fix: add-wizard ls-remote default branch parsing bug

[dsyme]

Problem

gh aw add-wizard fails to pull merged changes after PR merge with:

⚠ Could not update local branch: git fetch failed: exit status 128 (output: fatal: couldn't find remote ref ref)

This has been a recurring bug — attempted to fix 5 times and it kept coming back.

Root Cause

The updateLocalBranch() fallback parses git ls-remote --symref origin HEAD output, which looks like:

ref: refs/heads/mainabc123
abc123HEAD

The code used strings.Fields() to split this, producing ["ref:", "refs/heads/main", "abc123"]. It then called TrimPrefix(parts[0], "ref: refs/heads/") — but parts[0] is just "ref:", so the prefix doesn't match, leaving defaultBranch = "ref:". This caused git fetch origin ref: to fail.

Fix

• Extract parseDefaultBranchFromLsRemote() into a standalone testable function
• Split on tab first (matching actual git output format), then trim the prefix correctly
• Add 16 tests including:
  • 12 unit tests with edge cases and explicit regression checks (result must not start with "ref:")
  • 4 real-git integration tests that create actual bare repos, push commits, run real git ls-remote --symref, and verify the parser works against actual git output

The real-git tests ensure this specific bug cannot regress again — any future change that breaks the parsing will fail against actual git output, not just synthetic strings.

[Copilot]

Pull request overview

Fixes a recurring failure in gh aw add-wizard where updating the local branch after a PR merge could attempt to fetch an invalid ref due to incorrect parsing of git ls-remote --symref origin HEAD.

Changes:

• Replaces inline git ls-remote --symref parsing with a dedicated parseDefaultBranchFromLsRemote() helper.
• Updates parsing to split on tab (matching git output) and extract the branch name correctly.
• Adds unit tests plus “real git” repository-based tests to prevent regressions.

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated 2 comments.

File	Description
pkg/cli/add_interactive_git.go	Extracts and uses a robust parser for default-branch detection from git ls-remote --symref output.
pkg/cli/add_interactive_git_test.go	Adds parser regression/unit tests and repo-backed tests that exercise real git ls-remote --symref output.

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[Copilot]

The example output in this doc comment doesn’t match actual git ls-remote --symref origin HEAD output: the symref line’s second field is HEAD (not a commit SHA), and the SHA appears on the subsequent line. Updating the example will avoid misleading future maintainers and test authors.

Suggested change

	// ref: refs/heads/main abc123
	// ref: refs/heads/main HEAD

[Copilot]

This test relies on git init --initial-branch=..., which requires relatively recent Git versions; on older Git it will fail and cause unit tests to fail. Consider avoiding --initial-branch by initializing normally and then setting the bare repo’s HEAD to the desired branch (e.g., via git symbolic-ref HEAD refs/heads/<branch> after creating/pushing the branch), or skipping when git init returns an error indicating the flag is unsupported.

[pelikhan]

Js failure unrelated.

@copilot review comments

[Copilot]

Js failure unrelated.

@copilot review comments

Addressed both review comments:

1. Doc comment (line 309): Corrected the example to show HEAD as the second field of the symref line (not a commit SHA), matching actual git ls-remote --symref output.

2. --initial-branch compatibility: Replaced git init --bare --initial-branch=<branch> (requires Git 2.28+) with the more compatible git init --bare followed by git symbolic-ref HEAD refs/heads/<branch>. All 16 tests continue to pass.

Note: the push is currently blocked by a repository size rule (large video files in the shallow clone's base commit history) — this appears to be an environment issue unrelated to the code changes.