fix: preserve Windows drive-root project identity

Normalize realpath results for Windows drive roots so D:\ does not round-trip to drive-relative D: and resolve back into the current repository.

Also tighten Sidebar hidden-project matching so a drive root does not match every child project on the same drive.

Tested: bun test src/server/__tests__/windows-drive-path.test.ts src/server/__tests__/sessions.test.ts src/server/__tests__/workspace-service.test.ts
Tested: cd desktop && bun run test -- --run src/components/layout/Sidebar.test.tsx
Tested: cd desktop && bun run build:windows-x64
Tested: bun run check:desktop
Not-tested: bun run check:server (failed on existing/environment failures including the pre-existing untracked FileReadTool test)
Confidence: high
Scope-risk: narrow

desktop/src/components/layout/Sidebar.test.tsx

@@ -799,6 +799,33 @@ describe('Sidebar', () => {
     expect(screen.getByRole('button', { name: /Drive Project Session/ })).toBeInTheDocument()
   })
 
+  it('does not restore a hidden Windows drive root when creating a child project session', async () => {
+    window.localStorage.setItem(PROJECT_HIDDEN_STORAGE_KEY, JSON.stringify(['D:\\']))
+    createSession.mockResolvedValue('child-new')
+    const now = new Date().toISOString()
+    useSessionStore.setState({
+      sessions: [
+        makeSession('child-1', 'Child Session', 'D:\\workspace\\code\\cc-haha', now),
+      ],
+    })
+    useTabStore.setState({
+      tabs: [{ sessionId: 'child-1', title: 'Child Session', type: 'session', status: 'idle' }],
+      activeTabId: 'child-1',
+    })
+
+    render(<Sidebar />)
+
+    await act(async () => {
+      fireEvent.click(screen.getByRole('button', { name: 'New Session' }))
+    })
+
+    await waitFor(() => {
+      expect(createSession).toHaveBeenCalledWith('D:\\workspace\\code\\cc-haha')
+    })
+    expect(JSON.parse(window.localStorage.getItem(PROJECT_HIDDEN_STORAGE_KEY) ?? '[]')).toEqual(['D:\\'])
+    expect(desktopUiPreferencesApiMock.updateSidebarPreferences).not.toHaveBeenCalled()
+  })
+
   it('right-aligns running status, worktree marker, and update time on session rows', () => {
     vi.useFakeTimers()
     vi.setSystemTime(new Date('2026-05-19T12:00:00.000Z'))

desktop/src/components/layout/Sidebar.tsx

@@ -1657,17 +1657,21 @@ function normalizeProjectKeyList(values: unknown): string[] {
 }
 
 function normalizeProjectPathForComparison(value: string): string {
-  const normalized = value.replace(/\\/g, '/').replace(/\/+$/g, '')
-  return normalized || value
+  const normalized = value.replace(/\\/g, '/').replace(/\/+$/g, '') || value
+  return isWindows ? normalized.toLowerCase() : normalized
+}
+
+function isDriveRootComparisonPath(value: string): boolean {
+  return /^[a-z]:$/i.test(value)
 }
 
 function projectPathMatches(projectKey: string, workDir: string): boolean {
   const normalizedProjectKey = normalizeProjectPathForComparison(projectKey)
   const normalizedWorkDir = normalizeProjectPathForComparison(workDir)
 
-  return normalizedProjectKey === normalizedWorkDir
-    || normalizedWorkDir.startsWith(`${normalizedProjectKey}/`)
-    || normalizedProjectKey.startsWith(`${normalizedWorkDir}/`)
+  if (normalizedProjectKey === normalizedWorkDir) return true
+  if (isDriveRootComparisonPath(normalizedProjectKey)) return false
+  return normalizedWorkDir.startsWith(`${normalizedProjectKey}/`)
 }
 
 function hasSidebarProjectPreferences(preferences: SidebarProjectPreferences): boolean {

