fix(server): delegate_task names the CLI version that hides a model

apps/server/src/mcp/OrchestratorMcpService.test.ts

@@ -2512,6 +2512,10 @@ describe("OrchestratorMcpService provider resolution", () => {
               { slug: "claude-opus-4-1", isLegacy: true },
               ...Array.from({ length: 9 }, (_, index) => ({ slug: `claude-opus-5-${index + 1}` })),
             ].map((model) => ({ ...model, name: model.slug, isCustom: false, capabilities: null })),
+            version: "2.1.302",
+            updateRequiredModels: [
+              { slug: "claude-fable-5-2", name: "Claude Fable 5.2", minVersion: "2.1.321" },
+            ],
           },
         ]),
         adapterRegistryLayer([codexInstanceId]),
@@ -2549,6 +2553,11 @@ describe("OrchestratorMcpService provider resolution", () => {
             "claude-opus-5-6, claude-opus-5-7, claude-opus-5-8 and 2 more; " +
             "orchestrator_capabilities with search finds them.",
         );
+
+        const updateRequired = yield* refuse("claude-fable-5-2");
+        assert.equal(updateRequired.code, "model_unavailable");
+        assert.include(updateRequired.message, "v2.1.302");
+        assert.include(updateRequired.message, "2.1.321");
       }).pipe(Effect.provide(layerOrchestratorService.pipe(Layer.provide(layerDependencies))));
     }),
   );

apps/server/src/mcp/OrchestratorMcpService.ts

@@ -395,16 +395,26 @@ const advertisedModel = (provider: ServerProvider, model: string) =>
     candidate.aliases?.some((alias) => alias.toLowerCase() === model.toLowerCase()),
   );
 
+const withV = (version: string) => (version.startsWith("v") ? version : `v${version}`);
+
 /** A provider that lists no models accepts any slug. */
-export const requireAdvertisedModel = (provider: ServerProvider, model: string) =>
-  provider.models.length > 0 && advertisedModel(provider, model) === undefined
-    ? Effect.fail(
-        failure(
-          "model_unavailable",
-          `Model ${model} is not advertised by provider ${provider.instanceId}. ${advertisedModelsHint(provider.models, model)}`,
-        ),
-      )
-    : Effect.void;
+export const requireAdvertisedModel = (provider: ServerProvider, model: string) => {
+  if (provider.models.length === 0 || advertisedModel(provider, model) !== undefined) {
+    return Effect.void;
+  }
+  const updateRequired = provider.updateRequiredModels?.find(
+    (candidate) => candidate.slug === model,
+  );
+  const detectedVersion = provider.installedVersion ?? provider.version;
+  return Effect.fail(
+    failure(
+      "model_unavailable",
+      updateRequired === undefined
+        ? `Model ${model} is not advertised by provider ${provider.instanceId}. ${advertisedModelsHint(provider.models, model)}`
+        : `Model ${model} needs provider ${provider.instanceId} at ${withV(updateRequired.minVersion)} or newer, but the detected CLI is ${detectedVersion === null ? "an unknown version" : withV(detectedVersion)}. Ask the user to update it or point the provider's binary path at a newer install.`,
+    ),
+  );
+};
 
 function providerConstraints(
   provider: ServerProvider | undefined,