walnut-markdown-rendering

# Markdown & rich-HTML rendering Every visible model reply goes through `web/src/utils/markdown.ts`. Rich (HTML) replies additionally go through `web/src/utils/rich-blocks.ts` before rendering. Both files are incident-dense: each rule below is a shipped bug. ## Hard rules 1. **Never patch, fork, or vendor `marked`.** It has a public extension API (`marked.use({ tokenizer }|{ extensions })`); use it. Verify before believing otherwise: both installed copies (`node_modules/marked` and `web/node_modules/marked`, both 15.0.12) are byte-identical to the published tarball, and `patches/` holds exactly one patch, for an unrelated package that has no public switch for what it does. A patched renderer has to be re-applied on every install and blocks every upgrade. 2. **There are TWO `Marked` instances. A retune must be registered on both.** The global singleton serves chat, the session timeline, the file/diff preview, the context inspector and copy-as-rich-text; `noteMarked` (bottom of the file) serves task notes. `marked.use()` mutates only the instance it is called on, so a fix applied to one silently leaves the other broken. Do NOT unify them: `noteMarked` escapes raw inline HTML, which would turn chat's pre-injected task-ref and file-link anchors into visible escaped text. 3. **A tokenizer override returns `undefined`, never `false`.** `false` means "fall through to marked's default", which resurrects the exact behavior the override removes. This has been mis-"fixed" before; the...