[Feature Request] /inject command to steer an in-progress run without stopping it

Summary

Add a slash command (e.g. /inject) that injects a message into an
actively-processing run and has it picked up immediately, without
interrupting/stopping the current run or losing its context.

Problem

Today there are two options while Claude is working, and both have gaps:

• Queued messages are only picked up at the next step, and in practice

this feels too slow — often the message isn't processed until Claude has
effectively stopped.

• Stop / interrupt reacts immediately but is too blunt: it halts the run

and discards the momentum/context of what was in progress.

There's no middle option that says "keep going, but factor this in now."

Proposed solution

A command that steers the live run mid-step while preserving its context:

/inject don't worry about the architecture for now, let's get the UX sorted first

The injected text would be treated as a high-priority steering instruction
applied at the earliest possible point in the current run — not queued to the
end, and not requiring a full stop/restart.

Why this is different from existing behavior

• Unlike queue: it's responsive, applied at the next step rather than

after the run winds down.

• Unlike Stop: it does not terminate the run or lose in-progress context —

it redirects rather than restarts.

Example use case

While Claude is deep in an implementation plan, the user realizes the priority
has shifted. Instead of waiting for it to finish or killing the run and
re-explaining, they inject a one-line correction and Claude adjusts course
immediately.

Additional notes

Reported via Cowork mode. Responsiveness of current queuing is the core pain
point driving this request.