wave 1 (platform stream): background-observability accuracy + owner-driven follow-ups

- observability: liveness-gated stale-job recovery, extraction run registry on globalThis with
  explicit 'embedding' phase, /api/jobs force-dynamic, client refresh nudges at every seam
- headless: providerSafePng canonicalizer (multi-IDAT Chrome PNGs → single-IDAT) fixing qwen 400s
- composer: Enter routes through pure enterAction — accepts a pending plan verdict (owner decision)
- markdown chrome: session-scoped mermaid overlay + md-blocks component set + pan-zoom math,
  corner-copy (clipboard grant in electron main), math/table/code block fixes, heading weight 900

543/543 tests; typecheck/lint/build clean

components/ai-elements/reasoning.tsx

@@ -22,7 +22,8 @@ import {
 import { Streamdown } from "streamdown";
 
 import { transformMathDelimiters } from "@/src/core";
-import { mermaidOptions, streamdownPlugins } from "./message";
+import { streamdownPlugins } from "./message";
+import { mdComponents } from "@/components/md-blocks";
 import { Shimmer } from "./shimmer";
 
 interface ReasoningContextValue {
@@ -215,7 +216,7 @@ export const ReasoningContent = memo(
       )}
       {...props}
     >
-      <Streamdown mermaid={mermaidOptions} plugins={streamdownPlugins}>
+      <Streamdown components={mdComponents} plugins={streamdownPlugins}>
         {transformMathDelimiters(children)}
       </Streamdown>
     </CollapsibleContent>