fix(utils): support PowerShell as custom shellPath

packages/utils/CHANGELOG.md

@@ -2,6 +2,10 @@
 
 ## [Unreleased]
 
+### Fixed
+
+- Support PowerShell (`powershell.exe` / `pwsh`) as a custom `shellPath`: spawn paths now pass `-NoLogo -Command` (plus `-NoProfile` under `PI_BASH_NO_LOGIN`) instead of the POSIX `-l -c` pair, which PowerShell rejected with `The term '-l' is not recognized`.
+
 ## [17.2.9] - 2026-08-05
 
 ### Added

packages/utils/src/procmgr.ts

@@ -50,12 +50,19 @@ function buildSpawnEnv(shell: string): Record<string, string> {
 
 /**
  * Get shell args for the resolved shell.
- * cmd.exe takes `/c`; POSIX shells take `-c`, with `-l` unless
- * PI_BASH_NO_LOGIN / CLAUDE_BASH_NO_LOGIN is set.
+ * cmd.exe takes `/c`; PowerShell (powershell.exe / pwsh) takes
+ * `-NoLogo -Command`, with `-NoProfile` when PI_BASH_NO_LOGIN /
+ * CLAUDE_BASH_NO_LOGIN is set (profile scripts are PowerShell's login-shell
+ * analog); POSIX shells take `-c`, with `-l` unless the same env is set.
+ *
+ * Exported for tests; `env` overrides the process env gate.
  */
-function getShellArgs(shell: string): string[] {
+export function getShellArgs(shell: string, env: Record<string, string | undefined> = $env): string[] {
 	if (isCmdShell(shell)) return ["/c"];
-	const noLogin = $env.PI_BASH_NO_LOGIN || $env.CLAUDE_BASH_NO_LOGIN;
+	const noLogin = env.PI_BASH_NO_LOGIN || env.CLAUDE_BASH_NO_LOGIN;
+	if (isPowerShell(shell)) {
+		return noLogin ? ["-NoLogo", "-NoProfile", "-Command"] : ["-NoLogo", "-Command"];
+	}
 	return noLogin ? ["-c"] : ["-l", "-c"];
 }
 
@@ -65,6 +72,16 @@ export function isCmdShell(shell: string): boolean {
 	return basename === "cmd.exe" || basename === "cmd";
 }
 
+/**
+ * Whether the shell is Windows PowerShell or PowerShell Core (pwsh). Spawn
+ * paths must use `-Command`: passing the POSIX `-l -c` pair makes PowerShell
+ * parse `-l` as the command and fail with `The term '-l' is not recognized`.
+ */
+export function isPowerShell(shell: string): boolean {
+	const basename = shell.replace(/\\/g, "/").split("/").pop()?.toLowerCase();
+	return basename === "powershell.exe" || basename === "powershell" || basename === "pwsh.exe" || basename === "pwsh";
+}
+
 /**
  * Get shell prefix for wrapping commands (profilers, strace, etc.).
  */

packages/utils/test/procmgr.test.ts

@@ -3,7 +3,7 @@ import * as fs from "node:fs";
 import * as os from "node:os";
 import * as path from "node:path";
 import { getAgentDir, MAIN_CONFIG_FILENAMES } from "../src/dirs";
-import { getShellConfig, resolveWindowsShell } from "../src/procmgr";
+import { getShellArgs, getShellConfig, resolveWindowsShell } from "../src/procmgr";
 
 describe("getShellConfig", () => {
 	it("directs invalid custom shell paths to the canonical config file", () => {
@@ -15,6 +15,30 @@ describe("getShellConfig", () => {
 	});
 });
 
+describe("getShellArgs", () => {
+	it("uses -Command for PowerShell shells instead of the POSIX -l -c pair", () => {
+		// `powershell -l -c <cmd>` parses `-l` as the command and fails with
+		// `The term '-l' is not recognized`, breaking every spawn path for a
+		// shellPath pointed at PowerShell.
+		expect(getShellArgs("C:\\Windows\\System32\\WindowsPowerShell\\v1.0\\powershell.exe", {})).toEqual([
+			"-NoLogo",
+			"-Command",
+		]);
+		expect(getShellArgs("C:\\Program Files\\PowerShell\\7\\pwsh.exe", {})).toEqual(["-NoLogo", "-Command"]);
+		expect(getShellArgs("/usr/bin/pwsh", {})).toEqual(["-NoLogo", "-Command"]);
+	});
+
+	it("maps the no-login env gate to -NoProfile for PowerShell", () => {
+		expect(getShellArgs("pwsh.exe", { PI_BASH_NO_LOGIN: "1" })).toEqual(["-NoLogo", "-NoProfile", "-Command"]);
+	});
+
+	it("keeps cmd.exe and POSIX shell args unchanged", () => {
+		expect(getShellArgs("C:\\Windows\\System32\\cmd.exe", {})).toEqual(["/c"]);
+		expect(getShellArgs("/bin/bash", {})).toEqual(["-l", "-c"]);
+		expect(getShellArgs("/bin/bash", { PI_BASH_NO_LOGIN: "1" })).toEqual(["-c"]);
+	});
+});
+
 describe("resolveWindowsShell", () => {
 	const tempDirs: string[] = [];