Live: polling rework, source locks, preflight scaffolding, Vue previews

Carved out of #371, minus progressive publication. Everything here works
against real project source the way main's Live already does: the agent
writes variants into the file the browser loaded, HMR fires, Accept
promotes and carbonizes. Nothing is staged anywhere.

Poll lanes. Events now carry an explicit priority: accept/discard/exit
ahead of manual_edit_apply/steer/carbonize_cleanup ahead of generate. A
long generate can no longer sit in front of the Accept the user just
clicked. leaseEvent claims its lease before awaiting, so a slow prepare
cannot hand the same event to two pollers.

Source locks. A per-file mutex around every accept and discard path, keyed
on a digest of the absolute path. Staleness is decided by owner-pid
liveness rather than mtime, so a wedged lock clears when its owner dies
instead of after an arbitrary timeout, and a slow-but-live accept is never
stolen from. Only the owning process can release a lock.

Preflight scaffolding. The server runs live-wrap (or live-insert) before
the poll returns and hands the result back as event.scaffold. That walk is
measured at ~7.6s on a large repo; moving it off the agent's critical path
removes a deterministic tool round trip without touching the generated
design. Falls back cleanly to the agent running the helper itself.

Vue previews. previewMode: "vue-component" for Nuxt/Vue targets, matching
the existing Svelte component path: variants compile as real SFCs from a
dev-only directory so the route is never rewritten during generation, and
Vite mounts them without invalidating page state. Accept is the only route
write. Includes a Vue attr tokenizer that normalizes shorthand bindings
(@x, :x, #x) to their canonical forms.

Accept hardening. Every thrown failure now returns mode: 'error' rather
than an ambiguous unhandled result, so a real failure is never classified
as a deliberate manual handoff and silently dropped. The marker search
skips node_modules/.git/dist/build/.impeccable.

Shared CLI arg parsing extracted to scripts/lib/cli-args.mjs.

Assisted-by: Claude Code

skill/scripts/live-accept.mjs

@@ -30,7 +30,6 @@ import {
   inlineVueComponentAccept,
   retireVueComponentSession,
 } from './live/vue-component.mjs';
-import { removeGenerationArtifacts } from './live/generation-publisher.mjs';
 
 const EXTENSIONS = ['.html', '.jsx', '.tsx', '.vue', '.svelte', '.astro'];
 const ACCEPT_LOCK_WAIT_MS = 1_000;
@@ -154,10 +153,6 @@ Output (JSON):
         variantId: isDiscard ? null : String(variantNum),
         result,
       });
-      // The session is over: drop its staged revision artifacts. Leaving them
-      // behind is what let a later marker search find a decoy instead of real
-      // source. Only on success, so a failed accept can still be retried.
-      removeGenerationArtifacts(id, process.cwd());
     }
     console.log(JSON.stringify(result));
   };