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/mermaid-render.ts

@@ -0,0 +1,42 @@
+/**
+ * The app's ONE mermaid renderer (the chrome-melt wave, 2026-09-19): both the
+ * in-chat block (components/md-blocks.tsx) and the session-scoped focus
+ * overlay (components/session-overlay.tsx) render charts through this module
+ * — one dark-theme config, one plugin instance, unique render ids. This
+ * REPLACES streamdown's internal mermaid path entirely: its fullscreen portal
+ * was hard-wired `fixed inset-0` (covering the window-drag bar, X landing in
+ * drag territory) with no styling hook, which is what drove the custom
+ * component in the first place.
+ */
+
+import { createMermaidPlugin } from "@streamdown/mermaid";
+import type { MermaidConfig } from "mermaid";
+
+/** The chart's base font size (px) — mermaid sizes ALL text relative to
+ *  this, so it's the number the display-width cap (md-blocks) divides by:
+ *  a chart shown at its natural width renders text at exactly this size.
+ *  Pinned explicitly so a mermaid default change can't silently shift the
+ *  cap (owner rule, chrome-melt tweaks wave, 2026-09-19: chart text must
+ *  never render larger than the session's own text). */
+export const MERMAID_FONT_SIZE = 16;
+
+// The app is dark-only (html.dark in the root layout) — diagrams render in
+// mermaid's dark theme. (Moved from ai-elements/message.tsx when the
+// renderer became app-owned; the old `mermaid` prop wiring is retired.)
+export const mermaidTheme: MermaidConfig = {
+	fontFamily: "ui-sans-serif, system-ui, sans-serif",
+	fontSize: MERMAID_FONT_SIZE,
+	securityLevel: "strict",
+	theme: "dark",
+};
+
+const plugin = createMermaidPlugin();
+
+/** Render one chart source to an svg string. The id is unique per call —
+ *  mermaid caches rendered ids, and a repeated id across charts/renders
+ *  returns the stale svg (the bug streamdown's own id minting avoids). */
+export async function renderMermaid(chart: string): Promise<string> {
+	const id = `lh-mermaid-${Date.now().toString(36)}-${Math.random().toString(36).slice(2, 9)}`;
+	const { svg } = await plugin.getMermaid(mermaidTheme).render(id, chart);
+	return svg;
+}