diff --git a/open-sse/config/providerModels.ts b/open-sse/config/providerModels.ts
index 34504d8242..afffd4429b 100644
--- a/open-sse/config/providerModels.ts
+++ b/open-sse/config/providerModels.ts
@@ -170,14 +170,17 @@ export function findModelName(aliasOrId: string, modelId: string): string {
 }
 
 export function getModelTargetFormat(aliasOrId: string, modelId: string): string | null {
-  const models = PROVIDER_MODELS[aliasOrId];
+  // Accept either the public alias ("cmd") or the raw provider id ("command-code"),
+  // mirroring getProviderModels (same pattern as #2798/#3870).
+  const alias = PROVIDER_ID_TO_ALIAS[aliasOrId] || aliasOrId;
+  const models = PROVIDER_MODELS[alias];
   // Strip provider prefix if present: "openai/gpt-5.6-luna" → "gpt-5.6-luna"
-  const prefix = aliasOrId + "/";
+  const prefix = alias + "/";
   const bareModelId =
     typeof modelId === "string" && modelId.startsWith(prefix)
       ? modelId.slice(prefix.length)
       : modelId;
-  const found = models?.find((m) => m.id === bareModelId) || getGlobalModel(bareModelId);
+  const found = models?.find((m) => m.id === bareModelId);
   if (found?.targetFormat) return found.targetFormat;
   // #5842: OpenAI "*-pro" reasoning models (o1-pro, gpt-5.x-pro) are only served by
   // the native /v1/responses endpoint — /v1/chat/completions 404s ("only supported
@@ -185,10 +188,17 @@ export function getModelTargetFormat(aliasOrId: string, modelId: string): string
   // covers dynamically-synced ids that post-date the catalog (same spirit as the gh
   // executor's /codex/i routing, 9router#102). Scoped to the openai alias so other
   // providers shipping *-pro ids keep their own endpoint semantics.
-  if (aliasOrId === "openai" && /-pro$/i.test(modelId)) return "openai-responses";
-  return null;
+  if (alias === "openai" && /-pro$/i.test(modelId)) return "openai-responses";
+  // Model-level targetFormat is provider-scoped: a catalog entry declares how THIS
+  // provider's endpoint serves the model. When the provider has its own catalog but
+  // the model is not in it, do NOT import the global entry's tag — it encodes the
+  // DECLARING provider's endpoint semantics (e.g. ghe-copilot tags gpt-5.6-* as
+  // openai-responses, which must not hijack command-code's chat-shaped
+  // /alpha/generate → 502 "Invalid prompt: messages must not be empty"). Providers
+  // with no catalog at all keep the global fallback as their only metadata source.
+  if (models) return null;
+  return getGlobalModel(bareModelId)?.targetFormat ?? null;
 }
-
 export function getModelStripTypes(aliasOrId: string, modelId: string): string[] {
   const models = PROVIDER_MODELS[aliasOrId];
   if (!models)
diff --git a/tests/unit/provider-models-target-format-scoping.test.ts b/tests/unit/provider-models-target-format-scoping.test.ts
new file mode 100644
index 0000000000..b899eb960a
--- /dev/null
+++ b/tests/unit/provider-models-target-format-scoping.test.ts
@@ -0,0 +1,38 @@
+import assert from "node:assert/strict";
+import test from "node:test";
+
+import { getModelTargetFormat } from "../../open-sse/config/providerModels.ts";
+import { resolveChatCoreTargetFormat } from "../../open-sse/handlers/chatCore/targetFormat.ts";
+
+// Regression: #8835 tagged gpt-5.6-* with targetFormat "openai-responses" in the
+// ghe-copilot catalog. getModelTargetFormat falls back to getGlobalModel() when
+// the provider's own catalog lacks the model id, importing the DECLARING
+// provider's endpoint semantics into every other provider serving the same id.
+// command-code's chat-shaped /alpha/generate executor then received a
+// Responses-format body (input, not messages) and shipped `messages: []`
+// upstream — upstream rejected with "Invalid prompt: messages must not be empty"
+// (502). Model-level targetFormat is provider-scoped: it must not leak.
+test("model-level targetFormat does not leak across provider catalogs", () => {
+  // command-code serves gpt-5.6-luna over its chat-shaped /alpha/generate endpoint
+  assert.equal(getModelTargetFormat("cmd", "gpt-5.6-luna"), null);
+  // raw provider id form behaves identically (alias resolution)
+  assert.equal(getModelTargetFormat("command-code", "gpt-5.6-luna"), null);
+  // the declaring provider (ghe-copilot) keeps its Responses routing
+  assert.equal(getModelTargetFormat("gh", "gpt-5.6-luna"), "openai-responses");
+  assert.equal(getModelTargetFormat("ghe-copilot", "gpt-5.6-luna"), "openai-responses");
+  // unrelated models are unaffected
+  assert.equal(getModelTargetFormat("cmd", "kimi-k2"), null);
+});
+
+test("chat completions to command-code gpt-5.6-luna resolve to chat format", () => {
+  const resolved = resolveChatCoreTargetFormat({
+    provider: "command-code",
+    resolvedModel: "gpt-5.6-luna",
+    apiFormat: undefined,
+    sourceFormat: "openai",
+    customModelTargetFormat: undefined,
+    providerSpecificData: null,
+  });
+  assert.equal(resolved.alias, "cmd");
+  assert.equal(resolved.targetFormat, "openai");
+});