feat(pr_merge): gate it like tbd_ship — green CI, unprotected base, exactly one risk/low issue (#74) (#76)

Co-authored-by: Mathias <mthbqv@gmail.com>

internal/gitea/pulls.go

@@ -109,6 +109,8 @@ type MergePRArgs struct {
 	Do    string `json:"Do"`
 	Title string `json:"merge_message_title,omitempty"`
 	Body  string `json:"merge_message_field,omitempty"`
+	// HeadCommitID binds the merge to the commit whose CI was checked: if the PR branch moved, Gitea refuses.
+	HeadCommitID string `json:"head_commit_id,omitempty"`
 }
 
 func (c *Client) MergePullRequest(ctx context.Context, owner, repo string, index int, args MergePRArgs) error {