fix(lsp): run a pinned pyright in the pyright bunx fallback

packages/lsp/src/server/pyright.ts

@@ -4,8 +4,11 @@
 
 import type { LSPServerInfo } from './types'
 import { spawn } from 'node:child_process'
+import process from 'node:process'
 import { attachLSPProcessHandlers, log, nearestRoot } from './utils'
 
+export const PYRIGHT_VERSION = '1.1.414'
+
 export const PyrightServer: LSPServerInfo = {
   id: 'pyright',
   extensions: ['.py', '.pyi'],
@@ -16,20 +19,21 @@ export const PyrightServer: LSPServerInfo = {
     'pyrightconfig.json',
   ]),
   async spawn(root) {
-    const pyright = Bun.which('pyright-langserver')
+    // Read PATH now rather than the copy Bun captured at startup
+    const pyright = Bun.which('pyright-langserver', { PATH: process.env.PATH ?? '' })
     if (!pyright) {
-      // Try via bunx/npx
-      try {
-        const proc = spawn('bunx', ['pyright-langserver', '--stdio'], {
-          cwd: root,
-        })
-        attachLSPProcessHandlers(proc, 'pyright')
-        return { process: proc }
-      }
-      catch (err) {
-        log.error({ err }, 'Failed to spawn pyright-langserver via bunx')
+      // pyright-langserver is a bin of the pyright package, not a package itself.
+      // spawn reports a missing bunx only as an async 'error' event, so check for it first.
+      const bunx = Bun.which('bunx', { PATH: process.env.PATH ?? '' })
+      if (!bunx) {
+        log.warn({ root }, 'pyright not found. Install with: npm install pyright')
         return undefined
       }
+      const proc = spawn(bunx, ['-p', `pyright@${PYRIGHT_VERSION}`, 'pyright-langserver', '--stdio'], {
+        cwd: root,
+      })
+      attachLSPProcessHandlers(proc, 'pyright')
+      return { process: proc }
     }
 
     const proc = spawn(pyright, ['--stdio'], {

packages/lsp/test/unit/server.test.ts

@@ -595,6 +595,36 @@ describe.skipIf(process.platform === 'win32')('BiomeServer fallback', () => {
   })
 })
 
+describe.skipIf(process.platform === 'win32')('PyrightServer fallback', () => {
+  test('falls back to bunx with a pinned pyright when pyright-langserver is not installed', async () => {
+    const invoked = await spawnServerWith(PyrightServer, { bunx: recorder('bunx') })
+    expect(invoked).toBe('bunx -p pyright@1.1.414 pyright-langserver --stdio')
+  })
+
+  test('prefers pyright-langserver on PATH over bunx', async () => {
+    const invoked = await spawnServerWith(PyrightServer, { 'pyright-langserver': recorder('path'), 'bunx': recorder('bunx') })
+    expect(invoked).toBe('path --stdio')
+  })
+
+  test('returns undefined with the install hint when bunx is missing', async () => {
+    const emptyDir = await fs.mkdtemp(path.join(os.tmpdir(), 'lsp-fallback-empty-'))
+    const savedPath = process.env.PATH
+    const warn = spyOn(log, 'warn')
+    try {
+      process.env.PATH = emptyDir
+      const handle = await PyrightServer.spawn(emptyDir)
+      process.env.PATH = savedPath
+      expect(handle).toBeUndefined()
+      expect(warn).toHaveBeenCalledWith(expect.anything(), 'pyright not found. Install with: npm install pyright')
+    }
+    finally {
+      warn.mockRestore()
+      process.env.PATH = savedPath
+      await fs.rm(emptyDir, { recursive: true, force: true })
+    }
+  })
+})
+
 describe('VueServer', () => {
   test('has correct id', () => {
     expect(VueServer.id).toBe('vue')