perf(pi): skip rewriting current managed extensions on every terminal spawn (#38481)

Each local terminal spawn with a Pi agent home rewrote three Orca-owned
extension files (~54 KB) synchronously on the main thread even when their
contents were already current. Compare the read we already do for the
ownership check and write only when the content differs.

Co-authored-by: m4air <m4air@Mac.localdomain>

src/main/pi/titlebar-extension-service.test.ts

@@ -10,7 +10,9 @@ import {
   readFileSync,
   readdirSync,
   rmSync,
+  statSync,
   symlinkSync,
+  utimesSync,
   writeFileSync
 } from 'node:fs'
 import { tmpdir } from 'node:os'
@@ -512,6 +514,19 @@ describe('PiTitlebarExtensionService', () => {
     )
   })
 
+  it('leaves current Orca-owned extensions untouched on later spawns', () => {
+    const svc = new PiTitlebarExtensionService()
+    svc.buildPtyEnv('pty-current-1', piHome, 'pi')
+    const installed = ['orca-titlebar-spinner.ts', 'orca-prefill.ts', 'orca-agent-status.ts'].map(
+      (name) => join(piHome, 'extensions', name)
+    )
+    installed.forEach((path) => utimesSync(path, 0, 0))
+
+    svc.buildPtyEnv('pty-current-2', piHome, 'pi')
+
+    expect(installed.map((path) => statSync(path).mtimeMs)).toEqual([0, 0, 0])
+  })
+
   it("does not overwrite a user's same-named Orca extension file", () => {
     const userStatusExtension = 'user-owned status extension'
     writeFileSync(join(piHome, 'extensions', 'orca-agent-status.ts'), userStatusExtension, 'utf-8')

src/main/pi/titlebar-extension-service.ts

@@ -87,16 +87,17 @@ export class PiTitlebarExtensionService {
     safeRemoveOverlay(overlayDir, this.getOverlayRoot(kind))
   }
 
-  private canOverwriteManagedExtension(path: string): boolean {
-    try {
-      return readFileSync(path, 'utf8').includes(ORCA_MANAGED_EXTENSION_MARKER)
-    } catch {
-      return true
-    }
-  }
-
   private writeManagedExtension(path: string, source: string): ManagedExtensionWriteResult {
-    if (existsSync(path) && !this.canOverwriteManagedExtension(path)) {
+    let installed: string | undefined
+    try {
+      installed = readFileSync(path, 'utf8')
+    } catch {
+      installed = undefined
+    }
+    if (installed === source) {
+      return 'written'
+    }
+    if (installed !== undefined && !installed.includes(ORCA_MANAGED_EXTENSION_MARKER)) {
       return 'skipped-user-owned'
     }