From dbd89d8e3dbf80d249aee2d710e98eb834d5521e Mon Sep 17 00:00:00 2001
From: Jeremy <125112776+Frostbite1536@users.noreply.github.com>
Date: Thu, 26 Mar 2026 19:08:14 -0500
Subject: [PATCH] Claude/windows install compatibility tr di s (#3)
MIME-Version: 1.0
Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: 8bit

* Fix Windows PowerShell 5.1 compatibility in installer

Use $env:PROCESSOR_ARCHITECTURE for arch detection instead of
RuntimeInformation::OSArchitecture which may not be loaded in
every Windows PowerShell 5.1 session. Also fix null-reference
when user PATH environment variable is empty.

https://claude.ai/code/session_01VFiRDM2ZweyacXN5JneVoP

* Fix executable resolution and tar extraction on Windows

resolveExecutable() used `sh -lc "command -v ..."` which doesn't work
on Windows (no sh). Now uses `cmd /c where` on win32. Also make tar
workspace restoration tolerate symlink failures on Windows — .bin/
symlinks can't be created without Developer Mode, but the actual
package directories are extracted fine.

https://claude.ai/code/session_01VFiRDM2ZweyacXN5JneVoP

* Broad Windows compatibility fixes across the codebase

- runtime.ts: Use path.delimiter instead of hardcoded ":" for PATH
  construction — was completely broken on Windows
- executables.ts: Add Windows fallback paths for Chrome, Edge, Brave,
  and Pandoc in Program Files; skip macOS-only paths on win32
- node-version.ts, check-node-version.mjs, bin/feynman.js: Show
  Windows-appropriate install instructions (irm | iex, nodejs.org)
  instead of nvm/curl on win32
- preview.ts: Support winget for pandoc auto-install on Windows, and
  apt on Linux (was macOS/brew only)
- launch.ts: Catch unsupported signal errors on Windows
- README.md: Add Windows PowerShell commands alongside macOS/Linux
  for all install instructions

https://claude.ai/code/session_01VFiRDM2ZweyacXN5JneVoP

* fix: complete windows bootstrap hardening

---------

Co-authored-by: Claude <noreply@anthropic.com>
Co-authored-by: Advait Paliwal <advaitspaliwal@gmail.com>
---
 README.md                      | 24 +++++++++++++
 bin/feynman.js                 | 13 +++++---
 scripts/check-node-version.mjs |  9 +++--
 scripts/install/install.ps1    | 30 +++++++++++++----
 scripts/patch-embedded-pi.mjs  | 29 ++++++++++++----
 src/pi/launch.ts               |  6 +++-
 src/pi/runtime.ts              | 13 +++++---
 src/setup/preview.ts           | 34 +++++++++++++++----
 src/system/executables.ts      | 61 +++++++++++++++++++++-------------
 src/system/node-version.ts     |  9 +++--
 tests/pi-runtime.test.ts       | 40 ++++++++++++++++------
 website/public/install.ps1     | 30 +++++++++++++----
 12 files changed, 226 insertions(+), 72 deletions(-)

diff --git a/README.md b/README.md
index 539850a..081ce22 100644
--- a/README.md
+++ b/README.md
@@ -13,28 +13,52 @@
 
 ### Installation
 
+**macOS / Linux:**
+
 ```bash
 curl -fsSL https://feynman.is/install | bash
 ```
 
+**Windows (PowerShell):**
+
+```powershell
+irm https://feynman.is/install.ps1 | iex
+```
+
 If you install via `pnpm` or `bun` instead of the standalone bundle, Feynman requires Node.js `20.18.1` or newer.
 
 ### Skills Only
 
 If you want just the research skills without the full terminal app:
 
+**macOS / Linux:**
+
 ```bash
 curl -fsSL https://feynman.is/install-skills | bash
 ```
 
+**Windows (PowerShell):**
+
+```powershell
+irm https://feynman.is/install-skills.ps1 | iex
+```
+
 That installs the skill library into `~/.codex/skills/feynman`.
 
