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>

server/__tests__/s3-fail-closed.test.js

@@ -0,0 +1,84 @@
+/**
+ * @file S3 fails closed: a server that started with S3 keeps its
+ * server.conf when the file later fails to read (it never silently becomes
+ * "no S3", which would run a member's pane as the host account), and a tmux
+ * call whose account cannot be told under S3 fails instead of going to the
+ * host's own tmux server.
+ * @author Nguyễn Ngọc Trí Vĩ <vinnt@smartgift.vn>
+ */
+
+const { describe, it, after } = require("node:test");
+const assert = require("node:assert/strict");
+const fs = require("node:fs");
+const os = require("node:os");
+const path = require("node:path");
+
+const TMP = fs.mkdtempSync(path.join(os.tmpdir(), "s3-fail-closed-"));
+const CONF = path.join(TMP, "server.conf");
+process.env.AGENTHUB_SERVER_CONF = CONF;
+process.env.DASHBOARD_DB_PATH = path.join(TMP, "t.db");
+
+const linux = require("../lib/linux-accounts");
+const tmux = require("../lib/tmux");
+
+const writeConf = () =>
+  fs.writeFileSync(CONF, `HOST_USER=h\nHOST_UID=1000\nUSERS_ROOT=${path.join(TMP, "users")}\n`);
+const later = (ms) => {
+  const real = Date.now;
+  const t = real() + ms;
+  Date.now = () => t;
+  return () => (Date.now = real);
+};
+
+after(() => {
+  delete process.env.AGENTHUB_MODE;
+  linux.__resetConfCache();
+  tmux.__reset();
+});
+
+describe("S3 fails closed", () => {
+  it("keeps the last good server.conf in server mode when the file stops reading", () => {
+    process.env.AGENTHUB_MODE = "server";
+    linux.__resetConfCache();
+    writeConf();
+    assert.equal(linux.s3Enabled(), true);
+    fs.rmSync(CONF);
+    const restore = later(10_000); // past the 5 s cache
+    try {
+      assert.equal(linux.s3Enabled(), true, "still S3: never fall back to the host");
+      assert.equal(linux.serverConf().usersRoot, path.join(TMP, "users"));
+    } finally {
+      restore();
+    }
+  });
+
+  it("outside server mode a missing file is simply no S3", () => {
+    delete process.env.AGENTHUB_MODE;
+    linux.__resetConfCache();
+    writeConf();
+    linux.serverConf();
+    fs.rmSync(CONF);
+    const restore = later(10_000);
+    try {
+      assert.equal(linux.serverConf(), null);
+    } finally {
+      restore();
+    }
+  });
+
+  it("a tmux call whose account cannot be told under S3 fails, never reaching the host's tmux", () => {
+    process.env.AGENTHUB_MODE = "server";
+    linux.__resetConfCache();
+    writeConf();
+    const calls = [];
+    tmux.__setExecImpl((args) => {
+      calls.push(args);
+      return "";
+    });
+    tmux.__setAccountImpl(() => {
+      throw Object.assign(new Error("database is locked"), { code: "SQLITE_BUSY" });
+    });
+    assert.throws(() => tmux.sendText("agenthub-lane-7", "ls"), { code: "SQLITE_BUSY" });
+    assert.deepEqual(calls, [], "nothing ran on the host's tmux server");
+  });
+});