fix(shared): normalize a bare Windows drive root the same as C:\ / C:/ (#6189)

Co-authored-by: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

Author: arhxam

packages/shared/src/path.test.ts

@@ -4,6 +4,8 @@ import {
   isUncPath,
   isWindowsAbsolutePath,
   isWindowsDrivePath,
+  normalizeProjectPathForComparison,
+  normalizeProjectPathForDispatch,
 } from "./path.ts";
 
 describe("path helpers", () => {
@@ -31,4 +33,14 @@ describe("path helpers", () => {
     expect(isExplicitRelativePath("..\\repo")).toBe(true);
     expect(isExplicitRelativePath("~/repo")).toBe(false);
   });
+
+  it("normalizes a bare Windows drive root the same as one with a trailing separator", () => {
+    // `C:`, `C:\` and `C:/` all refer to the drive root and must compare equal.
+    expect(normalizeProjectPathForDispatch("C:")).toBe("C:\\");
+    expect(normalizeProjectPathForComparison("C:")).toBe("c:\\");
+    expect(normalizeProjectPathForComparison("C:")).toBe(normalizeProjectPathForComparison("C:\\"));
+    expect(normalizeProjectPathForComparison("C:")).toBe(normalizeProjectPathForComparison("C:/"));
+    // Non-root drive paths keep their trailing separator trimmed as before.
+    expect(normalizeProjectPathForDispatch("C:\\repo\\")).toBe("C:\\repo");
+  });
 });

packages/shared/src/path.ts

@@ -22,7 +22,11 @@ export function isExplicitRelativePath(value: string): boolean {
 }
 
 function isRootPath(value: string): boolean {
-  return value === "/" || value === "\\" || /^[a-zA-Z]:[/\\]?$/.test(value);
+  // The drive separator is required: a bare `C:` is not the drive root (it
+  // means "current directory on C:"), and treating it as already-canonical
+  // would leave it as `C:` while `C:\` and `C:/` normalize to the drive root,
+  // so the same location would fail project identity/dedup comparisons.
+  return value === "/" || value === "\\" || /^[a-zA-Z]:[/\\]$/.test(value);
 }
 
 function trimTrailingPathSeparators(value: string): string {