Test bullet parser; fix marker-less passthrough

The previous parser treated any non-empty non-header line as a bullet,
so 'plain paragraph' answers were silently rewrapped as <ul><li>. Now
we only count a line if it had a recognized bullet marker (- * • ·);
if none did, fall back to raw + <pre> as originally intended.

Tests cover dash/asterisk/unicode bullets, blank-line tolerance,
Summary:/TL;DR header stripping, HTML escaping, single-bullet output,
the no-marker passthrough path, and the IsQuestionReaction set.

internal/explainer/explainer.go

@@ -139,29 +139,36 @@ func (e *Explainer) summarize(headline, body string) (string, error) {
 func formatSummary(raw string) (plain, htmlBody string) {
 	lines := strings.Split(raw, "\n")
 	var bullets []string
+	sawMarker := false
 	for _, line := range lines {
 		line = strings.TrimSpace(line)
 		if line == "" {
 			continue
 		}
-		// Normalize common bullet markers
-		for _, prefix := range []string{"- ", "* ", "• ", "·"} {
-			if strings.HasPrefix(line, prefix) {
-				line = strings.TrimSpace(line[len(prefix):])
-				break
-			}
-		}
 		// Skip header-ish lines the model sometimes adds
 		low := strings.ToLower(line)
 		if strings.HasPrefix(low, "summary:") || strings.HasPrefix(low, "tl;dr") {
 			continue
 		}
+		// Normalize common bullet markers; only count this line if it had one.
+		hadMarker := false
+		for _, prefix := range []string{"- ", "* ", "• ", "·"} {
+			if strings.HasPrefix(line, prefix) {
+				line = strings.TrimSpace(line[len(prefix):])
+				hadMarker = true
+				break
+			}
+		}
+		if !hadMarker {
+			continue
+		}
+		sawMarker = true
 		if line == "" {
 			continue
 		}
 		bullets = append(bullets, line)
 	}
-	if len(bullets) == 0 {
+	if !sawMarker || len(bullets) == 0 {
 		// Model produced something but we couldn't parse bullets — pass through.
 		return raw, "<pre>" + html.EscapeString(raw) + "</pre>"
 	}

internal/explainer/explainer_test.go

@@ -0,0 +1,110 @@
+package explainer
+
+import (
+	"strings"
+	"testing"
+)
+
+func TestFormatSummary(t *testing.T) {
+	cases := []struct {
+		name      string
+		in        string
+		wantPlain string
+		wantHTML  string
+	}{
+		{
+			name:      "dash bullets",
+			in:        "- First point.\n- Second point.\n- Third point.",
+			wantPlain: "• First point.\n• Second point.\n• Third point.",
+			wantHTML:  "<ul><li>First point.</li><li>Second point.</li><li>Third point.</li></ul>",
+		},
+		{
+			name:      "asterisk bullets",
+			in:        "* alpha\n* beta",
+			wantPlain: "• alpha\n• beta",
+			wantHTML:  "<ul><li>alpha</li><li>beta</li></ul>",
+		},
+		{
+			name:      "unicode bullets",
+			in:        "• one\n• two",
+			wantPlain: "• one\n• two",
+			wantHTML:  "<ul><li>one</li><li>two</li></ul>",
+		},
+		{
+			name:      "blank lines ignored",
+			in:        "- a\n\n- b\n\n\n- c",
+			wantPlain: "• a\n• b\n• c",
+			wantHTML:  "<ul><li>a</li><li>b</li><li>c</li></ul>",
+		},
+		{
+			name:      "summary header stripped",
+			in:        "Summary:\n- first\n- second",
+			wantPlain: "• first\n• second",
+			wantHTML:  "<ul><li>first</li><li>second</li></ul>",
+		},
+		{
+			name:      "tldr header stripped",
+			in:        "TL;DR of the article\n- key point\n- other point",
+			wantPlain: "• key point\n• other point",
+			wantHTML:  "<ul><li>key point</li><li>other point</li></ul>",
+		},
+		{
+			name:      "single bullet",
+			in:        "- just one",
+			wantPlain: "• just one",
+			wantHTML:  "<ul><li>just one</li></ul>",
+		},
+		{
+			name:      "html escaped in bullets",
+			in:        `- A "quote" & <tag>`,
+			wantPlain: `• A "quote" & <tag>`,
+			wantHTML:  "<ul><li>A &#34;quote&#34; &amp; &lt;tag&gt;</li></ul>",
+		},
+		{
+			name:      "leading whitespace trimmed",
+			in:        "   - first\n   - second   ",
+			wantPlain: "• first\n• second",
+			wantHTML:  "<ul><li>first</li><li>second</li></ul>",
+		},
+	}
+	for _, c := range cases {
+		t.Run(c.name, func(t *testing.T) {
+			gotPlain, gotHTML := formatSummary(c.in)
+			if gotPlain != c.wantPlain {
+				t.Errorf("plain:\n got  %q\n want %q", gotPlain, c.wantPlain)
+			}
+			if gotHTML != c.wantHTML {
+				t.Errorf("html:\n got  %q\n want %q", gotHTML, c.wantHTML)
+			}
+		})
+	}
+}
+
+func TestFormatSummary_NoBulletsPassthrough(t *testing.T) {
+	in := "Just a single paragraph with no bullets at all."
+	plain, htmlBody := formatSummary(in)
+	if plain != in {
+		t.Errorf("plain should pass through raw, got %q", plain)
+	}
+	if !strings.HasPrefix(htmlBody, "<pre>") || !strings.HasSuffix(htmlBody, "</pre>") {
+		t.Errorf("html should wrap raw in <pre>, got %q", htmlBody)
+	}
+	if !strings.Contains(htmlBody, "single paragraph") {
+		t.Errorf("html should contain the body text, got %q", htmlBody)
+	}
+}
+
+func TestIsQuestionReaction(t *testing.T) {
+	want := []string{"❓", "❔", "⁉", "⁉️", "🤔", "?", "？"}
+	for _, k := range want {
+		if !IsQuestionReaction(k) {
+			t.Errorf("expected %q to trigger explain", k)
+		}
+	}
+	notQuestion := []string{"👍", "👎", "🔥", "", "??", "❤️"}
+	for _, k := range notQuestion {
+		if IsQuestionReaction(k) {
+			t.Errorf("expected %q to NOT trigger explain", k)
+		}
+	}
+}