extension-discovery.ts
@@ -8,24 +8,29 @@ function isExtensionFile(name: string): boolean {
 /**
  * Resolves the entry-point file(s) for a single extension directory.
  *
- * 1. If the directory contains a package.json with a `pi.extensions` array,
- *    each entry is resolved relative to the directory and returned (if it exists).
- * 2. Otherwise falls back to `index.ts` → `index.js`.
+ * 1. If the directory contains a package.json with a `pi` manifest object,
+ *    the manifest is authoritative:
+ *    - `pi.extensions` array → resolve each entry relative to the directory.
+ *    - `pi: {}` (no extensions) → return empty (library opt-out, e.g. cmux).
+ * 2. Only when no `pi` manifest exists does it fall back to `index.ts` → `index.js`.
  */
 export function resolveExtensionEntries(dir: string): string[] {
   const packageJsonPath = join(dir, 'package.json')
   if (existsSync(packageJsonPath)) {
     try {
       const pkg = JSON.parse(readFileSync(packageJsonPath, 'utf-8'))
-      const declared = pkg?.pi?.extensions
-      if (Array.isArray(declared)) {
-        const resolved = declared
+      if (pkg?.pi && typeof pkg.pi === 'object') {
+        // When a pi manifest exists, it is authoritative — don't fall through
+        // to index.ts/index.js auto-detection. This allows library directories
+        // (like cmux) to opt out by declaring "pi": {} with no extensions.
+        const declared = pkg.pi.extensions
+        if (!Array.isArray(declared) || declared.length === 0) {
+          return []
+        }
+        return declared
           .filter((entry: unknown): entry is string => typeof entry === 'string')
           .map((entry: string) => resolve(dir, entry))
           .filter((entry: string) => existsSync(entry))
-        if (resolved.length > 0) {
-          return resolved
-        }
       }
     } catch {
       // Ignore malformed manifests and fall back to index.ts/index.js discovery.
diff --git a/src/resources/extensions/cmux/index.ts b/src/resources/extensions/cmux/index.ts
index bac7d2f81..ca13d329b 100644
--- a/src/resources/extensions/cmux/index.ts
+++ b/src/resources/extensions/cmux/index.ts
@@ -289,10 +289,17 @@ export class CmuxClient {
   }
 
   async createSplit(direction: "right" | "down" | "left" | "up"): Promise<string | null> {
+    return this.createSplitFrom(this.config.surfaceId, direction);
+  }
+
+  async createSplitFrom(
+    sourceSurfaceId: string | undefined,
+    direction: "right" | "down" | "left" | "up",
+  ): Promise<string | null> {
     if (!this.config.splits) return null;
     const before = new Set(await this.listSurfaceIds());
     const args = ["new-split", direction];
-    const scopedArgs = this.appendSurface(this.appendWorkspace(args), this.config.surfaceId);
+    const scopedArgs = this.appendSurface(this.appendWorkspace(args), sourceSurfaceId);
     await this.runAsync(scopedArgs);
     const after = await this.listSurfaceIds();
     for (const id of after) {
@@ -301,6 +308,55 @@ export class CmuxClient {
     return null;
   }
 
+  /**
+   * Create a grid of surfaces for parallel agent execution.
+   *
+   * Layout strategy (gsd stays in the original surface):
+   *   1 agent:  [gsd | A]
+   *   2 agents: [gsd | A]
+   *             [    | B]
+   *   3 agents: [gsd | A]
+   *             [ C  | B]
+   *   4 agents: [gsd | A]
+   *             [ C  | B]  (D splits from B downward)
+   *             [    | D]
+   *
+   * Returns surface IDs in order, or empty array on failure.
