[FEATURE] Show an estimated time until the current prompt is done (ETA) and its cost so far, by default

What

While Claude Code works on a prompt, show how long until it is done — an estimated time of arrival for the current request — and what it has cost so far, by default, for every user, with no configuration.

For example, in the status line:

Opus | ETA ~25 min | $4.10 so far | Xmip

Why

A prompt can run for an hour or more, with background agents and long builds. Today the user cannot tell whether the answer comes in two minutes or two hours, nor what it is costing, without interrupting to ask. Claude often knows the shape of the remaining work (steps left, a build with N modules of which M are done) and could estimate it, updating as it goes.

Knowing time and money while the work runs lets a user decide whether to wait, leave, or stop the task — instead of finding out afterwards.

Suggested behaviour

• An estimated time remaining for the current prompt, refined as work progresses, shown while Claude is working; nothing when idle.
• The cost of the current prompt so far (and of the session), from the figures Claude Code already has.
• Both exposed in the status line's input JSON, so custom status lines can show them too, and shown by default when no statusLine is configured.

Related

#95196 (an interactive picker for built-in status line components) — an ETA and cost would be natural built-in components, shown by default.