refactor(app): extract composer-actions module with pure tests (#720)

Move composer cancel/queue/attachment/dispatch orchestration out of
composer.tsx into a React-free actions module. The module takes its
dependencies (send client, queue writer, stream writer, attachment
persister, image picker) as injected ports, so the new
composer-actions.test.ts can drive every action with inline fakes —
zero vi.mock of internal modules, zero JSDOM, zero React.

The old composer.test.tsx (heavy mocked component test) is removed
and replaced with composer-actions.test.ts (31 unit tests).

Also extract isWorkspaceAttachment / userAttachmentsOnly /
workspaceAttachmentToSubmitAttachment from composer-workspace-attachments.tsx
into a sibling .ts so the actions module (and composer-attachments.ts)
can use them without dragging React/RN/lucide into a pure test graph.

packages/app/src/attachments/composer-workspace-attachments.tsx

@@ -9,8 +9,12 @@ import type {
 } from "@/attachments/types";
 import { AttachmentPill } from "@/components/attachment-pill";
 import { useWorkspaceAttachmentsStore } from "@/attachments/workspace-attachments-store";
+import {
+  isWorkspaceAttachment,
+  userAttachmentsOnly,
+  workspaceAttachmentToSubmitAttachment,
+} from "@/attachments/workspace-attachment-utils";
 import { ICON_SIZE, type Theme } from "@/styles/theme";
-import type { AgentAttachment } from "@server/shared/messages";
 import { useClearReviewDraft } from "@/review/store";
 
 interface WorkspaceAttachmentBindingInput {
@@ -69,31 +73,6 @@ function getAttachmentKey(attachment: WorkspaceComposerAttachment): string {
   });
 }
 
-function isWorkspaceAttachment(
-  attachment: ComposerAttachment | undefined,
-): attachment is WorkspaceComposerAttachment {
-  return attachment?.kind === "review" || attachment?.kind === "browser_element";
-}
-
-function userAttachmentsOnly(attachments: readonly ComposerAttachment[]): UserComposerAttachment[] {
-  return attachments.filter(
-    (attachment): attachment is UserComposerAttachment =>
-      attachment.kind !== "review" && attachment.kind !== "browser_element",
-  );
-}
-
-function toSubmitAttachment(attachment: ComposerAttachment): AgentAttachment | null {
-  if (attachment.kind === "browser_element") {
-    return {
-      type: "text",
-      mimeType: "text/plain",
-      title: `Browser element · ${attachment.attachment.tag}`,
-      text: attachment.attachment.formatted,
-    };
-  }
-  return attachment.kind === "review" ? attachment.attachment : null;
-}
-
 function renderPill(args: RenderWorkspaceAttachmentPillArgs): ReactElement {
   return (
     <WorkspaceAttachmentPill
@@ -303,7 +282,7 @@ function WorkspaceAttachmentPill({
 export const composerWorkspaceAttachment = {
   is: isWorkspaceAttachment,
   renderPill,
-  toSubmitAttachment,
+  toSubmitAttachment: workspaceAttachmentToSubmitAttachment,
   userAttachmentsOnly,
   useBinding: useWorkspaceAttachmentBinding,
 };

packages/app/src/attachments/workspace-attachment-utils.ts

@@ -0,0 +1,35 @@
+import type {
+  ComposerAttachment,
+  UserComposerAttachment,
+  WorkspaceComposerAttachment,
+} from "@/attachments/types";
+import type { AgentAttachment } from "@server/shared/messages";
+
+export function isWorkspaceAttachment(
+  attachment: ComposerAttachment | undefined,
+): attachment is WorkspaceComposerAttachment {
+  return attachment?.kind === "review" || attachment?.kind === "browser_element";
+}
+
+export function userAttachmentsOnly(
+  attachments: readonly ComposerAttachment[],
+): UserComposerAttachment[] {
+  return attachments.filter(
+    (attachment): attachment is UserComposerAttachment =>
+      attachment.kind !== "review" && attachment.kind !== "browser_element",
+  );
+}
+
+export function workspaceAttachmentToSubmitAttachment(
+  attachment: ComposerAttachment,
+): AgentAttachment | null {
+  if (attachment.kind === "browser_element") {
+    return {
+      type: "text",
+      mimeType: "text/plain",
+      title: `Browser element · ${attachment.attachment.tag}`,
+      text: attachment.attachment.formatted,
+    };
+  }
+  return attachment.kind === "review" ? attachment.attachment : null;
+}