feat(models): add GLM-5.2 and harden reported-model fallback

Perplexity's model fields are inconsistent per model: Claude Sonnet 5 reports the real slug in user_selected_model with display_model "turbo", while GLM-5.2 reports the inverse. Pick whichever field is present and not "turbo", and fall back to the requested model when both are missing or "turbo".

Also add glm_5_2 to KNOWN_MODELS.

Refs #7 (follow-up comment)

src/search/client.ts

@@ -284,12 +284,14 @@ export async function searchPerplexity(
     answer: answer || "No answer text returned by Perplexity.",
     sources,
   };
-  // Prefer user_selected_model: display_model may report "turbo" even when the
-  // requested model was honored (see issue #7).
+  // The stream's model fields are inconsistent: either user_selected_model or
+  // display_model may report "turbo" even when the requested model was honored
+  // (see issue #7). Prefer whichever is present and not "turbo"; if both are
+  // missing or "turbo", fall back to the requested model.
   const reportedModel =
-    snapshot.user_selected_model && snapshot.user_selected_model !== "turbo"
-      ? snapshot.user_selected_model
-      : snapshot.display_model;
+    [snapshot.user_selected_model, snapshot.display_model].find(
+      (model) => model && model !== "turbo",
+    ) ?? params.model;
   if (reportedModel !== undefined) result.displayModel = reportedModel;
   if (snapshot.uuid !== undefined) result.uuid = snapshot.uuid;
 

src/search/models.ts

@@ -35,4 +35,5 @@ export const KNOWN_MODELS: ModelOption[] = [
   { value: "grok4", label: "Grok 4 Thinking" },
   { value: "nv_nemotron_3_super", label: "Nemotron 3 Super" },
   { value: "kimik25thinking", label: "Kimi K2.5 Thinking" },
+  { value: "glm_5_2", label: "GLM-5.2" },
 ];

test/search/client.test.ts

@@ -309,6 +309,21 @@ describe("searchPerplexity", () => {
 
     const fallback = await searchPerplexity({ query: "q", model: "pplx_pro_upgraded" }, "jwt");
     expect(fallback.displayModel).toBe("pplx_pro_upgraded");
+
+    globalThis.fetch = (async () =>
+      createSseResponse([
+        {
+          status: "COMPLETED",
+          final: true,
+          text: "answer",
+          display_model: "turbo",
+          user_selected_model: "turbo",
+          sources_list: [{ title: "S", url: "https://example.com" }],
+        },
+      ])) as unknown as typeof fetch;
+
+    const requested = await searchPerplexity({ query: "q", model: "glm_5_2" }, "jwt");
+    expect(requested.displayModel).toBe("glm_5_2");
   });
 
   test("returns EMPTY error when response has no answer and no sources", async () => {