fix(model-config): keep model selection valid and fix admin panel edge cases

- Fall back to the default server model when a saved one disappears
- Sync model config across tabs
- Validation uses the base path and sends the access code
- Model ids edited as drafts (no empty, duplicate or padded ids)
- Credential changes reset validation; stale validation results are dropped
- Admin: generateId over HTTP, env-locked group switches, discard and toggle fixes,
  clearing a secret field keeps the saved key, first provider not auto-default when .env sets AI_MODEL
- Model selector items use unique values

tests/unit/use-model-config.test.tsx

@@ -0,0 +1,133 @@
+import { act, cleanup, renderHook, waitFor } from "@testing-library/react"
+import { afterEach, beforeEach, describe, expect, it, vi } from "vitest"
+import { useModelConfig } from "@/hooks/use-model-config"
+import type { FlattenedServerModel } from "@/lib/server-model-config"
+import { STORAGE_KEYS } from "@/lib/storage"
+import type { MultiModelConfig } from "@/lib/types/model-config"
+
+const SERVER_MODELS: FlattenedServerModel[] = [
+    {
+        id: "server:openai-main:gpt-4o-mini",
+        modelId: "gpt-4o-mini",
+        provider: "openai",
+        providerLabel: "OpenAI Main",
+        isDefault: false,
+    },
+    {
+        id: "server:openai-main:gpt-4o",
+        modelId: "gpt-4o",
+        provider: "openai",
+        providerLabel: "OpenAI Main",
+        isDefault: true,
+    },
+]
+
+const USER_CONFIG: MultiModelConfig = {
+    version: 1,
+    providers: [
+        {
+            id: "p1",
+            provider: "openai",
+            apiKey: "sk-test",
+            models: [{ id: "m1", modelId: "gpt-4o" }],
+        },
+    ],
+}
+
+function storeConfig(config: MultiModelConfig) {
+    localStorage.setItem(STORAGE_KEYS.modelConfigs, JSON.stringify(config))
+}
+
+async function renderLoaded() {
+    const hook = renderHook(() => useModelConfig())
+    await waitFor(() => expect(hook.result.current.isLoaded).toBe(true))
+    return hook
+}
+
+beforeEach(() => {
+    localStorage.clear()
+    vi.stubGlobal(
+        "fetch",
+        vi.fn(async () => ({
+            ok: true,
+            json: async () => ({ models: SERVER_MODELS }),
+        })),
+    )
+})
+
+afterEach(() => {
+    cleanup()
+    vi.unstubAllGlobals()
+})
+
+describe("useModelConfig server model selection", () => {
+    it("replaces a saved server model that no longer exists", async () => {
+        storeConfig({
+            ...USER_CONFIG,
+            selectedModelId: "server:openai-production:gpt-4o",
+        })
+        const { result } = await renderLoaded()
+        expect(result.current.selectedModelId).toBe("server:openai-main:gpt-4o")
+    })
+
+    it("keeps a saved server model that still exists", async () => {
+        storeConfig({
+            ...USER_CONFIG,
+            selectedModelId: "server:openai-main:gpt-4o-mini",
+        })
+        const { result } = await renderLoaded()
+        expect(result.current.selectedModelId).toBe(
+            "server:openai-main:gpt-4o-mini",
+        )
+    })
+
+    it("keeps a selected user model", async () => {
+        storeConfig({ ...USER_CONFIG, selectedModelId: "m1" })
+        const { result } = await renderLoaded()
+        expect(result.current.selectedModelId).toBe("m1")
+    })
+
+    it("falls back to the default server model when the selected model is deleted", async () => {
+        storeConfig({ ...USER_CONFIG, selectedModelId: "m1" })
+        const { result } = await renderLoaded()
+        act(() => result.current.deleteModel("p1", "m1"))
+        expect(result.current.selectedModelId).toBe("server:openai-main:gpt-4o")
+    })
+
+    it("falls back to the default server model when the selected provider is deleted", async () => {
+        storeConfig({ ...USER_CONFIG, selectedModelId: "m1" })
+        const { result } = await renderLoaded()
+        act(() => result.current.deleteProvider("p1"))
+        expect(result.current.selectedModelId).toBe("server:openai-main:gpt-4o")
+    })
+})
+
+describe("useModelConfig across tabs", () => {
+    it("reloads the config when another tab saves it", async () => {
+        storeConfig({ ...USER_CONFIG, selectedModelId: "m1" })
+        const { result } = await renderLoaded()
+
+        const fromOtherTab: MultiModelConfig = {
+            ...USER_CONFIG,
+            providers: [
+                ...USER_CONFIG.providers,
+                {
+                    id: "p2",
+                    provider: "anthropic",
+                    apiKey: "sk-ant",
+                    models: [{ id: "m2", modelId: "claude-sonnet-4-5" }],
+                },
+            ],
+            selectedModelId: "m2",
+        }
+        act(() => {
+            storeConfig(fromOtherTab)
+            window.dispatchEvent(
+                new StorageEvent("storage", { key: STORAGE_KEYS.modelConfigs }),
+            )
+        })
+
+        expect(result.current.selectedModelId).toBe("m2")
+        expect(result.current.config.providers).toHaveLength(2)
+    })
+})