Function phase_commit_count 

pub fn phase_commit_count(
    project_root: &Path,
    git_flow: &GitFlowConfig,
    phase: u32,
) -> u32

Commits on the phase’s feature branch that are not on develop.

Derives the branch name from git_flow.feature_prefix and the zero-padded phase, verifies the branch exists with rev-parse --verify, and on success counts {git_flow.develop}..{branch} with rev-list --count. This is the single implementation of that count — evaluate_layer2 and pipeline_outcomes::handle_validate_outcome’s forward-progress check both call it rather than each re-deriving the branch name and re-running the same two git commands, which is what made the two counts able to silently diverge before this extraction.

Must be called with the main project_root, never a worktree path — git worktrees share refs and the object database, so a commit made inside a linked worktree is immediately visible to a count run from the main checkout, which is the property every caller already relies on.

A 0 return is deliberately indistinguishable across three causes: genuinely no commits, the branch does not exist, or git could not be run. Every consumer treats all three the same way.