+   */
+  async createGridLayout(count: number): Promise<string[]> {
+    if (!this.config.splits || count <= 0) return [];
+    const surfaces: string[] = [];
+
+    // First split: create right column from the gsd surface
+    const rightCol = await this.createSplitFrom(this.config.surfaceId, "right");
+    if (!rightCol) return [];
+    surfaces.push(rightCol);
+    if (count === 1) return surfaces;
+
+    // Second split: split right column down → bottom-right
+    const bottomRight = await this.createSplitFrom(rightCol, "down");
+    if (!bottomRight) return surfaces;
+    surfaces.push(bottomRight);
+    if (count === 2) return surfaces;
+
+    // Third split: split gsd surface down → bottom-left
+    const bottomLeft = await this.createSplitFrom(this.config.surfaceId, "down");
+    if (!bottomLeft) return surfaces;
+    surfaces.push(bottomLeft);
+    if (count === 3) return surfaces;
+
+    // Fourth+: split subsequent surfaces down from the last created
+    let lastSurface = bottomRight;
+    for (let i = 3; i < count; i++) {
+      const next = await this.createSplitFrom(lastSurface, "down");
+      if (!next) break;
+      surfaces.push(next);
+      lastSurface = next;
+    }
+
+    return surfaces;
+  }
+
   async sendSurface(surfaceId: string, text: string): Promise<boolean> {
     const payload = text.endsWith("\n") ? text : `${text}\n`;
     const stdout = await this.runAsync(["send-surface", "--surface", surfaceId, payload]);
diff --git a/src/resources/extensions/gsd/commands.ts b/src/resources/extensions/gsd/commands.ts
index a8973c080..e48eb68ff 100644
--- a/src/resources/extensions/gsd/commands.ts
+++ b/src/resources/extensions/gsd/commands.ts
@@ -159,7 +159,7 @@ async function guardRemoteSession(
 
 export function registerGSDCommand(pi: ExtensionAPI): void {
   pi.registerCommand("gsd", {
-    description: "GSD — Get Shit Done: /gsd help|start|templates|next|auto|stop|pause|status|visualize|queue|quick|capture|triage|dispatch|history|undo|skip|export|cleanup|mode|prefs|config|keys|hooks|run-hook|skill-health|doctor|forensics|changelog|migrate|remote|steer|knowledge|new-milestone|parallel|cmux|update",
+    description: "GSD — Get Shit Done: /gsd help|start|templates|next|auto|stop|pause|status|widget|visualize|queue|quick|capture|triage|dispatch|history|undo|rate|skip|export|cleanup|mode|prefs|config|keys|hooks|run-hook|skill-health|doctor|logs|forensics|changelog|migrate|remote|steer|knowledge|new-milestone|parallel|cmux|park|unpark|init|setup|inspect|extensions|update",
     getArgumentCompletions: (prefix: string) => {
       const subcommands = [
         { cmd: "help", desc: "Categorized command reference with descriptions" },
@@ -210,7 +210,11 @@ export function registerGSDCommand(pi: ExtensionAPI): void {
         { cmd: "templates", desc: "List available workflow templates" },
         { cmd: "extensions", desc: "Manage extensions (list, enable, disable, info)" },
       ];
+      const hasTrailingSpace = prefix.endsWith(" ");
       const parts = prefix.trim().split(/\s+/);
+      if (hasTrailingSpace && parts.length >= 1) {
+        parts.push("");
+      }
 
       if (parts.length <= 1) {
         return subcommands
@@ -536,6 +540,18 @@ export function registerGSDCommand(pi: ExtensionAPI): void {
           .map((p) => ({ value: `dispatch ${p.cmd}`, label: p.cmd, description: p.desc }));
       }
 
+      if (parts[0] === "rate" && parts.length <= 2) {
+        const tierPrefix = parts[1] ?? "";
+        const tiers = [
+          { cmd: "over", desc: "Model was overqualified for this task" },
+          { cmd: "ok", desc: "Model was appropriate for this task" },
