Use bundled ConPTY for LocalPtyProvider spawns on Windows

The daemon spawn path already passes useConptyDll: true (bundled modern
ConPTY); LocalPtyProvider spawns - degraded mode and fresh-local routing -
silently ran on the legacy system ConPTY, which the daemon path's own
comment blames for full-width TUI scrollback corruption.

src/main/providers/local-pty-utils-windows-fallback.test.ts

@@ -76,13 +76,13 @@ describe('spawnShellWithFallback on Windows', () => {
       1,
       PWSH7,
       attempts[0].shellArgs,
-      expect.objectContaining({ cwd: 'C:\\repo' })
+      expect.objectContaining({ cwd: 'C:\\repo', useConptyDll: true })
     )
     expect(ptySpawn).toHaveBeenNthCalledWith(
       2,
       WINDOWS_POWERSHELL,
       attempts[1].shellArgs,
-      expect.objectContaining({ cwd: 'C:\\repo' })
+      expect.objectContaining({ cwd: 'C:\\repo', useConptyDll: true })
     )
   })
 

src/main/providers/local-pty-utils.ts

@@ -160,6 +160,14 @@ export type ShellSpawnResult = {
  * executables with per-shell args, so when the primary fails we retry with the
  * next safe shell instead of leaving the user with no terminal.
  */
+// Why: match the daemon spawn path (pty-subprocess.ts) — the bundled ConPTY
+// has the modern wrap-marker behavior xterm expects; legacy system ConPTY can
+// corrupt full-width TUI rows in scrollback. Without this, degraded-mode and
+// fresh-local spawns silently behave differently from daemon terminals.
+function windowsConptyDllOptions(): { useConptyDll: true } | Record<string, never> {
+  return process.platform === 'win32' ? { useConptyDll: true } : {}
+}
+
 function spawnWindowsFallbackChain(
   params: ShellSpawnParams,
   primaryError: string
@@ -174,7 +182,8 @@ function spawnWindowsFallbackChain(
         cols,
         rows,
         cwd: attempt.effectiveCwd,
-        env
+        env,
+        ...windowsConptyDllOptions()
       })
       console.warn(
         `[pty] Primary shell "${params.shellPath}" failed (${primaryError}), fell back to "${attempt.shellPath}"`
@@ -217,7 +226,14 @@ export function spawnShellWithFallback(params: ShellSpawnParams): ShellSpawnResu
   if (!primaryError) {
     try {
       return {
-        process: ptySpawn(shellPath, shellArgs, { name: termName, cols, rows, cwd, env }),
+        process: ptySpawn(shellPath, shellArgs, {
+          name: termName,
+          cols,
+          rows,
+          cwd,
+          env,
+          ...windowsConptyDllOptions()
+        }),
         shellPath
       }
     } catch (err) {