feat(models): numbered OpenCode credential selection, labels, migration

Adopt the numbered OPENCODE_API_KEY_N scheme in the model picker and
concurrency surfaces.

- model-select: numeric sort of opencode-<n> keys (#2 before #10); friendly
  OpenCode #N labels (raw opencode-N/<model> value still selected/persisted);
  migrateLegacyModelName rewrites opencode/<model> -> opencode-1/<model>.
- ModelSelector: renders friendly key labels; surfaces a disappeared saved
  credential as UNAVAILABLE (disabled option + notice) without silently
  switching to another model.
- app store: DEFAULT_MODEL -> opencode-1/...; catalogs no longer auto-fallback
  the active model when the selected credential is absent; boot restore
  migrates persisted legacy opencode/<model> tab models idempotently.
- concurrency: providerLabel renders opencode-<n> as OpenCode #<n> in the
  limit rows and Add dropdown (raw provider id preserved on the wire).
- Tests: parsing/sorting/labels/migration, unavailable-state selector behavior,
  no-silent-fallback, and concurrency provider label; fixtures updated to the
  numbered scheme.

Verification: bun install, bun run typecheck (0 errors), bun run test
(1179 passed), bun run check (clean, exit 0), bun run build (vite OK).

3 files changed, 86 insertions, 24 deletions

diff --git a/src/app/App.test.ts b/src/app/App.test.ts
index f43a6b8..06e562f 100644
--- a/src/app/App.test.ts
+++ b/src/app/App.test.ts
@@ -58,7 +58,7 @@ function fakeFetchImpl(): typeof fetch {
   return async (input: string | URL | Request): Promise<Response> => {
     const url = typeof input === "string" ? input : input instanceof URL ? input.href : input.url;
     if (url.endsWith("/models")) {
-      return new Response(JSON.stringify({ models: ["opencode/deepseek-v4-flash"] }), {
+      return new Response(JSON.stringify({ models: ["opencode-1/deepseek-v4-flash"] }), {
         status: 200,
       });
     }
@@ -492,7 +492,7 @@ describe("App component interaction tests", () => {
     const failingFetch = async (input: string | URL | Request): Promise<Response> => {
       const url = typeof input === "string" ? input : input instanceof URL ? input.href : input.url;
       if (url.endsWith("/models")) {
-        return new Response(JSON.stringify({ models: ["opencode/deepseek-v4-flash"] }), {
+        return new Response(JSON.stringify({ models: ["opencode-1/deepseek-v4-flash"] }), {
           status: 200,
         });
       }
diff --git a/src/app/store.svelte.ts b/src/app/store.svelte.ts
index 8997ce0..e11a445 100644
--- a/src/app/store.svelte.ts
+++ b/src/app/store.svelte.ts
@@ -53,7 +53,7 @@ import {
   unsubscribe as protocolUnsubscribe,
 } from "../core/protocol";
 import type { ChatStore, HistorySync, MetricsSync } from "../features/chat";
-import { createChatStore } from "../features/chat";
+import { createChatStore, migrateLegacyModelName } from "../features/chat";
 import type { SetThinkingRequest, ThinkingResponse } from "../features/chat/reasoning-effort";
 import type {
   ConcurrencyCooldownResult,
@@ -91,7 +91,7 @@ import { resolveHttpUrl } from "./resolve-http-url";
 import { resolveWsUrl } from "./resolve-ws-url";
 import { randomId } from "./uuid";
 
-const DEFAULT_MODEL = "opencode/deepseek-v4-flash";
+const DEFAULT_MODEL = "opencode-1/deepseek-v4-flash";
 
