feat(gmw): public features #2-#6 — live moderation feed, toxic topic trends, channel timeline, CSV export, activity heatmap

- Live Moderation Feed: gateway publishes discord:moderation:action (Redis) → backend WS emits moderation_action → public web shows realtime stream.
- Toxic Topic Trends: backend moderation.trends aggregates categories/severity/action_type (read-only) → SVG bar + donut.
- Channel Timeline: messages view gets Feed/Timeline toggle with date-grouped separators.
- CSV Export: client-side downloadCsv for moderation actions (no backend write scope).
- Activity Heatmap: backend messages.activity (per-hour volume by channel) → pure-SVG grid.

User reputation deliberately excluded — no such feature exists in the codebase.
All read-only / public-facing / fully automatic per project rules.

services/backend/src/modules/messages/messages.repository.ts

@@ -459,6 +459,31 @@ export class MessagesRepository {
 
     return { data: trimmed, nextCursor };
   }
+
+  /**
+   * Per-hour message volume for the last `days` days, grouped by channel.
+   * Powers the public Activity Heatmap (read-only, no write scope).
+   * Returns a flat list of { channel_id, hour (0-23), count } buckets.
+   */
+  async getActivity(days = 30) {
+    const db = getDatabase();
+    const since = Date.now() - days * 24 * 60 * 60 * 1000;
+    const result = await db.execute(sql`
+      SELECT channel_id,
+             EXTRACT(HOUR FROM to_timestamp(created_at / 1000))::int AS hour,
+             COUNT(*)::int AS c
+      FROM messages
+      WHERE created_at >= ${since}
+      GROUP BY channel_id, hour
+      ORDER BY channel_id, hour
+    `);
+    const rows = (result.rows as Record<string, unknown>[]) || [];
+    return rows.map((r) => ({
+      channelId: String(r.channel_id ?? "unknown"),
+      hour: Number(r.hour ?? 0),
+      count: Number(r.c ?? 0),
+    }));
+  }
 }
 
 export const messagesRepository = new MessagesRepository();

services/backend/src/modules/messages/messages.service.ts

@@ -101,6 +101,10 @@ export class MessagesService {
     const results = hits.map((h) => mapSearchHit(h));
     return { results, nextCursor: null };
   }
+
+  async getActivity(days = 30) {
+    return messagesRepository.getActivity(days);
+  }
 }
 
 /** Shape returned to the frontend (text + metadata from the archive payload). */

services/backend/src/modules/moderation/moderation.repository.ts

@@ -164,6 +164,60 @@ export class ModerationRepository {
 
     return { data, nextCursor };
   }
+
+  /**
+   * Aggregate moderation trends over the last `days` days.
+   * - category counts (from the jsonb/text[] `categories` column, unnested)
+   * - severity distribution
+   * - action_type distribution
+   * Read-only; powers the public Toxic Topic Trends panel.
+   */
+  async getTrends(days: number) {
+    const db = getDatabase();
+    const since = Date.now() - days * 24 * 60 * 60 * 1000;
+
+    const cats = await db.execute(sql`
+      SELECT jsonb_array_elements_text(a.categories::jsonb) AS cat, COUNT(*)::int AS c
+      FROM moderation_actions a
+      WHERE a.created_at >= ${since} AND a.categories IS NOT NULL AND a.categories != '[]' AND a.categories != ''
+      GROUP BY cat
+      ORDER BY c DESC
+      LIMIT 15
+    `);
+    const catRows = (cats.rows as Record<string, unknown>[]) || [];
+
+    const sev = await db.execute(sql`
+      SELECT severity, COUNT(*)::int AS c
+      FROM moderation_actions
+      WHERE created_at >= ${since} AND severity IS NOT NULL
+      GROUP BY severity
+    `);
+    const sevRows = (sev.rows as Record<string, unknown>[]) || [];
+
+    const act = await db.execute(sql`
+      SELECT action_type, COUNT(*)::int AS c
+      FROM moderation_actions
+      WHERE created_at >= ${since}
+      GROUP BY action_type
+      ORDER BY c DESC
+    `);
+    const actRows = (act.rows as Record<string, unknown>[]) || [];
+
+    return {
+      categories: catRows.map((r) => ({
+        name: String(r.cat),
+        count: Number(r.c ?? 0),
+      })),
+      severities: sevRows.map((r) => ({
+        level: String(r.severity),
+        count: Number(r.c ?? 0),
+      })),
+      actions: actRows.map((r) => ({
+        type: String(r.action_type),
+        count: Number(r.c ?? 0),
+      })),
+    };
+  }
 }
 
 export const moderationRepository = new ModerationRepository();

services/backend/src/modules/moderation/moderation.service.ts

@@ -8,10 +8,13 @@ const logger = createChildLogger("moderation.service");
 
 export class ModerationService {
   async getStats() {
-    logger.debug("Fetching moderation stats");
     return moderationRepository.getStats();
   }
 
+  async getTrends(days = 30) {
+    return moderationRepository.getTrends(days);
+  }
+
   async listActions(query: ListModerationQuery) {
     logger.debug({ query }, "Listing moderation actions");
     return moderationRepository.listActions(query);

services/backend/src/orpc/router.ts

@@ -143,6 +143,14 @@ const messagesRouter = {
   semanticSearch: os
     .input(semanticSearchSchema)
     .handler(({ input }) => messagesService.semanticSearch(input)),
+  // Public, read-only activity heatmap data (per-hour volume by channel).
+  activity: os
+    .input(
+      z.object({
+        days: z.coerce.number().int().positive().max(365).default(30),
+      }),
+    )
+    .handler(({ input }) => messagesService.getActivity(input.days)),
 };
 
 // ── Moderation ───────────────────────────────────────────────────
@@ -165,6 +173,13 @@ const moderationRouter = {
         cursor: input.cursor,
       }),
     ),
+  trends: os
+    .input(
+      z.object({
+        days: z.coerce.number().int().positive().max(365).default(30),
+      }),
+    )
+    .handler(({ input }) => moderationService.getTrends(input.days)),
 };
 
 // ── Media ────────────────────────────────────────────────────────

services/backend/src/shared/redis-channels.ts

@@ -30,6 +30,7 @@ export const DISCORD_CHANNEL_TOPIC_UPDATED = "discord:channel:topic_updated";
 export const DISCORD_PRESENCE_UPDATED = "discord:presence:updated";
 export const DISCORD_GUILD_MEMBER_ADDED = "discord:guild_member:added";
 export const DISCORD_GUILD_MEMBER_REMOVED = "discord:guild_member:removed";
+export const DISCORD_MODERATION_ACTION = "discord:moderation:action";
 
 // ---------------------------------------------------------------------------
 // Command channels (backend -> discord-gateway)
@@ -126,4 +127,5 @@ export const DISCORD_CHANNEL_TO_WS_EVENT: Record<string, string> = {
   [DISCORD_PRESENCE_UPDATED]: "presence_updated",
   [DISCORD_GUILD_MEMBER_ADDED]: "guild_member_added",
   [DISCORD_GUILD_MEMBER_REMOVED]: "guild_member_removed",
+  [DISCORD_MODERATION_ACTION]: "moderation_action",
 };