fix(claude-code): set git safe.directory and gh credential helper via env

[gatezh]

What

Sets git config for every process in claude-code template containers through GIT_CONFIG_COUNT in containerEnv. This fixes the intermittent "dubious ownership" error on /workspace and lets git@github.com: remotes authenticate through the container's gh login.

Why

Closes #172.

• dubious ownership: the Dev Containers extension adds safe.directory to ~/.gitconfig only when its one-time ownership check at attach detects a mismatch (see Dev Containers fails safe.directory detection when folder path contains square brackets on Windows microsoft/vscode-remote-release#11021). Docker Desktop's reported ownership of the bind mount changes over time, so VS Code's Git extension fails some of the time.
• SSH remotes: gh only authenticates HTTPS, and the forwarded ssh-agent often has no keys (Secretive, 1Password, on-disk keys).
• Stale host credential: as the follow-up comment on claude-code template: VS Code's Git extension intermittently hits "dubious ownership" on /workspace, and SSH GitHub remotes can't use the container's gh login #172 notes, VS Code injects its own credential helper into /etc/gitconfig and ~/.gitconfig, which answers first with the host's GitHub credential. That credential may be stale.

Env-based config is git's command scope. Per git-config(1), that scope counts as protected configuration, so git honors safe.directory there. It also outranks the system and global files the extension writes. The two credential entries, an empty helper followed by !gh auth git-credential, are exactly what gh auth setup-git writes (cli/cli helper_config.go). It's gh's own way to "sever the chain of credential helpers", and gitcredentials(7) documents the empty value as a reset.

Changes

• claude-code/.devcontainer/devcontainer.json and claude-sandbox/devcontainer.json: four GIT_CONFIG_* entries in containerEnv:
  • safe.directory=/workspace
  • url.https://github.com/.insteadOf=git@github.com:
  • an empty credential.https://github.com.helper, then !gh auth git-credential
• claude-code/README.md: new "Git and GitHub Authentication" section covering each entry, the one-time gh auth login, how to inspect the config with --show-scope, and how to add entries. A link to it from "Key settings included".

Verification

Ran in ghcr.io/gatezh/devcontainers/claude-code:latest (git 2.47.3). /workspace was owned by UID 4242, and a stand-in for VS Code's credential helper was set in both /etc/gitconfig and ~/.gitconfig. The env values were parsed from each edited JSONC file:

Check	Without env	With env (both variants)
git status in /workspace	fatal: detected dubious ownership	works
git ls-remote --get-url git@github.com:owner/repo.git	unchanged SSH URL	https://github.com/owner/repo.git
git credential fill for github.com	stale host credential	gh's token
git credential fill for gitlab.com	VS Code helper	VS Code helper (unchanged)

Also confirmed: with only the gh helper and no empty reset, github.com still gets the stale host credential.

Notes

• After merging, downstream projects pick this up by re-syncing their .devcontainer/ (the devcontainer-upstream-sync skill) and rebuilding. No image rebuild is needed for the fix itself.
• Inside the container, git@github.com: remotes now always go over HTTPS through gh, even when the forwarded ssh-agent would have worked. The host's remotes and SSH setup don't change.
• Out of scope: this repo's own root .devcontainer/ has no gh config volume, so it isn't changed here. ssh://git@github.com/ remotes and gist hosts aren't covered.