chat: agent steps and thoughts sit closer together

[foxnne]

Stacked on #9.

A thought's line ("Thought >"), a tool step's line and a file link were each about 44pt tall, so an agent's turn of a few steps took most of a screen. Most of that was dvui's defaults stacked on the chat's own spacing: a label's padding is 6 all round and a button's margin is 4. Now those rows are about 20pt, close to Claude Code's and VSCode's chat transcripts:

• thought and tool rows: no button margin, 2pt vertical padding, the label's own padding dropped; the opened thought's text indented to line up with the label
• file links, an answered question's label, and "Not answered" the same way
• plan entries, a diff's header and lines, and a tool's output: 2pt text padding in place of 6, plan and diff boxes padded 6 in place of 8
• bubbles 6pt top and bottom in place of 8, messages 3pt apart in place of 4

Sizes and spacing only. Fonts, colours, and what is drawn are unchanged. Markdown paragraphs keep the markdown plugin's spacing: they're laid out by markdown.Api.renderInline, which takes no spacing option.

Seen

macOS, sandbox profile, the same content on both sides: a seeded transcript (a note, two questions, two agent turns with thoughts, four tool steps, markdown with a list), then the Sample client's reply (every block: diff open, failed step, a step with a question, code, image, plan). Driven by a demo tape, captured before (#9's build) and after this change:

• The seeded transcript: before, it scrolled (the first question and "Connected." were off the top). After, the whole thing fits, and tool rows read as a list.
• The Sample reply: the plan's three entries go from about 31pt each to 21pt. The question's buttons, the code block and the image are as they were.

Text stays readable at these sizes: the rows' text and icons are unchanged, only the air around them.

zig fmt --check src plugin.zig clean; built against the fizzy main SDK (--fork).

🤖 Generated with Claude Code