Refactor: shared exec utility, rename CustomMessageRenderer to HookMessageRenderer

- Extract execCommand to src/core/exec.ts, shared by hooks and custom-tools
- Rename CustomMessageRenderer -> HookMessageRenderer
- Rename registerCustomMessageRenderer -> registerMessageRenderer
- Renderer now receives HookMessage instead of CustomMessageEntry
- CustomMessageComponent now has setExpanded() and responds to Ctrl+E toggle
- Re-export ExecOptions/ExecResult from exec.ts for backward compatibility

packages/coding-agent/src/core/exec.ts

@@ -0,0 +1,104 @@
+/**
+ * Shared command execution utilities for hooks and custom tools.
+ */
+
+import { spawn } from "node:child_process";
+
+/**
+ * Options for executing shell commands.
+ */
+export interface ExecOptions {
+	/** AbortSignal to cancel the command */
+	signal?: AbortSignal;
+	/** Timeout in milliseconds */
+	timeout?: number;
+	/** Working directory */
+	cwd?: string;
+}
+
+/**
+ * Result of executing a shell command.
+ */
+export interface ExecResult {
+	stdout: string;
+	stderr: string;
+	code: number;
+	killed: boolean;
+}
+
+/**
+ * Execute a shell command and return stdout/stderr/code.
+ * Supports timeout and abort signal.
+ */
+export async function execCommand(
+	command: string,
+	args: string[],
+	cwd: string,
+	options?: ExecOptions,
+): Promise<ExecResult> {
+	return new Promise((resolve) => {
+		const proc = spawn(command, args, {
+			cwd,
+			shell: false,
+			stdio: ["ignore", "pipe", "pipe"],
+		});
+
+		let stdout = "";
+		let stderr = "";
+		let killed = false;
+		let timeoutId: NodeJS.Timeout | undefined;
+
+		const killProcess = () => {
+			if (!killed) {
+				killed = true;
+				proc.kill("SIGTERM");
+				// Force kill after 5 seconds if SIGTERM doesn't work
+				setTimeout(() => {
+					if (!proc.killed) {
+						proc.kill("SIGKILL");
+					}
+				}, 5000);
+			}
+		};
+
+		// Handle abort signal
+		if (options?.signal) {
+			if (options.signal.aborted) {
+				killProcess();
+			} else {
+				options.signal.addEventListener("abort", killProcess, { once: true });
+			}
+		}
+
+		// Handle timeout
+		if (options?.timeout && options.timeout > 0) {
+			timeoutId = setTimeout(() => {
+				killProcess();
+			}, options.timeout);
+		}
+
+		proc.stdout?.on("data", (data) => {
+			stdout += data.toString();
+		});
+
+		proc.stderr?.on("data", (data) => {
+			stderr += data.toString();
+		});
+
+		proc.on("close", (code) => {
+			if (timeoutId) clearTimeout(timeoutId);
+			if (options?.signal) {
+				options.signal.removeEventListener("abort", killProcess);
+			}
+			resolve({ stdout, stderr, code: code ?? 0, killed });
+		});
+
+		proc.on("error", (_err) => {
+			if (timeoutId) clearTimeout(timeoutId);
+			if (options?.signal) {
+				options.signal.removeEventListener("abort", killProcess);
+			}
+			resolve({ stdout, stderr, code: 1, killed });
+		});
+	});
+}