refactor(gateway): pin DEFAULT_AUTOCOMPLETE_MODEL by explicit id

Looking up by provider+model id instead of relying on array index makes
the default robust to reordering of the AUTOCOMPLETE_MODELS list, and
fails loudly at module load if the referenced entry is ever removed.
Adds a test asserting the default resolves to a real entry.

packages/kilo-gateway/src/autocomplete.ts

@@ -83,7 +83,20 @@ const models: AutocompleteModelDef[] = [
 
 export const AUTOCOMPLETE_MODELS: readonly AutocompleteModelDef[] = models
 
-export const DEFAULT_AUTOCOMPLETE_MODEL: AutocompleteModelDef = models[0]!
+export const DEFAULT_AUTOCOMPLETE_PROVIDER_ID: AutocompleteProviderID = "kilo"
+export const DEFAULT_AUTOCOMPLETE_MODEL_ID = "mistralai/codestral-2508"
+
+export const DEFAULT_AUTOCOMPLETE_MODEL: AutocompleteModelDef = (() => {
+  const found = models.find(
+    (m) => m.providerID === DEFAULT_AUTOCOMPLETE_PROVIDER_ID && m.modelID === DEFAULT_AUTOCOMPLETE_MODEL_ID,
+  )
+  if (!found) {
+    throw new Error(
+      `DEFAULT_AUTOCOMPLETE_MODEL not found: provider=${DEFAULT_AUTOCOMPLETE_PROVIDER_ID} model=${DEFAULT_AUTOCOMPLETE_MODEL_ID}`,
+    )
+  }
+  return found
+})()
 
 const aliases: Record<string, string> = {
   "inception/mercury-edit": "inception/mercury-edit-2",

packages/kilo-gateway/test/autocomplete.test.ts

@@ -0,0 +1,24 @@
+import { describe, expect, test } from "bun:test"
+import {
+  AUTOCOMPLETE_MODELS,
+  DEFAULT_AUTOCOMPLETE_MODEL,
+  DEFAULT_AUTOCOMPLETE_MODEL_ID,
+  DEFAULT_AUTOCOMPLETE_PROVIDER_ID,
+} from "../src/autocomplete"
+
+describe("DEFAULT_AUTOCOMPLETE_MODEL", () => {
+  test("resolves to an entry that exists in AUTOCOMPLETE_MODELS", () => {
+    const match = AUTOCOMPLETE_MODELS.find(
+      (m) => m.providerID === DEFAULT_AUTOCOMPLETE_PROVIDER_ID && m.modelID === DEFAULT_AUTOCOMPLETE_MODEL_ID,
+    )
+    expect(match).toBeDefined()
+    expect(DEFAULT_AUTOCOMPLETE_MODEL).toBe(match!)
+  })
+
+  test("points at the expected provider and model", () => {
+    expect(DEFAULT_AUTOCOMPLETE_PROVIDER_ID).toBe("kilo")
+    expect(DEFAULT_AUTOCOMPLETE_MODEL_ID).toBe("mistralai/codestral-2508")
+    expect(DEFAULT_AUTOCOMPLETE_MODEL.providerID).toBe("kilo")
+    expect(DEFAULT_AUTOCOMPLETE_MODEL.modelID).toBe("mistralai/codestral-2508")
+  })
+})