[patch] Unstage with reset so it works before the first commit

[matt-edmondson]

Unstage(path) now works in a repository that has no commits yet. Before this, it failed every time there: ExecuteAsync threw GitCommandException ("fatal: could not resolve HEAD") and TryExecuteAsync returned Success = false.

Cause

On git 2.23 and later, GitRestoreBuilder built git restore --staged -- <path>. With no --source, restore --staged reads the index back from HEAD, and on an unborn branch HEAD doesn't resolve.

Fix

GitRestoreBuilder now always builds git reset -q -- <path>, the option the triage recommended:

• For a committed path, it copies the entry from HEAD into the index, which is what restore --staged did.
• On an unborn branch, it removes the entry, which leaves the file untracked.
• It behaves the same on every supported git. That makes the version probe (ProbeVersionAsync, the ExecuteAsync/TryExecuteAsync overrides) and the reset HEAD fallback unnecessary, so they're removed.
• -q stops reset printing its "Unstaged changes after reset" list.
• The bare -- separator stays, so a dash-leading path is still safe; checked against git 2.43 with a file named -dash.

The public surface is unchanged: IGitRestoreBuilder and GitRepository.Unstage. The builder class keeps its name because it's internal.

Tests

New integration tests against real git (they ran here, none skipped):

• UnstageBeforeTheFirstCommitLeavesTheFileUntrackedAsync is the issue's acceptance case: Add().All() then Unstage on an unborn branch. Neither call throws, and the file comes back untracked.
• UnstageAfterACommitRestoresTheIndexAndKeepsTheWorkingTreeAsync guards the ordinary case. The staged change leaves the index and stays in the working tree.

Unit tests:

• GitRestoreBuilderTests now pins the reset -q -- <path> vector, the bare --, and a single invocation with no version probe.
• Two tests are removed: FallsBackToResetOnAGitOlderThanRestoreAsync and TreatsExactlyTwoTwentyThreeAsSupportedAsync. The branch they tested no longer exists.

Verification:

• Verified by reversal: the unborn-branch test fails on main with the issue's exact error, git exited with code 128: fatal: could not resolve HEAD, and passes with the fix.
• The full suite passes: 727/727.

docs/superpowers/specs/2026-09-24-patch-verbs-design.md still describes the restore-plus-fallback design. I left it alone because it's a dated design record, not current documentation.

Fixes #122

🤖 Generated with Claude Code

https://claude.ai/code/session_01PNmrp6FP3tBU47owLsiovc

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Generated by Claude Code

[sonarqubecloud]

Quality Gate passed

Issues
2 New issues
0 Accepted issues

Measures
0 Security Hotspots
100.0% Coverage on New Code
0.0% Duplication on New Code

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