[BUG] Path encoding collision causes unrelated projects to share sessions and memory

Preflight Checklist

• [x] I have searched existing issues 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?

Bug Description

Claude Code uses a path encoding scheme to create project data directories under ~/.claude/projects/. The encoding simply replaces / with -, which causes a hash collision between two completely different filesystem paths.

In our monorepo setup, we have two unrelated services at different directory levels:

| Path | Description |
|---|---|
| ~/work/data-platform/datahub-api-proxy | Standalone API proxy service (its own repo) |
| ~/work/data-platform/datahub/api-proxy | API proxy sub-module within the DataHub monorepo |

Both paths encode to the same directory name -work-data-platform-datahub-api-proxy under ~/.claude/projects/, causing them to share session history, memory files, and project state.

Steps to Reproduce

1. Create two directories:

mkdir -p ~/work/data-platform/datahub-api-proxy
mkdir -p ~/work/data-platform/datahub/api-proxy

1. Open Claude in ~/work/data-platform/datahub-api-proxy and start a session.
2. Open Claude in ~/work/data-platform/datahub/api-proxy.
3. Run /sessions — you will see the session from the other directory in the list.
4. Both directories also share the same memory/ folder, so memories saved in one project are automatically loaded in the other, even though the projects are unrelated.

Root Cause

The encoding is a simple path.replace('/', '-'), which is a lossy mapping:

datahub-api-proxy  (single directory with hyphens)
datahub/api-proxy  (two directories: datahub/ → -datahub-, api-proxy)

Both produce -datahub-api-proxy after encoding.

This is effectively a hash collision — any pair of paths where A/B-C and A/B/C coexist will collide. Common patterns that trigger this:

• foo-bar/baz and foo/bar-baz
• my-app and my/app
• data-hub/api and data/hub-api

Expected Behavior

Each distinct filesystem path should map to a unique project data directory. The encoding should be bijective (reversible), so that no two real paths produce the same encoded name.

Actual Behavior

Two unrelated paths share the same ~/.claude/projects/ subdirectory, leading to:

1. Session list pollution — sessions from one project appear in another unrelated project's /sessions list
2. Memory cross-contamination — memory/ files (user, feedback, project, reference) are shared between unrelated projects, causing incorrect context to be loaded automatically
3. Potential concurrent write issues — running Claude in both directories simultaneously causes them to read/write the same state files

Environment

• Claude Code version: 2.1.150
• OS: macOS (Darwin 25.5.0)

Suggested Fix

Use an encoding that doesn't produce collisions:

1. Base64-encode the full path (URL-safe base64, strip padding)
2. SHA-256 hash of the path (truncated to 32 chars for readability)
3. Percent-encode / as %2F instead of replacing with -

Any of these would be collision-free while remaining reasonably debuggable.

What Should Happen?

Each distinct filesystem path should map to a unique project data directory. The encoding should be bijective (reversible), so that no two real paths produce the same encoded name.

Error Messages/Logs

Steps to Reproduce

1. Create two directories:

mkdir -p ~/work/data-platform/datahub-api-proxy
mkdir -p ~/work/data-platform/datahub/api-proxy

1. Open Claude in ~/work/data-platform/datahub-api-proxy and start a session.
2. Open Claude in ~/work/data-platform/datahub/api-proxy.
3. Run /sessions — you will see the session from the other directory in the list.
4. Both directories also share the same memory/ folder, so memories saved in one project are automatically loaded in the other, even though the projects are unrelated.

Claude Model

None

Is this a regression?

Yes, this worked in a previous version

Last Working Version

_No response_

Claude Code Version

2.1.150

Platform

Anthropic API

Operating System

macOS

Terminal/Shell

iTerm2

Additional Information

_No response_