FN-9094: omit unsupported Grok auto-update flag

Align Grok ACP expectations with the released CLI contract.

- Update runtime routing and adapter assertions to omit --no-auto-update by default.
- Cover explicit false and default argument behavior in ACP settings tests.
- Document the released CLI incompatibility and opt-in escape hatch.

Files changed:
 docs/grok-cli-contract.md                                  |  7 ++++---
 packages/engine/src/__tests__/grok-runtime-routing.test.ts | 14 +++++++++-----
 .../src/__tests__/acp-settings.test.ts                     |  2 ++
 .../src/__tests__/runtime-adapter.test.ts                  | 14 ++++++++++----
 4 files changed, 25 insertions(+), 12 deletions(-)

Fusion-Task-Id: FN-9094

Fusion-Task-Lineage: f776e401-8473-45b2-a8b2-8d8251b4713e

Co-authored-by: Fusion (runfusion.ai) <noreply@runfusion.ai>

docs/grok-cli-contract.md

@@ -32,12 +32,13 @@ The previously documented https://github.com/superagent-ai/grok-cli contract is
 Fusion's `GrokRuntimeAdapter` drives Grok as an ACP (Agent Client Protocol) agent over JSON-RPC/stdio, following [xAI Headless & Scripting](https://docs.x.ai/build/cli/headless-scripting#acp):
 
 ```bash
-# Official automation shape (docs.x.ai): suppress update checks in CI/scripts
-grok --no-auto-update agent stdio
+grok agent stdio
 # with optional model + session skills plugin:
-grok --no-auto-update agent --plugin-dir <session-plugin> -m grok-4.6 stdio
+grok agent --plugin-dir <session-plugin> -m grok-4.6 stdio
 ```
 
+xAI's [Headless & Scripting docs](https://docs.x.ai/build/cli/headless-scripting#acp) suggest `--no-auto-update`, but released Grok CLI v1.0.0 exits with "unexpected argument" when it is passed. Fusion therefore defaults it OFF and exposes it only as the opt-in `buildGrokAcpArgs({ noAutoUpdate: true })` argument, which prepends the flag before `agent`.
+
 ACP session lifecycle (official contract):
 
 1. `initialize` (protocolVersion 1)

packages/engine/src/__tests__/grok-runtime-routing.test.ts

@@ -230,12 +230,16 @@ describe("Grok CLI runtime routing (FN-7725)", () => {
     expect(result.runtimeId).toBe("grok");
     expect(result.wasConfigured).toBe(true);
     expect(mockCreateFnAgent).not.toHaveBeenCalled();
-    // FNXC:GrokAcp 2026-07-11-14:00 / 15:00: ACP args include --no-auto-update
-    // (official headless scripting docs), session-scoped --plugin-dir for Fusion
-    // skills, then stdio (optional -m when a model is set).
+    /*
+    FNXC:GrokAcp 2026-08-15-12:41:
+    Default ACP argv omits `--no-auto-update` because released Grok CLI v1.0.0
+    rejects it as an unexpected argument. The flag remains an explicit opt-in;
+    session argv starts with agent, scopes Fusion skills by --plugin-dir, may add
+    -m, and ends with stdio.
+    */
     const acpArgs = settingsOut[0]?.acpArgs as string[];
-    expect(acpArgs).toContain("--no-auto-update");
-    expect(acpArgs).toContain("agent");
+    expect(acpArgs).not.toContain("--no-auto-update");
+    expect(acpArgs[0]).toBe("agent");
     expect(acpArgs).toContain("--plugin-dir");
     expect(acpArgs.at(-1)).toBe("stdio");
 

plugins/fusion-plugin-grok-runtime/src/__tests__/acp-settings.test.ts

@@ -13,6 +13,7 @@ describe("acp-settings", () => {
     // --no-auto-update is opt-in only; the released Grok CLI does not support it.
     expect(buildGrokAcpArgs()).toEqual(["agent", "stdio"]);
     expect(buildGrokAcpArgs({})).toEqual(["agent", "stdio"]);
+    expect(buildGrokAcpArgs({ noAutoUpdate: false })).toEqual(["agent", "stdio"]);
     expect(buildGrokAcpArgs({ noAutoUpdate: true })).toEqual(["--no-auto-update", "agent", "stdio"]);
   });
 
@@ -58,6 +59,7 @@ describe("acp-settings", () => {
     const settings = buildGrokAcpRuntimeSettings({ binary: "/usr/local/bin/grok", model: "grok-cli/grok-4.5" });
     expect(settings.acpBinaryPath).toBe("/usr/local/bin/grok");
     expect(settings.acpArgs).toEqual(["agent", "-m", "grok-4.5", "stdio"]);
+    expect(settings.acpArgs).not.toContain("--no-auto-update");
     expect(settings.acpEnvAllowList).toEqual([...GROK_ACP_ENV_ALLOWLIST]);
     expect(settings.acpFsRead).toBe(false);
     expect(settings.acpFsWrite).toBe(false);

plugins/fusion-plugin-grok-runtime/src/__tests__/runtime-adapter.test.ts

@@ -64,6 +64,11 @@ function makeFakeAcpAdapter(overrides?: {
 }
 
 describe("GrokRuntimeAdapter (ACP)", () => {
+  /*
+  FNXC:GrokAcp 2026-08-15-12:41:
+  Grok CLI v1.0.0 rejects `--no-auto-update`, so default ACP sessions must
+  omit it. The low-level argv builder retains the flag as an explicit opt-in.
+  */
   it("creates a session with default model fallback", async () => {
     const settingsOut: Record<string, unknown>[] = [];
     const adapter = new GrokRuntimeAdapter({ createAcpAdapter: makeFakeAcpAdapter({ settingsOut }) });
@@ -71,7 +76,7 @@ describe("GrokRuntimeAdapter (ACP)", () => {
     expect(result.session.model).toBe("grok/default");
     expect(result.session.systemPrompt).toBe("sys");
     const args = settingsOut[0]?.acpArgs as string[];
-    expect(args).toContain("--no-auto-update");
+    expect(args).not.toContain("--no-auto-update");
     expect(args).toContain("agent");
     expect(args).toContain("--plugin-dir");
     expect(args.at(-1)).toBe("stdio");
@@ -85,12 +90,13 @@ describe("GrokRuntimeAdapter (ACP)", () => {
     expect(session.model).toBe("grok-4.5");
     expect(settingsOut[0]?.acpBinaryPath).toBe("grok");
     const args = settingsOut[0]?.acpArgs as string[];
-    expect(args).toContain("--no-auto-update");
+    expect(args).not.toContain("--no-auto-update");
     expect(args).toContain("--plugin-dir");
     expect(args).toEqual(expect.arrayContaining(["-m", "grok-4.5", "stdio"]));
-    // plugin-dir precedes model flag; no-auto-update precedes agent
-    expect(args.indexOf("--no-auto-update")).toBeLessThan(args.indexOf("agent"));
+    // Agent leads the argv; plugin-dir precedes the selected model.
+    expect(args[0]).toBe("agent");
     expect(args.indexOf("--plugin-dir")).toBeLessThan(args.indexOf("-m"));
+    expect(args.at(-1)).toBe("stdio");
   });
 
   it("forwards operator MCP servers and Fusion custom tools into createSession", async () => {