FN-7715: clarify GrokRuntimeAdapter no-op stub with intent documentation

Documents that GrokRuntimeAdapter.promptWithFallback is an intentional no-op rather than unfinished work, and updates its regression test to assert that contract explicitly.

- Add FNXC:GrokCli comment on promptWithFallback explaining Grok streaming already flows through the pi/xAI OpenAI-compatible path from FN-7711, that the grok CLI has no documented non-interactive prompt/stream subcommand, and that this stub is only reached via an unused runtimeConfig.runtimeHint === "grok" path
- Remove the stale TODO(FN-7705) comment
- Rename/expand the promptWithFallback test to assert the intentional no-op contract (resolves without throwing, returns undefined)

Files changed:
 .../src/__tests__/runtime-adapter.test.ts              | 11 ++++++++++-
 .../fusion-plugin-grok-runtime/src/runtime-adapter.ts  | 18 ++++++++++++++++--
 2 files changed, 26 insertions(+), 3 deletions(-)

Fusion-Task-Id: FN-7715

Fusion-Task-Lineage: 118639d3-5530-45d5-bc66-de9b1f18fbc4

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

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

@@ -9,8 +9,17 @@ describe("GrokRuntimeAdapter", () => {
     expect(result.session.systemPrompt).toBe("sys");
   });
 
-  it("promptWithFallback resolves without throwing", async () => {
+  // FN-7715: promptWithFallback is an INTENTIONAL no-op — Grok streaming
+  // flows through the pi/xAI OpenAI-compatible path registered by FN-7711,
+  // not through this plugin runtime adapter (which is only reached via
+  // runtimeConfig.runtimeHint === "grok", which nothing in the product
+  // sets). This module imports no process-spawning seam (compare
+  // process-manager.ts's `runGrokCommand`), so this asserts the intentional
+  // no-op contract at the only observable boundary: it resolves without
+  // throwing and returns no value, taking no action.
+  it("promptWithFallback is an intentional no-op: resolves without throwing, returns undefined", async () => {
     const adapter = new GrokRuntimeAdapter();
+
     await expect(adapter.promptWithFallback()).resolves.toBeUndefined();
   });
 

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

@@ -13,9 +13,23 @@ export class GrokRuntimeAdapter {
     };
   }
 
+  /*
+  FNXC:GrokCli 2026-07-09-00:00:
+  FN-7715: this is an INTENTIONAL no-op, not unfinished work. FN-7711 already
+  routes `grok-cli/*` model selections through the standard pi/openai-completions
+  streaming path against https://api.x.ai/v1 — that is the real, exercised Grok
+  streaming path. The `grok` binary (see provider.ts / process-manager.ts) is
+  wired for discovery/probe only (`grok models`, `grok --version`); there is no
+  documented non-interactive prompt/stream subcommand to invoke here, and
+  inventing one would violate the external-integration-evidence policy. This
+  adapter's `promptWithFallback` is only reached when an agent's
+  `runtimeConfig.runtimeHint === "grok"`, which nothing in the product sets
+  today. Mirrors the identical intentional stub in the sibling Cursor plugin
+  (`fusion-plugin-cursor-runtime/src/runtime-adapter.ts`, TODO(FN-3396)). If a
+  stable non-interactive `grok` CLI streaming contract is confirmed upstream in
+  the future, a follow-up task can revisit this.
+  */
   async promptWithFallback(): Promise<void> {
-    // TODO(FN-7705): Implement Grok CLI prompt streaming once a stable
-    // invocation contract beyond probe/discovery commands is confirmed.
     return;
   }