diff --git a/packages/coding-agent/CHANGELOG.md b/packages/coding-agent/CHANGELOG.md
index 93eababc8..d5179a2f7 100644
--- a/packages/coding-agent/CHANGELOG.md
+++ b/packages/coding-agent/CHANGELOG.md
@@ -10,6 +10,8 @@
 
 ### Fixed
 
+- The Windows RPC host supervisor now creates its internal socket directory recursively, so launching `--internal-rpc-host-supervisor` directly on a fresh profile no longer crashes with `ENOENT ... mkdir '<agentDir>\rpc-host-daemon\internal-<uuid>'` ([#1370](https://github.com/code-yeongyu/senpi/issues/1370))
+
 ### Removed
 
 ## [2026.9.6] - 2026-09-06
diff --git a/packages/coding-agent/docs/rpc.md b/packages/coding-agent/docs/rpc.md
index 3d089e9ef..833e0e9f5 100644
--- a/packages/coding-agent/docs/rpc.md
+++ b/packages/coding-agent/docs/rpc.md
@@ -147,6 +147,8 @@ The command response reports only `{ cancelled }`, so this event is the only pus
 
 The lifecycle supervisor is also available to bundled/rebranded runtimes through the hidden internal launch route `--internal-rpc-host-supervisor`. This route is wire-invisible and intended only for desktop launchers: it receives the public socket, ownership directory, and the runtime command/arguments to wrap, then runs the same `host-lifecycle.ts` implementation used by `ensureHost()`. Normal CLI modes do not use or advertise this route. Compiled standalone binaries also re-enter themselves through this route automatically: a bun executable always boots its embedded entrypoint, so the script-path re-entry used under a JS runtime would be parsed as CLI arguments (`Unknown option: --socket`) and the host could never start.
 
+On win32 the supervisor's internal hop lives under `<agentDir>/rpc-host-daemon/internal-<uuid>`, and that directory is created recursively, so a launcher may take this route on a fresh profile where `rpc-host-daemon` does not exist yet. The public socket secret is not self-provisioned: on win32 the supervisor still reads `<publicSocket>.secret`, which `ensureHost()` writes before spawning, so a direct launch must provision it the same way.
+
 Hosts started through `ensureHost()` are wrapped by a lifecycle supervisor that owns the public socket and spawns the
 real RPC host on a private internal hop. The policy lives in `<agentDir>/rpc-host-daemon/settings.json`:
 
diff --git a/packages/coding-agent/src/modes/rpc/changes.md b/packages/coding-agent/src/modes/rpc/changes.md
index 25c149e02..b422fc0cb 100644
--- a/packages/coding-agent/src/modes/rpc/changes.md
+++ b/packages/coding-agent/src/modes/rpc/changes.md
@@ -1,5 +1,25 @@
 # changes
 
+## win32 supervisor creates its internal socket directory recursively (2026-09-07)
+
+### What changed
+
+- `packages/coding-agent/src/modes/rpc/host-lifecycle.ts`: the win32 branch of `createInternalSocketPath()` now creates `<baseDir>/internal-<uuid>` with `recursive: true` instead of `recursive: false`. The function is exported and takes an injectable `platform`, mirroring `spawnableChildLaunch(launch, platform)` in the same module, so the win32 bootstrap is coverable from any host. The posix branch is unchanged.
+- `packages/coding-agent/docs/rpc.md`: the shared-host lifecycle section records that the win32 internal hop directory is created recursively, and that the public socket secret is still caller-provisioned.
+- `packages/coding-agent/test/suite/regressions/1370-rpc-internal-socket-mkdir.test.ts`: regression coverage for the win32 bootstrap against a missing `rpc-host-daemon`, plus a guard that the posix branch stays rooted in the OS temp dir.
+
+### Why
+
+- `runHostSupervisor()` passes `paths.dir` (`<agentDir>/rpc-host-daemon`) as the base directory. `ensureHost()` creates that parent before spawning, but the hidden `--internal-rpc-host-supervisor` launch route does not, so on a fresh Windows profile the supervisor died during bootstrap with `ENOENT: no such file or directory, mkdir '<agentDir>\rpc-host-daemon\internal-<uuid>'` (#1370). The posix branch never hit this because it roots the directory in `tmpdir()`, which always exists.
+
+### Why an extension could not handle it
+
+- The failure happens inside the supervisor's own bootstrap, before any session, runtime, or extension surface exists.
+
+### Expected merge conflict zones
+
+- LOW: the `createInternalSocketPath` signature and its win32 `mkdir` call in `host-lifecycle.ts`, and the internal launch route paragraph in `docs/rpc.md`.
+
 ## Shared-host logical sessions are unlimited by default (2026-09-06)
 
