/branch causes massive context inflation — 6% to 73% after single message

Preflight Checklist

• [x] I searched existing issues and found no duplicates
• [x] I am using the latest version of Claude Code

What's Wrong?

After using /branch to create a branch from a conversation at 6% context (59.7k/1M tokens), the new branch shows 73% context (735k/1M tokens) after sending a single short message.

The system/tools/memory/skills categories remain identical between parent and branch — the entire inflation is in the Messages category:

• Before branch: Messages = 40.5k tokens (4.0%)
• After branch + 1 message: Messages = 715.6k tokens (71.6%)

That's ~675k tokens appearing from nowhere. One short message cannot account for this.

Steps to Reproduce

1. Have a conversation at ~6% context usage (59.7k tokens)
2. Run /context to confirm usage
3. Run /branch
4. Send one short message in the new branch
5. Run /context again

Expected Behavior

Context usage in the branch should be roughly the same as the parent session plus the new message/response — maybe 7-8%, not 73%.

Actual Behavior

Context jumps from 6% (59.7k) to 73% (735k). The Messages category inflates from 40.5k to 715.6k tokens.

All non-message categories are identical between parent and branch:

• System prompt: 6.5k (0.6%)
• System tools: 7.9k (0.8%)
• MCP tools: ~2.2k (0.2%)
• Memory files: 2.9k (0.3%)
• Skills: 1.2k (0.1%)
• Autocompact buffer: 21k (2.1%)

Only Messages inflates: 40.5k → 715.6k. This suggests /branch is either duplicating/expanding message history without compaction, or the token counter is miscalculating after a branch.

Screenshots

Will attach /context screenshots (before and after) in comments.

Claude Model

Opus 4.6 (1M context)

Is this a regression?

I don't know

Last Working Version

_No response_

Claude Code Version

2.1.96

Platform

Anthropic API

Operating System

macOS (Darwin 24.6.0)

Terminal/Shell

zsh

Additional Information

This is distinct from the general token consumption issues (#41930, #40524, #41607) — those are about cache invalidation and compaction bugs. This is specifically about /branch inflating the Messages token count by ~18x immediately.