[BUG] Client self created "heart beat" keeps session alive forever and drains tokens...

### Preflight Checklist

- [x] I have searched [existing issues](https://github.com/anthropics/claude-code/issues?q=is%3Aissue%20state%3Aopen%20label%3Abug) and this hasn't been reported yet
- [x] This is a single bug report (please file separate reports for different bugs)
- [x] I am using the latest version of Claude Code

### What's Wrong?

Why is this even a thing?? This has to be toggled by a hard config setting that is off by default....
Thats resending the entire chat no matter at what tokens/context level used.... specially if its fable? IT drains accounts for no reason.... who thought this was a good idea to have on by default or even create?? Pure slop coding architecture

### What Should Happen?

Not drain my account with heartbeats...

### Error Messages/Logs

```shell

```

### Steps to Reproduce

It did it by itself, no idea...

### Claude Model

Opus

### Is this a regression?

Yes, this worked in a previous version

### Last Working Version

2.1.261

### Claude Code Version

2.1.263

### Platform

Anthropic API

### Operating System

Ubuntu/Debian Linux

### Terminal/Shell

PowerShell

### Additional Information

_No response_

No source file, test, log, or reproduction command is identified in the report. Start by reproducing the behavior on Claude Code 2.1.263 and compare it with 2.1.261, using Anthropic API usage and session activity to confirm the heartbeat and token drain. Done means the unintended keep-alive no longer occurs by default and the regression is covered by a test.

索引モデルが issue の本文から書いたものです。