Add Module Composer API (#33284)

* Spec composer API

* Add composer api implementation

* Tests

* Copyright

* update sigs

* cleanup

* a snap

* cleanup

* linting

* Tidy up

* Adjust

apps/web/src/modules/Api.ts

@@ -33,6 +33,8 @@ import { StoresApi } from "./StoresApi.ts";
 import { WidgetLifecycleApi } from "./WidgetLifecycleApi.ts";
 import { WidgetApi } from "./WidgetApi.ts";
 import { CustomisationsApi } from "./customisationsApi.ts";
+import { ComposerApi } from "./ComposerApi.ts";
+import defaultDispatcher from "../dispatcher/dispatcher.ts";
 
 const legacyCustomisationsFactory = <T extends object>(baseCustomisations: T) => {
     let used = false;
@@ -94,6 +96,7 @@ export class ModuleApi implements Api {
     public readonly rootNode = document.getElementById("matrixchat")!;
     public readonly client = new ClientApi();
     public readonly stores = new StoresApi();
+    public readonly composer = new ComposerApi(defaultDispatcher);
 
     public createRoot(element: Element): Root {
         return createRoot(element);

apps/web/src/modules/ComposerApi.ts

@@ -0,0 +1,23 @@
+/*
+Copyright 2026 Element Creations Ltd.
+
+SPDX-License-Identifier: AGPL-3.0-only OR GPL-3.0-only OR LicenseRef-Element-Commercial
+Please see LICENSE files in the repository root for full details.
+*/
+
+import { type ComposerApi as ModuleComposerApi } from "@element-hq/element-web-module-api";
+
+import type { MatrixDispatcher } from "../dispatcher/dispatcher";
+import { Action } from "../dispatcher/actions";
+import type { ComposerInsertPayload } from "../dispatcher/payloads/ComposerInsertPayload";
+
+export class ComposerApi implements ModuleComposerApi {
+    public constructor(private readonly dispatcher: MatrixDispatcher) {}
+
+    public insertPlaintextIntoComposer(plaintext: string): void {
+        this.dispatcher.dispatch({
+            action: Action.ComposerInsert,
+            text: plaintext,
+        } satisfies ComposerInsertPayload);
+    }
+}