 For a repo-local install instead:
 
+**macOS / Linux:**
+
 ```bash
 curl -fsSL https://feynman.is/install-skills | bash -s -- --repo
 ```
 
+**Windows (PowerShell):**
+
+```powershell
+& ([scriptblock]::Create((irm https://feynman.is/install-skills.ps1))) -Scope Repo
+```
+
 That installs into `.agents/skills/feynman` under the current repository.
 
 ---
diff --git a/bin/feynman.js b/bin/feynman.js
index 3d77cca..9c9111f 100755
--- a/bin/feynman.js
+++ b/bin/feynman.js
@@ -17,10 +17,15 @@ function compareNodeVersions(left, right) {
 }
 
 if (compareNodeVersions(parseNodeVersion(process.versions.node), parseNodeVersion(MIN_NODE_VERSION)) < 0) {
+  const isWindows = process.platform === "win32";
   console.error(`feynman requires Node.js ${MIN_NODE_VERSION} or later (detected ${process.versions.node}).`);
-  console.error("Switch to Node 20 with `nvm install 20 && nvm use 20`, or use the standalone installer:");
-  console.error("curl -fsSL https://feynman.is/install | bash");
+  console.error(isWindows
+    ? "Install a newer Node.js from https://nodejs.org, or use the standalone installer:"
+    : "Switch to Node 20 with `nvm install 20 && nvm use 20`, or use the standalone installer:");
+  console.error(isWindows
+    ? "irm https://feynman.is/install.ps1 | iex"
+    : "curl -fsSL https://feynman.is/install | bash");
   process.exit(1);
 }
-await import("../scripts/patch-embedded-pi.mjs");
-await import("../dist/index.js");
+await import(new URL("../scripts/patch-embedded-pi.mjs", import.meta.url).href);
+await import(new URL("../dist/index.js", import.meta.url).href);
diff --git a/scripts/check-node-version.mjs b/scripts/check-node-version.mjs
index 8c8cf57..8b4170c 100644
--- a/scripts/check-node-version.mjs
+++ b/scripts/check-node-version.mjs
@@ -20,10 +20,15 @@ function isSupportedNodeVersion(version = process.versions.node) {
 }
 
 function getUnsupportedNodeVersionLines(version = process.versions.node) {
+	const isWindows = process.platform === "win32";
 	return [
 		`feynman requires Node.js ${MIN_NODE_VERSION} or later (detected ${version}).`,
-		"Switch to Node 20 with `nvm install 20 && nvm use 20`, or use the standalone installer:",
-		"curl -fsSL https://feynman.is/install | bash",
+		isWindows
+			? "Install a newer Node.js from https://nodejs.org, or use the standalone installer:"
+			: "Switch to Node 20 with `nvm install 20 && nvm use 20`, or use the standalone installer:",
+		isWindows
+			? "irm https://feynman.is/install.ps1 | iex"
+			: "curl -fsSL https://feynman.is/install | bash",
 	];
 }
 
diff --git a/scripts/install/install.ps1 b/scripts/install/install.ps1
index cd06e40..c75b672 100644
--- a/scripts/install/install.ps1
+++ b/scripts/install/install.ps1
@@ -73,12 +73,26 @@ function Resolve-ReleaseMetadata {
 }
 
 function Get-ArchSuffix {
-  $arch = [System.Runtime.InteropServices.RuntimeInformation]::OSArchitecture
-  switch ($arch.ToString()) {
-    "X64" { return "x64" }
-    "Arm64" { return "arm64" }
-    default { throw "Unsupported architecture: $arch" }
+  # Prefer PROCESSOR_ARCHITECTURE which is always available on Windows.
+  # RuntimeInformation::OSArchitecture requires .NET 4.7.1+ and may not
+  # be loaded in every Windows PowerShell 5.1 session.
+  $envArch = $env:PROCESSOR_ARCHITECTURE
+  if ($envArch) {
+    switch ($envArch) {
+      "AMD64" { return "x64" }
+      "ARM64" { return "arm64" }
+    }
   }
+
+  try {
+    $arch = [System.Runtime.InteropServices.RuntimeInformation]::OSArchitecture
+    switch ($arch.ToString()) {
+      "X64" { return "x64" }
+      "Arm64" { return "arm64" }
+    }
+  } catch {}
+
+  throw "Unsupported architecture: $envArch"
 }
 
