feat(resume): Resume in the kebab menu (A1) + harden the resume kickoff (A2)

A1 — SessionMenu gains a Resume item, gated to status!=="finalized" && !archived
(matching the backend's 409 read-only guard), wired in AppShell to doResume ->
POST /sessions/:id/resume. SessionMenu.test.tsx (3 tests); frontend 96/96, tsc clean.

A2 — diagnosis-first clean-room repro driving `pi --mode rpc` with the backend's
exact resume handshake shows the cold-start stall NO LONGER reproduces on pi
0.79.4 (8/8 chained into `tht session show` + `read SKILL.md` in-turn, fresh and
partway sessions). The earlier narrate-and-stop predates the pi upgrade.
Defense-in-depth anyway: RIPRENDI_KICKOFF hardened to force the in-turn tool call
(gate_resume_kickoff.test.js + live regression 2/2). Gate JS 34/34.

PROJECT_STATE open-item #1 (resume stall) flipped to RESOLVED; cross-model resume
robustness folded into workstream G.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

frontend/src/shell/SessionMenu.tsx

@@ -5,6 +5,7 @@ import type { SessionSummary } from "../api/types";
 interface Props {
   session: SessionSummary;
   groups: string[];
+  onResume: () => void;
   onView: () => void;
   onRename: () => void;
   onMove: (group: string) => void;
@@ -16,7 +17,10 @@ interface Props {
 const itemCls =
   "flex w-full cursor-default select-none items-center rounded-md px-2 py-1.5 text-sm outline-none data-highlighted:bg-accent data-highlighted:text-accent-foreground";
 
-export function SessionMenu({ session, groups, onView, onRename, onMove, onNewGroup, onArchiveToggle, onDelete }: Props) {
+export function SessionMenu({ session, groups, onResume, onView, onRename, onMove, onNewGroup, onArchiveToggle, onDelete }: Props) {
+  // Resume re-enters the workflow; only meaningful while the session is still live
+  // (the backend returns 409 for finalized/archived, matching this guard).
+  const canResume = session.status !== "finalized" && !session.archived;
   return (
     <Menu.Root>
       <Menu.Trigger
@@ -29,6 +33,9 @@ export function SessionMenu({ session, groups, onView, onRename, onMove, onNewGr
       <Menu.Portal>
         <Menu.Positioner side="bottom" align="end" sideOffset={4}>
           <Menu.Popup className="z-50 min-w-44 rounded-lg bg-popover p-1 text-popover-foreground shadow-md ring-1 ring-foreground/10 outline-none">
+            {canResume && (
+              <Menu.Item className={itemCls} onClick={onResume}>Resume</Menu.Item>
+            )}
             <Menu.Item className={itemCls} onClick={onView}>Split view</Menu.Item>
             <Menu.Item className={itemCls} onClick={onRename}>Rename</Menu.Item>
             <Menu.SubmenuRoot>