Branch name validation rejects valid git branch names containing #

[pbosch]

Bug

The branch name validation regex rejects #, which is a valid character in git branch names. This causes the action to fail on PRs from branches like put-back-arm64-#2 with:

##[error] Invalid branch name: "put-back-arm64-#2". Branch names must start with an
alphanumeric character and contain only alphanumeric characters, forward slashes,
hyphens, underscores, or periods.

Context

The validation at src/github/operations/branch.ts uses regex ^[a-zA-Z0-9][a-zA-Z0-9/_.-]*$ which excludes #. Per git-check-ref-format, # is allowed in branch names.

This validation makes sense for branches the action creates, but for pull_request events where the action only reads an existing branch (checked out by actions/checkout), there's no reason to reject it. The branch already exists in git — rejecting it just prevents the review from running.

Expected behavior

For pull_request events (review mode), the action should accept whatever branch name GitHub provides via the event context, since it's already a valid git ref.

Reproduction

1. Create a branch with # in the name: git checkout -b "fix-arm64-#2"
2. Push and open a PR
3. Run claude-code-action on the PR → fails with the error above

Suggested fix

Either:

• Relax the regex to allow # and other git-valid characters
• Skip branch name validation for pull_request events where the action is reading (not creating) branches
• Add an input to override/skip branch validation