wave E stage 3: demos run in the app's own Chromium (browser-service helper)

Demos execute JS and need a browser; the app's own binary now provides
one: main.cjs boots a hidden window + CDP port under --browser-service
(before the single-instance lock - a helper is deliberately a second
instance of this binary), lifetime tied to the server's stdin (EOF =
quit, no orphans). headless.ts connects over CDP as PRIMARY (owner
ruling 2026-10-10), system Chrome stays the fallback, graceful refusal
when neither. Electron's CDP has no Target.createTarget, so the helper's
pre-created window is THE page, reused and reset per job behind a
serialized queue. PDFs and SVGs never reach a browser anymore (native
since stages 1-2); stale Chrome wording in model-facing tool copy made
engine-neutral. Live-proofed end-to-end from the dev tree (helper seen
by process watch, js-ran 42 probe, no orphan). Gates 1523/1523.

src/agent/subagents/visual-maker.ts

@@ -8,7 +8,8 @@ import { getHeadless, type HeadlessApi } from "./headless.ts";
 
 /**
  * The visual-maker sub-agent (vision §2.5): authors ONE precise SVG from a
- * brief, renders it to a PNG in the SAME headless Chrome, LOOKS at the
+ * brief, renders it to a PNG with the same rasterizer the transcript
+ * will use, LOOKS at the
  * result, and iterates until correct — a direct port of the vault POC's
  * svg-maker doctrine ("the one rule that matters: verify by looking").
  *
@@ -64,7 +65,7 @@ Your three tools:
 - edit_svg({ old_text, new_text }) — a surgical exact-match replacement in the current SVG:
   old_text must appear EXACTLY ONCE; it is replaced by new_text. Call write_svg first. For anything
   beyond a one-spot fix (new elements, restructured layout), write_svg the whole document again.
-- render_svg({}) — rasterize the current SVG in headless Chrome. The render arrives as an image in the
+- render_svg({}) — rasterize the current SVG to a PNG. The render arrives as an image in the
   message right after the tool result.
 
 THE ONE RULE THAT MATTERS MOST: verify by looking. You are done only when you have LOOKED at the