feat(cli): enable GCP Shielded VM (Secure Boot) by default

Provision every GCP instance as a Shielded VM (Secure Boot + vTPM +
integrity monitoring) by default. This is what the Cloudflare (CF) skill
needs to attest the VM, and is good hygiene for all spawns. GCP's default
Ubuntu LTS images are Shielded-VM-compatible, so boots are unaffected.

Opt out with the new --no-secure-boot flag (sets GCP_NO_SECURE_BOOT=1)
for custom images that are not UEFI/Secure-Boot-capable.

Secure Boot is GCP-only here; AWS spawns run on Lightsail, which does not
expose Secure Boot, so the flag is a no-op on other clouds.

README.md

@@ -54,6 +54,7 @@ spawn delete -c hetzner                  # Delete a server on Hetzner
 | `spawn <agent> <cloud> --config <file>` | Load options from a JSON config file |
 | `spawn <agent> <cloud> --steps <list>` | Comma-separated setup steps to enable |
 | `spawn <agent> <cloud> --custom` | Show interactive size/region pickers |
+| `spawn <agent> gcp --no-secure-boot` | Disable GCP Shielded VM (Secure Boot is on by default) |
 | `spawn <agent>` | Show available clouds for an agent |
 | `spawn <cloud>` | Show available agents for a cloud |
 | `spawn matrix` | Full agent x cloud matrix |
@@ -159,6 +160,22 @@ spawn claude gcp --beta tarball --beta parallel
 
 `--fast` enables `tarball`, `images`, and `parallel` (not `recursive`).
 
+#### Secure Boot (GCP)
+
+GCP instances are provisioned as [Shielded VMs](https://cloud.google.com/security/shielded-cloud/shielded-vm)
+**by default** — Secure Boot, vTPM, and integrity monitoring are all enabled. This
+hardens the boot chain and is required for the Cloudflare (CF) skill to attest the VM.
+GCP's default Ubuntu LTS images are Shielded-VM-compatible, so this works out of the box.
+
+Opt out for a custom image that is not UEFI/Secure-Boot-capable:
+
+```bash
+spawn claude gcp --no-secure-boot
+```
+
+> Secure Boot is a GCP-only feature here. AWS spawns run on Lightsail, which does not
+> expose Secure Boot; the flag is a no-op on other clouds.
+
 #### Recursive Spawn
 
 Use `--beta recursive` to let spawned VMs create their own child VMs:

packages/cli/src/__tests__/gcp-cov.test.ts

@@ -3,7 +3,7 @@ import { mockBunSpawn, mockClackPrompts } from "./test-helpers";
 
 mockClackPrompts();
 
-import { DEFAULT_MACHINE_TYPE, DEFAULT_ZONE, getConnectionInfo } from "../gcp/gcp";
+import { buildShieldedArgs, DEFAULT_MACHINE_TYPE, DEFAULT_ZONE, getConnectionInfo } from "../gcp/gcp";
 
 // ─── Helpers ─────────────────────────────────────────────────────────────────
 
@@ -82,6 +82,31 @@ describe("gcp/getConnectionInfo", () => {
   });
 });
 
+// ─── buildShieldedArgs (Secure Boot default) ─────────────────────────────────
+
+describe("gcp/buildShieldedArgs", () => {
+  it("enables Shielded VM (Secure Boot) by default", () => {
+    delete process.env.GCP_NO_SECURE_BOOT;
+    expect(buildShieldedArgs()).toEqual([
+      "--shielded-secure-boot",
+      "--shielded-vtpm",
+      "--shielded-integrity-monitoring",
+    ]);
+  });
+
+  it("returns no shielded flags when GCP_NO_SECURE_BOOT=1", () => {
+    process.env.GCP_NO_SECURE_BOOT = "1";
+    expect(buildShieldedArgs()).toEqual([]);
+  });
+
+  it("only opts out for the exact value '1' (any other value stays on)", () => {
+    process.env.GCP_NO_SECURE_BOOT = "0";
+    expect(buildShieldedArgs()).toContain("--shielded-secure-boot");
+    process.env.GCP_NO_SECURE_BOOT = "true";
+    expect(buildShieldedArgs()).toContain("--shielded-secure-boot");
+  });
+});
+
 // ─── promptMachineType ───────────────────────────────────────────────────────
 
