[FEATURE]: Plugin API to format delimited blocks in message text #55440

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Describe the enhancement you want to request

Tools and plugins that send prompts on a user's behalf often wrap machine metadata in a delimited block at the top of the message, for example:

[vibeterm_metadata]
call: vibeterm_spawn_session
process_id: 2597181
sent_at: 2026-10-14T13:04:13.949Z
[/vibeterm_metadata]

In the transcript that is plain text indistinguishable from what the person typed, and a markdown pass makes it worse ([name] reads as a link reference).

Proposal: let a TUI plugin, or tui.json, register a formatter for a delimited block in message text: an opening line, a closing line, and a format. yaml would color key: value lines (keys, values by type, delimiter lines muted); any other value would be a language id colored by its grammar. A * in the opening line would match a run of non-space characters and stand for the same name in the closing line, so one rule covers [tool_*] ... [/tool_*]. Only colors change; the text reads and wraps as written. For example a plugin API api.blocks.register({ open, close, format }) next to api.slots, and syntax.blocks in tui.json.

This is AI generated, but under direct supervision and on request of @Nowaker.