[FEATURE] Persistent context usage indicator (not just a warning near the limit)

Preflight Checklist

• [x] I have searched existing requests and this feature hasn't been requested yet
• [x] This is a single feature request (not multiple features)

Problem Statement

Note: Related to #41536, #65290 and #25125, which cover warning users before the context limit is hit. This request is about a different mechanism: a persistent indicator rather than a threshold warning. Filing separately since #41536 is locked.
Problem
Existing requests focus on alerting users at a threshold. A warning at 80% still forces a reactive decision under pressure — usually mid-task, which is the worst possible moment to reorganise a conversation.
Proposal
A small, always-visible capacity indicator — a thin bar or percentage near the input field — showing how much of the context window the current conversation has consumed.
Why this is better than a threshold warning

Users can plan proactively: seeing a session fill up early allows splitting work, summarising, or starting fresh before being deep into a task
No interruption: an ambient indicator carries no modal or alert overhead
It scales: users learn over time what kinds of work consume how much capacity

Optional addition
A one-click "continue in a new chat with a summary of this one" action, available at any time rather than only at the limit. This turns the context limit from a hard stop into a clean handoff.

Proposed Solution

The interface should show a small, always-visible capacity indicator near the input field — a thin progress bar or a percentage — reflecting how much of the context window the current conversation has consumed. It updates after each turn and requires no interaction.
There should be a setting to choose the display style (bar, percentage, or hidden) for users who find it distracting.
Unlike a threshold warning, this is ambient: no modal, no alert, nothing to dismiss. The value is that I can glance at it at any point and decide myself whether to keep going, summarise, or start a fresh chat — before I'm deep into a task rather than in the middle of one.

Alternative Solutions

Currently I work around this by guessing. I split conversations preemptively when they feel long, which often means starting a new chat far earlier than necessary and losing context I still needed — or misjudging it and hitting the limit anyway.
A threshold warning (as proposed in #41536 and related issues) would be an improvement, but it's still reactive: it arrives when the decision is already urgent, usually mid-task.
Other tools solve this with a visible token or context counter in the interface, which lets the user manage session length themselves rather than being told when it's too late.

Priority

Critical - Blocking my work

Feature Category

CLI commands and flags

Use Case Example

_No response_

Additional Context

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