diff --git a/docs/operations/development.md b/docs/operations/development.md
index ea7f10a6ba2dd..9b5346e4b0476 100644
--- a/docs/operations/development.md
+++ b/docs/operations/development.md
@@ -167,7 +167,10 @@ Put that value in the main checkout's gitignored `.env`:
 T3CODE_DEV_AUTH_TOKEN=<the value generated above>
 ```
 
-The `t3.json` Setup Worktree action links that file to each worktree's `.env`. The dev runner reads repository env files at startup. `.env.local` and inherited process
+The `t3.json` Setup Worktree action links that file to each worktree's `.env`. Where symlinks are
+not allowed, such as Windows without Developer Mode, it copies the file instead. A copy does not pick
+up later changes; delete it and rerun setup to refresh it.
+The dev runner reads repository env files at startup. `.env.local` and inherited process
 environment values override `.env`, so no per-worktree export is needed after setup.
 
 For a manual worktree or launcher without that link, export the same fixed value instead:
diff --git a/scripts/setup-worktree.test.ts b/scripts/setup-worktree.test.ts
new file mode 100644
index 0000000000000..f82ccd635f50a
--- /dev/null
+++ b/scripts/setup-worktree.test.ts
@@ -0,0 +1,86 @@
+// @effect-diagnostics nodeBuiltinImport:off - Runs the real setup script against a fixture checkout.
+import * as NodeChildProcess from "node:child_process";
+import * as NodeFS from "node:fs";
+import * as NodeOS from "node:os";
+import * as NodePath from "node:path";
+import { describe, expect, it } from "vite-plus/test";
+
+// Windows without Developer Mode or admin rights rejects every symlink this way.
+const DENY_SYMLINKS = `import fs from "node:fs";
+import { syncBuiltinESMExports } from "node:module";
+fs.symlinkSync = () => {
+  throw Object.assign(new Error("EPERM: operation not permitted, symlink"), { code: "EPERM" });
+};
+syncBuiltinESMExports();
+`;
+
+describe("setup-worktree", () => {
+  it("copies env files when symlinks are denied and keeps the copies on later runs", () => {
+    const root = NodeFS.mkdtempSync(NodePath.join(NodeOS.tmpdir(), "t3-setup-worktree-"));
+    try {
+      const main = NodePath.join(root, "main");
+      const worktree = NodePath.join(root, "worktree");
+      const bin = NodePath.join(root, "bin");
+      for (const dir of [
+        NodePath.join(main, "infra", "relay"),
+        NodePath.join(worktree, "infra", "relay"),
+        NodePath.join(worktree, "node_modules"),
+        NodePath.join(worktree, "scripts"),
+        bin,
+      ]) {
+        NodeFS.mkdirSync(dir, { recursive: true });
+      }
+      NodeFS.writeFileSync(NodePath.join(main, ".env"), "ROOT=1\n");
+      NodeFS.writeFileSync(NodePath.join(main, "infra", "relay", ".env"), "RELAY=1\n");
+      const script = NodePath.join(worktree, "scripts", "setup-worktree.ts");
+      NodeFS.copyFileSync(NodePath.join(import.meta.dirname, "setup-worktree.ts"), script);
+      NodeFS.writeFileSync(NodePath.join(worktree, "scripts", "package.json"), '{"type":"module"}');
+      // A no-op install keeps the run on the env-file step.
+      NodeFS.writeFileSync(NodePath.join(bin, "vp"), "#!/bin/sh\n", { mode: 0o755 });
+      NodeFS.writeFileSync(NodePath.join(bin, "vp.cmd"), "@exit /b 0\r\n");
+      NodeFS.writeFileSync(NodePath.join(worktree, "node_modules", ".modules.yaml"), "{}");
+
+      const setup = () => {
+        const run = NodeChildProcess.spawnSync(
+          process.execPath,
+          ["--import", `data:text/javascript,${encodeURIComponent(DENY_SYMLINKS)}`, script],
+          {
+            cwd: worktree,
+            encoding: "utf8",
+            env: {
+              ...process.env,
+              PATH: `${bin}${NodePath.delimiter}${process.env.PATH ?? ""}`,
+              T3CODE_PROJECT_ROOT: main,
+            },
+          },
+        );
+        expect(run.status, run.stderr).toBe(0);
+      };
+      const envFiles = () =>
+        [".env", NodePath.join("infra", "relay", ".env")].map((file) => {
+          const target = NodePath.join(worktree, file);
+          return {
+            symlink: NodeFS.lstatSync(target).isSymbolicLink(),
+            text: NodeFS.readFileSync(target, "utf8"),
+          };
+        });
+
+      setup();
+      expect(NodeFS.existsSync(NodePath.join(worktree, ".t3", "setup-done"))).toBe(true);
+      expect(envFiles()).toEqual([
+        { symlink: false, text: "ROOT=1\n" },
+        { symlink: false, text: "RELAY=1\n" },
+      ]);
+
+      NodeFS.writeFileSync(NodePath.join(main, ".env"), "ROOT=2\n");
+      NodeFS.writeFileSync(NodePath.join(worktree, "infra", "relay", ".env"), "LOCAL=1\n");
+      setup();
+      expect(envFiles()).toEqual([
+        { symlink: false, text: "ROOT=1\n" },
+        { symlink: false, text: "LOCAL=1\n" },
+      ]);
+    } finally {
+      NodeFS.rmSync(root, { recursive: true, force: true });
+    }
+  });
+});
diff --git a/scripts/setup-worktree.ts b/scripts/setup-worktree.ts
index 100a7af168105..cea1c4c97ec1b 100644
--- a/scripts/setup-worktree.ts
+++ b/scripts/setup-worktree.ts
@@ -99,7 +99,8 @@ if (
   );
 }
 
-// Worktrees link main-checkout env files; replace only symlinks so real files always survive.
+// Worktrees link main-checkout env files, or copy them where Windows denies symlinks.
+// Only symlinks are replaced, so real files always survive.
 for (const file of ENV_FILES) {
   const source = NodePath.join(projectRoot, file);
   const sourceStat = NodeFS.lstatSync(source, { throwIfNoEntry: false });
@@ -112,5 +113,13 @@ for (const file of ENV_FILES) {
   const existing = NodeFS.lstatSync(target, { throwIfNoEntry: false });
   if (existing && !existing.isSymbolicLink()) continue;
   if (existing) NodeFS.rmSync(target);
-  NodeFS.symlinkSync(source, target);
+  try {
+    NodeFS.symlinkSync(source, target);
+  } catch (error) {
+    if (!(error instanceof Error && "code" in error && error.code === "EPERM")) throw error;
+    NodeFS.copyFileSync(source, target, NodeFS.constants.COPYFILE_EXCL);
+    process.stderr.write(
+      `Copied ${file}: symlinks are not allowed here. Delete it and rerun setup to pick up later changes to ${source}.\n`,
+    );
+  }
 }