fix(lsp): remove unreliable Windows binary availability check

The isBinaryAvailableOnWindows() function used spawnSync("where")

which fails even when the binary IS on PATH, causing false negatives.

Removed the redundant pre-check and let nodeSpawn handle binary

resolution naturally with proper OS-level error messages.

Fixes #1805

src/tools/lsp/lsp-process.test.ts

@@ -0,0 +1,37 @@
+import { mkdtempSync, rmSync } from "node:fs"
+import { tmpdir } from "node:os"
+import { join } from "node:path"
+
+import { describe, expect, it, spyOn } from "bun:test"
+
+describe("spawnProcess", () => {
+  it("proceeds to node spawn on Windows when command is available", async () => {
+    // #given
+    const originalPlatform = process.platform
+    const rootDir = mkdtempSync(join(tmpdir(), "lsp-process-test-"))
+    const childProcess = await import("node:child_process")
+    const nodeSpawnSpy = spyOn(childProcess, "spawn")
+
+    try {
+      Object.defineProperty(process, "platform", { value: "win32" })
+      const { spawnProcess } = await import("./lsp-process")
+
+      // #when
+      let result: ReturnType<typeof spawnProcess> | null = null
+      expect(() => {
+        result = spawnProcess(["node", "--version"], {
+          cwd: rootDir,
+          env: process.env,
+        })
+      }).not.toThrow(/Binary 'node' not found/)
+
+      // #then
+      expect(nodeSpawnSpy).toHaveBeenCalled()
+      expect(result).not.toBeNull()
+    } finally {
+      Object.defineProperty(process, "platform", { value: originalPlatform })
+      nodeSpawnSpy.mockRestore()
+      rmSync(rootDir, { recursive: true, force: true })
+    }
+  })
+})

src/tools/lsp/lsp-process.ts

@@ -1,5 +1,5 @@
 import { spawn as bunSpawn } from "bun"
-import { spawn as nodeSpawn, spawnSync, type ChildProcess } from "node:child_process"
+import { spawn as nodeSpawn, type ChildProcess } from "node:child_process"
 import { existsSync, statSync } from "fs"
 import { log } from "../../shared/logger"
 // Bun spawn segfaults on Windows (oven-sh/bun#25798) — unfixed as of v1.3.8+
@@ -21,24 +21,6 @@ export function validateCwd(cwd: string): { valid: boolean; error?: string } {
     return { valid: false, error: `Cannot access working directory: ${cwd} (${err instanceof Error ? err.message : String(err)})` }
   }
 }
-function isBinaryAvailableOnWindows(command: string): boolean {
-  if (process.platform !== "win32") return true
-
-  if (command.includes("/") || command.includes("\\")) {
-    return existsSync(command)
-  }
-
-  try {
-    const result = spawnSync("where", [command], {
-      shell: true,
-      windowsHide: true,
-      timeout: 5000,
-    })
-    return result.status === 0
-  } catch {
-    return true
-  }
-}
 interface StreamReader {
   read(): Promise<{ done: boolean; value: Uint8Array | undefined }>
 }
@@ -158,13 +140,6 @@ export function spawnProcess(
   }
   if (shouldUseNodeSpawn()) {
     const [cmd, ...args] = command
-    if (!isBinaryAvailableOnWindows(cmd)) {
-      throw new Error(
-        `[LSP] Binary '${cmd}' not found on Windows. ` +
-          `Ensure the LSP server is installed and available in PATH. ` +
-          `For npm packages, try: npm install -g ${cmd}`
-      )
-    }
     log("[LSP] Using Node.js child_process on Windows to avoid Bun spawn segfault")
     const proc = nodeSpawn(cmd, args, {
       cwd: options.cwd,