feat: locate CLI binary

Search PATH, then standard install dirs, since the packaged app often
starts with a minimal PATH.

src/agent/claude-code/binary.ts

@@ -0,0 +1,61 @@
+import * as fs from "node:fs";
+import * as os from "node:os";
+import * as path from "node:path";
+
+type BinaryLookup = {
+	env: Record<string, string | undefined>;
+	platform: NodeJS.Platform;
+	homeDir: string;
+	isExecutable: (path: string) => boolean;
+};
+
+type SearchSpec = {
+	paths: path.PlatformPath;
+	names: string[];
+	knownDirs: string[];
+};
+
+function getWindowsSearchSpec(env: BinaryLookup["env"], homeDir: string): SearchSpec {
+	const paths = path.win32;
+	const appData = env.APPDATA ?? paths.join(homeDir, "AppData", "Roaming");
+	return {
+		paths,
+		names: ["claude.cmd", "claude.exe"],
+		knownDirs: [paths.join(homeDir, ".local", "bin"), paths.join(homeDir, ".claude", "local"), env.npm_config_prefix ?? paths.join(appData, "npm")],
+	};
+}
+
+function getPosixSearchSpec(env: BinaryLookup["env"], homeDir: string): SearchSpec {
+	const paths = path.posix;
+	const npmBin = env.npm_config_prefix ? paths.join(env.npm_config_prefix, "bin") : paths.join(homeDir, ".npm-global", "bin");
+	return {
+		paths,
+		names: ["claude"],
+		knownDirs: [paths.join(homeDir, ".local", "bin"), paths.join(homeDir, ".claude", "local"), npmBin, "/opt/homebrew/bin", "/usr/local/bin"],
+	};
+}
+
+export function resolveClaudeBinary({ env, platform, homeDir, isExecutable }: BinaryLookup): string | null {
+	const { paths, names, knownDirs } = platform === "win32" ? getWindowsSearchSpec(env, homeDir) : getPosixSearchSpec(env, homeDir);
+	const pathDirs = (env.PATH ?? "").split(paths.delimiter).filter(Boolean);
+	for (const dir of [...pathDirs, ...knownDirs]) {
+		for (const name of names) {
+			const candidate = paths.join(dir, name);
+			if (isExecutable(candidate)) return candidate;
+		}
+	}
+	return null;
+}
+
+function isExecutableFile(filePath: string): boolean {
+	try {
+		fs.accessSync(filePath, fs.constants.X_OK);
+		return fs.statSync(filePath).isFile();
+	} catch {
+		return false;
+	}
+}
+
+export function getClaudeBinary(): string | null {
+	return resolveClaudeBinary({ env: process.env, platform: process.platform, homeDir: os.homedir(), isExecutable: isExecutableFile });
+}