Suggestion: collapse long messages into a file-icon placeholder by default

[BlessedChild]

When a message body is very long — whether sent by the user (e.g. pasting a long document) or returned by the agent — the chat currently renders it fully unrolled in the conversation. Scrolling past it to read further or to reach the input box takes a noticeable amount of time. It would help to default long messages to a collapsed file-icon style placeholder, expandable on click, similar to how many chat clients handle long pasted text or log dumps.

Steps to reproduce

1. Send (or have the agent send) a message whose rendered length spans multiple screen heights — e.g. paste a long Markdown file, or ask for a long technical explanation.
2. Try to scroll past it to reach the input box or the next message.

Expected behavior (suggested)

Messages above a length threshold (say, > N lines or > M characters) render as a compact placeholder:

• A file-icon style chip with the first line / a one-line summary / line count.
• Click to expand inline, click again to collapse.
• Threshold and default behavior optionally user-configurable in preferences.

Actual behavior

Long messages are always rendered fully expanded. There is no way to collapse them — as long as the message is on screen, the user must scroll through its entire content.

Notes

This is a quality-of-life enhancement rather than a bug. Prior art: Slack and many chat clients collapse long pastes into snippets; code-review tools collapse large diff blocks; etc.

Environment

• App: Finch 1.2.1 (build 247) — Desktop
• OS: macOS 26.4.1 (25E253)