feat(wechat): channel split with stub-safe page delivery

Introduce wechat/ channel package; never send stub HTML links to service-account users.

wechat/handlers/page-generate.mjs

@@ -0,0 +1,54 @@
+import { buildPagePublishFailureText } from '../prompts/page-generate.mjs';
+import { selectSendableHtmlArtifacts, verifyPageArtifactContent } from '../verify/page-artifact.mjs';
+
+export function evaluatePageGenerateSendableArtifacts({ verifiedArtifacts = [], confirmedArtifacts = [] } = {}) {
+  const sendable = selectSendableHtmlArtifacts({ verifiedArtifacts, confirmedArtifacts });
+  const verified = sendable.filter((artifact) => verifyPageArtifactContent(artifact).ok);
+  return verified.length > 0 ? verified : sendable;
+}
+
+/**
+ * Decide whether a page.generate reply may be delivered to the user.
+ * Returns { action: 'send'|'fail'|'session_retry', failureText?, reason? }
+ */
+export function resolvePageGenerateOutcome({
+  reply,
+  confirmedArtifacts = [],
+  verifiedArtifacts = [],
+  suspiciousPublishClaim = false,
+  bareCompletionReply = false,
+  htmlGenerationNeedsRetry = false,
+  replyHasPublicLinks = false,
+}) {
+  const sendable = evaluatePageGenerateSendableArtifacts({ verifiedArtifacts, confirmedArtifacts });
+
+  if (sendable.length > 0) {
+    return { action: 'send', artifacts: sendable };
+  }
+
+  if (
+    suspiciousPublishClaim ||
+    bareCompletionReply ||
+    (htmlGenerationNeedsRetry && replyHasPublicLinks && confirmedArtifacts.length === 0)
+  ) {
+    return { action: 'session_retry', reason: 'poisoned_or_fake_claim' };
+  }
+
+  if (htmlGenerationNeedsRetry || suspiciousPublishClaim) {
+    return {
+      action: 'fail',
+      failureText: buildPagePublishFailureText(),
+      reason: 'skill_or_stub',
+    };
+  }
+
+  if (!String(reply?.text ?? '').trim() && sendable.length === 0) {
+    return {
+      action: 'fail',
+      failureText: buildPagePublishFailureText(),
+      reason: 'empty_reply',
+    };
+  }
+
+  return { action: 'send', artifacts: sendable };
+}