fix: model selection precedence to prefer provider default over agent model (#36)

Fixes #35. The app was selecting claude-sonnet-4-6 (agent default) instead of gpt-5.4 (provider default), causing send_message failures in CI where only Azure provider is available.

src/lib/model-selection.test.ts

@@ -0,0 +1,50 @@
+import { test } from "node:test"
+import assert from "node:assert/strict"
+import { chooseModelSelection } from "./model-selection.ts"
+
+const providers = [
+  {
+    id: "azure",
+    models: [{ id: "gpt-5.4" }, { id: "gpt-5.2" }],
+  },
+]
+
+test("keeps existing selection when still available", () => {
+  const selected = chooseModelSelection({
+    providers,
+    defaults: { azure: "gpt-5.4" },
+    existing: { providerID: "azure", modelID: "gpt-5.2" },
+    agentModel: { providerID: "azure", modelID: "claude-sonnet-4-6" },
+  })
+  assert.deepEqual(selected, { providerID: "azure", modelID: "gpt-5.2" })
+})
+
+test("prefers provider default over unavailable agent model", () => {
+  const selected = chooseModelSelection({
+    providers,
+    defaults: { azure: "gpt-5.4" },
+    existing: null,
+    agentModel: { providerID: "azure", modelID: "claude-sonnet-4-6" },
+  })
+  assert.deepEqual(selected, { providerID: "azure", modelID: "gpt-5.4" })
+})
+
+test("falls back to first connected provider model when default missing", () => {
+  const selected = chooseModelSelection({
+    providers,
+    defaults: {},
+    existing: null,
+    agentModel: null,
+  })
+  assert.deepEqual(selected, { providerID: "azure", modelID: "gpt-5.4" })
+})
+
+test("returns null when no connected providers", () => {
+  const selected = chooseModelSelection({
+    providers: [],
+    defaults: {},
+    existing: null,
+    agentModel: null,
+  })
+  assert.equal(selected, null)
+})

src/lib/model-selection.ts

@@ -0,0 +1,50 @@
+export interface ProviderModelRef {
+  id: string
+}
+
+export interface ProviderRef {
+  id: string
+  models: ProviderModelRef[]
+}
+
+export interface ModelSelection {
+  providerID: string
+  modelID: string
+}
+
+export function isModelAvailable(
+  providers: ProviderRef[],
+  selection: ModelSelection | null | undefined,
+): selection is ModelSelection {
+  if (!selection) return false
+  const provider = providers.find((p) => p.id === selection.providerID)
+  if (!provider) return false
+  return provider.models.some((m) => m.id === selection.modelID)
+}
+
+export function chooseModelSelection(params: {
+  providers: ProviderRef[]
+  defaults: Record<string, string>
+  existing: ModelSelection | null
+  agentModel: ModelSelection | null
+}): ModelSelection | null {
+  const { providers, defaults, existing, agentModel } = params
+
+  if (isModelAvailable(providers, existing)) return existing
+
+  for (const provider of providers) {
+    const defaultModelID = defaults[provider.id]
+    if (!defaultModelID) continue
+    if (provider.models.some((m) => m.id === defaultModelID)) {
+      return { providerID: provider.id, modelID: defaultModelID }
+    }
+  }
+
+  if (providers.length > 0 && providers[0].models.length > 0) {
+    return { providerID: providers[0].id, modelID: providers[0].models[0].id }
+  }
+
+  if (isModelAvailable(providers, agentModel)) return agentModel
+
+  return null
+}