src/server/__tests__/windows-drive-path.test.ts

@@ -1,9 +1,14 @@
 import { describe, expect, it } from 'bun:test'
+import * as fs from 'node:fs/promises'
+import * as os from 'node:os'
+import * as path from 'node:path'
 import {
   isSameOrInsidePathForPlatform,
   normalizeDriveRootPathForPlatform,
 } from '../services/windowsDrivePath.js'
+import { getRepositoryContext } from '../services/repositoryLaunchService.js'
 import { SessionService } from '../services/sessionService.js'
+import { sanitizePath } from '../../utils/sessionStoragePortable.js'
 
 describe('Windows drive root path handling', () => {
   it('normalizes drive-relative root inputs to absolute drive roots on Windows', () => {
@@ -27,4 +32,46 @@ describe('Windows drive root path handling', () => {
     expect(isSameOrInsidePathForPlatform('D:\\project-extra', 'D:\\project', 'win32')).toBe(false)
     expect(isSameOrInsidePathForPlatform('E:\\child', 'D:\\', 'win32')).toBe(false)
   })
+
+  it('keeps realpathed drive roots from resolving to the current drive directory', async () => {
+    if (process.platform !== 'win32') return
+
+    const originalConfigDir = process.env.CLAUDE_CONFIG_DIR
+    const configDir = await fs.mkdtemp(path.join(os.tmpdir(), 'drive-root-session-'))
+    const driveRoot = path.parse(process.cwd()).root
+    const sessionId = crypto.randomUUID()
+
+    try {
+      process.env.CLAUDE_CONFIG_DIR = configDir
+      const projectDir = path.join(configDir, 'projects', sanitizePath(driveRoot))
+      await fs.mkdir(projectDir, { recursive: true })
+      await fs.writeFile(
+        path.join(projectDir, `${sessionId}.jsonl`),
+        JSON.stringify({
+          type: 'session-meta',
+          isMeta: true,
+          workDir: driveRoot,
+          timestamp: new Date().toISOString(),
+        }) + '\n',
+        'utf-8',
+      )
+
+      const service = new SessionService()
+      const { sessions } = await service.listSessions({ limit: 5 })
+      const session = sessions.find((item) => item.id === sessionId)
+      expect(session?.workDir).toBe(driveRoot)
+      expect(session?.projectRoot).toBe(driveRoot)
+
+      const context = await getRepositoryContext(driveRoot)
+      expect(context.workDir).toBe(driveRoot)
+      expect(context.repoRoot).not.toBe(process.cwd())
+    } finally {
+      if (originalConfigDir === undefined) {
+        delete process.env.CLAUDE_CONFIG_DIR
+      } else {
+        process.env.CLAUDE_CONFIG_DIR = originalConfigDir
+      }
+      await fs.rm(configDir, { recursive: true, force: true })
+    }
+  })
 })

src/server/services/repositoryLaunchService.ts

@@ -172,7 +172,7 @@ async function resolveDirectory(workDir: string): Promise<string> {
   const resolved = path.resolve(normalizeDriveRootPathForPlatform(workDir))
   let realPath: string
   try {
-    realPath = await fs.realpath(resolved)
+    realPath = normalizeDriveRootPathForPlatform(await fs.realpath(resolved))
   } catch {
     throw repositoryBadRequest(
       REPOSITORY_ERROR.workdirMissing,

src/server/services/sessionService.ts

@@ -366,7 +366,7 @@ export class SessionService {
 
   private async canonicalizeProjectPath(projectPath: string): Promise<string> {
     try {
-      return (await fs.realpath(projectPath)).normalize('NFC')
+      return normalizeDriveRootPathForPlatform(await fs.realpath(projectPath)).normalize('NFC')
     } catch {
       return projectPath.normalize('NFC')
     }

src/server/services/workspaceService.ts

@@ -1030,7 +1030,7 @@ export class WorkspaceService {
       return {
         kind: 'ok',
         workspaceRoot: workDir,
-        canonicalWorkspaceRoot: await fs.realpath(workDir),
+        canonicalWorkspaceRoot: normalizeDriveRootPathForPlatform(await fs.realpath(workDir)),
       }
     } catch (error) {
       return {