fix(sse): guard model-less registry entries in getUnsupportedParams (mimocode) (#4015)

Real bugfix: guard model-less registry entries (mimocode) in getUnsupportedParams so handleChatCore no longer throws 'entry.models is not iterable' / reports 'All models failed' for unrelated requests. Includes a regression test. Fast QG green.

open-sse/config/providerRegistry.ts

@@ -189,7 +189,8 @@ function ensureUnsupportedParamsPopulated(): void {
   if (_unsupportedParamsPopulated) return;
   _unsupportedParamsPopulated = true;
   for (const entry of Object.values(REGISTRY)) {
-    for (const model of entry.models) {
+    // Some entries (e.g. the `mimocode` proxy) legitimately have no model catalogue.
+    for (const model of entry.models ?? []) {
       if (model.unsupportedParams && !_unsupportedParamsMap.has(model.id)) {
         _unsupportedParamsMap.set(model.id, model.unsupportedParams);
       }
@@ -207,7 +208,7 @@ export function getUnsupportedParams(provider: string, modelId: string): readonl
   ensureUnsupportedParamsPopulated();
   // 1. Check current provider's registry (exact match)
   const entry = getRegistryEntry(provider);
-  const modelEntry = entry?.models.find((m) => m.id === modelId);
+  const modelEntry = entry?.models?.find((m) => m.id === modelId);
   if (modelEntry?.unsupportedParams) return modelEntry.unsupportedParams;
 
   // 2. O(1) lookup in precomputed map (handles cross-provider routing)

tests/unit/provider-registry-models-guard.test.ts

@@ -0,0 +1,23 @@
+import { test } from "node:test";
+import assert from "node:assert/strict";
+import { getUnsupportedParams } from "../../open-sse/config/providerRegistry.ts";
+
+// Regression guard for `TypeError: entry.models is not iterable`.
+//
+// A registry entry can legitimately have no static model catalogue — e.g. the
+// `mimocode` proxy provider, whose `models` is `undefined`. The byModelId map
+// builder already tolerates this (`if (entry.models && entry.models.length > 0)`),
+// but `getUnsupportedParams` had two unguarded accesses:
+//   - `ensureUnsupportedParamsPopulated()` iterated `entry.models` for EVERY entry,
+//   - the per-provider lookup did `entry?.models.find(...)`.
+// Either one threw on the first call once a model-less entry existed, which made
+// `handleChatCore` report "All models failed" for unrelated requests.
+
+test("getUnsupportedParams does not throw when a registry entry has no models (mimocode regression)", () => {
+  // This call triggers ensureUnsupportedParamsPopulated() which walks ALL entries.
+  assert.doesNotThrow(() => getUnsupportedParams("openai", "gpt-4o"));
+});
+
+test("getUnsupportedParams returns [] for a model-less proxy provider", () => {
+  assert.deepEqual(getUnsupportedParams("mimocode", "anything"), []);
+});