feat(terminal): POSIX 也预检 shell 可执行文件，统一 shell-not-found 错误码

tests/pty-helpers.spec.ts

@@ -25,6 +25,7 @@ import {
   splitShellArgs,
   unquotePath,
 } from '../src/pty-manager.ts'
+import { SidebarError } from '../src/wire.ts'
 
 describe('pty helpers', () => {
   it('prefers an explicit shell, then SHELL, then the account login shell on POSIX', () => {
@@ -114,8 +115,41 @@ describe('pty helpers', () => {
       .toThrow('shell executable not found: "missing-shell"')
   })
 
-  it('keeps POSIX bare shell resolution delegated to execvp', () => {
-    expect(resolveShellExecutable('  zsh  ', { platform: 'linux', env: {}, exists: () => false })).toBe('zsh')
+  it('POSIX: resolves bare names along PATH and names a missing configured shell', () => {
+    const options = {
+      platform: 'linux' as const,
+      env: { PATH: '/usr/local/bin:/usr/bin' },
+      exists: (path: string) => path === join('/usr/bin', 'zsh'),
+    }
+    expect(resolveShellExecutable('zsh', options)).toBe(join('/usr/bin', 'zsh'))
+    const thrown = (() => {
+      try {
+        resolveShellExecutable('nope', options)
+        return undefined
+      } catch (error) {
+        return error
+      }
+    })()
+    expect(thrown).toBeInstanceOf(SidebarError)
+    expect((thrown as SidebarError).code).toBe('shell-not-found')
+    expect((thrown as SidebarError).message).toBe('shell executable not found: "nope"')
+    expect((thrown as SidebarError).meta?.shell).toBe('nope')
+  })
+
+  it('POSIX: checks an absolute path exists and passes it through verbatim', () => {
+    expect(resolveShellExecutable('/explicit/zsh', { platform: 'linux', env: {}, exists: () => true }))
+      .toBe('/explicit/zsh')
+    expect(() => resolveShellExecutable('/missing/zsh', { platform: 'linux', env: {}, exists: () => false }))
+      .toThrow('shell executable not found: "/missing/zsh"')
+  })
+
+  it('unquotes the configured shell before resolving (Windows probe included)', () => {
+    const options = {
+      platform: 'win32' as const,
+      env: { PATH: 'C:\\Tools' },
+      exists: (path: string) => path.replaceAll('\\', '/') === 'C:/Tools/pwsh.exe',
+    }
+    expect(resolveShellExecutable('"pwsh.exe"', options).replaceAll('\\', '/')).toBe('C:/Tools/pwsh.exe')
   })
 
   it('trims the configured shell and defaults it to auto for old documents', () => {