 $archSuffix = Get-ArchSuffix
@@ -134,7 +148,11 @@ Workarounds:
 "@ | Set-Content -Path $shimPath -Encoding ASCII
 
   $currentUserPath = [Environment]::GetEnvironmentVariable("Path", "User")
-  if (-not $currentUserPath.Split(';').Contains($installBinDir)) {
+  $alreadyOnPath = $false
+  if ($currentUserPath) {
+    $alreadyOnPath = $currentUserPath.Split(';') -contains $installBinDir
+  }
+  if (-not $alreadyOnPath) {
     $updatedPath = if ([string]::IsNullOrWhiteSpace($currentUserPath)) {
       $installBinDir
     } else {
diff --git a/scripts/patch-embedded-pi.mjs b/scripts/patch-embedded-pi.mjs
index 74afae5..22eb29a 100644
--- a/scripts/patch-embedded-pi.mjs
+++ b/scripts/patch-embedded-pi.mjs
@@ -139,12 +139,18 @@ function restorePackagedWorkspace(packageSpecs) {
 		timeout: 300000,
 	});
 
+	// On Windows, tar may exit non-zero due to symlink creation failures in
+	// .bin/ directories. These are non-fatal — check whether the actual
+	// package directories were extracted successfully.
+	const packagesPresent = packageSpecs.every((spec) => existsSync(resolve(workspaceRoot, parsePackageName(spec))));
+	if (packagesPresent) return true;
+
 	if (result.status !== 0) {
 		if (result.stderr?.length) process.stderr.write(result.stderr);
 		return false;
 	}
 
-	return packageSpecs.every((spec) => existsSync(resolve(workspaceRoot, parsePackageName(spec))));
+	return false;
 }
 
 function refreshPackagedWorkspace(packageSpecs) {
@@ -156,12 +162,18 @@ function resolveExecutable(name, fallbackPaths = []) {
 		if (existsSync(candidate)) return candidate;
 	}
 
-	const result = spawnSync("sh", ["-lc", `command -v ${name}`], {
-		encoding: "utf8",
-		stdio: ["ignore", "pipe", "ignore"],
-	});
+	const isWindows = process.platform === "win32";
+	const result = isWindows
+		? spawnSync("cmd", ["/c", `where ${name}`], {
+				encoding: "utf8",
+				stdio: ["ignore", "pipe", "ignore"],
+			})
+		: spawnSync("sh", ["-lc", `command -v ${name}`], {
+				encoding: "utf8",
+				stdio: ["ignore", "pipe", "ignore"],
+			});
 	if (result.status === 0) {
-		const resolved = result.stdout.trim();
+		const resolved = result.stdout.trim().split(/\r?\n/)[0];
 		if (resolved) return resolved;
 	}
 	return null;
@@ -541,6 +553,11 @@ if (alphaHubAuthPath && existsSync(alphaHubAuthPath)) {
 	if (source.includes(oldError)) {
 		source = source.replace(oldError, newError);
 	}
+	const brokenWinOpen = "else if (plat === 'win32') execSync(`start \"${url}\"`);";
+	const fixedWinOpen = "else if (plat === 'win32') execSync(`cmd /c start \"\" \"${url}\"`);";
+	if (source.includes(brokenWinOpen)) {
+		source = source.replace(brokenWinOpen, fixedWinOpen);
+	}
 	writeFileSync(alphaHubAuthPath, source, "utf8");
 }
 
