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.

server/README.md

@@ -764,6 +764,9 @@ HTTP surface for the tmux-backed terminal run: one session per workspace, named
 | `GET`    | `/api/run/cwds`               | Suggested cwds (dashboard, home, recent from sessions) |
 | `POST`   | `/api/run/drop-image`          | An image dropped on the Workspace terminal. Raw body, `Content-Type` one of `image/png\|jpeg\|gif\|webp`, ≤20 MB. Saved `0600` under `<data dir>/drops/` (`0700`, never a guessable name in the shared tmp; S3: the member's own `~/.agenthub/handoff/drops/`) with a RANDOM name (nothing from the request names the file); files older than a day are pruned on each write. Answers `{ path }`, which `TerminalView` pastes into the pane — what a local terminal does on a drop, and how `claude` attaches the image. 400 for any other type |
 | `POST`   | `/api/run/drop-file?name=…`    | Any file (or image) dropped on the Workspace terminal or pasted/dropped into a prompt box. Raw body of any type, ≤20 MB, same directory (S3: `?laneId=` saves it AS the account that workspace's panes run as, so the pane can read it), `0600` and day-old pruning as `drop-image`. The name is the file's own, reduced to a `[A-Za-z0-9._-]` basename behind a random 16-hex prefix (so it can neither leave the directory nor collide, and space-joined paths stay parseable). Answers `{ path }`; 400 for an empty body or a name that sanitizes to nothing. The client uses this for every drop; `drop-image` is kept for API callers |
+| `GET`    | `/api/run/drop/:name`          | A dropped IMAGE served back, so a chat turn shows the picture instead of its path. Only a name `drop-image`/`drop-file` made (16-hex prefix, no separator) with a png/jpg/gif/webp extension, only a regular file in the REQUESTER's drop dir (S3: their member account's, owned by that account — an admin viewing a member's session gets the name chip, not the image); under `nosniff` and a `sandbox` CSP like `/git/raw`. 404 otherwise, and once the day-old prune removed it |
+| `GET`    | `/api/run/:id/permission-mode` | A live **claude** pane's permission mode, read off the mode line Claude Code prints under its prompt (`server/lib/pane-mode.js`): `{ mode }` — `default`, `acceptEdits`, `plan`, `auto`, `bypassPermissions`, `dontAsk`, or `null` while a menu hides it. 404 for a pane that is not running, 400 `EUNSUPPORTED` for a non-claude pane |
+| `POST`   | `/api/run/:id/permission-mode` | `{ mode }` → steps the pane there with Shift+Tab, the only way a running session changes mode, reading every step back before the next key. `{ mode }` on success; 400 `EBADMODE` outside the five settable modes; 409 `EMODEUNKNOWN` (no mode line — nothing is pressed — or a step did not change it), `EMODEUNAVAILABLE` (not in this session's cycle, e.g. Bypass in a session not started with it; the pane is back on its starting mode), `EBUSY` (a change is already running on that pane) |
 | `GET`    | `/api/run/files?cwd=…&q=…`    | Fuzzy file search inside `cwd` for the run panel's `@`-file autocomplete. Skips `node_modules`, `.git`, `dist`, `build`, `.next`, `.cache`, `coverage`, `vendor`, etc. Cwd is required and must exist; results are capped and ranked by basename match |
 | `POST`   | `/api/run`                    | Create-or-adopt the workspace's tmux session. Body: `{ laneId, cwd, initialPrompt?, model?, permissionMode?, effort?, resumeSessionId? }`. The CLI comes from the workspace row, never from the body. An existing session whose pane sits at a shell prompt gets the argv typed into it; a pane already running a program is adopted unchanged |
 | `GET`    | `/api/run/:id`                | One run handle, or 404 once its tmux session is gone |