SSH mirrors fail on gitcache -u because URL normalization drops the username #159

Affected versions: v1.0.20 onwards (since commit 54147ff "feature: Normalize URLs to maximize cache usage.")

Description

Mirrors created from SSH URLs (both ssh://user@host/... and scp-style git@host:path) fail to
update via gitcache -u or once the update interval triggers a fetch.

Root cause

1. GitMirror._clone() stores self.normalized_url in the database, and GitMirror.normalize_url()
   discards the user@ part of the URL.
2. git_update_all_mirrors() constructs each GitMirror from its path only, so self.url is read
   back from the database and no longer contains the username.
3. _add_credentials_to_remote() then compares self.url with strip_credentials(self.url); they
   are equal, so the credentials are never restored on the origin remote (the "Temporarily
   restoring credentials..." message never appears). The fetch runs against host:path without a
   username and SSH authentication fails (it uses the local login name instead of e.g. git).

Mirrors created before v1.0.20 still have the full git@... URL in the database, so they
restore credentials and update fine. This makes the failure look inconsistent: mirrors of the same
host can pass or fail depending on when they were first cloned.

The bug is an interaction of two features: normalize_url() dropping user@ from the database URL
(commit 54147ff, v1.0.20) and the credential handling from #131 / #134 assuming the database URL is
a usable source of truth for restoring credentials. For SSH URLs it is not, because the username was
already lost during normalization.

A note on intent (please correct me if I read this wrongly)

I am guessing at the original intention here, so please treat the following as an inference rather
than a statement of fact:

• Dropping user@ in normalize_url() (54147ff) looks deliberate for cache deduplication, and at
  the time it was harmless: before Feature: Handle credentials in URLs #134, the database URL was never used for fetching, as updates
  used the mirror's own remote.origin.url which still contained the full clone URL.
• The credential stripping from Support the use case of running in CI with temporary Git credentials #131 / Feature: Handle credentials in URLs #134 / Feature: Mask credentials #137 appears to be aimed at secrets in http(s) URLs
  (GitLab CI tokens, user:token@); every example in the Support the use case of running in CI with temporary Git credentials #131 discussion is https, and SSH is not
  mentioned. Since strip_credentials() applies the same regex to all URL shapes, it also removes
  the bare username from scp-style URLs, where a password is not even syntactically possible.
• The stated goal in Feature: Handle credentials in URLs #134 was that "fetch and pull actions still work" via temporary restoration.
  For SSH URLs read from the database this no longer holds, which is why I suspect the SSH username
  removal is unintended collateral rather than a design decision.

I am aware the SSH LFS tests added later (test_15_lfs.py, PR #139) assert the database URL without
git@, so if stripping the SSH username is intended behaviour, I would be happy to hear the
reasoning and what the recommended setup is (e.g. relying on ~/.ssh/config to supply the user).

Steps to reproduce

1. gitcache git clone git@<some-host>:<group>/<repo>.git (with gitcache >= 1.0.20)
2. Note that ~/.gitcache/db stores "url": "<some-host>:<group>/<repo>" without git@.
3. gitcache -u
4. The update fails with an SSH authentication/permission error; the log shows no "Temporarily
   restoring credentials on the mirror remote URLs." line.

Suggested fix

The username of an SSH URL is not a credential secret; it is required to authenticate. Suggested
changes:

• normalize_url(): keep user@ for ssh:// and scp-style URLs (dropping only a password), so the
  database retains a usable upstream URL. The mirror path can continue to ignore the username so
  cache sharing still works.
• helpers.strip_credentials(): for SSH-style URLs, keep the username and strip/mask only the
  password; keep current behaviour for http(s)/ftp(s).

Note: existing databases with already-stripped URLs cannot be repaired automatically since the
username is lost; affected users need to re-add the username to ~/.gitcache/db or re-create the
mirror.

I have a patch with unit tests ready and can open a PR if this approach is acceptable.

This issue was investigated and drafted with the assistance of Claude Code; the analysis of the
repository history and the proposed fix were reviewed by a human before posting.