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

scripts/lib/transformers/providers.js

@@ -22,10 +22,7 @@ export const PROVIDERS = {
   },
   'claude-code': {
     provider: 'claude-code',
-    // live-progressive: Live delivers variant 1 as soon as it validates instead of
-    // one atomic edit. Claude Code polls in a background task, so the extra
-    // publish calls do not stall its control lane.
-    providerTags: ['claude-code', 'claude', 'live-progressive'],
+    providerTags: ['claude-code', 'claude'],
     configDir: '.claude',
     displayName: 'Claude Code',
     frontmatterFields: ['user-invocable', 'argument-hint', 'license', 'compatibility', 'metadata', 'allowed-tools'],
@@ -43,7 +40,7 @@ export const PROVIDERS = {
   },
   codex: {
     provider: 'codex',
-    providerTags: ['codex', 'live-progressive'],
+    providerTags: ['codex'],
     configDir: '.codex',
     displayName: 'Codex',
     frontmatterFields: [],
@@ -57,7 +54,7 @@ export const PROVIDERS = {
   },
   agents: {
     provider: 'agents',
-    providerTags: ['agents', 'codex', 'live-progressive'],
+    providerTags: ['agents', 'codex'],
     configDir: '.agents',
     displayName: 'Codex Repo Skills',
     placeholderProvider: 'codex',