fix(cron): respect subagents.model in isolated cron sessions (#11474)

* fix(cron): respect subagents.model in isolated cron sessions

* fix(cron): enforce model allowlist for subagents.model

* Cron: fix isolated subagent model gate regressions

---------

Co-authored-by: Tak Hoffman <781889+Takhoffman@users.noreply.github.com>

src/agents/model-selection.test.ts

@@ -6,8 +6,9 @@ import {
   inferUniqueProviderFromConfiguredModels,
   parseModelRef,
   buildModelAliasIndex,
-  modelKey,
+  normalizeModelSelection,
   normalizeProviderId,
+  modelKey,
   resolveAllowedModelRef,
   resolveConfiguredModelRef,
   resolveModelRefFromString,
@@ -470,3 +471,31 @@ describe("model-selection", () => {
     });
   });
 });
+
+describe("normalizeModelSelection", () => {
+  it("returns trimmed string for string input", () => {
+    expect(normalizeModelSelection("ollama/llama3.2:3b")).toBe("ollama/llama3.2:3b");
+  });
+
+  it("returns undefined for empty/whitespace string", () => {
+    expect(normalizeModelSelection("")).toBeUndefined();
+    expect(normalizeModelSelection("   ")).toBeUndefined();
+  });
+
+  it("extracts primary from object", () => {
+    expect(normalizeModelSelection({ primary: "google/gemini-2.5-flash" })).toBe(
+      "google/gemini-2.5-flash",
+    );
+  });
+
+  it("returns undefined for object without primary", () => {
+    expect(normalizeModelSelection({ fallbacks: ["a"] })).toBeUndefined();
+    expect(normalizeModelSelection({})).toBeUndefined();
+  });
+
+  it("returns undefined for null/undefined/number", () => {
+    expect(normalizeModelSelection(undefined)).toBeUndefined();
+    expect(normalizeModelSelection(null)).toBeUndefined();
+    expect(normalizeModelSelection(42)).toBeUndefined();
+  });
+});