 /** Outcome of a manual `POST /chat/warm` (the "warm now" affordance). */
 export type WarmResult =
@@ -1112,7 +1112,10 @@ export function createAppStore(opts?: CreateAppStoreOptions): AppStore {
           // authoritative conversation record is the source of truth, so a
           // differing tab workspace is corrected here.
           tabsStore.setTitle(conv.id, conv.title);
-          if (tabsStore.tabs.find((t) => t.conversationId === conv.id)?.workspaceId !== conv.workspaceId) {
+          if (
+            tabsStore.tabs.find((t) => t.conversationId === conv.id)?.workspaceId !==
+            conv.workspaceId
+          ) {
             tabsStore.setWorkspaceId(conv.id, conv.workspaceId);
           }
         }
@@ -1231,12 +1234,13 @@ export function createAppStore(opts?: CreateAppStoreOptions): AppStore {
       if (data === undefined) return;
       models = data.models;
       modelInfo = data.modelInfo ?? {};
-      if (data.models.length > 0 && !data.models.includes(activeModel)) {
-        const first = data.models[0];
-        if (first !== undefined) {
-          activeModel = first;
-          draftStore.setModel(first);
-        }
+      // Do NOT silently switch the active model when the current selection is
+      // missing from the catalog (e.g. a saved numbered OpenCode credential was
+      // removed). The model selector surfaces it as unavailable; the user picks
+      // explicitly. activeModel is still normalized through the legacy-migration
+      // helper so an old `opencode/...` value is rewritten once.
+      if (migrateLegacyModelName(activeModel) !== activeModel) {
+        activeModel = migrateLegacyModelName(activeModel);
       }
     })
     .catch((err) => {
@@ -1262,7 +1266,14 @@ export function createAppStore(opts?: CreateAppStoreOptions): AppStore {
   const persistedState = storageAdapter.load();
   if (persistedState !== null && persistedState.tabs.length > 0) {
     for (const tab of persistedState.tabs) {
-      const store = createChatFor(tab.conversationId, tab.model, tab.workspaceId);
+      // One-time persisted-state migration: rewrite a legacy `opencode/<model>`
+      // tab model to the numbered `opencode-1/<model>` namespace, and persist the
+      // migrated value back so a re-load is a no-op (idempotent).
+      const model = migrateLegacyModelName(tab.model);
+      if (model !== tab.model) {
+        tabsStore.setModel(tab.conversationId, model);
+      }
+      const store = createChatFor(tab.conversationId, model, tab.workspaceId);
       chatStores.set(tab.conversationId, store);
       void store.load();
       // Watch each restored conversation's live turns: after a reload mid-turn the
@@ -1275,7 +1286,7 @@ export function createAppStore(opts?: CreateAppStoreOptions): AppStore {
         (t) => t.conversationId === persistedState.activeConversationId,
       );
       if (activeTab !== undefined) {
-        activeModel = activeTab.model;
+        activeModel = migrateLegacyModelName(activeTab.model);
       }
     }
   }
diff --git a/src/app/store.test.ts b/src/app/store.test.ts
index 47c3977..16d1760 100644
--- a/src/app/store.test.ts
+++ b/src/app/store.test.ts
@@ -107,7 +107,7 @@ interface FakeFetchOptions {
 }
 
 function fakeFetchImpl(opts?: FakeFetchOptions): typeof fetch {
-  const models = opts?.models ?? ["opencode/deepseek-v4-flash", "openai/gpt-4o"];
+  const models = opts?.models ?? ["opencode-1/deepseek-v4-flash", "openai/gpt-4o"];
   const history = opts?.history ?? {};
   return async (input: string | URL | Request): Promise<Response> => {
     const url = typeof input === "string" ? input : input instanceof URL ? input.href : input.url;
@@ -524,7 +524,7 @@ describe("createAppStore", () => {
       const url = typeof input === "string" ? input : input instanceof URL ? input.href : input.url;
       fetchedUrls.push(url);
       if (url.endsWith("/models")) {
-        return new Response(JSON.stringify({ models: ["opencode/deepseek-v4-flash"] }), {
+        return new Response(JSON.stringify({ models: ["opencode-1/deepseek-v4-flash"] }), {
           status: 200,
         });
       }
@@ -573,7 +573,7 @@ describe("createAppStore", () => {
     const store = createAppStore({
       socketFactory: () => ws,
       fetchImpl: fakeFetchImpl({
-        models: ["opencode/deepseek-v4-flash", "openai/gpt-4o", "anthropic/claude-3"],
+        models: ["opencode-1/deepseek-v4-flash", "openai/gpt-4o", "anthropic/claude-3"],
       }),
       localStorage: createFakeStorage(),
     });
@@ -582,7 +582,7 @@ describe("createAppStore", () => {
     await new Promise((r) => setTimeout(r, 50));
 
     expect(store.models).toEqual([
-      "opencode/deepseek-v4-flash",
+      "opencode-1/deepseek-v4-flash",
       "openai/gpt-4o",
       "anthropic/claude-3",
     ]);
@@ -599,11 +599,62 @@ describe("createAppStore", () => {
     });
     ws.resolveOpen();
 
-    expect(store.activeModel).toBe("opencode/deepseek-v4-flash");
+    expect(store.activeModel).toBe("opencode-1/deepseek-v4-flash");
 
     store.dispose();
   });
 
