Feature request: support steering and interrupting active chat/actions mid-run

## Feature request

Please add better controls for **steering** and **interrupting** an active chat / action while the agent is working.

## Problem

During longer agent runs, I sometimes want to:
- stop the current direction
- steer the agent toward a different approach
- interrupt an action before it finishes
- inject a correction or constraint without waiting for the whole turn to end

Right now this feels too rigid. Once the run is underway, it is hard to intervene in a smooth way.

## What I want

A better mid-run control model, for example:
- interrupt the current run/action cleanly
- send a steering message / correction while the session is still active
- pause / resume if appropriate
- keep the workflow context while changing direction

## Why this matters

For real coding workflows, steering is often necessary when:
- the agent misunderstood the task
- a new constraint appears
- I want to redirect effort before more time/tokens are spent
- I can already see the action is going the wrong way

## Suggested UX directions

Possible implementations:
- a visible `Interrupt` / `Steer` control while a run is active
- allow an inline follow-up instruction that becomes a higher-priority steering message
- support a distinction between:
- hard cancel
- soft steer / redirect
- preserve visible context so the conversation does not feel reset after intervention

## Scope

This request is specifically about **live intervention during active work**, not only cancelling after the fact.

No files, tests, or entry points are named. Start by locating the active chat/action lifecycle and any existing cancellation handling, then determine where live controls and steering messages would fit. Done means supporting clean interruption, mid-run steering, and preserved workflow context as described, with behavior for hard cancel versus soft redirect defined.

Written by the indexing model from the issue text.