fix: normalize Windows backslash paths in bash command strings (#1436) (#1863)

On Windows, paths embedded in bash command strings have backslashes
stripped by the shell (e.g. C:\Users\user becomes C:Useruser), causing
cd and other commands to fail silently. This left ~1.4 GB orphaned
worktree directories after milestone completion.

- Normalize all paths to forward slashes before embedding in the
  subagent cmux bash script (cd, tee, process args)
- Add post-teardown orphan detection: warn and attempt rmSync fallback
  if the worktree directory persists after removeWorktree
- Add regression tests for Windows path normalization

Closes #1436

Co-authored-by: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

src/resources/extensions/gsd/auto-worktree.ts

@@ -761,6 +761,24 @@ export function teardownAutoWorktree(
     branch,
     deleteBranch: !preserveBranch,
   });
+
+  // Verify cleanup succeeded — warn if the worktree directory is still on disk.
+  // On Windows, bash-based cleanup can silently fail when paths contain
+  // backslashes (#1436), leaving ~1 GB+ orphaned directories.
+  const wtDir = worktreePath(originalBasePath, milestoneId);
+  if (existsSync(wtDir)) {
+    console.error(
+      `[GSD] WARNING: Worktree directory still exists after teardown: ${wtDir}\n` +
+        `  This is likely an orphaned directory consuming disk space.\n` +
+        `  Remove it manually with: rm -rf "${wtDir.replaceAll("\\", "/")}"`,
+    );
+    // Attempt a direct filesystem removal as a fallback
+    try {
+      rmSync(wtDir, { recursive: true, force: true });
+    } catch {
+      // Non-fatal — the warning above tells the user how to clean up
+    }
+  }
 }
 
 /**

src/resources/extensions/gsd/tests/windows-path-normalization.test.ts

@@ -0,0 +1,99 @@
+/**
+ * windows-path-normalization.test.ts — Verify Windows backslash paths are
+ * normalised to forward slashes before embedding in bash command strings.
+ *
+ * Regression test for #1436: on Windows, `cd C:\Users\user\project` in bash
+ * strips backslashes (escape characters), producing `C:Usersuserproject`.
+ */
+
+import { createTestContext } from "./test-helpers.ts";
+
+const { assertEq, assertTrue, report } = createTestContext();
+
+// ─── shellEscape + path normalization ──────────────────────────────────────
+
+// Replicate the shellEscape helper from cmux/index.ts
+function shellEscape(value: string): string {
+  return `'${value.replace(/'/g, `'\\''`)}'`;
+}
+
+// The bashPath pattern used in subagent/index.ts
+function bashPath(p: string): string {
+  return shellEscape(p.replaceAll("\\", "/"));
+}
+
+console.log("\n=== Windows backslash path normalization (#1436) ===");
+
+// Backslash paths are converted to forward slashes
+assertEq(
+  bashPath("C:\\Users\\user\\project"),
+  "'C:/Users/user/project'",
+  "backslash path normalised to forward slashes in shell-escaped string",
+);
+
+// Unix paths pass through unchanged
+assertEq(
+  bashPath("/home/user/project"),
+  "'/home/user/project'",
+  "Unix path unchanged",
+);
+
+// Mixed separators are normalised
+assertEq(
+  bashPath("C:\\Users/user\\project/src"),
+  "'C:/Users/user/project/src'",
+  "mixed separators normalised",
+);
+
+// Paths with single quotes are still properly escaped
+assertEq(
+  bashPath("C:\\Users\\o'brien\\project"),
+  "'C:/Users/o'\\''brien/project'",
+  "single quote in path is escaped after normalisation",
+);
+
+// UNC paths
+assertEq(
+  bashPath("\\\\server\\share\\dir"),
+  "'//server/share/dir'",
+  "UNC path normalised",
+);
+
+// Empty string
+assertEq(
+  bashPath(""),
+  "''",
+  "empty string handled",
+);
+
+// ─── cd command construction ───────────────────────────────────────────────
+
+console.log("\n=== cd command construction with normalised paths ===");
+
+const windowsCwd = "C:\\Users\\user\\project\\.gsd\\worktrees\\M001";
+const cdCommand = `cd ${bashPath(windowsCwd)}`;
+assertEq(
+  cdCommand,
+  "cd 'C:/Users/user/project/.gsd/worktrees/M001'",
+  "cd command uses forward slashes for Windows worktree path",
+);
+
+// Verify the mangled form from #1436 is NOT produced
+assertTrue(
+  !cdCommand.includes("C:Users"),
+  "mangled path C:Usersuserproject must not appear",
+);
+
+// ─── Worktree teardown orphan detection ────────────────────────────────────
+
+console.log("\n=== teardown orphan warning path formatting ===");
+
+const windowsWtDir = "C:\\Users\\user\\project\\.gsd\\worktrees\\M001";
+const helpCommand = `rm -rf "${windowsWtDir.replaceAll("\\", "/")}"`;
+assertEq(
+  helpCommand,
+  'rm -rf "C:/Users/user/project/.gsd/worktrees/M001"',
+  "orphan cleanup help command uses forward slashes",
+);
+
+report();

src/resources/extensions/subagent/index.ts

@@ -516,12 +516,16 @@ async function runSingleAgentInCmuxSplit(
 		const bundledPaths = (process.env.GSD_BUNDLED_EXTENSION_PATHS ?? "").split(path.delimiter).map((s) => s.trim()).filter(Boolean);
 		const extensionArgs = bundledPaths.flatMap((p) => ["--extension", p]);
 		const processArgs = [process.env.GSD_BIN_PATH!, ...extensionArgs, ...buildSubagentProcessArgs(agent, task, tmpPromptPath)];
+		// Normalize all paths to forward slashes before embedding in bash strings.
+		// On Windows, backslashes are interpreted as escape characters by bash,
+		// mangling paths like C:\Users\user into C:Useruser (#1436).
+		const bashPath = (p: string) => shellEscape(p.replaceAll("\\", "/"));
 		const innerScript = [
-			`cd ${shellEscape(cwd ?? defaultCwd)}`,
+			`cd ${bashPath(cwd ?? defaultCwd)}`,
 			"set -o pipefail",
-			`${shellEscape(process.execPath)} ${processArgs.map(shellEscape).join(" ")} 2> >(tee ${shellEscape(stderrPath)} >&2) | tee ${shellEscape(stdoutPath)}`,
+			`${bashPath(process.execPath)} ${processArgs.map(a => bashPath(a)).join(" ")} 2> >(tee ${bashPath(stderrPath)} >&2) | tee ${bashPath(stdoutPath)}`,
 			"status=${PIPESTATUS[0]}",
-			`printf '%s' "$status" > ${shellEscape(exitPath)}`,
+			`printf '%s' "$status" > ${bashPath(exitPath)}`,
 		].join("; ");
 
 		const sent = await cmuxClient.sendSurface(cmuxSurfaceId, `bash -lc ${shellEscape(innerScript)}`);