feat: add commit message normalizer

Standardize commit messages before they reach git: trim whitespace,
capitalize subject, remove trailing periods, truncate to 72 chars,
and enforce blank line between subject and body.

Nightshift-Task: commit-normalize
Nightshift-Ref: https://github.com/marcus/nightshift

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Author: marcus

internal/plugins/gitstatus/commit_normalize.go

@@ -0,0 +1,74 @@
+package gitstatus
+
+import (
+	"strings"
+	"unicode"
+	"unicode/utf8"
+)
+
+const maxSubjectLen = 72
+
+// NormalizeCommitMessage standardizes a commit message:
+// - trims surrounding whitespace
+// - capitalizes the first letter of the subject line
+// - removes a trailing period from the subject
+// - truncates the subject to 72 characters (with ellipsis)
+// - ensures a blank line between subject and body
+func NormalizeCommitMessage(msg string) string {
+	msg = strings.TrimSpace(msg)
+	if msg == "" {
+		return ""
+	}
+
+	// Split into subject and optional body.
+	// A body is separated by at least one blank line.
+	subject, body := splitSubjectBody(msg)
+
+	subject = strings.TrimSpace(subject)
+	if subject == "" {
+		return ""
+	}
+
+	// Capitalize the first letter
+	subject = capitalizeFirst(subject)
+
+	// Remove trailing period
+	subject = strings.TrimRight(subject, ".")
+
+	// Truncate long subjects
+	if len(subject) > maxSubjectLen {
+		subject = subject[:maxSubjectLen-1] + "…"
+	}
+
+	if body == "" {
+		return subject
+	}
+	return subject + "\n\n" + body
+}
+
+// splitSubjectBody splits at the first blank line. If there is no blank line
+// but the message is multi-line, the first line is the subject and the rest
+// is the body (with an enforced blank-line separator).
+func splitSubjectBody(msg string) (subject, body string) {
+	// Look for a blank-line separator
+	if idx := strings.Index(msg, "\n\n"); idx >= 0 {
+		return msg[:idx], strings.TrimSpace(msg[idx+2:])
+	}
+
+	// Single line
+	if !strings.Contains(msg, "\n") {
+		return msg, ""
+	}
+
+	// Multi-line without blank separator – split on first newline
+	parts := strings.SplitN(msg, "\n", 2)
+	return parts[0], strings.TrimSpace(parts[1])
+}
+
+func capitalizeFirst(s string) string {
+	r, size := utf8.DecodeRuneInString(s)
+	if r == utf8.RuneError || size == 0 {
+		return s
+	}
+	return string(unicode.ToUpper(r)) + s[size:]
+}

internal/plugins/gitstatus/commit_normalize_test.go

@@ -0,0 +1,58 @@
+package gitstatus
+
+import (
+	"strings"
+	"testing"
+)
+
+func TestNormalizeCommitMessage(t *testing.T) {
+	tests := []struct {
+		name string
+		in   string
+		want string
+	}{
+		{name: "empty", in: "", want: ""},
+		{name: "whitespace only", in: "   \n\t  ", want: ""},
+		{name: "trim whitespace", in: "  fix bug  ", want: "Fix bug"},
+		{name: "capitalize first letter", in: "fix bug", want: "Fix bug"},
+		{name: "already capitalized", in: "Fix bug", want: "Fix bug"},
+		{name: "remove trailing period", in: "Fix bug.", want: "Fix bug"},
+		{name: "remove multiple trailing periods", in: "Fix bug...", want: "Fix bug"},
+		{name: "keep interior periods", in: "Fix v1.2.3 bug.", want: "Fix v1.2.3 bug"},
+		{name: "short subject unchanged", in: "Add feature", want: "Add feature"},
+		{
+			name: "truncate long subject",
+			in:   strings.Repeat("a", 80),
+			want: "A" + strings.Repeat("a", 70) + "…",
+		},
+		{
+			name: "subject with body separated by blank line",
+			in:   "fix bug\n\nMore details here.",
+			want: "Fix bug\n\nMore details here.",
+		},
+		{
+			name: "enforce blank line between subject and body",
+			in:   "fix bug\nMore details here.",
+			want: "Fix bug\n\nMore details here.",
+		},
+		{
+			name: "body preserves multiple lines",
+			in:   "fix bug\n\nLine one.\nLine two.",
+			want: "Fix bug\n\nLine one.\nLine two.",
+		},
+		{
+			name: "single char",
+			in:   "x",
+			want: "X",
+		},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			got := NormalizeCommitMessage(tt.in)
+			if got != tt.want {
+				t.Errorf("NormalizeCommitMessage(%q)\n got  %q\n want %q", tt.in, got, tt.want)
+			}
+		})
+	}
+}

internal/plugins/gitstatus/update_handlers.go

@@ -813,7 +813,7 @@ func (p *Plugin) updateCommit(msg tea.KeyMsg) (plugin.Plugin, tea.Cmd) {
 
 // tryCommit attempts to execute the commit (or amend) if message is valid.
 func (p *Plugin) tryCommit() tea.Cmd {
-	message := strings.TrimSpace(p.commitMessage.Value())
+	message := NormalizeCommitMessage(p.commitMessage.Value())
 	if message == "" {
 		p.commitError = "Commit message cannot be empty"
 		return nil