Shift+Esc: soft interrupt to append context to an in-flight response

Background

Esc already works as a hard stop — cancel generation immediately. This is the panic button and it's useful. This request is for the softer case.

Problem

When Claude Code is mid-generation you sometimes realise you forgot to include a piece of context — a constraint, a correction, a clarification — that would change the output. Your options right now are:

• Let it finish and correct after (wasted generation, possible rework)
• Hit Esc and restart with the amended prompt (loses the momentum, you retype everything)

Neither is great when what you actually wanted was to add one thing without stopping.

Proposed behaviour: Shift+Esc

1. Pause generation and buffer any output so far
2. Open a small inline input field: append to prompt…
3. User types the additional context and confirms
4. Generation resumes with the original prompt + appended context merged, continuing from where it paused

Why this is different from just sending a follow-up message

A follow-up message queues as a new top-level job — it arrives after the committed output, as a correction rather than a steering input. Shift+Esc would fold the addition into the current generation context before the model has finished committing to a direction.

Use cases

• Keep going but also consider X
• Spotted a typo or ambiguity in the original prompt mid-stream
• Want to add a constraint without restarting (btw, don't touch the tests)

Hard stop (Esc) stays unchanged — this doesn't replace it.