feat(ui): submit task composers with Enter by default (#19272)

Use Enter to submit task replies and new tasks, with Shift+Enter for a new line. Add an experimental preference to require Command/Ctrl+Enter.

Preserve autocomplete selection and IME confirmation, and retain the modifier shortcut until saved settings load.

Co-Authored-By: Paperclip <noreply@paperclip.ing>

server/src/__tests__/instance-settings-service.test.ts

@@ -10,6 +10,14 @@ import {
 import type { ManagedInstanceConfig } from "../services/managed-config.js";
 
 describe("instance settings service", () => {
+  it("retains the legacy composer preference through saved and unrelated settings updates", () => {
+    expect(normalizeExperimentalSettings({}).enableLegacyComposerSubmit).toBe(false);
+    const enabled = applyExperimentalSettingsPatch({}, { enableLegacyComposerSubmit: true });
+    const saved = JSON.parse(JSON.stringify(enabled));
+    expect(normalizeExperimentalSettings(saved).enableLegacyComposerSubmit).toBe(true);
+    expect(applyExperimentalSettingsPatch(saved, { enableCases: true }).enableLegacyComposerSubmit).toBe(true);
+    expect(applyExperimentalSettingsPatch(saved, { enableLegacyComposerSubmit: false }).enableLegacyComposerSubmit).toBe(false);
+  });
   it("defaults remote workspace enrollment on while preserving explicit operator choices", () => {
     expect(instanceExperimentalSettingsSchema.parse({}).remoteWorkspaceStorageEnabled).toBe(true);
     expect(INSTANCE_FEATURE_CATALOG.remoteWorkspaceStorageEnabled).toMatchObject({ cloudDefault: true, selfHostedDefault: true });
@@ -118,6 +126,7 @@ describe("instance settings service", () => {
       enableGoogleWorkspaceConnector: false,
       enableConferenceRoomChat: false,
       enableClassicTaskInterface: false,
+      enableLegacyComposerSubmit: false,
       enableExternalObjects: false,
       enableSmokeLab: false,
       enableCases: false,

server/src/services/instance-settings.ts

@@ -272,6 +272,7 @@ export function normalizeExperimentalSettings(raw: unknown): InstanceExperimenta
       enableArtifactsV1: parsed.data.enableArtifactsV1 ?? true,
       enableConferenceRoomChat: parsed.data.enableConferenceRoomChat ?? false,
       enableClassicTaskInterface: parsed.data.enableClassicTaskInterface ?? false,
+      enableLegacyComposerSubmit: parsed.data.enableLegacyComposerSubmit ?? false,
       enableIssuePlanDecompositions: parsed.data.enableIssuePlanDecompositions ?? false,
       enableExperimentalFileViewer: parsed.data.enableExperimentalFileViewer ?? false,
       enableExternalObjects: parsed.data.enableExternalObjects ?? false,
@@ -330,6 +331,7 @@ export function normalizeExperimentalSettings(raw: unknown): InstanceExperimenta
     enableArtifactsV1: true,
     enableConferenceRoomChat: false,
     enableClassicTaskInterface: false,
+    enableLegacyComposerSubmit: false,
     enableIssuePlanDecompositions: false,
     enableExperimentalFileViewer: false,
     enableExternalObjects: false,