+          { cmd: "under", desc: "Model was underqualified for this task" },
+        ];
+        return tiers
+          .filter((t) => t.cmd.startsWith(tierPrefix))
+          .map((t) => ({ value: `rate ${t.cmd}`, label: t.cmd, description: t.desc }));
+      }
+
       return [];
     },
 
diff --git a/src/resources/extensions/gsd/tests/cmux.test.ts b/src/resources/extensions/gsd/tests/cmux.test.ts
index d174285b1..f25953542 100644
--- a/src/resources/extensions/gsd/tests/cmux.test.ts
+++ b/src/resources/extensions/gsd/tests/cmux.test.ts
@@ -100,6 +100,99 @@ test("buildCmuxStatusLabel and progress prefer deepest active unit", () => {
   assert.deepEqual(buildCmuxProgress(state), { value: 0.4, label: "2/5 tasks" });
 });
 
+describe("createGridLayout", () => {
+  // Create a mock CmuxClient that tracks createSplitFrom calls
+  function makeMockClient() {
+    let nextId = 1;
+    const calls: Array<{ source: string | undefined; direction: string }> = [];
+
+    const client = {
+      calls,
+      async createGridLayout(count: number) {
+        // Simulate the grid layout logic with a fake client
+        if (count <= 0) return [];
+        const surfaces: string[] = [];
+
+        const createSplitFrom = async (source: string | undefined, direction: string) => {
+          calls.push({ source, direction });
+          return `surface-${nextId++}`;
+        };
+
+        const rightCol = await createSplitFrom("gsd-surface", "right");
+        surfaces.push(rightCol);
+        if (count === 1) return surfaces;
+
+        const bottomRight = await createSplitFrom(rightCol, "down");
+        surfaces.push(bottomRight);
+        if (count === 2) return surfaces;
+
+        const bottomLeft = await createSplitFrom("gsd-surface", "down");
+        surfaces.push(bottomLeft);
+        if (count === 3) return surfaces;
+
+        let lastSurface = bottomRight;
+        for (let i = 3; i < count; i++) {
+          const next = await createSplitFrom(lastSurface, "down");
+          surfaces.push(next);
+          lastSurface = next;
+        }
+
+        return surfaces;
+      },
+    };
+    return client;
+  }
+
+  test("1 agent creates single right split", async () => {
+    const mock = makeMockClient();
+    const surfaces = await mock.createGridLayout(1);
+    assert.equal(surfaces.length, 1);
+    assert.deepEqual(mock.calls, [
+      { source: "gsd-surface", direction: "right" },
+    ]);
+  });
+
+  test("2 agents creates right column then splits it down", async () => {
+    const mock = makeMockClient();
+    const surfaces = await mock.createGridLayout(2);
+    assert.equal(surfaces.length, 2);
+    assert.deepEqual(mock.calls, [
+      { source: "gsd-surface", direction: "right" },
+      { source: "surface-1", direction: "down" },
+    ]);
+  });
+
+  test("3 agents creates 2x2 grid (gsd + 3 agent surfaces)", async () => {
+    const mock = makeMockClient();
+    const surfaces = await mock.createGridLayout(3);
+    assert.equal(surfaces.length, 3);
+    assert.deepEqual(mock.calls, [
+      { source: "gsd-surface", direction: "right" },
+      { source: "surface-1", direction: "down" },
+      { source: "gsd-surface", direction: "down" },
+    ]);
+  });
+
+  test("4 agents creates 2x2 grid with extra split", async () => {
+    const mock = makeMockClient();
+    const surfaces = await mock.createGridLayout(4);
+    assert.equal(surfaces.length, 4);
+    assert.deepEqual(mock.calls, [
+      { source: "gsd-surface", direction: "right" },
+      { source: "surface-1", direction: "down" },
+      { source: "gsd-surface", direction: "down" },
+      { source: "surface-2", direction: "down" },
+    ]);
+  });
+
