fix(git-env): skip the HTTP header probe for non-HTTP effective URLs

[Arnaud (arnaudoisel)]

Description

Since 0.30.0, apm install cannot download a private Git dependency when the user's Git config holds an insteadOf rule that rewrites the fetched URL to SSH:

url."git@github.com:".insteadOf = https://github.com/

The install fails with Unable to verify Git URL rewrite safety (Git URL-match probe failed) and tells the user to remove a legitimate, very common rule.

Root cause. _validated_git_url_rewrite_policy resolves the rewrite, then asks _has_applicable_http_authorization whether an HTTP extraHeader applies to the effective URL. On the authenticated retry APM has injected http.extraheader = Authorization: ... in the command scope, so the header group is non-empty and _urlmatched_header_group runs:

git config --null --get-urlmatch http.extraHeader git@github.com:owner/repo

Git rejects SCP-style syntax there with fatal: invalid URL scheme name or missing '://' suffix and exit status 128 -- neither 0 nor 1 -- so the probe raises GitUrlRewriteProbeError. Measured with git 2.55.0 and an injected GIT_CONFIG_KEY_0=http.extraheader:

URL passed to --get-urlmatch	exit status
https://github.com/o/r	0
ssh://git@github.com/o/r	0
git@github.com:o/r	128

That explains the three conditions needed to trigger it: only the authenticated retry (a public dependency never injects a header), only a rule that matches the fetched URL, and only when something must actually be downloaded.

Fix. An HTTP header can never reach a non-HTTP transport, so the answer is already known without asking Git. _has_applicable_http_authorization now returns False for any effective URL that is not HTTP(S), before spawning the probe. The single guard covers both callers, including GitConfigInsteadOfResolver.resolve in deps/transport_selection.py. _build_git_auth_fence already had the equivalent scheme guard.

The credential-origin rules in validate_resolved_git_url_rewrite only apply to http/https targets, so no rewrite that was rejected before is accepted now. Cross-host, HTTPS-downgrade, remote-helper and credential-bearing rewrites are all still rejected, as their existing tests confirm.

Secondary: the remaining non-zero branch of the probe now names the exit status instead of only saying the probe failed, so a genuine failure is diagnosable. No raw Git output is rendered.

Fixes #2898

Type of change

• Bug fix
• New feature
• Documentation
• Maintenance / refactor

Testing

• Tested locally
• All existing tests pass
• Added tests for new functionality (if applicable)

Two regression tests in tests/unit/cache/test_git_env.py, both under the existing windows_compat marker:

• test_clone_allows_scp_ssh_rewrite_while_a_header_is_injected drives clone_git_worktree through the real git config with an Authorization header and url.git@git.example.com:.insteadOf. On main it fails with the exact error from the issue; with the fix the clone proceeds.
• test_scp_ssh_url_reports_no_http_authorization_without_probing_git asserts the probe subprocess is never spawned for an SCP-style URL.

Verified green: tests/unit/cache/test_git_env.py (87), plus test_git_transport_policy.py, test_transport_selection.py, test_public_github_anonymous_first.py, test_validation_strict_transport.py, test_proxy_compat.py (244 total). ruff check and ruff format --check clean on the changed files, and lint_architecture_boundaries.py passes.

Also reproduced end to end on Windows 11 with git 2.55.0 and the rule set globally: installing a private dependency with an empty cache logs the probe failure on 0.30.0 and no longer does with this change.

Spec conformance (OpenAPM v0.1)

• N/A -- this PR does not change OpenAPM-observable behaviour.

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