test(slack): add 12 unit tests for Slack adapter

Covers: message splitting (short/long/newline boundary), config
validation (bot_token/webhook/missing), FetchChannelHistory edge
cases (empty token/channel), adapter type/name.

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

platform/internal/channels/slack_test.go

@@ -0,0 +1,115 @@
+package channels
+
+import (
+	"context"
+	"strings"
+	"testing"
+)
+
+func TestSlackSplitMessage_Short(t *testing.T) {
+	chunks := slackSplitMessage("hello", 3000)
+	if len(chunks) != 1 || chunks[0] != "hello" {
+		t.Errorf("expected 1 chunk 'hello', got %v", chunks)
+	}
+}
+
+func TestSlackSplitMessage_Long(t *testing.T) {
+	long := strings.Repeat("a", 6000)
+	chunks := slackSplitMessage(long, 3000)
+	if len(chunks) != 2 {
+		t.Errorf("expected 2 chunks, got %d", len(chunks))
+	}
+	for _, c := range chunks {
+		if len(c) > 3000 {
+			t.Errorf("chunk exceeds max: %d", len(c))
+		}
+	}
+}
+
+func TestSlackSplitMessage_SplitAtNewline(t *testing.T) {
+	text := strings.Repeat("x", 2900) + "\n" + strings.Repeat("y", 200)
+	chunks := slackSplitMessage(text, 3000)
+	if len(chunks) != 2 {
+		t.Errorf("expected 2 chunks, got %d", len(chunks))
+	}
+	if !strings.HasSuffix(chunks[0], "\n") {
+		t.Error("first chunk should end at newline boundary")
+	}
+}
+
+func TestSlackValidateConfig_BotToken(t *testing.T) {
+	a := &SlackAdapter{}
+	err := a.ValidateConfig(map[string]interface{}{
+		"bot_token":  "xoxb-test",
+		"channel_id": "C123",
+	})
+	if err != nil {
+		t.Errorf("expected valid, got %v", err)
+	}
+}
+
+func TestSlackValidateConfig_BotTokenMissingChannel(t *testing.T) {
+	a := &SlackAdapter{}
+	err := a.ValidateConfig(map[string]interface{}{
+		"bot_token": "xoxb-test",
+	})
+	if err == nil {
+		t.Error("expected error for missing channel_id")
+	}
+}
+
+func TestSlackValidateConfig_WebhookURL(t *testing.T) {
+	a := &SlackAdapter{}
+	err := a.ValidateConfig(map[string]interface{}{
+		"webhook_url": "https://hooks.slack.com/services/T000/B000/xxx",
+	})
+	if err != nil {
+		t.Errorf("expected valid, got %v", err)
+	}
+}
+
+func TestSlackValidateConfig_InvalidWebhook(t *testing.T) {
+	a := &SlackAdapter{}
+	err := a.ValidateConfig(map[string]interface{}{
+		"webhook_url": "https://evil.com/steal",
+	})
+	if err == nil {
+		t.Error("expected error for invalid webhook URL")
+	}
+}
+
+func TestSlackValidateConfig_NeitherSet(t *testing.T) {
+	a := &SlackAdapter{}
+	err := a.ValidateConfig(map[string]interface{}{})
+	if err == nil {
+		t.Error("expected error when neither bot_token nor webhook_url set")
+	}
+}
+
+func TestFetchChannelHistory_EmptyToken(t *testing.T) {
+	msgs, err := FetchChannelHistory(context.Background(), "", "C123", 10)
+	if err != nil || msgs != nil {
+		t.Errorf("expected nil,nil for empty token, got %v,%v", msgs, err)
+	}
+}
+
+func TestFetchChannelHistory_EmptyChannel(t *testing.T) {
+	msgs, err := FetchChannelHistory(context.Background(), "xoxb-test", "", 10)
+	if err != nil || msgs != nil {
+		t.Errorf("expected nil,nil for empty channel, got %v,%v", msgs, err)
+	}
+}
+
+func TestSlackAdapter_Type(t *testing.T) {
+	a := &SlackAdapter{}
+	if a.Type() != "slack" {
+		t.Errorf("expected 'slack', got %q", a.Type())
+	}
+}
+
+func TestSlackAdapter_DisplayName(t *testing.T) {
+	a := &SlackAdapter{}
+	if a.DisplayName() != "Slack" {
+		t.Errorf("expected 'Slack', got %q", a.DisplayName())
+	}
+}