[FEATURE] Let plugins set the session color without printing a /color echo

Preflight Checklist

• [x] I have searched existing requests and this feature hasn't been requested yet
• [x] This is a single feature request (not multiple features)

Problem Statement

I use a plugin (a function-hooks mod) that gives every new session a random /color, so I can tell terminal windows apart at a glance. The only way a plugin can set the color is $.command.run({ command: 'color', args }), and that prints a ❯ /color green echo at the top of every new session.

A ui.render hook can hide the CommandOutput row ("Session color set to: green"), but the echo above it never goes through ui.render. A catch-all ui.render logger only ever sees the CommandOutput. Session color also isn't one of the rows in $.config.list(), and there's no CLI flag for it. So a plugin can't set the color without leaving that line in the transcript.

Proposed Solution

Any one of these would solve it:

• Expose session color as a writable $.config row (or on $.session), so a plugin can set it directly.
• Draw the echo of plugin-originated commands through ui.render (as a UserMessage with origin.kind: 'plugin'), so the plugin can hide its own echo.
• Add a silent option to $.command.run for commands with no output the user needs to see.

Alternative Solutions

Hiding the CommandOutput row works, but the echo stays. Typing /color by hand in each session avoids the echo problem but defeats the point of automating it.

Priority

Low - Nice to have

Feature Category

Developer tools/SDK

Use Case Example

1. I open three Claude Code sessions in different terminal windows.
2. The plugin gives each one a random color at session start.
3. Today each session opens with ❯ /color pink as its first transcript line.
4. With this feature, the color would be set and the transcript would start clean.

Additional Context

Claude Code v2.1.288, macOS. Related but different: #94797 (more /color options), #96295 (/clear resets /color).