fix(tui): improve multiline markdown list readability

[fcoury-oai]

Why

Numbered Markdown findings become hard to scan when long items visually run together or when wrapped explanatory paragraphs lose their list indentation. This is especially visible in review output: the next number can look attached to the previous finding, and paragraph continuation rows can jump back toward the left margin instead of staying grouped beneath their item.

Before

After

What Changed

• Insert a blank separator before a sibling list item when the previous item occupies more than one rendered line.
• Preserve compact rendering for lists whose sibling items each render on one line.
• Preserve list-body leading whitespace when transient streamed assistant rows require another wrapping pass for history display, so wrapped paragraphs stay aligned beneath their item.
• Share the existing leading-whitespace prefix logic used by history insertion instead of introducing a second indentation rule.
• Keep streamed Markdown output aligned with completed rendering and add snapshots for findings-style spacing and streamed paragraph indentation.

How to Test

1. Start Codex from this branch and open the recorded repro session 019e563f-7d58-7ff2-8ec7-828f20fa61ca.
2. Inspect the numbered Findings list whose items contain explanatory paragraphs.
3. Confirm each multiline finding is separated from the next numbered finding by one blank line.
4. Confirm wrapped rows of each indented paragraph remain aligned beneath the finding body, rather than returning to the left edge.
5. Render a short one-line numbered or unordered list and confirm its items remain compact without added blank rows.

Targeted tests:

• just test -p codex-tui history_cell insert_history markdown_render markdown_stream streaming::controller
• just argument-comment-lint-from-source -p codex-tui

Related Work

PR #24346 changes Markdown table column allocation in parallel. This PR is intentionally limited to list-item readability and history wrapping; both branches touch codex-rs/tui/src/markdown_render.rs, so a small merge conflict may need resolution depending on merge order.

[etraut-openai]

Looks good. I especially like the color treatment on the numbers.

My only (small) concern is about copy behavior, but that was already a problem prior to this change because of the leading two spaces. This adds more spaces.

The code looks good.

I manually verified the fix and confirmed that formatting looks good and it reflows correctly when resizing the terminal.

[fcoury-oai]

My only (small) concern is about copy behavior, but that was already a problem prior to this change because of the leading two spaces. This adds more spaces.

Agreed, I will see if there's something we can do when falling back to raw mode in that regard.