 ### What changed
diff --git a/packages/coding-agent/src/modes/rpc/host-lifecycle.ts b/packages/coding-agent/src/modes/rpc/host-lifecycle.ts
index cb2b76198..9af19c5fc 100644
--- a/packages/coding-agent/src/modes/rpc/host-lifecycle.ts
+++ b/packages/coding-agent/src/modes/rpc/host-lifecycle.ts
@@ -101,13 +101,18 @@ const CHILD_WATCH_FD = 3;
  * The internal hop must stay short enough for sun_path (104 bytes on macOS)
  * regardless of where the public socket lives, and private against other local
  * users, so it gets its own 0700 directory under the OS temp directory.
+ *
+ * On win32 the directory lives under the caller-supplied rpc-host-daemon
+ * directory, which ensureHost() creates but a direct --internal-rpc-host-supervisor
+ * launch does not, so the parent is created recursively.
  */
-async function createInternalSocketPath(
+export async function createInternalSocketPath(
 	baseDir = tmpdir(),
+	platform: NodeJS.Platform = process.platform,
 ): Promise<{ socket: string; dir?: string; secretPath?: string }> {
-	if (process.platform === "win32") {
+	if (platform === "win32") {
 		const dir = join(baseDir, `internal-${randomUUID()}`);
-		await mkdir(dir, { recursive: false, mode: 0o700 });
+		await mkdir(dir, { recursive: true, mode: 0o700 });
 		return {
 			socket: `\\\\.\\pipe\\senpi-rpc-internal-${randomUUID()}`,
 			dir,
diff --git a/packages/coding-agent/test/suite/regressions/1370-rpc-internal-socket-mkdir.test.ts b/packages/coding-agent/test/suite/regressions/1370-rpc-internal-socket-mkdir.test.ts
new file mode 100644
index 000000000..b73e7241c
--- /dev/null
+++ b/packages/coding-agent/test/suite/regressions/1370-rpc-internal-socket-mkdir.test.ts
@@ -0,0 +1,41 @@
+import { existsSync, mkdtempSync, rmSync } from "node:fs";
+import { tmpdir } from "node:os";
+import { dirname, join } from "node:path";
+import { afterEach, describe, expect, it } from "vitest";
+import { createInternalSocketPath } from "../../../src/modes/rpc/host-lifecycle.ts";
+
+// Regression coverage for https://github.com/code-yeongyu/senpi/issues/1370
+describe("createInternalSocketPath", () => {
+	const created: string[] = [];
+
+	afterEach(() => {
+		for (const dir of created.splice(0)) rmSync(dir, { recursive: true, force: true });
+	});
+
+	it("creates the win32 internal directory when rpc-host-daemon does not exist yet", async () => {
+		const agentDir = mkdtempSync(join(tmpdir(), "senpi-hlc-win32-"));
+		created.push(agentDir);
+		const daemonDir = join(agentDir, "rpc-host-daemon");
+		expect(existsSync(daemonDir)).toBe(false);
+
+		const internal = await createInternalSocketPath(daemonDir, "win32");
+
+		const dir = internal.dir;
+		if (dir === undefined) throw new Error("expected an internal socket directory");
+		expect(existsSync(dir)).toBe(true);
+		expect(dirname(dir)).toBe(daemonDir);
+		expect(internal.socket.startsWith("\\\\.\\pipe\\")).toBe(true);
+		expect(internal.secretPath).toBe(join(dir, "secret"));
+	});
+
+	it("keeps the posix internal directory in the OS temp dir", async () => {
+		const internal = await createInternalSocketPath(join(tmpdir(), "senpi-hlc-unused"), "linux");
+
+		const dir = internal.dir;
+		if (dir === undefined) throw new Error("expected an internal socket directory");
+		created.push(dir);
+		expect(existsSync(dir)).toBe(true);
+		expect(dirname(dir)).toBe(tmpdir());
+		expect(internal.socket).toBe(join(dir, "host.sock"));
+	});
+});