fix(prompts): stop spawning PowerShell for the OS name on Windows

The system prompt's SYSTEM INFORMATION section called os-name on every
request. On Windows its windows-release dependency runs wmic, then
`powershell (Get-CimInstance Win32_OperatingSystem).caption`, through
execaSync with no timeout, on the extension host's only JavaScript thread.

Where wmic has been removed (recent Windows 11 builds), PowerShell starts
on every request. I measured 3 to 4.5 s per call, during which the
extension host is blocked. In one observed freeze, the PowerShell process
did not exit, and the extension host stayed blocked: the request was never
sent, Stop did nothing, and only reloading the window recovered.

On Windows, read the product name from os.version(), which spawns nothing
and costs well under a microsecond. Other platforms keep os-name, which
does not spawn a process there, with the existing fallback.

Fixes #2448

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

Author: LouisClt

src/core/prompts/sections/__tests__/system-info.spec.ts

@@ -12,15 +12,15 @@ vi.mock("../../../../utils/shell", () => ({
 import { getSystemInfoSection } from "../system-info"
 import osName from "os-name"
 
-const mockOsName = osName as unknown as ReturnType<typeof vi.fn>
+const mockOsName = vi.mocked(osName)
 
 describe("getSystemInfoSection", () => {
 	const mockCwd = "/test/workspace"
 	const mockHomeDir = "/home/user"
 
 	beforeEach(() => {
 		vi.spyOn(os, "homedir").mockReturnValue(mockHomeDir)
-		vi.spyOn(os, "platform").mockReturnValue("linux" as any)
+		vi.spyOn(os, "platform").mockReturnValue("linux")
 		vi.spyOn(os, "release").mockReturnValue("5.15.0")
 	})
 
@@ -34,6 +34,7 @@ describe("getSystemInfoSection", () => {
 
 	afterEach(() => {
 		vi.clearAllMocks()
+		vi.restoreAllMocks()
 	})
 
 	it("should return system info with os-name when available", () => {
@@ -47,29 +48,64 @@ describe("getSystemInfoSection", () => {
 		expect(result).toContain(`Current Workspace Directory: ${mockCwd}`)
 	})
 
-	it("should fallback to platform and release when os-name throws error", () => {
-		mockOsName.mockImplementation(() => {
-			throw new Error("Command failed with ENOENT: powershell")
+	it.each([
+		{
+			platform: "linux" as const,
+			release: "5.15.0",
+			makeLookupThrow: () =>
+				mockOsName.mockImplementation(() => {
+					throw new Error("Command failed with ENOENT: powershell")
+				}),
+		},
+		{
+			platform: "win32" as const,
+			release: "10.0.26300",
+			makeLookupThrow: () =>
+				vi.spyOn(os, "version").mockImplementation(() => {
+					throw new Error("uv_os_uname failed")
+				}),
+		},
+	])(
+		"falls back to platform and release when the OS lookup throws on $platform",
+		({ platform, release, makeLookupThrow }) => {
+			vi.spyOn(os, "platform").mockReturnValue(platform)
+			vi.spyOn(os, "release").mockReturnValue(release)
+			makeLookupThrow()
+
+			const result = getSystemInfoSection(mockCwd, policyFor())
+
+			expect(result).toContain(`Operating System: ${platform} ${release}`)
+			expect(result).toContain("Default Shell: /bin/bash")
+			expect(result).toContain(`Home Directory: ${mockHomeDir}`)
+			expect(result).toContain(`Current Workspace Directory: ${mockCwd}`)
+		},
+	)
+
+	describe("on Windows", () => {
+		beforeEach(() => {
+			vi.spyOn(os, "platform").mockReturnValue("win32")
+			vi.spyOn(os, "release").mockReturnValue("10.0.26300")
 		})
 
-		const result = getSystemInfoSection(mockCwd, policyFor())
+		it("reads the product name from os.version() without calling os-name", () => {
+			// os-name runs wmic and PowerShell synchronously on Windows; a PowerShell that never
+			// exits freezes the extension host, so it must not be reached at all.
+			vi.spyOn(os, "version").mockReturnValue("Windows 11 Pro")
 
-		expect(result).toContain("Operating System: linux 5.15.0")
-		expect(result).toContain("Default Shell: /bin/bash")
-		expect(result).toContain(`Home Directory: ${mockHomeDir}`)
-		expect(result).toContain(`Current Workspace Directory: ${mockCwd}`)
-	})
+			const result = getSystemInfoSection(mockCwd, policyFor())
 
-	it("should handle Windows platform in fallback", () => {
-		mockOsName.mockImplementation(() => {
-			throw new Error("Command failed with ENOENT: powershell")
+			expect(result).toContain("Operating System: Windows 11 Pro")
+			expect(mockOsName).not.toHaveBeenCalled()
 		})
-		vi.spyOn(os, "platform").mockReturnValue("win32" as any)
-		vi.spyOn(os, "release").mockReturnValue("10.0.19043")
 
-		const result = getSystemInfoSection(mockCwd, policyFor())
+		it("falls back to platform and release when os.version() is empty", () => {
+			vi.spyOn(os, "version").mockReturnValue("")
 
-		expect(result).toContain("Operating System: win32 10.0.19043")
+			const result = getSystemInfoSection(mockCwd, policyFor())
+
+			expect(result).toContain("Operating System: win32 10.0.26300")
+			expect(mockOsName).not.toHaveBeenCalled()
+		})
 	})
 
 	it("omits the terminal sentence when execute_command is absent", () => {

src/core/prompts/sections/system-info.ts

@@ -5,6 +5,28 @@ import { getShell } from "../../../utils/shell"
 
 import type { EffectiveToolPolicy } from "../tools/effective-tool-policy"
 
+/**
+ * Describes the host operating system for the system prompt.
+ *
+ * Windows bypasses `os-name`: its `windows-release` dependency runs `wmic`, then PowerShell,
+ * through `execaSync` with no timeout. This section is built for every request, so that call
+ * blocks the extension host for as long as the process runs. `os.version()` reads the product
+ * name without starting a process.
+ */
+function getOsInfo(): string {
+	const fallback = `${os.platform()} ${os.release()}`
+
+	try {
+		if (os.platform() === "win32") {
+			return os.version() || fallback
+		}
+
+		return osName()
+	} catch {
+		return fallback
+	}
+}
+
 /**
  * Builds the SYSTEM INFORMATION section of the system prompt.
  *
@@ -16,16 +38,7 @@ import type { EffectiveToolPolicy } from "../tools/effective-tool-policy"
  * @param policy The request's effective tool policy.
  */
 export function getSystemInfoSection(cwd: string, policy: EffectiveToolPolicy): string {
-	// Try to get detailed OS name, fall back to basic info if it fails
-	let osInfo: string
-	try {
-		osInfo = osName()
-	} catch {
-		// Fallback when os-name fails (e.g., PowerShell not available on Windows)
-		const platform = os.platform()
-		const release = os.release()
-		osInfo = `${platform} ${release}`
-	}
+	const osInfo = getOsInfo()
 
 	const executeCommandAvailable = policy.tools.has("execute_command")
 

src/eslint-suppressions.json

@@ -644,11 +644,6 @@
 			"count": 55
 		}
 	},
-	"core/prompts/sections/__tests__/system-info.spec.ts": {
-		"@typescript-eslint/no-explicit-any": {
-			"count": 2
-		}
-	},
 	"core/prompts/tools/__tests__/filter-tools-for-mode.spec.ts": {
 		"@typescript-eslint/no-explicit-any": {
 			"count": 14