[Bug] git-credential-nostr absolute path with spaces breaks credential.helper (Projects + agents)

[bcrdejong]

Summary

Buzz injects an absolute path to git-credential-nostr into git credential.helper (Projects via GIT_CONFIG_*, agents via spawn env). Git runs helpers through the shell (sh -c). If that path contains whitespace (or '), the value is word-split / broken and auth fails.

This is adjacent to #3025 / #3023 (backslash mangling on Git for Windows). Forward-slash normalization alone does not fix spaces.

Called out by @wpfleger96 on #3023:

there's a pre-existing issue adjacent to this fix that the PR intentionally didn't touch. Git parses the credential.helper value as a shell command line, so a helper path containing spaces gets word-split — reproducible with git -c credential.helper="/path with spaces/helper", which fails with is not a git command. The forward-slash normalization here (credential_helper_config_value in project_git_exec.rs and the GIT_CONFIG_VALUE_0 write in runtime.rs) doesn't quote the path, so a buzz install under a spaced directory (e.g. a Windows username with a space, depending on where the helper lands) would still break. The fix is quoting the value ("'{path}'" or shell-escaping) at both call sites — worth its own small PR rather than piling onto this one.

Platforms

Any OS where the helper path contains spaces (most often Windows usernames like Buzz User; also possible on macOS/Linux). Paths without spaces should keep today's absolute-path helper form.

Expected

Helper path with spaces still authenticates to relay git (Projects Remote / agent git).

Actual

Shell word-splits the helper path; clone/fetch/auth fails (e.g. No such file or directory / is not a git command).

Proposed fix direction

At both call sites, format via shared helper:

• Always normalize \ to /.
• If path has whitespace or ', emit !'...' (POSIX single-quote escaping).
• Otherwise keep plain absolute path (no happy-path launch-style change).

Local verification used Git for Windows with a spaced helper path; unit tests cover plain / spaces / apostrophe fixtures.