+  test("0 agents returns empty", async () => {
+    const mock = makeMockClient();
+    const surfaces = await mock.createGridLayout(0);
+    assert.equal(surfaces.length, 0);
+    assert.equal(mock.calls.length, 0);
+  });
+});
+
 describe("cmux extension discovery opt-out", () => {
   test("cmux directory has package.json with pi manifest to prevent auto-discovery as extension", () => {
     const cmuxDir = path.resolve(
diff --git a/src/resources/extensions/subagent/index.ts b/src/resources/extensions/subagent/index.ts
index b60e8b2d6..c9609572f 100644
--- a/src/resources/extensions/subagent/index.ts
+++ b/src/resources/extensions/subagent/index.ts
@@ -452,7 +452,7 @@ async function runSingleAgent(
 
 async function runSingleAgentInCmuxSplit(
 	cmuxClient: CmuxClient,
-	direction: "right" | "down",
+	directionOrSurfaceId: "right" | "down" | string,
 	defaultCwd: string,
 	agents: AgentConfig[],
 	agentName: string,
@@ -503,7 +503,12 @@ async function runSingleAgentInCmuxSplit(
 		const stdoutPath = path.join(tmpOutputDir, "stdout.jsonl");
 		const stderrPath = path.join(tmpOutputDir, "stderr.log");
 		const exitPath = path.join(tmpOutputDir, "exit.code");
-		const cmuxSurfaceId = await cmuxClient.createSplit(direction);
+		// Accept either a pre-created surface ID or a direction to create a new split
+		const isDirection = directionOrSurfaceId === "right" || directionOrSurfaceId === "down"
+			|| directionOrSurfaceId === "left" || directionOrSurfaceId === "up";
+		const cmuxSurfaceId = isDirection
+			? await cmuxClient.createSplit(directionOrSurfaceId as "right" | "down" | "left" | "up")
+			: directionOrSurfaceId;
 		if (!cmuxSurfaceId) {
 			return runSingleAgent(defaultCwd, agents, agentName, task, cwd, step, signal, onUpdate, makeDetails);
 		}
@@ -806,12 +811,16 @@ export default function (pi: ExtensionAPI) {
 				const MAX_RETRIES = 1; // Retry failed tasks once
 				const batchId = crypto.randomUUID();
 				const batchSize = params.tasks.length;
+				// Pre-create a grid layout for cmux splits so agents get a clean tiled arrangement
+				const gridSurfaces = cmuxSplitsEnabled
+					? await cmuxClient.createGridLayout(Math.min(batchSize, MAX_CONCURRENCY))
+					: [];
 				const results = await mapWithConcurrencyLimit(params.tasks, MAX_CONCURRENCY, async (t, index) => {
 					const workerId = registerWorker(t.agent, t.task, index, batchSize, batchId);
 					const runTask = () => cmuxSplitsEnabled
 						? runSingleAgentInCmuxSplit(
 							cmuxClient,
-							index % 2 === 0 ? "right" : "down",
+							gridSurfaces[index] ?? (index % 2 === 0 ? "right" : "down"),
 							ctx.cwd,
 							agents,
 							t.agent,
diff --git a/src/tests/extension-discovery.test.ts b/src/tests/extension-discovery.test.ts
new file mode 100644
index 000000000..b3744c5ba
--- /dev/null
+++ b/src/tests/extension-discovery.test.ts
@@ -0,0 +1,121 @@
+import test, { describe } from 'node:test'
+import assert from 'node:assert/strict'
+import { mkdirSync, writeFileSync, rmSync } from 'node:fs'
+import { join } from 'node:path'
+import { tmpdir } from 'node:os'
+import { resolveExtensionEntries, discoverExtensionEntryPaths } from '../extension-discovery.ts'
+
+function makeTempDir(): string {
+  const dir = join(tmpdir(), `ext-discovery-test-${Date.now()}-${Math.random().toString(36).slice(2)}`)
+  mkdirSync(dir, { recursive: true })
+  return dir
+}
+
+describe('resolveExtensionEntries', () => {
+  test('returns index.ts when no package.json exists', () => {
+    const dir = makeTempDir()
+    try {
+      writeFileSync(join(dir, 'index.ts'), 'export default function() {}')
+      const entries = resolveExtensionEntries(dir)
