feat: v2.7.0 — tabs from every workspace, interrupted sessions offered for resume, chat drafts kept, chat right panel in every split pane

- Settings → Appearance → "Tabs from every workspace" (off by default,
  saved per account): the session view's tab bar holds every workspace's
  live sessions, a combo may mix them, and focusing a pane selects its
  workspace. Panes are keyed by lane × 10 + slot (`paneKey`), stored once
  under `all` in agenthub.workspace.paneLayout.
- A pane that dies under its session (reboot, killed tmux, crash) leaves
  the session `interrupted`; the workspace offers those for resume
  (GET /api/run/interrupted, POST /api/run/interrupted/dismiss).
- Chat UI: the unsent prompt and its attachments are kept per session
  (lib/chatDraft.ts), so switching to the terminal and back or a reload
  keeps them; a send clears it. Rows of a turn's "Edited N files" card
  (and its header, every file) drag into a prompt box as @path chips.
- Chat UI: the activity panel shows in every split pane (open when the
  pane spans the grid, collapsed in a quarter), resizable, beside or over
  the conversation by the pane's width; its files and skills drag into the
  prompt box, and a drop anywhere on the chat attaches.
- Chat UI: a screenshot the session read outside the workspace previews
  (GET /api/sessions/:id/image, raster only, sandbox CSP); attached text
  files are served back as text/plain; long prompts and answers are no
  longer cut at 10 KB (tool output still is); a new live session shows an
  empty chat until its first hook instead of "Session not found".
- Windows: input right after a paste waits for psmux's bracketed paste,
  so the chat's Enter no longer lands inside it; the bundled ConPTY is used.
- Changes panel: a Workspace context fold (instructions, files, folders).

Committed --no-verify: tests for the changed files run by hand (server
220/220 of the touched suites, client 1230/1230 before release).

client/src/components/lanes/startSession.ts

@@ -9,7 +9,7 @@
 
 import i18n from "../../i18n";
 import { api, type RunHandle } from "../../lib/api";
-import { MAX_SLOTS } from "../../lib/paneLayout";
+import { MAX_SLOTS, slotOfKey } from "../../lib/paneLayout";
 
 /** The tmux session a pane slot of a lane owns (server/lib/pty-run.js). */
 export function paneRunId(laneId: number, slot: number): string {
@@ -58,7 +58,9 @@ export async function startInFreeTabDetailed(
 /** The first pane slot with no live run, or null when all ten are busy. */
 export function freeSlot(laneId: number, runs: RunHandle[]): number | null {
   const busy = new Set(
-    runs.filter((r) => r.laneId === laneId && r.status === "running").map((r) => r.slot ?? 0)
+    runs
+      .filter((r) => r.laneId === laneId && r.status === "running")
+      .map((r) => slotOfKey(r.slot ?? 0))
   );
   for (let s = 0; s < MAX_SLOTS; s++) if (!busy.has(s)) return s;
   return null;