diff --git a/src/pi/launch.ts b/src/pi/launch.ts
index e2c35cf..0d8bdc1 100644
--- a/src/pi/launch.ts
+++ b/src/pi/launch.ts
@@ -29,7 +29,11 @@ export async function launchPiChat(options: PiRuntimeOptions): Promise<void> {
 		child.on("error", reject);
 		child.on("exit", (code, signal) => {
 			if (signal) {
-				process.kill(process.pid, signal);
+				try {
+					process.kill(process.pid, signal);
+				} catch {
+					process.exitCode = 1;
+				}
 				return;
 			}
 			process.exitCode = code ?? 0;
diff --git a/src/pi/runtime.ts b/src/pi/runtime.ts
index 9a85aa3..9208854 100644
--- a/src/pi/runtime.ts
+++ b/src/pi/runtime.ts
@@ -1,5 +1,5 @@
 import { existsSync, readFileSync } from "node:fs";
-import { dirname, resolve } from "node:path";
+import { delimiter, dirname, resolve } from "node:path";
 
 import {
 	BROWSER_FALLBACK_PATHS,
@@ -83,11 +83,11 @@ export function buildPiEnv(options: PiRuntimeOptions): NodeJS.ProcessEnv {
 
 	const currentPath = process.env.PATH ?? "";
 	const binEntries = [paths.nodeModulesBinPath, resolve(paths.piWorkspaceNodeModulesPath, ".bin"), feynmanNpmBinPath];
-	const binPath = binEntries.join(":");
+	const binPath = binEntries.join(delimiter);
 
 	return {
 		...process.env,
-		PATH: `${binPath}:${currentPath}`,
+		PATH: `${binPath}${delimiter}${currentPath}`,
 		FEYNMAN_VERSION: options.feynmanVersion,
 		FEYNMAN_SESSION_DIR: options.sessionDir,
 		FEYNMAN_MEMORY_DIR: resolve(dirname(options.feynmanAgentDir), "memory"),
@@ -100,7 +100,10 @@ export function buildPiEnv(options: PiRuntimeOptions): NodeJS.ProcessEnv {
 		MERMAID_CLI_PATH: process.env.MERMAID_CLI_PATH ?? resolveExecutable("mmdc", MERMAID_FALLBACK_PATHS),
 		PUPPETEER_EXECUTABLE_PATH:
 			process.env.PUPPETEER_EXECUTABLE_PATH ?? resolveExecutable("google-chrome", BROWSER_FALLBACK_PATHS),
-		NPM_CONFIG_PREFIX: process.env.NPM_CONFIG_PREFIX ?? feynmanNpmPrefixPath,
-		npm_config_prefix: process.env.npm_config_prefix ?? feynmanNpmPrefixPath,
+		// Always pin npm's global prefix to the Feynman workspace. npm injects
+		// lowercase config vars into child processes, which would otherwise leak
+		// the caller's global prefix into Pi.
+		NPM_CONFIG_PREFIX: feynmanNpmPrefixPath,
+		npm_config_prefix: feynmanNpmPrefixPath,
 	};
 }
diff --git a/src/setup/preview.ts b/src/setup/preview.ts
index df06bfe..788d9bd 100644
--- a/src/setup/preview.ts
+++ b/src/setup/preview.ts
@@ -13,13 +13,35 @@ export function setupPreviewDependencies(): PreviewSetupResult {
 		return { status: "ready", message: `pandoc already installed at ${pandocPath}` };
 	}
 
