fix(submit): derive default PR title from first commit message

The default PR title is now derived from the subject of the first
commit in the branch (the oldest commit unique to the branch) instead
of the branch name.

Falls back to the branch-name-based title if no commits are available.

Author: boneskull

cmd/submit.go

@@ -281,8 +281,8 @@ func createPRForBranch(g *git.Git, ghClient *github.Client, cfg *config.Config,
 	// Determine if draft (not targeting trunk = middle of stack)
 	draft := base != trunk
 
-	// Generate default title from branch name
-	defaultTitle := generateTitleFromBranch(branch)
+	// Generate default title from first commit message (falls back to branch name)
+	defaultTitle := generateDefaultTitle(g, base, branch)
 
 	// Generate PR body from commits
 	defaultBody, bodyErr := generatePRBody(g, base, branch)
@@ -326,6 +326,18 @@ func createPRForBranch(g *git.Git, ghClient *github.Client, cfg *config.Config,
 	return pr.Number, false, nil
 }
 
+// generateDefaultTitle creates a PR title from the first commit message.
+// Falls back to branch name if no commits are available.
+func generateDefaultTitle(g *git.Git, base, branch string) string {
+	commits, err := g.GetCommits(base, branch)
+	if err != nil || len(commits) == 0 {
+		// Fall back to branch name
+		return generateTitleFromBranch(branch)
+	}
+	// Use the first commit's subject (oldest commit is last in array since GetCommits returns newest first)
+	return commits[len(commits)-1].Subject
+}
+
 // generateTitleFromBranch creates a PR title from a branch name.
 // Replaces - and _ with spaces and converts to title case.
 func generateTitleFromBranch(branch string) string {