feat: gate decision-type validation, force-advance, and frontend fixes

Gate (tht-gate.js):
- Pre-validate decision types against workflow.yaml before showing reviewer widget
- Reject decisions emitted by later phases (min-phase check)
- Copy top-level `kind` into artifact when model forgets it (prevents loop)
- Force-advance on reviewer_decide/schema_linking when advance:true — skip
  redundant reviewer_confirm gate

Backend:
- Emit agent_end on clean Pi exit (code 0 + bridge idle) instead of marking failed

Frontend:
- Strip <think> tags from transcript and activity panel
- Fix mermaid render with offscreen container + cleanup
- Graceful mermaid error: show source code instead of red error, fall back to table

Workflow:
- F2 now emits table_promoted and table_excluded (early schema linking decisions)

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

frontend/src/shell/CentralStatus.tsx

@@ -5,6 +5,8 @@ import { isNearBottom } from "./activityScroll";
 function transcriptLines(transcript: Array<{ text: string }>): string[] {
   return transcript.flatMap(({ text }) =>
     text
+      .replace(/<think>[\s\S]*?<\/think>/g, "")
+      .replace(/<\/?think>/g, "")
       .split("\n")
       .map((line) => line.trimEnd())
       .filter((line) => line.trim() !== ""),

frontend/src/shell/ModelActivityPanel.tsx

@@ -25,6 +25,8 @@ export function isVisibleModelActivity(entry: ActivityEntry): boolean {
 
 export function formatModelActivity(text: string): string {
   return text
+    .replace(/<think>[\s\S]*?<\/think>/g, "")
+    .replace(/<\/?think>/g, "")
     .replace(/\r\n?/g, "\n")
     .replace(/([.!?])(?=[A-ZÀ-ÖØ-Þ])/g, "$1\n\n")
     .replace(/^[\t ]*[•‣–]\s+/gm, "- ")

frontend/src/viewers/MarkdownView.tsx

@@ -16,7 +16,7 @@ function MermaidBlock({ code }: { code: string }) {
       );
   }, [code]);
 
-  if (error) return <pre className="text-destructive text-xs">{error}</pre>;
+  if (error) return <pre className="overflow-auto rounded-lg bg-muted p-3 text-xs opacity-60">{code}</pre>;
   if (!svg) return <pre className="text-xs opacity-50">{code}</pre>;
   // eslint-disable-next-line react/no-danger
   return <div dangerouslySetInnerHTML={{ __html: svg }} />;

frontend/src/viewers/SchemaLinkingViewer.tsx

@@ -116,9 +116,9 @@ export function SchemaLinkingViewer({ linking }: { linking: SchemaLinking }) {
     if (view !== "chart" || oversized) return;
     let cancelled = false;
     const def = buildErDiagram(promoted, linking.joins);
-    renderMermaid(def).then((s) => {
-      if (!cancelled) setSvg(s);
-    });
+    renderMermaid(def)
+      .then((s) => { if (!cancelled) setSvg(s); })
+      .catch(() => { if (!cancelled) setView("table"); });
     return () => {
       cancelled = true;
     };

frontend/src/viewers/mermaid.ts

@@ -7,6 +7,15 @@ export async function renderMermaid(def: string): Promise<string> {
     _initialized = true;
   }
   const id = `mermaid-${Math.random().toString(36).slice(2)}`;
-  const { svg } = await mermaid.render(id, def);
-  return svg;
+  const container = document.createElement("div");
+  container.style.position = "absolute";
+  container.style.left = "-9999px";
+  document.body.appendChild(container);
+  try {
+    const { svg } = await mermaid.render(id, def, container);
+    return svg;
+  } finally {
+    container.remove();
+    document.getElementById(id)?.remove();
+  }
 }