feat(chat): turn /btw into an isolated composer (#3398)

* feat(chat): turn /btw into an isolated composer

* fix(chat): preserve direct BTW sends and isolate pending preparation

---------

Co-authored-by: Bohdan Triapitsyn <artmore@protonmail.com>

packages/ui/src/sync/input-store.ts

@@ -120,6 +120,11 @@ export type SyntheticContextPart = {
   metadata?: ContextPartMetadata
 }
 
+type PendingBtwComposerRequest = {
+  parentSessionId: string
+  text: string
+}
+
 export type VSCodeActiveEditorFile = {
   filePath: string
   fileName: string
@@ -144,6 +149,7 @@ export type InputState = {
    * narrow layouts); consumed by ChatInput, which owns the command-aware submit.
    */
   pendingPresetSubmit: { text: string; type: "command" | "skill" } | null
+  pendingBtwComposerRequest: PendingBtwComposerRequest | null
   attachedFiles: AttachedFile[]
   activeEditorFile: VSCodeActiveEditorFile | null
 
@@ -151,6 +157,8 @@ export type InputState = {
   consumePendingInputText: () => { text: string; mode: "replace" | "append" | "append-inline" } | null
   requestPresetSubmit: (text: string, type: "command" | "skill") => void
   consumePendingPresetSubmit: () => { text: string; type: "command" | "skill" } | null
+  requestBtwComposer: (request: PendingBtwComposerRequest) => void
+  consumePendingBtwComposerRequest: (parentSessionId: string | null) => PendingBtwComposerRequest | null
   setPendingSyntheticParts: (parts: SyntheticContextPart[] | null) => void
   consumePendingSyntheticParts: () => SyntheticContextPart[] | null
   addAttachedFile: (file: File) => Promise<boolean>
@@ -176,6 +184,7 @@ export const useInputStore = create<InputState>()((set, get) => ({
   pendingInputMode: "replace",
   pendingSyntheticParts: null,
   pendingPresetSubmit: null,
+  pendingBtwComposerRequest: null,
   attachedFiles: [],
   activeEditorFile: null,
 
@@ -198,6 +207,15 @@ export const useInputStore = create<InputState>()((set, get) => ({
     return pendingPresetSubmit
   },
 
+  requestBtwComposer: (request) => set({ pendingBtwComposerRequest: request }),
+
+  consumePendingBtwComposerRequest: (parentSessionId) => {
+    const request = get().pendingBtwComposerRequest
+    if (!request || request.parentSessionId !== parentSessionId) return null
+    set({ pendingBtwComposerRequest: null })
+    return request
+  },
+
   setPendingSyntheticParts: (parts) => set({ pendingSyntheticParts: parts }),
 
   consumePendingSyntheticParts: () => {