Bracketed side conversations with model switching

Feature Request

Allow users to open a temporary "side conversation" with a different model mid-session, then return to the main conversation as if it never happened.

Use case

I use Opus 4.6 as my default model for complex software engineering work. Occasionally mid-session, I have a quick, unrelated question (e.g., "how do I print hello world in python?") that doesn't warrant Opus. I want to quickly ask Haiku 4.5, get my answer, and return to my main conversation without polluting the context.

Proposed UX

Something like:

/aside haiku
> how do I format a date in bash?
... Haiku answers ...
/end

• The side conversation uses the specified model
• The main conversation context is preserved and unaffected
• The side conversation messages are not added to the main context window
• /end returns to the main session exactly where you left off

Current workarounds

• /model to switch and switch back — pollutes the main context with unrelated exchanges
• Second terminal with claude --model haiku -p "..." — works but clunky, loses the convenience of being in-session

Why this matters

Context window is precious on long sessions. Injecting throwaway Q&A into a complex engineering session degrades context quality and wastes tokens on the primary model when it resumes.