fix: pre-create project log dir before launching CLI

[anthony-maio]

Summary

• pre-create the Claude project log directory before launching the CLI subprocess
• resolve the config root from CLAUDE_CONFIG_DIR, HOME, or USERPROFILE in the child environment
• add regression tests covering both HOME and CLAUDE_CONFIG_DIR overrides

Problem

When callers override HOME or CLAUDE_CONFIG_DIR per agent, the CLI can try to write ~/.claude/projects/<sanitized-cwd>/<session>.jsonl before that per-project directory exists. In multi-agent environments this shows up as ENOENT on startup.

Test Plan

• python -m pytest tests/test_transport.py -k "not concurrent_writes"
• python -m pytest tests/test_transport.py -k "project_log_dir or CLAUDE_CONFIG_DIR"
• python -m ruff check src/claude_agent_sdk/_internal/transport/subprocess_cli.py tests/test_transport.py
• python -m mypy src/

Notes

Two existing tests/test_transport.py cases still require the optional trio backend in this environment, so I excluded -k concurrent_writes from the broader pytest run.

Fixes #513

[Copilot]

Pull request overview

This PR addresses Claude Code CLI startup failures in multi-agent setups by ensuring the per-project log directory is created before the CLI subprocess is launched, using the child process’s resolved config root.

Changes:

• Add child-environment-aware resolution of the Claude config directory (CLAUDE_CONFIG_DIR, HOME, USERPROFILE) and pre-create the CLI project log directory before spawning the subprocess.
• Add regression tests covering directory creation for both HOME and CLAUDE_CONFIG_DIR overrides.

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated 3 comments.

File	Description
src/claude_agent_sdk/_internal/transport/subprocess_cli.py	Resolves config directory from child env and ensures projects/<sanitized-cwd> exists before launching the CLI.
tests/test_transport.py	Adds tests asserting the project log directory is created under overridden HOME and CLAUDE_CONFIG_DIR.

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