+      assert.equal(entries.length, 1)
+      assert.ok(entries[0].endsWith('index.ts'))
+    } finally {
+      rmSync(dir, { recursive: true, force: true })
+    }
+  })
+
+  test('returns index.js when no package.json and no index.ts', () => {
+    const dir = makeTempDir()
+    try {
+      writeFileSync(join(dir, 'index.js'), 'module.exports = function() {}')
+      const entries = resolveExtensionEntries(dir)
+      assert.equal(entries.length, 1)
+      assert.ok(entries[0].endsWith('index.js'))
+    } finally {
+      rmSync(dir, { recursive: true, force: true })
+    }
+  })
+
+  test('returns declared extensions from pi.extensions array', () => {
+    const dir = makeTempDir()
+    try {
+      writeFileSync(join(dir, 'package.json'), JSON.stringify({
+        pi: { extensions: ['main.js'] }
+      }))
+      writeFileSync(join(dir, 'main.js'), 'module.exports = function() {}')
+      writeFileSync(join(dir, 'index.js'), 'should not be returned')
+      const entries = resolveExtensionEntries(dir)
+      assert.equal(entries.length, 1)
+      assert.ok(entries[0].endsWith('main.js'))
+    } finally {
+      rmSync(dir, { recursive: true, force: true })
+    }
+  })
+
+  test('returns empty array when pi manifest has no extensions (library opt-out)', () => {
+    const dir = makeTempDir()
+    try {
+      writeFileSync(join(dir, 'package.json'), JSON.stringify({
+        name: '@gsd/cmux',
+        pi: {}
+      }))
+      writeFileSync(join(dir, 'index.js'), 'export function utility() {}')
+      const entries = resolveExtensionEntries(dir)
+      assert.equal(entries.length, 0, 'pi: {} should opt out of extension discovery')
+    } finally {
+      rmSync(dir, { recursive: true, force: true })
+    }
+  })
+
+  test('returns empty array when pi.extensions is an empty array', () => {
+    const dir = makeTempDir()
+    try {
+      writeFileSync(join(dir, 'package.json'), JSON.stringify({
+        pi: { extensions: [] }
+      }))
+      writeFileSync(join(dir, 'index.js'), 'should not be returned')
+      const entries = resolveExtensionEntries(dir)
+      assert.equal(entries.length, 0)
+    } finally {
+      rmSync(dir, { recursive: true, force: true })
+    }
+  })
+
+  test('falls back to index.ts when package.json has no pi field', () => {
+    const dir = makeTempDir()
+    try {
+      writeFileSync(join(dir, 'package.json'), JSON.stringify({ name: 'some-pkg' }))
+      writeFileSync(join(dir, 'index.ts'), 'export default function() {}')
+      const entries = resolveExtensionEntries(dir)
+      assert.equal(entries.length, 1)
+      assert.ok(entries[0].endsWith('index.ts'))
+    } finally {
+      rmSync(dir, { recursive: true, force: true })
+    }
+  })
+})
+
+describe('discoverExtensionEntryPaths', () => {
+  test('skips library directories with pi: {} opt-out', () => {
+    const root = makeTempDir()
+    try {
+      // Real extension
+      const extDir = join(root, 'my-ext')
+      mkdirSync(extDir)
+      writeFileSync(join(extDir, 'index.js'), 'module.exports = function() {}')
+
+      // Library with opt-out (like cmux)
+      const libDir = join(root, 'cmux')
+      mkdirSync(libDir)
+      writeFileSync(join(libDir, 'package.json'), JSON.stringify({ pi: {} }))
+      writeFileSync(join(libDir, 'index.js'), 'export function utility() {}')
+
+      const paths = discoverExtensionEntryPaths(root)
+      assert.equal(paths.length, 1, 'should discover my-ext but skip cmux')
+      assert.ok(paths[0].includes('my-ext'))
+      assert.ok(!paths.some(p => p.includes('cmux')), 'cmux should not be discovered')
+    } finally {
+      rmSync(root, { recursive: true, force: true })
+    }
+  })
+})