claude-code - 💡(How to fix) Fix [BUG] uncacheable system prompt caused by `Primary working directory:` in git worktree [1 comments, 2 participants]

What's Wrong?

asking the same question from two different worktrees costs thousands of tokens (only the tools-cache hits) resulting in a 5x-surcharge

• even with includeGitInstructions=false to mitigate https://github.com/anthropics/claude-code/issues/47107
• even with 'the exact same question' to mitigate https://github.com/anthropics/claude-code/issues/47098

This also seems to apply to subagent worktrees isolation: worktree

What Should Happen?

system-prompt, skills and most of the system-messages should also hit a cache. and even the user prompt could be a cache-hit for a lot of usecases... (imaginary 30k-token long 'please analyze the following...' launched on multiple featurebranches / git-bisect)

Error Messages/Logs

via ANTHROPIC_BASE_URL:

anthropicReq.system[2]:
[...]
# Environment
You have been invoked in the following environment:
 - Primary working directory: /tmp/the_project/feature 
  - Is a git repository: true
 - Platform: linux
[...]

Steps to Reproduce

mkdir the_project && cd the_project
git init --bare -b master .git
git worktree add master
pushd master && GIT_AUTHOR_NAME=dummy GIT_AUTHOR_EMAIL=dummy GIT_COMMITTER_NAME=dummy GIT_COMMITTER_EMAIL=dummy git commit --allow-empty -m "Dummy commit" && popd
git worktree add feature

pushd master && CLAUDE_CODE_DISABLE_GIT_INSTRUCTIONS=1 claude "Hello" && popd
> /exit
# 3 input, 12 output, 0 cache read, 15.9k cache write ($0.0597)
# ^^  expected initial warmup

pushd master && CLAUDE_CODE_DISABLE_GIT_INSTRUCTIONS=1 claude "Hello" && popd
> /exit
# 3 input, 12 output, 15.9k cache read, 0 cache write ($0.0050)
# ^^ great result

pushd feature && CLAUDE_CODE_DISABLE_GIT_INSTRUCTIONS=1 claude "Hello" && popd
> /exit
#  3 input, 12 output, 10.4k cache read, 5.4k cache write ($0.0237)
# ^^ 10k-cache-read fits the `tools` - 5k-cache-write fits systemprompt + skills + system-message - **what is terrible**

observe a 5x cost inflation that rly should not be needed...

Claude Model

Sonnet (default)

Is this a regression?

I don't know

Last Working Version

No response

Claude Code Version

2.1.108

Platform

Anthropic API

Operating System

Ubuntu/Debian Linux

Terminal/Shell

Xterm

Additional Information

the rest of the # Environment block seems to be rather stable, but the - Primary working directory: ... (and its little friend Is a git repository: true|false) lines should either come a lot later or not even be there at all...

• 'not there at all' is likely iffy - if not an impossible thing... -> in many tools.description´s claude gets instructed to specifically use absolute paths

• but it doesnt rly go well into system-messages either: -- for two clones of the same repository skills & project-claude.md could also be a cache-hit... -- same for git-worktrees not agent-worktrees, but a user launching claude in a worktree -- but also for agent-worktrees: having multiple agents not hit each others cache on launch gets expensive when only the tools-block gets a hit

To the extend that it almost needs to go after not into the last system-message -> and then cache_control tags on the system-message with claude.md, not this directory-line

Notable: agents seem to have there own trouble with this...

• https://github.com/anthropics/claude-code/issues/30667 -> appears claude does not make a difference if its a worktree "you created as its own project" or "claude agent launched this" what would have different expectations about where memory would live...
• https://github.com/anthropics/claude-code/issues/36182

Also note that aboves demo uses a worktree on purpose:

• there is also a problematic You have a persistent, file-based memory system at /home/you/.claude/projects/.../memory/. line in the system prompt for worktrees this appears to be getting normalized so it is currently not causing an extra cache miss, but in turn is causing the [BUG] Auto-memory above - what when fixed in place will make this cache miss again!

Attention: currently this issue gets "masked" by two other issues that even break the in-same-directory cache, follow the reproduction above precisely to workaround them when testing for this issue.

• https://github.com/anthropics/claude-code/issues/47107
• https://github.com/anthropics/claude-code/issues/47098