feat(tools): add run_shell, edit_file, write_file + read_file directory listing

Four standard-tier tool extensions (one tool per extension, zero ABI change):
- tool-read-file: read_file now lists directory contents (sorted, /-suffixed subdirs)
- tool-shell: run_shell (foreground, streamed, cancellable, cwd, timeout + output cap)
- tool-edit-file: edit_file (oldString/newString/replaceAll; errors on absent/non-unique)
- tool-write-file: write_file (explicit overwrite flag)
Registered in host-bin CORE_EXTENSIONS. Live boot clean (shell capability accepted).
686 vitest + 89 bun = 775 tests; tsc -b EXIT 0; biome clean.

1 files changed, 46 insertions, 0 deletions

diff --git a/packages/tool-shell/src/spawn.ts b/packages/tool-shell/src/spawn.ts
new file mode 100644
index 0000000..9025c26
--- /dev/null
+++ b/packages/tool-shell/src/spawn.ts
@@ -0,0 +1,46 @@
+import { spawn as nodeSpawn } from "node:child_process";
+import type { SpawnResult, SpawnShell } from "./shell.js";
+
+export const realSpawn: SpawnShell = (params): Promise<SpawnResult> => {
+	return new Promise<SpawnResult>((resolve) => {
+		const child = nodeSpawn("sh", ["-c", params.command], {
+			cwd: params.cwd,
+			stdio: ["ignore", "pipe", "pipe"],
+		});
+
+		let timedOut = false;
+		let killed = false;
+		const timer = setTimeout(() => {
+			timedOut = true;
+			child.kill("SIGKILL");
+		}, params.timeout);
+
+		const onAbort = () => {
+			killed = true;
+			child.kill("SIGKILL");
+		};
+		params.signal.addEventListener("abort", onAbort, { once: true });
+
+		child.stdout.on("data", (chunk: Buffer) => {
+			params.onOutput(chunk.toString(), "stdout");
+		});
+
+		child.stderr.on("data", (chunk: Buffer) => {
+			params.onOutput(chunk.toString(), "stderr");
+		});
+
+		child.on("close", (code) => {
+			clearTimeout(timer);
+			params.signal.removeEventListener("abort", onAbort);
+			resolve({ exitCode: code, timedOut });
+		});
+
+		child.on("error", () => {
+			clearTimeout(timer);
+			params.signal.removeEventListener("abort", onAbort);
+			if (!killed && !timedOut) {
+				resolve({ exitCode: 1, timedOut: false });
+			}
+		});
+	});
+};