feat(run): show externally started Claude sessions in the active-runs list

The Workspace active-runs list only knew about runs this dashboard spawned,
so two `claude` sessions started by hand in terminal tabs showed up nowhere —
the list read "no active runs" while two agents were working.

Poll GET /api/sessions?status=active alongside the run list and merge those
sessions in as live rows, deduped against dashboard runs by session_id and
filtered to local sources with a cwd (a remote-source or cwd-less session
cannot be resumed on this machine).

External rows get no Attach action: the dashboard owns no tmux session for
them, so there is no PTY to bridge. They offer Resume, which reuses the
existing ensure-lane + start-with-resumeSessionId path to spawn a new
tmux-backed `claude --resume` in that folder — a second process on the same
transcript, not a view of the original terminal.

client/src/components/run/__tests__/RunHistory.test.tsx

@@ -17,6 +17,7 @@ import { beforeEach, describe, expect, it, vi } from "vitest";
 import i18n from "i18next";
 import { ActiveRunsSwitcher, RunsModal, type UnifiedRunRow } from "../RunHistory";
 import type { DashboardRunHistoryItem, RunListResponse } from "../../../lib/api";
+import type { Session } from "../../../lib/types";
 
 const LIVE_ID = "run-live";
 const PAST_ID = "run-past";
@@ -67,6 +68,21 @@ const HEADLESS = historyItem({
   started_at: new Date(1000).toISOString(),
 });
 
+function externalSession(over: Partial<Session> = {}): Session {
+  return {
+    id: "sess-external",
+    name: "the external prompt",
+    status: "active",
+    cwd: "/tmp/external",
+    model: "claude-opus-5",
+    started_at: new Date(3000).toISOString(),
+    ended_at: null,
+    updated_at: new Date(3000).toISOString(),
+    source: "local",
+    ...over,
+  } as unknown as Session;
+}
+
 function renderSwitcher(overrides: Partial<React.ComponentProps<typeof ActiveRunsSwitcher>> = {}) {
   const spies = {
     onAttach: vi.fn(),
@@ -188,6 +204,44 @@ describe("ActiveRunsSwitcher", () => {
     expect(screen.queryByText("stale copy")).toBeNull();
   });
 
+  it("counts and lists a session started outside the dashboard, resumable not attachable", () => {
+    const { spies } = renderSwitcher({
+      activeRuns: null,
+      runHistory: [],
+      externalSessions: [externalSession()],
+    });
+    fireEvent.click(screen.getByText(i18n.t("run:runs.viewActive_other", { count: 1 })));
+    expect(screen.getByText("the external prompt")).toBeTruthy();
+    expect(screen.getByText(i18n.t("run:runs.externalBadge"))).toBeTruthy();
+    // No tmux session of ours to attach to — Resume is the only action.
+    expect(screen.queryByText(i18n.t("run:runs.attachLabel", "Attach"))).toBeNull();
+    fireEvent.click(screen.getByText(i18n.t("run:resume.resumeOption")));
+    expect(spies.onResumeFromHistory).toHaveBeenCalledWith(
+      expect.objectContaining({
+        id: "session:sess-external",
+        session_id: "sess-external",
+        cwd: "/tmp/external",
+        status: "running",
+        isLive: true,
+      })
+    );
+  });
+
+  it("skips external sessions already covered by a run, remote ones, and cwd-less ones", () => {
+    renderSwitcher({
+      runHistory: [],
+      externalSessions: [
+        externalSession({ id: "sess-live" }), // same session as the live run
+        externalSession({ id: "sess-remote", source: "remote-1" }),
+        externalSession({ id: "sess-nocwd", cwd: null }),
+      ],
+    });
+    fireEvent.click(screen.getByText(i18n.t("run:runs.viewActive_other", { count: 1 })));
+    expect(screen.getByText("the live prompt")).toBeTruthy();
+    expect(screen.queryByText("the external prompt")).toBeNull();
+    expect(screen.queryByText(i18n.t("run:runs.externalBadge"))).toBeNull();
+  });
+
   it("fires attach with the run id of the row that was clicked", () => {
     const { spies } = renderSwitcher();
     openModal();