From 8e90ce6197297b8ea67660843c1c4788ae1d56e8 Mon Sep 17 00:00:00 2001
From: James <jamescollard2005@gmail.com>
Date: Fri, 21 Aug 2026 15:31:40 +0100
Subject: [PATCH] fix(server): alias Grok's product-name model slug to a valid
 ACP modelId
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Grok's ACP session/set_model only accepts "grok-4.6"/"grok-4.5", but T3
sent "grok-build" verbatim as the default modelId — that's the Grok
Build CLI's own product name, not a model id, so every Grok session
start failed with "unknown model id" immediately.

Add a MODEL_SLUG_ALIASES_BY_PROVIDER entry for the Grok driver, same as
Claude and Codex already have for their own display/legacy slugs, so
normalizeModelSlug resolves it to "grok-4.6" before it ever reaches the
wire. Updated the mock ACP agent used by GrokAdapter's tests to accept
"grok-4.6" instead of the never-actually-valid "grok-build", matching
what the real Grok ACP accepts.

Fixes #7791
---
 apps/server/scripts/acp-mock-agent.ts               | 6 ++++--
 apps/server/src/provider/acp/GrokAcpSupport.test.ts | 7 +++++--
 packages/contracts/src/model.ts                     | 8 ++++++++
 packages/shared/src/model.test.ts                   | 6 ++++++
 4 files changed, 23 insertions(+), 4 deletions(-)

diff --git a/apps/server/scripts/acp-mock-agent.ts b/apps/server/scripts/acp-mock-agent.ts
index bc7828dd8547..23d30cec867d 100644
--- a/apps/server/scripts/acp-mock-agent.ts
+++ b/apps/server/scripts/acp-mock-agent.ts
@@ -278,15 +278,17 @@ function modeState(): AcpSchema.SessionModeState {
   };
 }
 
+// Mirrors the real Grok ACP: it only accepts "grok-4.6"/"grok-4.5" as
+// modelIds, never the CLI's own "grok-build" product name (see #7791).
 const grokAcpModels: ReadonlyArray<AcpSchema.ModelInfo> = [
-  { modelId: "grok-build", name: "Grok Build" },
+  { modelId: "grok-4.6", name: "Grok 4.6" },
   { modelId: "grok-mock-alt", name: "Grok Mock Alt" },
 ];
 
 function modelState(): AcpSchema.SessionModelState {
   const modelId = grokAcpModels.some((model) => model.modelId === currentModelId)
     ? currentModelId
-    : "grok-build";
+    : "grok-4.6";
   return {
     currentModelId: modelId,
     availableModels: grokAcpModels,
diff --git a/apps/server/src/provider/acp/GrokAcpSupport.test.ts b/apps/server/src/provider/acp/GrokAcpSupport.test.ts
index 02d60976b24c..443cfaee8789 100644
--- a/apps/server/src/provider/acp/GrokAcpSupport.test.ts
+++ b/apps/server/src/provider/acp/GrokAcpSupport.test.ts
@@ -10,8 +10,11 @@ import {
 
 describe("resolveGrokAcpBaseModelId", () => {
   it("normalizes empty and custom Grok model ids", () => {
-    expect(resolveGrokAcpBaseModelId(undefined)).toBe("grok-build");
-    expect(resolveGrokAcpBaseModelId("   ")).toBe("grok-build");
+    // "grok-build" is the CLI's product name, not a modelId its ACP accepts —
+    // it must resolve to a real model alias, not pass through verbatim.
+    expect(resolveGrokAcpBaseModelId(undefined)).toBe("grok-4.6");
+    expect(resolveGrokAcpBaseModelId("   ")).toBe("grok-4.6");
+    expect(resolveGrokAcpBaseModelId("grok-build")).toBe("grok-4.6");
     expect(resolveGrokAcpBaseModelId("  grok-test-custom-model  ")).toBe("grok-test-custom-model");
   });
 });
diff --git a/packages/contracts/src/model.ts b/packages/contracts/src/model.ts
index 9fcd0d266dd6..290cf4616b7c 100644
--- a/packages/contracts/src/model.ts
+++ b/packages/contracts/src/model.ts
@@ -211,6 +211,14 @@ export const MODEL_SLUG_ALIASES_BY_PROVIDER: Partial<
     "opus-4.5-thinking": "claude-opus-4-5",
     "opus-4.5": "claude-opus-4-5",
   },
+  [GROK_DRIVER_KIND]: {
+    // "grok-build" is the Grok Build CLI's own product name, not a model id
+    // its ACP accepts — sending it verbatim as `session/set_model`'s modelId
+    // fails with "unknown model id". Grok's ACP only knows "grok-4.6" and
+    // "grok-4.5"; alias the default/display slug to the current one so the
+    // wire-level id is always valid.
+    "grok-build": "grok-4.6",
+  },
   [OPENCODE_DRIVER_KIND]: {},
 };
 
diff --git a/packages/shared/src/model.test.ts b/packages/shared/src/model.test.ts
index b67c45744734..4bc641c8cbba 100644
--- a/packages/shared/src/model.test.ts
+++ b/packages/shared/src/model.test.ts
@@ -154,4 +154,10 @@ describe("model slug normalization", () => {
     expect(normalizeModelSlug("opus", claude)).toBe("claude-opus-5");
     expect(normalizeCustomModelSlug(" opus ")).toBe("opus");
   });
+
+  it("aliases Grok's product-name slug to a modelId its ACP accepts", () => {
+    const grok = ProviderDriverKind.make("grok");
+
+    expect(normalizeModelSlug("grok-build", grok)).toBe("grok-4.6");
+  });
 });