-	const brewPath = resolveExecutable("brew", BREW_FALLBACK_PATHS);
-	if (process.platform === "darwin" && brewPath) {
-		const result = spawnSync(brewPath, ["install", "pandoc"], { stdio: "inherit" });
-		if (result.status !== 0) {
-			throw new Error("Failed to install pandoc via Homebrew.");
+	if (process.platform === "darwin") {
+		const brewPath = resolveExecutable("brew", BREW_FALLBACK_PATHS);
+		if (brewPath) {
+			const result = spawnSync(brewPath, ["install", "pandoc"], { stdio: "inherit" });
+			if (result.status !== 0) {
+				throw new Error("Failed to install pandoc via Homebrew.");
+			}
+			return { status: "installed", message: "Preview dependency installed: pandoc" };
+		}
+	}
+
+	if (process.platform === "win32") {
+		const wingetPath = resolveExecutable("winget");
+		if (wingetPath) {
+			const result = spawnSync(wingetPath, ["install", "--id", "JohnMacFarlane.Pandoc", "-e"], { stdio: "inherit" });
+			if (result.status === 0) {
+				return { status: "installed", message: "Preview dependency installed: pandoc (via winget)" };
+			}
+		}
+	}
+
+	if (process.platform === "linux") {
+		const aptPath = resolveExecutable("apt-get");
+		if (aptPath) {
+			const result = spawnSync(aptPath, ["install", "-y", "pandoc"], { stdio: "inherit" });
+			if (result.status === 0) {
+				return { status: "installed", message: "Preview dependency installed: pandoc (via apt)" };
+			}
 		}
-		return { status: "installed", message: "Preview dependency installed: pandoc" };
 	}
 
 	return {
diff --git a/src/system/executables.ts b/src/system/executables.ts
index ad2d5a9..b0c3f7f 100644
--- a/src/system/executables.ts
+++ b/src/system/executables.ts
@@ -1,27 +1,36 @@
 import { spawnSync } from "node:child_process";
 import { existsSync } from "node:fs";
 
-export const PANDOC_FALLBACK_PATHS = [
-	"/opt/homebrew/bin/pandoc",
-	"/usr/local/bin/pandoc",
-];
+const isWindows = process.platform === "win32";
+const programFiles = process.env.PROGRAMFILES ?? "C:\\Program Files";
+const localAppData = process.env.LOCALAPPDATA ?? "";
 
-export const BREW_FALLBACK_PATHS = [
-	"/opt/homebrew/bin/brew",
-	"/usr/local/bin/brew",
-];
+export const PANDOC_FALLBACK_PATHS = isWindows
+	? [`${programFiles}\\Pandoc\\pandoc.exe`]
+	: ["/opt/homebrew/bin/pandoc", "/usr/local/bin/pandoc"];
 
-export const BROWSER_FALLBACK_PATHS = [
-	"/Applications/Google Chrome.app/Contents/MacOS/Google Chrome",
-	"/Applications/Chromium.app/Contents/MacOS/Chromium",
-	"/Applications/Brave Browser.app/Contents/MacOS/Brave Browser",
-	"/Applications/Microsoft Edge.app/Contents/MacOS/Microsoft Edge",
-];
+export const BREW_FALLBACK_PATHS = isWindows
+	? []
+	: ["/opt/homebrew/bin/brew", "/usr/local/bin/brew"];
 
-export const MERMAID_FALLBACK_PATHS = [
-	"/opt/homebrew/bin/mmdc",
-	"/usr/local/bin/mmdc",
-];
+export const BROWSER_FALLBACK_PATHS = isWindows
+	? [
+			`${programFiles}\\Google\\Chrome\\Application\\chrome.exe`,
+			`${programFiles} (x86)\\Google\\Chrome\\Application\\chrome.exe`,
+			`${localAppData}\\Google\\Chrome\\Application\\chrome.exe`,
+			`${programFiles}\\Microsoft\\Edge\\Application\\msedge.exe`,
+			`${programFiles}\\BraveSoftware\\Brave-Browser\\Application\\brave.exe`,
+		]
+	: [
+			"/Applications/Google Chrome.app/Contents/MacOS/Google Chrome",
+			"/Applications/Chromium.app/Contents/MacOS/Chromium",
+			"/Applications/Brave Browser.app/Contents/MacOS/Brave Browser",
+			"/Applications/Microsoft Edge.app/Contents/MacOS/Microsoft Edge",
+		];
+
+export const MERMAID_FALLBACK_PATHS = isWindows
+	? []
+	: ["/opt/homebrew/bin/mmdc", "/usr/local/bin/mmdc"];
 
 export function resolveExecutable(name: string, fallbackPaths: string[] = []): string | undefined {
 	for (const candidate of fallbackPaths) {
@@ -30,13 +39,19 @@ export function resolveExecutable(name: string, fallbackPaths: string[] = []): s
 		}
 	}
 
