fix(terminal): read host IDE shell from CLINE_TERMINAL_SHELL_PATH instead of COMSPEC/SHELL

Host integrations (the JetBrains plugin) forwarded the user's IDE terminal
shell by overriding COMSPEC on Windows. COMSPEC is an OS-level contract that
must keep pointing at cmd.exe: cross-spawn, Node's shell:true, and npm .cmd
shims all pass cmd-style /d /s /c arguments to whatever it references.
With IntelliJ's default terminal shell (PowerShell) forwarded as COMSPEC,
every .cmd-shimmed child process spawned by cline-core broke - e.g. the
Claude Code provider failed with:
  /d : The term '/d' is not recognized ...

Introduce a dedicated CLINE_TERMINAL_SHELL_PATH env var that hosts can set
safely. It takes precedence in getShell() - which the SDK backend's
backgroundExec path resolves through via getShellForProfile() in
vscode-run-commands-tool - while COMSPEC/SHELL keep their OS semantics.
(The standalone terminal previously patched here was removed on main
by #11972; backgroundExec is now the only standalone exec path.)

Fixes #11290
(cherry picked from commit 602097477 on legacy-extension)

apps/vscode/src/test/shell.test.ts

@@ -15,7 +15,7 @@ const osMock = () => ({ ...osMockNamespace, default: osMockNamespace })
 mock.module("os", osMock)
 mock.module("node:os", osMock)
 
-import { getShell } from "@utils/shell"
+import { getShell, HOST_SHELL_ENV_VAR } from "@utils/shell"
 
 describe("Shell Detection Tests", () => {
 	let originalPlatform: string
@@ -49,6 +49,7 @@ describe("Shell Detection Tests", () => {
 		// Clear environment variables for a clean test
 		delete process.env.SHELL
 		delete process.env.COMSPEC
+		delete process.env[HOST_SHELL_ENV_VAR]
 
 		// Default userInfo() mock
 		userInfoImpl = (() => ({ shell: null })) as any
@@ -62,6 +63,42 @@ describe("Shell Detection Tests", () => {
 		userInfoImpl = originalUserInfo
 	})
 
+	// --------------------------------------------------------------------------
+	// Host-Provided Shell Override (CLINE_TERMINAL_SHELL_PATH)
+	// --------------------------------------------------------------------------
+	describe("Host-Provided Shell Override", () => {
+		it("wins over VS Code config, userInfo, and COMSPEC on Windows", () => {
+			Object.defineProperty(process, "platform", { value: "win32" })
+			mockVsCodeConfig("windows", "PowerShell", {
+				PowerShell: { path: "C:\\Program Files\\PowerShell\\7\\pwsh.exe" },
+			})
+			userInfoImpl = (() => ({ shell: "C:\\Custom\\PowerShell.exe" })) as any
+			process.env.COMSPEC = "C:\\Windows\\System32\\cmd.exe"
+			process.env[HOST_SHELL_ENV_VAR] = "C:\\Windows\\System32\\WindowsPowerShell\\v1.0\\powershell.exe"
+
+			expect(getShell()).to.equal("C:\\Windows\\System32\\WindowsPowerShell\\v1.0\\powershell.exe")
+		})
+
+		it("wins over userInfo and SHELL on POSIX", () => {
+			Object.defineProperty(process, "platform", { value: "darwin" })
+			vscode.workspace.getConfiguration = () => ({ get: () => undefined }) as any
+			userInfoImpl = (() => ({ shell: "/bin/zsh" })) as any
+			process.env.SHELL = "/bin/bash"
+			process.env[HOST_SHELL_ENV_VAR] = "/usr/local/bin/fish"
+
+			expect(getShell()).to.equal("/usr/local/bin/fish")
+		})
+
+		it("is ignored when blank", () => {
+			Object.defineProperty(process, "platform", { value: "darwin" })
+			vscode.workspace.getConfiguration = () => ({ get: () => undefined }) as any
+			userInfoImpl = (() => ({ shell: "/bin/zsh" })) as any
+			process.env[HOST_SHELL_ENV_VAR] = "   "
+
+			expect(getShell()).to.equal("/bin/zsh")
+		})
+	})
+
 	// --------------------------------------------------------------------------
 	// Windows Shell Detection
 	// --------------------------------------------------------------------------

apps/vscode/src/utils/shell.ts

@@ -48,6 +48,28 @@ interface LinuxTerminalProfile {
 
 type LinuxTerminalProfiles = Record<string, LinuxTerminalProfile>
 
+// -----------------------------------------------------
+// 0) Host-Provided Shell Override
+// -----------------------------------------------------
+
+/**
+ * Environment variable through which host integrations (e.g. the JetBrains
+ * plugin) forward the user's IDE terminal profile shell to cline-core.
+ *
+ * A dedicated variable is used instead of overriding COMSPEC/SHELL because
+ * COMSPEC is an OS-level contract that must keep pointing at cmd.exe:
+ * cross-spawn, Node's `shell: true`, and npm `.cmd` shims all pass cmd-style
+ * `/d /s /c` arguments to whatever COMSPEC references. Overriding it with
+ * PowerShell breaks every such child process (see cline/cline#11290).
+ */
+export const HOST_SHELL_ENV_VAR = "CLINE_TERMINAL_SHELL_PATH"
+
+/** Returns the shell explicitly forwarded by the host IDE, or null. */
+export function getHostProvidedShell(): string | null {
+	const shell = process.env[HOST_SHELL_ENV_VAR]?.trim()
+	return shell || null
+}
+
 // -----------------------------------------------------
 // 1) VS Code Terminal Configuration Helpers
 // -----------------------------------------------------
@@ -305,6 +327,12 @@ export function getShellForProfile(profileId: string): string {
 // -----------------------------------------------------
 
 export function getShell(): string {
+	// 0. A shell explicitly forwarded by the host IDE wins over detection.
+	const hostShell = getHostProvidedShell()
+	if (hostShell) {
+		return hostShell
+	}
+
 	// 1. Check VS Code config first.
 	if (process.platform === "win32") {
 		// Special logic for Windows