+  it("does not silently switch the active model when the selected one is absent from the catalog", async () => {
+    // The catalog only has umans; the active (default/selected) OpenCode model is
+    // NOT available. The FE must NOT auto-fall back to the first catalog model —
+    // it keeps the selection and lets the model selector surface it as unavailable.
+    const ws = fakeSocket();
+    const store = createAppStore({
+      socketFactory: () => ws,
+      fetchImpl: fakeFetchImpl({ models: ["umans/umans-glm-5.2"] }),
+      localStorage: createFakeStorage(),
+    });
+    ws.resolveOpen();
+    await new Promise((r) => setTimeout(r, 50));
+
+    expect(store.models).toEqual(["umans/umans-glm-5.2"]);
+    expect(store.activeModel).toBe("opencode-1/deepseek-v4-flash");
+
+    store.dispose();
+  });
+
+  it("migrates a legacy persisted opencode/<model> tab model to opencode-1/<model>", async () => {
+    const ws = fakeSocket();
+    // Seed localStorage with a persisted tab whose model is the OBSOLETE
+    // `opencode/deepseek-v4-flash` namespace.
+    const storage = createFakeStorage();
+    storage.setItem(
+      "dispatch.tabs",
+      JSON.stringify({
+        tabs: [
+          {
+            conversationId: "c-legacy",
+            title: "Legacy",
+            model: "opencode/deepseek-v4-flash",
+            workspaceId: "default",
+          },
+        ],
+        activeConversationId: null,
+      }),
+    );
+    const store = createAppStore({
+      socketFactory: () => ws,
+      fetchImpl: fakeFetchImpl(),
+      localStorage: storage,
+    });
+    ws.resolveOpen();
+    // After restore, the restored tab's model + the persisted store are migrated.
+    const restored = store.tabs.find((t) => t.conversationId === "c-legacy");
+    expect(restored?.model).toBe("opencode-1/deepseek-v4-flash");
+    expect(store.activeModel).toBe("opencode-1/deepseek-v4-flash");
+    store.dispose();
+  });
+
   it("draft: sending the first message creates a tab titled from the message", () => {
     const ws = fakeSocket();
     const store = createAppStore({
@@ -679,7 +730,7 @@ describe("createAppStore", () => {
     store.send("first message");
 
     // New tab opens with the default model until the persisted-model fetch resolves.
-    expect(store.activeModel).toBe("opencode/deepseek-v4-flash");
+    expect(store.activeModel).toBe("opencode-1/deepseek-v4-flash");
 
     // Wait for the persisted model fetch to resolve.
     await vi.waitFor(() => expect(store.activeModel).toBe("openai/gpt-4o"));
@@ -1212,7 +1263,7 @@ describe("createAppStore", () => {
       const url = typeof input === "string" ? input : input instanceof URL ? input.href : input.url;
       fetchedUrls.push(url);
       if (url.endsWith("/models")) {
-        return new Response(JSON.stringify({ models: ["opencode/deepseek-v4-flash"] }), {
+        return new Response(JSON.stringify({ models: ["opencode-1/deepseek-v4-flash"] }), {
           status: 200,
         });
       }
@@ -1518,7 +1569,7 @@ describe("createAppStore", () => {
     const limits = opts?.limits ?? {
       limits: [
         { providerId: "umans", limit: 4 },
-        { providerId: "openai-compat", limit: 5 },
+        { providerId: "opencode-1", limit: 5 },
       ],
     };
     const limit = opts?.limit ?? { providerId: "umans", limit: 4 };
@@ -1526,7 +1577,7 @@ describe("createAppStore", () => {
       providers: [
         { providerId: "umans", limit: 4, inFlight: 2, queued: 1, paused: false },
         {
-          providerId: "openai-compat",
+          providerId: "opencode-1",
           limit: 5,
           inFlight: 5,
           queued: 3,
@@ -1586,7 +1637,7 @@ describe("createAppStore", () => {
     if (!result.ok) throw new Error("unreachable");
     expect(result.limits).toEqual([
       { providerId: "umans", limit: 4 },
-      { providerId: "openai-compat", limit: 5 },
+      { providerId: "opencode-1", limit: 5 },
     ]);
     store.dispose();
   });
@@ -1758,7 +1809,7 @@ describe("createAppStore", () => {
       autoReduced: false,
     });
     expect(result.providers[1]).toMatchObject({
-      providerId: "openai-compat",
+      providerId: "opencode-1",
       paused: true,
       pausedUntil: 1_719_408_000_000,
       cooldownMs: 350,