fix(plugins): composer commands run on current state, report failures, and reach the overflow sheet

Draft commands read the state captured at render, so a plugin's
`await setProvider(); await setModel()` acted on a stale provider. The draft
form and options are now plain stores that commands read live, and
`setProvider`/`setModel` reject an unavailable provider or a model the loaded
catalog does not list. Draft `options` include the plugin's pending edits.

Shared composer controls own the pending state and show a rejected command as
an error toast, like the built-in controls. Callback payloads are objects
(`{ value }`, `onPress(event)`) so they can grow without breaking plugins.

The overflow sheet's content portals to the app root and lost the composer's
agent, input, toast and query contexts, so plugin items drew nothing in it.
`useComposerSheetBridge` carries them across.

packages/app/src/plugins/composer-items/model.test.ts

@@ -69,7 +69,11 @@ function fakeAgent(context: ComposerAgent["context"]) {
     thinking: null,
     options: { effort: "high" },
     metadata: { flag: true },
-    setProvider: async (provider) => void calls.push(`provider:${provider}`),
+    // A running agent keeps its provider, as the real adapter does.
+    setProvider: async (provider) => {
+      if (context === "agent") throw new Error("A running agent cannot change provider.");
+      calls.push(`provider:${provider}`);
+    },
     setModel: async (model) => void calls.push(`model:${model}`),
     setMode: async (mode) => void calls.push(`mode:${mode}`),
     setThinking: async (thinking) => void calls.push(`thinking:${thinking}`),
@@ -133,14 +137,12 @@ describe("toPluginComposer", () => {
         composerInput: input,
         prompt: "",
       });
-      await composer.setProvider("codex");
       await composer.setModel("gpt");
       await composer.setMode("plan");
       await composer.setThinking("high");
       await composer.setOptions({ effort: "low" });
       await composer.setMetadata({ flag: null });
       expect(calls).toEqual([
-        "provider:codex",
         "model:gpt",
         "mode:plan",
         "thinking:high",
@@ -150,6 +152,29 @@ describe("toPluginComposer", () => {
     },
   );
 
+  it("lets a draft change provider and tells a running agent it cannot", async () => {
+    const { input } = fakeInput();
+    const draft = fakeAgent("draft");
+    await toPluginComposer({
+      plugin: installed(),
+      agent: draft.agent,
+      composerInput: input,
+      prompt: "",
+    }).setProvider("codex");
+    expect(draft.calls).toEqual(["provider:codex"]);
+
+    const running = fakeAgent("agent");
+    await expect(
+      toPluginComposer({
+        plugin: installed(),
+        agent: running.agent,
+        composerInput: input,
+        prompt: "",
+      }).setProvider("codex"),
+    ).rejects.toThrow("A running agent cannot change provider.");
+    expect(running.calls).toEqual([]);
+  });
+
   it("changes the prompt and inserts at the cursor", () => {
     const { agent } = fakeAgent("draft");
     const { input, state } = fakeInput();

packages/app/src/plugins/react-native/composer-controls.tsx

@@ -43,7 +43,7 @@ export function Toggle({ title, icon, disabled, value, onValueChange }: TogglePr
       icon: Icon,
       highlight: value ? "blue" : undefined,
       value,
-      onChange: onValueChange,
+      onChange: (next) => onValueChange({ value: next }),
     }),
     [Icon, onValueChange, title, value],
   );
@@ -67,7 +67,7 @@ export function Select<Value extends string>({
       icon: Icon,
       value,
       choices: options,
-      onChange: (next) => onValueChange(next as Value),
+      onChange: (next) => onValueChange({ value: next as Value }),
       showCaret: true,
     }),
     [Icon, onValueChange, options, title, value],
@@ -78,7 +78,7 @@ export function Select<Value extends string>({
 export function Action({ title, icon, disabled, onPress }: ActionProps) {
   const Icon = usePluginControlIcon(icon);
   const item = useMemo<ComposerControlItem>(
-    () => ({ id: "plugin-action", type: "action", title, icon: Icon, onPress }),
+    () => ({ id: "plugin-action", type: "action", title, icon: Icon, onPress: () => onPress({}) }),
     [Icon, onPress, title],
   );
   return <PluginComposerControl item={item} disabled={disabled} />;