-	const result = spawnSync("sh", ["-lc", `command -v ${name}`], {
-		encoding: "utf8",
-		stdio: ["ignore", "pipe", "ignore"],
-	});
+	const isWindows = process.platform === "win32";
+	const result = isWindows
+		? spawnSync("cmd", ["/c", `where ${name}`], {
+				encoding: "utf8",
+				stdio: ["ignore", "pipe", "ignore"],
+			})
+		: spawnSync("sh", ["-lc", `command -v ${name}`], {
+				encoding: "utf8",
+				stdio: ["ignore", "pipe", "ignore"],
+			});
 
 	if (result.status === 0) {
-		const resolved = result.stdout.trim();
+		const resolved = result.stdout.trim().split(/\r?\n/)[0];
 		if (resolved) {
 			return resolved;
 		}
diff --git a/src/system/node-version.ts b/src/system/node-version.ts
index 6842aba..4bd7bb8 100644
--- a/src/system/node-version.ts
+++ b/src/system/node-version.ts
@@ -26,10 +26,15 @@ export function isSupportedNodeVersion(version = process.versions.node): boolean
 }
 
 export function getUnsupportedNodeVersionLines(version = process.versions.node): string[] {
+	const isWindows = process.platform === "win32";
 	return [
 		`feynman requires Node.js ${MIN_NODE_VERSION} or later (detected ${version}).`,
-		"Switch to Node 20 with `nvm install 20 && nvm use 20`, or use the standalone installer:",
-		"curl -fsSL https://feynman.is/install | bash",
+		isWindows
+			? "Install a newer Node.js from https://nodejs.org, or use the standalone installer:"
+			: "Switch to Node 20 with `nvm install 20 && nvm use 20`, or use the standalone installer:",
+		isWindows
+			? "irm https://feynman.is/install.ps1 | iex"
+			: "curl -fsSL https://feynman.is/install | bash",
 	];
 }
 
diff --git a/tests/pi-runtime.test.ts b/tests/pi-runtime.test.ts
index b388d98..1bbca63 100644
--- a/tests/pi-runtime.test.ts
+++ b/tests/pi-runtime.test.ts
@@ -30,6 +30,11 @@ test("buildPiArgs includes configured runtime paths and prompt", () => {
 });
 
 test("buildPiEnv wires Feynman paths into the Pi environment", () => {
+	const previousUppercasePrefix = process.env.NPM_CONFIG_PREFIX;
+	const previousLowercasePrefix = process.env.npm_config_prefix;
+	process.env.NPM_CONFIG_PREFIX = "/tmp/global-prefix";
+	process.env.npm_config_prefix = "/tmp/global-prefix-lower";
+
 	const env = buildPiEnv({
 		appRoot: "/repo/feynman",
 		workingDir: "/workspace",
@@ -38,17 +43,30 @@ test("buildPiEnv wires Feynman paths into the Pi environment", () => {
 		feynmanVersion: "0.1.5",
 	});
 
