feat: harden runtime readiness and session workflow

frontend/src/shell/NavSessions.tsx

@@ -1,15 +1,28 @@
 // frontend/src/shell/NavSessions.tsx
 import type { ReactNode } from "react";
 import type { SessionSummary } from "../api/types";
+import { Checkbox } from "../components/ui/checkbox";
 
 interface Props {
   sessions: SessionSummary[];
   activeSessionId: string | null;
   onOpenPanel: (id: string) => void;
   menuFor: (session: SessionSummary) => ReactNode;
+  selectedIds?: ReadonlySet<string>;
+  onSelectionChange?: (id: string, selected: boolean) => void;
 }
 
-export function NavSessions({ sessions, activeSessionId, onOpenPanel, menuFor }: Props) {
+function statusIndicator(status: string) {
+  if (status === "finalized") return { color: "bg-[oklch(var(--success))]", label: "Completed" };
+  if (status === "closed") return { color: "bg-[oklch(var(--warning))]", label: "Stopped by user" };
+  if (status === "failed") return { color: "bg-destructive", label: "Stopped by system error" };
+  return { color: "bg-muted-foreground/50", label: "In progress" };
+}
+
+export function NavSessions({
+  sessions, activeSessionId, onOpenPanel, menuFor,
+  selectedIds = new Set<string>(), onSelectionChange = () => undefined,
+}: Props) {
   if (sessions.length === 0) {
     return (
       <p className="px-1 py-6 text-center text-xs text-muted-foreground">
@@ -22,6 +35,7 @@ export function NavSessions({ sessions, activeSessionId, onOpenPanel, menuFor }:
       {sessions.map((s) => {
         const active = s.id === activeSessionId;
         const label = s.name || s.question || s.id;
+        const indicator = statusIndicator(s.status);
         return (
           <li key={s.id}>
             <div
@@ -42,22 +56,19 @@ export function NavSessions({ sessions, activeSessionId, onOpenPanel, menuFor }:
                 "group flex w-full cursor-pointer items-center gap-2 rounded-lg px-2 py-1 text-left transition-colors focus:outline-none focus-visible:ring-2 focus-visible:ring-ring/40",
                 // The in-progress (active) session is marked in yellow — both its dot
                 // and its row background — so it stands out from the rest of the rail.
-                active ? "bg-[oklch(var(--warning)/0.22)]" : "hover:bg-accent",
+                active ? "bg-accent" : "hover:bg-accent",
               ].join(" ")}
             >
+              <Checkbox
+                checked={selectedIds.has(s.id)}
+                aria-label={`Select ${label}`}
+                onCheckedChange={(selected) => onSelectionChange(s.id, selected === true)}
+                onClick={(event) => event.stopPropagation()}
+              />
               <span
                 aria-hidden
-                title={s.status}
-                className={[
-                  "size-1.5 shrink-0 rounded-full",
-                  active
-                    ? "bg-[oklch(var(--warning))]"
-                    : s.status === "open"
-                      ? "bg-[oklch(var(--success))]"
-                      : s.status === "finalized"
-                        ? "bg-primary"
-                        : "bg-muted-foreground/50",
-                ].join(" ")}
+                title={indicator.label}
+                className={["size-1.5 shrink-0 rounded-full", indicator.color].join(" ")}
               />
               <span
                 className={[