feat(run): Enter sends the prompt, and a busy lane attaches instead of failing

- The prompt box sends on Enter (Ctrl/Cmd+Enter still works); Shift+Enter
  inserts a newline, and IME composition (Vietnamese/CJK) never sends.
- Starting or resuming into a lane that still holds a live run answered a
  raw 409 ERUNLIVE; the console now attaches to that run with a notice.
  Checked by error code, since the server's message is prose.
- Active runs gains a two-click Kill for live dashboard-spawned rows, the
  way to free a lane when the previous session really should go.

client/src/components/run/LaneConsolePane.tsx

@@ -15,6 +15,15 @@
  * swaps the whole pane over to the new lane — its cwd, its tool, its history,
  * and its live tmux session — instead of leaving the previous lane's terminal
  * on screen under a new lane's header.
+ *
+ * A lane's pane is one tmux session, so starting or resuming into a lane
+ * already holding a live run answers 409 ERUNLIVE rather than overwriting a
+ * prompt in flight — `onStartFromSetup` and `onResumeFromHistory` both catch
+ * that and attach to the still-live session instead of failing outright
+ * (with a notice explaining what happened), since that session is still
+ * reachable and the user did not ask to kill it. `killRun` is the other half:
+ * the Active runs list's Kill button (`RunHistory.tsx`), for when the user
+ * DOES want that previous session gone so a fresh start/resume can proceed.
  * @author Nguyễn Ngọc Trí Vĩ <vinnt@smartgift.vn>
  */
 
@@ -246,12 +255,16 @@ export function LaneConsolePane({
             resumeLast: args.resumeLast,
           });
         } catch (laneErr: unknown) {
-          const msg = laneErr instanceof Error ? laneErr.message : String(laneErr);
-          if (msg.includes("409") || msg.includes("ERUNLIVE")) {
+          // A code-only check: the server's message is human prose ("lane
+          // already has a live run"), never the literal strings "409" or
+          // "ERUNLIVE" — matching against `.message` here is dead code that
+          // always falls through to the raw error below.
+          if ((laneErr as { code?: string })?.code === "ERUNLIVE") {
             const fresh = await api.lanes.list().catch(() => null);
             const updatedLane = fresh?.lanes.find((l) => l.id === targetLaneId);
             if (updatedLane?.run_id) {
               await attachToRun(updatedLane.run_id);
+              setError(t("errors.attachedToLiveInstead"));
               return;
             }
           }
@@ -307,13 +320,34 @@ export function LaneConsolePane({
             onLaneCreated(ensureResult.lane);
           }
 
-          const laneStartResult = await api.lanes.action(targetLaneId, "start", {
-            prompt: "",
-            model: item.model || undefined,
-            permissionMode: item.permission_mode || undefined,
-            effort: item.effort || undefined,
-            resumeSessionId: item.session_id,
-          });
+          let laneStartResult;
+          try {
+            laneStartResult = await api.lanes.action(targetLaneId, "start", {
+              prompt: "",
+              model: item.model || undefined,
+              permissionMode: item.permission_mode || undefined,
+              effort: item.effort || undefined,
+              resumeSessionId: item.session_id,
+            });
+          } catch (laneErr: unknown) {
+            // The lane's own pane is still busy with a PREVIOUS live session —
+            // that session is still active and reachable, so land on it
+            // instead of failing outright. Killing it (Active runs → Kill) is
+            // what actually frees the lane for this resume. Checked by `.code`
+            // — the server's `.message` is prose, never the literal string
+            // "ERUNLIVE" or "409".
+            if ((laneErr as { code?: string })?.code === "ERUNLIVE") {
+              const fresh = await api.lanes.list().catch(() => null);
+              const updatedLane = fresh?.lanes.find((l) => l.id === targetLaneId);
+              if (updatedLane?.run_id) {
+                onLaneIdChange(targetLaneId);
+                await attachToRun(updatedLane.run_id);
+                setError(t("errors.attachedToLiveInstead"));
+                return;
+              }
+            }
+            throw laneErr;
+          }
 
           if (!laneStartResult.lane?.run_id) {
             throw new Error("No run_id returned from lane start");
@@ -343,7 +377,7 @@ export function LaneConsolePane({
         setBusy(null);
       }
     },
-    [busy, refreshList, t, lanes, onLaneCreated, onLaneIdChange]
+    [busy, refreshList, t, lanes, onLaneCreated, onLaneIdChange, attachToRun]
   );
 
   const onViewFromHistory = useCallback(
@@ -360,6 +394,28 @@ export function LaneConsolePane({
     setError(null);
   }, []);
 
+  // Frees a lane blocked by a live run nobody wants anymore (see Active
+  // runs' Kill button) — the lane's own `run_id` self-heals to null the next
+  // time it's read (routes/lanes.js's healRunId), so no lane-side call here.
+  const killRun = useCallback(
+    async (id: string) => {
+      setBusy("kill");
+      setError(null);
+      try {
+        await api.run.kill(id);
+        if (handle?.id === id) newRun();
+        refreshList();
+      } catch (err) {
+        setError(
+          t("errors.killFailed", { message: err instanceof Error ? err.message : "unknown" })
+        );
+      } finally {
+        setBusy(null);
+      }
+    },
+    [handle, newRun, refreshList, t]
+  );
+
   if (laneId === null && showLaneSelector) {
     return (
       <div data-testid="pane-empty" className="flex min-h-0 flex-1 flex-col gap-2 p-4">
@@ -438,6 +494,7 @@ export function LaneConsolePane({
           externalSessions={externalSessions}
           onResumeFromHistory={onResumeFromHistory}
           onViewFromHistory={onViewFromHistory}
+          onKill={killRun}
           onRefresh={refreshList}
         />
       </header>