diff --git a/src/resources/extensions/gsd/auto.ts b/src/resources/extensions/gsd/auto.ts
index a65c16ae3..bb1227a92 100644
--- a/src/resources/extensions/gsd/auto.ts
+++ b/src/resources/extensions/gsd/auto.ts
@@ -69,11 +69,13 @@ import {
   getProjectTotals, formatCost, formatTokenCount,
 } from "./metrics.js";
 import { dirname, join } from "node:path";
+import { sep as pathSep } from "node:path";
 import { readdirSync, readFileSync, existsSync, mkdirSync, writeFileSync, unlinkSync } from "node:fs";
 import { execSync, execFileSync } from "node:child_process";
 import {
   autoCommitCurrentBranch,
   captureIntegrationBranch,
+  detectWorktreeName,
   getCurrentBranch,
   getMainBranch,
   MergeConflictError,
@@ -505,7 +507,8 @@ export async function startAuto(
     if (currentMilestoneId) setActiveMilestoneId(base, currentMilestoneId);
 
     // ── Auto-worktree: re-enter worktree on resume if not already inside ──
-    if (currentMilestoneId && originalBasePath && !isInAutoWorktree(basePath)) {
+    // Skip if already inside a worktree (manual /worktree) to prevent nesting.
+    if (currentMilestoneId && originalBasePath && !isInAutoWorktree(basePath) && !detectWorktreeName(basePath) && !detectWorktreeName(originalBasePath)) {
       try {
         const existingWtPath = getAutoWorktreePath(originalBasePath, currentMilestoneId);
         if (existingWtPath) {
@@ -668,8 +671,22 @@ export async function startAuto(
 
   // ── Auto-worktree: create or enter worktree for the active milestone ──
   // Store the original project root before any chdir so we can restore on stop.
+  // Skip if already inside a worktree (manual /worktree or another auto-worktree)
+  // to prevent nested worktree creation.
   originalBasePath = base;
-  if (currentMilestoneId) {
+
+  const isUnderGsdWorktrees = (p: string): boolean => {
+    // Prevent creating nested auto-worktrees when running from within any
+    // `.gsd/worktrees/...` directory (including manual worktrees).
+    const marker = `${pathSep}.gsd${pathSep}worktrees${pathSep}`;
+    if (p.includes(marker)) {
+      return true;
+    }
+    const worktreesSuffix = `${pathSep}.gsd${pathSep}worktrees`;
+    return p.endsWith(worktreesSuffix);
+  };
+
+  if (currentMilestoneId && !detectWorktreeName(base) && !isUnderGsdWorktrees(base)) {
     try {
       const existingWtPath = getAutoWorktreePath(base, currentMilestoneId);
       if (existingWtPath) {