Show an agent's own model in the composer when the catalog lacks it (#5796)

The composer fell back to the catalog's default model whenever the agent's
model was missing from the loaded model list, so a Codex subagent started
on a model the catalog did not list yet was labeled as the default model,
with that model's thinking options.

Fixes #5791

Co-authored-by: paseo-bot[bot] <266920839+paseo-bot[bot]@users.noreply.github.com>

packages/app/src/composer/agent-controls/utils.test.ts

@@ -186,4 +186,30 @@ describe("resolveAgentModelSelection", () => {
     expect(selection.selectedThinkingId).toBe("low");
     expect(selection.displayThinking).toBe("Low");
   });
+
+  it("shows the agent's own model when the catalog does not list it", () => {
+    const selection = resolveAgentModelSelection({
+      models: [
+        {
+          id: "gpt-6-sol",
+          provider: "codex",
+          label: "GPT-6-Sol",
+          isDefault: true,
+          thinkingOptions: [
+            { id: "medium", label: "medium" },
+            { id: "max", label: "max" },
+          ],
+          defaultThinkingOptionId: "medium",
+        },
+      ],
+      runtimeModelId: "gpt-6.1-sol",
+      configuredModelId: "gpt-6.1-sol",
+      explicitThinkingOptionId: "max",
+    });
+
+    expect(selection.selectedModel).toBeNull();
+    expect(selection.activeModelId).toBe("gpt-6.1-sol");
+    expect(selection.displayModel).toBe("gpt-6.1-sol");
+    expect(selection.displayThinking).toBe("Max");
+  });
 });

packages/app/src/composer/agent-controls/utils.ts

@@ -79,10 +79,10 @@ function pickSelectedModel(
   preferredModelId: string | null,
   fallbackModel: AgentModelDefinition | null,
 ): AgentModelDefinition | null {
-  if (!models || !preferredModelId) {
+  if (!preferredModelId) {
     return fallbackModel;
   }
-  return findModelById(models, preferredModelId) ?? fallbackModel;
+  return findModelById(models, preferredModelId);
 }
 
 function resolveThinkingId(
@@ -164,7 +164,7 @@ export function resolveAgentModelSelection(input: {
   const thinkingOptions = selectedModel?.thinkingOptions ?? null;
   const resolvedThinkingId = resolveThinkingId(explicitThinkingOptionId, selectedModel);
   const effectiveThinking = resolveEffectiveThinking(thinkingOptions, resolvedThinkingId);
-  const selectedThinkingId = effectiveThinking?.id ?? null;
+  const selectedThinkingId = effectiveThinking?.id ?? resolvedThinkingId;
   const displayThinking = resolveThinkingDisplay(
     effectiveThinking,
     selectedThinkingId,