chore(code-mode): remove dead acpx code paths and stale copy

Code mode now runs through the code_agent_run tool (owning the ACP client), so the
legacy acpx shell-out paths are dead. Remove them:

- core: envForCommand (acpx-only CLAUDE_CODE_EXECUTABLE injection) from
  executeCommand; getCodeModeCommandLabel (acpx run-status label).
- renderer: the acpx-detection "switch agent / auto-flip the code-mode chip" flow —
  App.tsx executeCommand detection, the permission-request onSwitchAgent button +
  badge, and the composer's code-mode-detected listener.
- copy: Settings -> Code Mode and the code-with-agents skill summary no longer
  mention acpx; tidy stale comments (claude-exec, command-executor).

No behavior change for code mode; the general executeCommand tool is unaffected.

apps/x/packages/core/src/application/assistant/skills/index.ts

@@ -99,7 +99,7 @@ const definitions: SkillDefinition[] = [
   {
     id: "code-with-agents",
     title: "Code with Agents",
-    summary: "Write code, build projects, create scripts, or fix bugs by delegating to Claude Code or Codex via acpx.",
+    summary: "Write code, build projects, create scripts, or fix bugs by delegating to Claude Code or Codex.",
     content: codeWithAgentsSkill,
   },
   {

apps/x/packages/core/src/application/lib/builtin-tools.ts

@@ -15,7 +15,6 @@ import { executeAction as executeComposioAction, isConfigured as isComposioConfi
 import { CURATED_TOOLKITS, CURATED_TOOLKIT_SLUGS } from "@x/shared/dist/composio.js";
 import { BrowserControlInputSchema, type BrowserControlInput } from "@x/shared/dist/browser-control.js";
 import { BackgroundTaskSchema, TriggersSchema } from "@x/shared/dist/background-task.js";
-import { resolveClaudeExeOnWindows } from "../../code-mode/acp/claude-exec.js";
 import type { CodeModeManager } from "../../code-mode/acp/manager.js";
 import type { CodePermissionRegistry } from "../../code-mode/acp/permission-registry.js";
 import { ICodeModeConfigRepo } from "../../code-mode/repo.js";
@@ -94,14 +93,6 @@ const LLMPARSE_MIME_TYPES: Record<string, string> = {
     '.tiff': 'image/tiff',
 };
 
-function envForCommand(command: string): NodeJS.ProcessEnv | undefined {
-    if (process.platform !== 'win32') return undefined;
-    if (!/\bacpx\b/.test(command)) return undefined;
-    if (process.env.CLAUDE_CODE_EXECUTABLE) return undefined;
-    const exe = resolveClaudeExeOnWindows();
-    if (!exe) return undefined;
-    return { ...process.env, CLAUDE_CODE_EXECUTABLE: exe };
-}
 
 export const BuiltinTools: z.infer<typeof BuiltinToolsSchema> = {
     loadSkill: {
@@ -763,14 +754,11 @@ export const BuiltinTools: z.infer<typeof BuiltinToolsSchema> = {
                 //     };
                 // }
 
-                const envOverride = envForCommand(command);
-
                 // Use abortable version when we have a signal
                 if (ctx?.signal) {
                     const { promise, process: proc } = executeCommandAbortable(command, {
                         cwd: workingDir,
                         signal: ctx.signal,
-                        env: envOverride,
                         onData: (chunk: string) => {
                             ctx.publish({
                                 runId: ctx.runId,
@@ -800,7 +788,7 @@ export const BuiltinTools: z.infer<typeof BuiltinToolsSchema> = {
                 }
 
                 // Fallback to original for backward compatibility
-                const result = await executeCommand(command, { cwd: workingDir, env: envOverride });
+                const result = await executeCommand(command, { cwd: workingDir });
 
                 return {
                     success: result.exitCode === 0,

apps/x/packages/core/src/application/lib/command-executor.ts

@@ -80,7 +80,7 @@ export async function executeCommand(
     cwd?: string;
     timeout?: number; // timeout in milliseconds
     maxBuffer?: number; // max buffer size in bytes
-    env?: NodeJS.ProcessEnv; // override environment (e.g. CLAUDE_CODE_EXECUTABLE for acpx)
+    env?: NodeJS.ProcessEnv; // override environment
   }
 ): Promise<CommandResult> {
   try {

apps/x/packages/core/src/code-mode/acp/claude-exec.ts

@@ -5,7 +5,7 @@ import { commonInstallPaths } from '../status.js';
 
 // Windows-only: Node refuses to spawn `.cmd` files without `shell: true` (EINVAL),
 // and the Claude ACP adapter spawns its executable directly. So we pre-resolve
-// claude's real `.exe` from the npm-shim layout. Also used by the legacy acpx path.
+// claude's real `.exe` from the npm-shim layout. Used by resolveClaudeExecutable below.
 export function resolveClaudeExeOnWindows(): string | undefined {
     // Candidate dirs = everything on PATH, plus well-known npm/pnpm/volta global
     // bin dirs. Electron's runtime PATH can omit these even when the user's shell