| name | pr-base-branch-merge-base |
| description | Resolve PRBaseBranch for mcp__drm-copilot__collect_pr_context using merge-base ancestry. Use when orchestrators or review workflows need the correct comparison base branch and must select the branch with the most recent common ancestor commit with HEAD. |
PR Base Branch (Merge-Base)
Deterministic branch-selection rules for PR context collection.
When to Use This Skill
Use this skill when:
- running
mcp__drm-copilot__collect_pr_context,
- delegating post-implementation review that depends on
PRBaseBranch,
- constructing PR context artifacts where the base must not be hard-coded.
Selection Contract
PRBaseBranch MUST be resolved from git ancestry, not guessed.
Definition of correct base:
- choose the candidate branch whose merge-base with
HEAD has the most recent commit timestamp,
- this implements “find the branch with the most recent commit in common.”
Deterministic Procedure
- Enumerate candidate branches from local and remotes, excluding
HEAD and detached refs.
- For each candidate
B, compute merge-base commit M = git merge-base HEAD B.
- Compute
merge_base_epoch(B) from git show -s --format=%ct M.
- Select branch with maximum
merge_base_epoch(B).
- Tie-breakers (in order):
developmentmainmaster- lexical ascending branch name
Guardrails
- Do not default to
main unless merge-base resolution fails for all candidates.
- If all candidates fail, surface explicit error context and stop unless repository metadata directly identifies the default branch.
- Persist chosen
PRBaseBranch in orchestration state and reuse it within the same run.
Collector Invocation Rule
When invoking PR context collection, pass the resolved base explicitly:
mcp__drm-copilot__collect_pr_context with base=<resolved-PRBaseBranch>
Evidence Recommendation
For auditability, include in logs/checkpoint:
- selected branch name,
- selected merge-base SHA,
- selected merge-base timestamp,
- top competing candidates with timestamps when available.
