feat: v2.7.7 — File Explorer on workspaces and the user's home, clone with per-user git identity

- File Explorer (Files in the sidebar, /files; also from a workspace's Files
  tab, portalled so no panel clips it), laid out like GNOME Files: places
  (Home, workspaces, Trash), Back/Forward/Up, path bar, search, icon grid with
  image thumbnails or list, labelled New/Upload, selection action bar, hidden
  files behind Ctrl+H, right-click menus and the usual keys.
  Make, rename, move, copy (within a workspace, between workspaces, home ↔
  workspace), delete into a per-account trash restorable for 7 days, streamed
  upload of files and whole folders (≤ 500 MB a batch, Replace / Keep both /
  Skip on a taken name), download a file or a zip of anything.
  server/lib/file-explorer.js, /api/lanes/:id/fs/*, /api/homes/:who/fs/*.
- The user's home: every dot entry at its top stays hidden and refused
  (also via a symlink, download, zip or as a copy source); an admin may view
  other users' homes read-only, audited.
- write-as learns move/copy (re-run `sudo agenthub server install-system`).
- Hardening: a write to a workspace re-checks its owner by the live role;
  S3 keeps its server.conf if the file stops reading and a tmux call never
  falls back to the host's server; the AI Proxy gateway marks what it relays
  and the dashboard refuses it; a NUL in a pane's argv/env is refused.
- OpenAPI for the new routes (server/openapi-extra/files.js); docs (API,
  SERVER-MODE, CLAUDE.md) updated.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

docs/SERVER-MODE.md

@@ -713,6 +713,20 @@ Every command below runs as the **host account** (the one that runs the
 dashboard) unless it says `sudo`. `agenthub server install-system` calls sudo
 itself, once.
 
+### After an update that changes the member helpers
+
+`write-as`, `pane-launch` and the sudoers file are copied to
+`/opt/agenthub/libexec` by `install-system` only — an update of AgentHub does
+not touch root-owned files. When a release changes them (v2.7.7: `write-as`
+learned `move`/`copy` for the File Explorer), re-run it once:
+
+```bash
+sudo agenthub server install-system
+```
+
+Until then the File Explorer's move, copy and delete in a member's folder
+answer `409 EUPGRADE` (listing, upload, new folder/file and zip work).
+
 ### What a new machine needs before `install-system`
 
 `install-system` does not do any of this:
@@ -955,6 +969,8 @@ To remove everything:
 | `409 ENOTSHARED` on a member's start | That tool is not published to `/opt/agenthub/tools` yet: `agenthub server tools`. |
 | `403 EMEMBERLANE` | Worktree mode and the runtime layer are not offered in a member's folder; use Repo mode and the prompt box's New worktree. |
 | `400 EMEMBERCRED` | Older builds only: a member's typed git login was refused. Now it goes into their own store (Settings → Git → **Your git identity**). |
+| `409 EOWNERFOLDER` (on a write to an existing workspace) | Its owner may no longer own that folder by their CURRENT role — typically an admin demoted to developer whose workspace is outside the users root (it runs as the host). Reads still work; an admin reassigns the workspace or restores the role. |
+| `403 EGATEWAY` | A request relayed by the AI Proxy gateway reached the dashboard itself (a proxy profile whose base URL points back at AgentHub). Point the profile at the real proxy. |
 | `409 ESTOREUNREADABLE` | The dashboard cannot read the member's `~/.config/agenthub/git-credentials` (the unit lost `CAP_DAC_READ_SEARCH`, or the file is not the member's own regular file); nothing is rewritten. Check `grep CapAmb /proc/<pid>/status` shows `0000000000000004`. |
 | `403 EPEER` on a hook | The hook came from an account that is neither the host nor an enabled member, or the uid could not be read. |
 | `403 EFOREIGN` on a hook | A member's hook named a folder, session or pane outside their own home. |