/talk renders code with highlighting and copy, and tables, as it streams, without jumping #8834

Most of #8816 was already on main. /talk already ran agent turns through renderMarkdown, which highlights fenced code with the forge's tokenizer and renders tables and safe links. The script already puts a Copy button on each code block. This pull fills the remaining gaps.

What changed

• Styling: agent turns now carry the prose class, so tables, links and highlighted code are styled like the rest of the forge. src/web/pages/talk_client.ts adds a few overrides:

- A wide table scrolls inside its own box instead of widening the page. - Block spacing stays tight and the last block has no trailing margin.

• Tests in test/talk-page.test.ts:

- <script> in prose, in a code block and in a table cell renders escaped, and javascript: links are refused. - Highlighted code, a table and a link render. - An unfinished fence closes itself, and the markup above it is byte-identical to the finished render's. - Byte budget: the stylesheet stays under 3.5 KB (now about 2.8 KB) and the script under 6.5 KB (now about 6 KB). The /talk page with a highlighted block is about 23 KB and must stay under 40 KB.

What I chose not to do

• No partial-text streaming. Turns are written whole today, so the "unfinished block while streaming" case only happens in the markdown renderer, and the test above covers it.
• No change to src/web/markdown.ts; I did not add a separate src/text/ module for it.

Checks: bun test test/talk-page.test.ts passes (25 tests), bun x tsc --noEmit is clean, and bun scripts/gate.ts and bun scripts/design-lint.ts are clean. I did not run the full suite; the forge's check does that on push.

To try it: open /talk and ask the forge for a code sample and a table. Code should be highlighted with a Copy button, and the table should stay inside the column.

Closes #8816

Most of #8816 was already on main. /talk already ran agent turns through renderMarkdown, which highlights fenced code with the forge's tokenizer and renders tables and safe links. The script already puts a Copy button on each code block. This pull fills the remaining gaps.

What changed

• Styling: agent turns now carry the prose class, so tables, links and highlighted code are styled like the rest of the forge. src/web/pages/talk_client.ts adds a few overrides:

- A wide table scrolls inside its own box instead of widening the page. - Block spacing stays tight and the last block has no trailing margin.

• Tests in test/talk-page.test.ts:

- <script> in prose, in a code block and in a table cell renders escaped, and javascript: links are refused. - Highlighted code, a table and a link render. - An unfinished fence closes itself, and the markup above it is byte-identical to the finished render's. - Byte budget: the stylesheet stays under 3.5 KB (now about 2.8 KB) and the script under 6.5 KB (now about 6 KB). The /talk page with a highlighted block is about 23 KB and must stay under 40 KB.

What I chose not to do

• No partial-text streaming. Turns are written whole today, so the "unfinished block while streaming" case only happens in the markdown renderer, and the test above covers it.
• No change to src/web/markdown.ts; I did not add a separate src/text/ module for it.

Checks: bun test test/talk-page.test.ts passes (25 tests), bun x tsc --noEmit is clean, and bun scripts/gate.ts and bun scripts/design-lint.ts are clean. I did not run the full suite; the forge's check does that on push.

To try it: open /talk and ask the forge for a code sample and a table. Code should be highlighted with a Copy button, and the table should stay inside the column.

All four points from @juniper are addressed and pushed. The gate, tsc, design-lint and test/talk-page.test.ts (28 tests) are green. I did not check the layout at 360px in a browser; the CSS reset is only asserted in a test.

What changed

• Layout: .talk-body.prose now resets padding: 0 and font-size: inherit, and .talk-body.prose > * sets max-width: none (src/web/pages/talk_client.ts). Both selectors outrank .prose, so agent turns sit in the column like person turns. A test asserts those two rules are in the stylesheet.
• "Without jumping": I added two DOM tests in the "script driven against a DOM" suite.

- A turn that arrives again is not drawn twice or replaced. Earlier turns and their Copy buttons stay the same nodes. - A turn arriving while scrolled up does not scroll the page.

• Narrowed claim: the client never replaces a turn, so there is no mid-stream reflow to prove. A reply is stored whole and arrives as one finished turn. The feature doc now says this instead of claiming a streamed, growing render.
• docs/features/talk.md:

- A new section covers code highlighting, tables, Copy and the page's byte budgets. Those budgets are the stylesheet under 3.5 KB, the script under 6.5 KB, and a page with a code reply under 40 KB. - The features table row for highlighting is updated. - The section states that Copy buttons are drawn by script only. With JS off there are none, and the code stays selectable.

I did not touch the README, as you asked.