-	assert.equal(env.FEYNMAN_SESSION_DIR, "/sessions");
-	assert.equal(env.FEYNMAN_BIN_PATH, "/repo/feynman/bin/feynman.js");
-	assert.equal(env.FEYNMAN_MEMORY_DIR, "/home/.feynman/memory");
-	assert.equal(env.FEYNMAN_NPM_PREFIX, "/home/.feynman/npm-global");
-	assert.equal(env.NPM_CONFIG_PREFIX, "/home/.feynman/npm-global");
-	assert.equal(env.npm_config_prefix, "/home/.feynman/npm-global");
-	assert.ok(
-		env.PATH?.startsWith(
-			"/repo/feynman/node_modules/.bin:/repo/feynman/.feynman/npm/node_modules/.bin:/home/.feynman/npm-global/bin:",
-		),
-	);
+	try {
+		assert.equal(env.FEYNMAN_SESSION_DIR, "/sessions");
+		assert.equal(env.FEYNMAN_BIN_PATH, "/repo/feynman/bin/feynman.js");
+		assert.equal(env.FEYNMAN_MEMORY_DIR, "/home/.feynman/memory");
+		assert.equal(env.FEYNMAN_NPM_PREFIX, "/home/.feynman/npm-global");
+		assert.equal(env.NPM_CONFIG_PREFIX, "/home/.feynman/npm-global");
+		assert.equal(env.npm_config_prefix, "/home/.feynman/npm-global");
+		assert.ok(
+			env.PATH?.startsWith(
+				"/repo/feynman/node_modules/.bin:/repo/feynman/.feynman/npm/node_modules/.bin:/home/.feynman/npm-global/bin:",
+			),
+		);
+	} finally {
+		if (previousUppercasePrefix === undefined) {
+			delete process.env.NPM_CONFIG_PREFIX;
+		} else {
+			process.env.NPM_CONFIG_PREFIX = previousUppercasePrefix;
+		}
+		if (previousLowercasePrefix === undefined) {
+			delete process.env.npm_config_prefix;
+		} else {
+			process.env.npm_config_prefix = previousLowercasePrefix;
+		}
+	}
 });
 
 test("resolvePiPaths includes the Promise.withResolvers polyfill path", () => {
diff --git a/website/public/install.ps1 b/website/public/install.ps1
index cd06e40..c75b672 100644
--- a/website/public/install.ps1
+++ b/website/public/install.ps1
@@ -73,12 +73,26 @@ function Resolve-ReleaseMetadata {
 }
 
 function Get-ArchSuffix {
-  $arch = [System.Runtime.InteropServices.RuntimeInformation]::OSArchitecture
-  switch ($arch.ToString()) {
-    "X64" { return "x64" }
-    "Arm64" { return "arm64" }
-    default { throw "Unsupported architecture: $arch" }
+  # Prefer PROCESSOR_ARCHITECTURE which is always available on Windows.
+  # RuntimeInformation::OSArchitecture requires .NET 4.7.1+ and may not
+  # be loaded in every Windows PowerShell 5.1 session.
+  $envArch = $env:PROCESSOR_ARCHITECTURE
+  if ($envArch) {
+    switch ($envArch) {
+      "AMD64" { return "x64" }
+      "ARM64" { return "arm64" }
+    }
   }
+
+  try {
+    $arch = [System.Runtime.InteropServices.RuntimeInformation]::OSArchitecture
+    switch ($arch.ToString()) {
+      "X64" { return "x64" }
+      "Arm64" { return "arm64" }
+    }
+  } catch {}
+
+  throw "Unsupported architecture: $envArch"
 }
 
 $archSuffix = Get-ArchSuffix
@@ -134,7 +148,11 @@ Workarounds:
 "@ | Set-Content -Path $shimPath -Encoding ASCII
 
   $currentUserPath = [Environment]::GetEnvironmentVariable("Path", "User")
-  if (-not $currentUserPath.Split(';').Contains($installBinDir)) {
+  $alreadyOnPath = $false
+  if ($currentUserPath) {
+    $alreadyOnPath = $currentUserPath.Split(';') -contains $installBinDir
+  }
+  if (-not $alreadyOnPath) {
     $updatedPath = if ([string]::IsNullOrWhiteSpace($currentUserPath)) {
       $installBinDir
     } else {