feat: v2.6.0 — Chat UI composer (+ menu, project files, activity panel, permission mode, Stop), git on a workspace's extra folders (#70), long paste as a file (#68), S3 server mode (experimental)

Chat UI:
- Each Claude/Codex session keeps its own chat/terminal view; Settings only
  sets how new sessions open.
- Composer + menu: upload, project files and folders (#54, also dragged from
  the Files/Changes tree), context files, recent uploads, skills, plugins.
- Activity side panel (progress, outputs, files read, uploads, memory,
  skills, connectors) with a file preview; edited-file counts per turn.
- Permission-mode chip (Shift+Tab steps, read back from the pane:
  server/lib/pane-mode.js, GET|POST /api/run/:id/permission-mode).
- Stop (Esc) while the main agent works; the status is checked per agent
  (with session_id /api/agents ignores its status filter) and re-read every
  5 s while Stop shows.
- Dropped images shown in the conversation (GET /api/run/drop/:name, the
  requester's own drop dir), full-size viewer.
- A plain-text paste over 5,000 characters is attached as pasted-text.txt,
  so no prompt reaches tmux/argv limits (#68).

Changes panel: every /api/lanes/:id/git* route takes ?source=<lane_sources
id> (sourceFolder; ENOSOURCE otherwise) and a folder picker switches the
whole panel to a workspace's extra folder (#70).

Server mode S3 (one Linux user per account) — experimental, verified with
fake sudo plus a P6 managed-settings spike on a test account:
- member tmux listing runs in the background (cached, 15 s => unknown);
- transcript snapshot copy is async, chunked, temp file + rename;
- Express Layer patch only on Express 4;
- tmux capturePane/sendKey go to the member's own server.

Docs: the multi-user design moved in as docs/plans/server-mode/README.md
(the AgentHub-Server repo is gone); S3-PLAN P6 result; LANES/API/openapi.

client/src/lib/promptAttach.ts

@@ -0,0 +1,101 @@
+/**
+ * @file promptAttach.ts
+ * @description What a prompt box can attach besides a fresh upload: a project
+ * file or folder dragged from the Files panel (`ATTACH_MIME`, read back by
+ * `PromptEditor`'s drop) and the files uploaded through a prompt box in the
+ * last day (`recentUploads`, kept in this browser). An attachment is a path
+ * sent with the prompt, so nothing here touches the server.
+ * @author Nguyễn Ngọc Trí Vĩ <vinnt@smartgift.vn>
+ */
+
+import type { DragEvent } from "react";
+
+/** One attachment, shaped like `PromptImage`: what is sent, and its label. */
+export interface Attachment {
+  path: string;
+  name: string;
+  url?: string;
+}
+
+export const ATTACH_MIME = "application/x-agenthub-attach";
+
+/** A project path (relative to the box's folder) as Claude Code's `@` mention. */
+export function projectAttachment(rel: string): Attachment {
+  const name = rel.replace(/\/$/, "").split("/").pop() || rel;
+  return { path: `@${rel}`, name: rel.endsWith("/") ? `${name}/` : name };
+}
+
+/** Start a drag carrying `rel` (a Files panel row) to a prompt box; plain
+ *  text too, so a drop elsewhere (a terminal, an editor) gets the path. */
+export function dragProjectPath(e: DragEvent, rel: string) {
+  e.dataTransfer.setData(ATTACH_MIME, JSON.stringify(projectAttachment(rel)));
+  e.dataTransfer.setData("text/plain", rel);
+  e.dataTransfer.effectAllowed = "copy";
+}
+
+/** The attachment a drop carries, if it is one of ours. */
+export function droppedAttachment(dt: DataTransfer | null | undefined): Attachment | null {
+  try {
+    const v: unknown = JSON.parse(dt?.getData(ATTACH_MIME) || "null");
+    const a = v as Attachment | null;
+    return a && typeof a.path === "string" && typeof a.name === "string"
+      ? { path: a.path, name: a.name }
+      : null;
+  } catch {
+    return null;
+  }
+}
+
+/** `prev` plus whichever of `items` it does not hold yet. */
+export function addAttachments<T extends Attachment>(prev: T[], items: T[]): T[] {
+  const fresh = items.filter(
+    (a, i) =>
+      !prev.some((p) => p.path === a.path) && items.findIndex((b) => b.path === a.path) === i
+  );
+  return fresh.length ? [...prev, ...fresh] : prev;
+}
+
+const RECENT_KEY = "agenthub.prompt.recentUploads";
+const RECENT_MAX = 20;
+// The server prunes an upload a day after it was written (`saveDrop`).
+// ponytail: a client-side guess of that TTL, a few minutes short; a listing
+// route instead if uploads must outlive it or follow the user to another browser.
+const RECENT_TTL_MS = 23.9 * 60 * 60_000;
+
+interface Recent extends Attachment {
+  at: number;
+}
+
+function readRecent(): Recent[] {
+  try {
+    const v: unknown = JSON.parse(localStorage.getItem(RECENT_KEY) || "[]");
+    const cutoff = Date.now() - RECENT_TTL_MS;
+    return (Array.isArray(v) ? (v as Recent[]) : []).filter(
+      (r) => typeof r?.path === "string" && typeof r.name === "string" && r.at > cutoff
+    );
+  } catch {
+    return [];
+  }
+}
+
+export function recentUploads(): Attachment[] {
+  return readRecent().map(({ path, name, url }) => ({ path, name, ...(url ? { url } : {}) }));
+}
+
+/** Remember uploads just saved, newest first; an image keeps a thumbnail
+ *  through `GET /api/run/drop/:name` (its local blob URL dies with the page). */
+export function rememberUploads(items: { path: string; name: string; image: boolean }[]) {
+  const at = Date.now();
+  const added: Recent[] = items.map(({ path, name, image }) => ({
+    path,
+    name,
+    at,
+    ...(image ? { url: `/api/run/drop/${encodeURIComponent(path.split("/").pop() || "")}` } : {}),
+  }));
+  const kept = readRecent().filter((r) => !added.some((a) => a.path === r.path));
+  try {
+    localStorage.setItem(RECENT_KEY, JSON.stringify([...added, ...kept].slice(0, RECENT_MAX)));
+  } catch {
+    /* storage full or blocked: the list is a convenience */
+  }
+}