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/__tests__/lanes-api.test.js

@@ -2017,6 +2017,70 @@ describe("a session's own worktree (claude --worktree)", () => {
   });
 });
 
+describe("an extra folder's own repo (?source=)", () => {
+  const { execFileSync } = require("child_process");
+  const gitEnv = Object.fromEntries(
+    Object.entries(process.env).filter(([k]) => !k.startsWith("GIT_"))
+  );
+  const gitIn = (dir, ...args) =>
+    execFileSync("git", ["-C", dir, "-c", "user.name=t", "-c", "user.email=t@t", ...args], {
+      encoding: "utf8",
+      env: gitEnv,
+    });
+  let ws, extra, laneId, otherLaneId, sourceId, fileSourceId;
+
+  before(async () => {
+    const root = fs.realpathSync(fs.mkdtempSync(path.join(os.tmpdir(), "lane-src-git-")));
+    ws = path.join(root, "ws");
+    extra = path.join(root, "extra");
+    for (const dir of [ws, extra]) {
+      fs.mkdirSync(dir);
+      gitIn(dir, "init", "-q", "-b", "main");
+      fs.writeFileSync(path.join(dir, "a.txt"), "a\n");
+      gitIn(dir, "add", ".");
+      gitIn(dir, "commit", "-qm", "init");
+    }
+    laneId = (await request("POST", "/api/lanes", { cwd: ws })).body.lane.id;
+    otherLaneId = (await request("POST", "/api/lanes", { cwd: extra })).body.lane.id;
+    const src = require("../lib/lane-sources");
+    sourceId = src.addFolder(laneId, extra).id;
+    fileSourceId = require("../db")
+      .db.prepare(
+        "INSERT INTO lane_sources (lane_id, kind, path, name, added_at) VALUES (?, 'file', ?, 'f', '2026-10-09T00:00:00Z')"
+      )
+      .run(laneId, path.join(extra, "a.txt")).lastInsertRowid;
+  });
+
+  it("reads and writes git in the extra folder, never falling back", async () => {
+    fs.writeFileSync(path.join(extra, "only-in-extra.txt"), "x\n");
+    const inExtra = await request("GET", `/api/lanes/${laneId}/git/changes?source=${sourceId}`);
+    assert.ok(inExtra.body.files.some((f) => f.path === "only-in-extra.txt"));
+    const facts = await request("GET", `/api/lanes/${laneId}/git?source=${sourceId}`);
+    assert.equal(facts.body.base, "main");
+    const main = await request("GET", `/api/lanes/${laneId}/git/changes`);
+    assert.ok(!main.body.files.some((f) => f.path === "only-in-extra.txt"));
+    const ok = await request("POST", `/api/lanes/${laneId}/git/stage?source=${sourceId}`, {
+      paths: ["only-in-extra.txt"],
+    });
+    assert.equal(ok.status, 200);
+    assert.match(gitIn(extra, "diff", "--cached", "--name-only"), /only-in-extra\.txt/);
+  });
+
+  it("answers ENOSOURCE for a source that is not this workspace's folder", async () => {
+    for (const id of ["nope", "999999", String(fileSourceId)]) {
+      const r = await request("POST", `/api/lanes/${laneId}/git/stage?source=${id}`, {
+        paths: ["only-in-extra.txt"],
+      });
+      assert.equal(r.status, 404, id);
+      assert.equal(r.body.error.code, "ENOSOURCE", id);
+    }
+    // Another workspace's request may not borrow this one's source id.
+    const r = await request("GET", `/api/lanes/${otherLaneId}/git/changes?source=${sourceId}`);
+    assert.equal(r.status, 404);
+    assert.equal(r.body.error.code, "ENOSOURCE");
+  });
+});
+
 // The server, not a stale client list, picks the tab and refuses a second pane
 // on a session one already holds.
 describe("start: slot auto and a session already live", () => {