feat(web): support image messages in pico chat (#2299)

pkg/agent/context.go

@@ -602,14 +602,16 @@ func (cb *ContextBuilder) BuildMessages(
 	// Add conversation history
 	messages = append(messages, history...)
 
-	// Add current user message
-	if strings.TrimSpace(currentMessage) != "" {
+	// Add current user message. Media-only turns must still be preserved so
+	// multimodal providers receive the uploaded image even when the user sends
+	// no accompanying text.
+	if strings.TrimSpace(currentMessage) != "" || len(media) > 0 {
 		msg := providers.Message{
 			Role:    "user",
 			Content: currentMessage,
 		}
 		if len(media) > 0 {
-			msg.Media = media
+			msg.Media = append([]string(nil), media...)
 		}
 		messages = append(messages, msg)
 	}

pkg/agent/context_cache_test.go

@@ -707,6 +707,38 @@ func TestEmptyWorkspaceBaselineDetectsNewFiles(t *testing.T) {
 	}
 }
 
+func TestBuildMessages_IncludesMediaOnlyCurrentMessage(t *testing.T) {
+	tmpDir := setupWorkspace(t, nil)
+	defer os.RemoveAll(tmpDir)
+
+	cb := NewContextBuilder(tmpDir)
+	msgs := cb.BuildMessages(
+		nil,
+		"",
+		"",
+		[]string{"data:image/png;base64,abc123"},
+		"pico",
+		"chat-1",
+		"",
+		"",
+	)
+
+	if len(msgs) != 2 {
+		t.Fatalf("len(msgs) = %d, want 2", len(msgs))
+	}
+
+	userMsg := msgs[1]
+	if userMsg.Role != "user" {
+		t.Fatalf("userMsg.Role = %q, want %q", userMsg.Role, "user")
+	}
+	if userMsg.Content != "" {
+		t.Fatalf("userMsg.Content = %q, want empty string", userMsg.Content)
+	}
+	if len(userMsg.Media) != 1 || userMsg.Media[0] != "data:image/png;base64,abc123" {
+		t.Fatalf("userMsg.Media = %#v, want image payload", userMsg.Media)
+	}
+}
+
 // BenchmarkBuildMessagesWithCache measures caching performance.
 func BenchmarkBuildMessagesWithCache(b *testing.B) {
 	tmpDir, _ := os.MkdirTemp("", "picoclaw-bench-*")