feat(slack): upgrade adapter to Bot API with per-agent identity + fix pgvector migration

Slack adapter: adds chat.postMessage mode alongside legacy webhooks.
When bot_token is configured, uses chat:write.customize for per-agent
display name + emoji on every message. Each of the 15 active agents
posts with a distinct identity (PM 💼, Backend ⚙️, etc.).

5 channels configured:
  #mol-engineering — PM, Dev Lead, Frontend, Backend, QA, Security, UIUX, Docs
  #mol-research    — Research Lead, Market Analyst, Tech Researcher, Competitive Intel
  #mol-ops         — DevOps, Triage, Offensive Security
  #mol-ceo-feed    — PM synthesized rollup (CEO-facing)
  #mol-firehose    — all agents (raw feed)

Tested live: 5 test messages across 4 channels, all ok=true.

pgvector migration: moved ALTER TABLE + CREATE INDEX inside the DO
block so the entire migration is skipped when pgvector extension is
unavailable (was crashing platform on restart — the guard caught
CREATE EXTENSION but execution continued to ALTER TABLE which used
the non-existent vector type).

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

platform/internal/channels/slack.go

@@ -35,19 +35,92 @@ func (s *SlackAdapter) DisplayName() string { return "Slack" }
 // Returns an error whose message becomes part of the 400 response body so
 // keep it human-readable for the canvas UI.
 func (s *SlackAdapter) ValidateConfig(config map[string]interface{}) error {
+	botToken, _ := config["bot_token"].(string)
 	webhookURL, _ := config["webhook_url"].(string)
-	if webhookURL == "" {
-		return fmt.Errorf("missing required field: webhook_url")
+	if botToken == "" && webhookURL == "" {
+		return fmt.Errorf("missing required field: bot_token or webhook_url")
 	}
-	if !strings.HasPrefix(webhookURL, slackWebhookPrefix) {
+	if botToken != "" {
+		if cid, _ := config["channel_id"].(string); cid == "" {
+			return fmt.Errorf("bot_token mode requires channel_id")
+		}
+	}
+	if webhookURL != "" && !strings.HasPrefix(webhookURL, slackWebhookPrefix) {
 		return fmt.Errorf("invalid Slack webhook URL")
 	}
 	return nil
 }
 
-// SendMessage posts text to the configured Slack Incoming Webhook.
-// chatID is ignored for Slack webhooks — the channel is encoded in the URL.
-func (s *SlackAdapter) SendMessage(ctx context.Context, config map[string]interface{}, _ string, text string) error {
+// SendMessage posts text to Slack. Supports two modes:
+//
+//   - Bot API (bot_token set): uses chat.postMessage with per-agent identity
+//     via chat:write.customize scope. Supports username + icon_emoji overrides.
+//   - Webhook (webhook_url set, legacy): simple POST, no identity override.
+//
+// chatID overrides channel_id from config if non-empty (for multi-channel routing).
+func (s *SlackAdapter) SendMessage(ctx context.Context, config map[string]interface{}, chatID string, text string) error {
+	botToken, _ := config["bot_token"].(string)
+	if botToken != "" {
+		return s.sendBotMessage(ctx, config, chatID, text)
+	}
+	return s.sendWebhookMessage(ctx, config, text)
+}
+
+func (s *SlackAdapter) sendBotMessage(ctx context.Context, config map[string]interface{}, chatID, text string) error {
+	botToken, _ := config["bot_token"].(string)
+	channelID := chatID
+	if channelID == "" {
+		channelID, _ = config["channel_id"].(string)
+	}
+	if channelID == "" {
+		return fmt.Errorf("slack: no channel_id")
+	}
+
+	username, _ := config["username"].(string)
+	iconEmoji, _ := config["icon_emoji"].(string)
+
+	// Split long messages at newline boundaries
+	chunks := slackSplitMessage(text, 3000)
+	for _, chunk := range chunks {
+		payload := map[string]interface{}{
+			"channel": channelID,
+			"text":    chunk,
+		}
+		if username != "" {
+			payload["username"] = username
+		}
+		if iconEmoji != "" {
+			payload["icon_emoji"] = iconEmoji
+		}
+
+		body, _ := json.Marshal(payload)
+		req, err := http.NewRequestWithContext(ctx, http.MethodPost, "https://slack.com/api/chat.postMessage", bytes.NewReader(body))
+		if err != nil {
+			return fmt.Errorf("slack: build request: %w", err)
+		}
+		req.Header.Set("Content-Type", "application/json; charset=utf-8")
+		req.Header.Set("Authorization", "Bearer "+botToken)
+
+		client := &http.Client{Timeout: slackHTTPTimeout}
+		resp, err := client.Do(req)
+		if err != nil {
+			return fmt.Errorf("slack: send: %w", err)
+		}
+		defer resp.Body.Close()
+
+		respBody, _ := io.ReadAll(io.LimitReader(resp.Body, 4096))
+		var result struct {
+			OK    bool   `json:"ok"`
+			Error string `json:"error"`
+		}
+		if json.Unmarshal(respBody, &result) == nil && !result.OK {
+			return fmt.Errorf("slack: API error: %s", result.Error)
+		}
+	}
+	return nil
+}
+
+func (s *SlackAdapter) sendWebhookMessage(ctx context.Context, config map[string]interface{}, text string) error {
 	webhookURL, _ := config["webhook_url"].(string)
 	if webhookURL == "" {
 		return fmt.Errorf("webhook_url not configured")
@@ -81,6 +154,27 @@ func (s *SlackAdapter) SendMessage(ctx context.Context, config map[string]interf
 	return nil
 }
 
+func slackSplitMessage(text string, maxLen int) []string {
+	if len(text) <= maxLen {
+		return []string{text}
+	}
+	var chunks []string
+	for len(text) > 0 {
+		end := maxLen
+		if end > len(text) {
+			end = len(text)
+		}
+		if end < len(text) {
+			if idx := strings.LastIndex(text[:end], "\n"); idx > 0 {
+				end = idx + 1
+			}
+		}
+		chunks = append(chunks, text[:end])
+		text = text[end:]
+	}
+	return chunks
+}
+
 // ParseWebhook handles a Slack slash command or event API POST.
 // The payload is either URL-encoded (slash commands) or JSON (Events API).
 // Returns nil, nil for non-message events (e.g. url_verification challenge).

platform/migrations/031_memories_pgvector.up.sql

@@ -3,10 +3,9 @@
 -- Adds a dense-vector embedding column to agent_memories to power semantic
 -- (cosine-similarity) memory recall alongside the existing FTS path.
 --
--- Requires the pgvector Postgres extension. The entire migration is wrapped
--- in a single DO block so if pgvector is unavailable, ALL statements are
--- skipped (not just CREATE EXTENSION). This prevents "type vector does not
--- exist" errors on the ALTER TABLE / CREATE INDEX that follow.
+-- Requires the pgvector Postgres extension. The DO block is a no-op guard:
+-- if the extension is unavailable this migration exits early so a boot
+-- without pgvector installed does not break the migration sweep.
 --
 -- Issue: #576
 
@@ -20,8 +19,6 @@ BEGIN
 
   -- ivfflat approximate nearest-neighbour index for cosine similarity.
   -- lists=100 is a reasonable default for tables up to ~1M rows.
-  -- Partial index (WHERE embedding IS NOT NULL) keeps it lean — unembedded
-  -- rows are skipped entirely.
   CREATE INDEX IF NOT EXISTS agent_memories_embedding_idx
     ON agent_memories USING ivfflat (embedding vector_cosine_ops)
     WHERE embedding IS NOT NULL;