Live v2: root manifest, mount-ack protocol, AST scaffolder, mechanical accept

A ground-up hardening of live mode, driven by a production session in a
nested-app monorepo that hit six distinct failure classes. Full design
rationale in docs/LIVE-REWRITE-PLAN.md; every Codex-reported failure now
has a mechanical fix and a regression test.

Roots: live/roots.mjs resolves appRoot/repoRoot/contextRoot once at boot
(keyed on dev-server configs, not monorepo brand markers), persists a
manifest, and every live CLI re-anchors onto it at startup, so a helper
run from the wrong directory can no longer fork session state. Context
files are discovered upward to the git root.

Render truth: variant_mounted / variant_mount_failed events give the
journal per-variant mount state; failures reach the agent's poll queue,
raise a persistent error card with Retry (no more localStorage wipe), and
an attach probe names root/dev-server mismatches explicitly. The browser
rehydrates from the server when localStorage is gone.

Svelte: the scaffolder now parses with the app's own svelte 5 compiler.
Control flow survives (an each collection crosses the contract as one
structured prop), keyed each blocks hydrate synthetic keys, and anything
a detached preview cannot support falls back to source-preview instead of
shipping a wrong scaffold. Preview modules live in per-publish revision
directories, defeating stale transform caches.

Accept: CSS is reconciled, not appended. Matching selectors are replaced,
params bake from params.json kinds, the compiler's unused-selector pass
prunes superseded rules (pre-existing dead rules protected), a selector-
loss postcondition refuses any write that would drop hand-written rules,
and live-complete refuses to finish while live plumbing remains in source.

Also: framework registry (live/frameworks/) with a crash-safe injection
journal, session-store snapshot caching with read-only reads, protocol
enum consolidation, steer Send button, honest DESIGN-panel empty states.

Testing: new unit suites (roots, AST scaffolder, accept CSS, accept
pipeline, framework conformance); e2e now fails on preview-tree 404s,
proves computed-style mount for every variant, drives the Tune panel
through baked params, and injects failures (broken mounts, republish,
storage loss). New runtime fixtures: monorepo-nested-vite (repo root !=
app root) and vite8-sveltekit-stateful (each blocks + state). Nightly
full-matrix cron. An independent adversarial review pass preceded this
commit; its blocker and major findings are fixed and regression-tested.

This work was produced with AI assistance (Claude Code).

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

skill/scripts/live/event-validation.mjs

@@ -5,17 +5,26 @@
 
 import { canCreateInsert } from './insert-ui.mjs';
 
-// The accepted visual action values come from the canonical vocabulary so the
-// validator, the picker UI, and the marketing demo never drift. Imported (not
-// just re-exported) so it is also in scope for the validators below.
-import { VISUAL_ACTIONS } from './vocabulary.mjs';
-export { VISUAL_ACTIONS };
+// The accepted protocol values come from the canonical vocabulary so the
+// validator, the store, the server, and the picker UI never drift. Imported
+// (not just re-exported) so they are also in scope for the validators below.
+import { AGENT_PHASES, CLIENT_EVENT_TYPES, VISUAL_ACTIONS } from './vocabulary.mjs';
+export { AGENT_PHASES, CLIENT_EVENT_TYPES, VISUAL_ACTIONS };
+
+const AGENT_PHASE_SET = new Set(AGENT_PHASES);
 
 const ID_PATTERN = /^[0-9a-f]{8}$/;
 const VARIANT_ID_PATTERN = /^[0-9]{1,3}$/;
 const INSERT_POSITIONS = new Set(['before', 'after']);
 const FORBIDDEN_MANUAL_EDIT_TEXT_CHARS = ['<', '{', '}', '`'];
 
+// Mount acknowledgements carry a module URL and a raw exception message from
+// the page. Both are attacker-adjacent (any script on the page can POST them
+// with the token it can already read), so they are length-capped before they
+// reach the journal.
+export const MOUNT_URL_MAX_LENGTH = 2000;
+export const MOUNT_ERROR_MAX_LENGTH = 1000;
+
 function isValidId(v) { return typeof v === 'string' && ID_PATTERN.test(v); }
 function isValidVariantId(v) { return typeof v === 'string' && VARIANT_ID_PATTERN.test(v); }
 
@@ -92,6 +101,36 @@ function validateManualEditEvent(msg, label) {
   return null;
 }
 
+function isValidMountVariant(value) {
+  return Number.isInteger(value) && value >= 1 && value <= 999;
+}
+
+/**
+ * Mount acknowledgements are the browser's answer to "did the thing you
+ * published actually render". They are validated strictly because the render
+ * truth in the session snapshot is built from them: a malformed ack that slid
+ * through would report a variant as mounted that never was.
+ */
+function validateMountAck(msg) {
+  if (!isValidId(msg.id)) return 'variant_mounted: missing or malformed id';
+  if (!isValidMountVariant(msg.variant)) return 'variant_mounted: variant must be an integer 1-999';
+  if (msg.url !== undefined) {
+    if (typeof msg.url !== 'string') return 'variant_mounted: url must be string';
+    if (msg.url.length > MOUNT_URL_MAX_LENGTH) return 'variant_mounted: url too long';
+  }
+  return null;
+}
+
+function validateMountFailure(msg) {
+  if (!isValidId(msg.id)) return 'variant_mount_failed: missing or malformed id';
+  if (!isValidMountVariant(msg.variant)) return 'variant_mount_failed: variant must be an integer 1-999';
+  if (typeof msg.url !== 'string' || !msg.url.trim()) return 'variant_mount_failed: url required';
+  if (msg.url.length > MOUNT_URL_MAX_LENGTH) return 'variant_mount_failed: url too long';
+  if (typeof msg.error !== 'string' || !msg.error.trim()) return 'variant_mount_failed: error required';
+  if (msg.error.length > MOUNT_ERROR_MAX_LENGTH) return 'variant_mount_failed: error too long';
+  return null;
+}
+
 export function validateEvent(msg) {
   if (!msg || typeof msg !== 'object' || !msg.type) return 'Missing or invalid message';
   switch (msg.type) {
@@ -120,13 +159,21 @@ export function validateEvent(msg) {
       return null;
     case 'agent_phase':
       if (!isValidId(msg.id)) return 'agent_phase: missing or malformed id';
-      if (typeof msg.phase !== 'string' || !/^[a-z][a-z0-9_]{1,63}$/.test(msg.phase)) {
-        return 'agent_phase: missing or malformed phase';
+      if (typeof msg.phase !== 'string' || !msg.phase) return 'agent_phase: missing phase';
+      // The enum, not a shape pattern. A phase the browser cannot rank is a
+      // phase the progress bar cannot show, so accepting an arbitrary
+      // lowercase word only defers the failure to the UI.
+      if (!AGENT_PHASE_SET.has(msg.phase)) {
+        return 'agent_phase: unknown phase ' + msg.phase + ' (expected one of ' + AGENT_PHASES.join(', ') + ')';
       }
       if (msg.durationMs !== undefined && (!Number.isFinite(msg.durationMs) || msg.durationMs < 0)) {
         return 'agent_phase: durationMs must be a non-negative number';
       }
       return null;
+    case 'variant_mounted':
+      return validateMountAck(msg);
+    case 'variant_mount_failed':
+      return validateMountFailure(msg);
     case 'exit':
       return null;
     case 'prefetch':