 describe("gcp/promptMachineType", () => {

packages/cli/src/__tests__/unknown-flags.test.ts

@@ -87,6 +87,7 @@ describe("Unknown Flag Detection", () => {
         "--debug",
         "--name",
         "--reauth",
+        "--no-secure-boot",
         "--prune",
         "--json",
         "--yes",
@@ -216,6 +217,7 @@ describe("KNOWN_FLAGS completeness", () => {
       "--clear",
       "--custom",
       "--reauth",
+      "--no-secure-boot",
       "--zone",
       "--region",
       "--machine-type",

packages/cli/src/flags.ts

@@ -24,6 +24,7 @@ export const KNOWN_FLAGS = new Set([
   "--clear",
   "--custom",
   "--reauth",
+  "--no-secure-boot",
   "--zone",
   "--region",
   "--machine-type",

packages/cli/src/gcp/gcp.ts

@@ -148,6 +148,30 @@ export const DEFAULT_ZONE = "us-central1-a";
 
 export const DEFAULT_DISK_SIZE_GB = 40;
 
+// ─── Shielded VM (Secure Boot) ───────────────────────────────────────────────
+
+/**
+ * GCP Shielded VM flags, enabled by DEFAULT on every spawned instance.
+ *
+ * Secure Boot + a measured (vTPM) and integrity-monitored boot chain is what
+ * the Cloudflare (CF) skill needs to attest the VM, and it is good hygiene for
+ * every spawn. GCP's Ubuntu LTS images (the default here) are
+ * Shielded-VM-compatible, so turning this on does not break boots.
+ *
+ * Opt out with the `--no-secure-boot` CLI flag (sets `GCP_NO_SECURE_BOOT=1`),
+ * for the rare case of a custom image that is not UEFI/Secure-Boot-capable.
+ */
+export function buildShieldedArgs(): string[] {
+  if (process.env.GCP_NO_SECURE_BOOT === "1") {
+    return [];
+  }
+  return [
+    "--shielded-secure-boot",
+    "--shielded-vtpm",
+    "--shielded-integrity-monitoring",
+  ];
+}
+
 // ─── State ──────────────────────────────────────────────────────────────────
 
 interface GcpState {
@@ -781,6 +805,7 @@ export async function createInstance(
         ]
       : []),
     `--metadata=ssh-keys=${sshKeysMetadata}`,
+    ...buildShieldedArgs(),
     `--project=${_state.project}`,
     "--quiet",
   ];

packages/cli/src/index.ts

@@ -146,6 +146,7 @@ function checkUnknownFlags(args: string[]): void {
     console.error(`    ${pc.cyan("--model, -m <id>")}    Set the LLM model (e.g. openai/gpt-5.3-codex)`);
     console.error(`    ${pc.cyan("--name")}              Set the spawn/resource name`);
     console.error(`    ${pc.cyan("--reauth")}            Force re-prompting for cloud credentials`);
+    console.error(`    ${pc.cyan("--no-secure-boot")}     Disable GCP Shielded VM (Secure Boot, on by default)`);
     console.error(`    ${pc.cyan("--config <path>")}     Load config from JSON file`);
     console.error(`    ${pc.cyan("--steps <list>")}      Comma-separated setup steps to enable`);
     console.error(`    ${pc.cyan("--repo <slug|url>")}  Clone a template repo and apply spawn.md`);
@@ -928,6 +929,14 @@ async function main(): Promise<void> {
     process.env.SPAWN_REAUTH = "1";
   }
 
+  // Extract --no-secure-boot boolean flag — opt out of GCP Shielded VM
+  // (Secure Boot + vTPM + integrity monitoring), which is on by default.
+  const noSecureBootIdx = filteredArgs.indexOf("--no-secure-boot");
+  if (noSecureBootIdx !== -1) {
+    filteredArgs.splice(noSecureBootIdx, 1);
+    process.env.GCP_NO_SECURE_BOOT = "1";
+  }
+
   // Extract --fast boolean flag — enables images + tarballs + parallel setup
   const fastIdx = filteredArgs.indexOf("--fast");
   if (fastIdx !== -1) {