refactor(backend): drop backend-driven Fabric broadcast — agent-driven model

The backend no longer broadcasts topic lifecycle events to Fabric. The
new model (per design discussion 2026-05-23 evening):

  - Proposing agent posts a single recruitment fabric-send-message
    immediately after creating a topic (carries topic_id + signup
    window + debate window + title).
  - Downstream agents that decide to participate book a HF on_call
    slot covering the debate window via `hf calendar schedule on_call
    <time> <duration> --job DEBATE-<topic_id>`.
  - HF wakes the agent naturally at slot start; the wake payload
    carries event_data with the DEBATE-<topic_id> code so the agent
    knows why it was woken.
  - The backend stays a pure data + state-machine service and doesn't
    know about Fabric.

Code removed:

  - internal/fabric/announce.go (entire file + empty dir)
  - ticker.go: broadcastLifecycle + broadcastAnnouncement + topicTarget
    helpers; announcer field on Ticker; announce field/arg on NewTicker
  - models/topic.go: AnnounceGuildBaseURL + AnnounceChannelID fields
  - store/topic_store.go: same fields on CreateTopicInput + INSERT
  - handlers/topics.go: same fields on createTopicBody + validation +
    parameter passing to store
  - handlers/verdict.go: announcer field + lifecycle broadcast on
    verdict submit
  - config/config.go: FabricSystemAPIKey field + DIALECTIC_FABRIC_SYSTEM_API_KEY
    env read
  - main.go + routes.go: announcer wiring

Database:

  - migrations/003_drop_topic_announce_target.sql drops the two columns
    added by migration 002. Counterpart commit on the deployment side
    needs DIALECTIC_FABRIC_SYSTEM_API_KEY env removed from
    docker-compose.yml; harmless if left as the backend no longer
    reads it.

Pairs with:
  - Dialectic.OpenclawPlugin: rip announce_* params from
    dialectic_propose_topic (next commit)
  - Fabric.Backend.Center: rip serviceEndpoint field + cli
  - Fabric.Backend.Guild: rip system-key bypass on ApiKeyGuard and
    announce-only-system limit on messaging.controller
  - ClawSkills: rewrite participate-debate + analyze-intel step 4 +
    delete rotate-fabric-system-key workflow

internal/httpapi/handlers/topics.go

@@ -109,12 +109,6 @@ type createTopicBody struct {
 	SignupCloseAt   string `json:"signup_close_at"`
 	DebateStartAt   string `json:"debate_start_at"`
 	DebateEndAt     string `json:"debate_end_at"`
-	// Optional: per-topic announce-channel target. Both must be set
-	// (or both omitted = no broadcasts). Creator picks based on the
-	// debate's intended audience (different guilds may host different
-	// communities, different channels may serve different categories).
-	AnnounceGuildBaseURL string `json:"announce_guild_base_url,omitempty"`
-	AnnounceChannelID    string `json:"announce_channel_id,omitempty"`
 }
 
 // POST /api/topics
@@ -147,31 +141,16 @@ func (h *TopicsHandler) Create(w http.ResponseWriter, r *http.Request) {
 		http.Error(w, err.Error(), http.StatusBadRequest)
 		return
 	}
-	// Announce target: both fields required or both empty; one-of-two
-	// is a config error caught here rather than silently treated as
-	// "no broadcast".
-	var aGuild, aChannel *string
-	if body.AnnounceGuildBaseURL != "" || body.AnnounceChannelID != "" {
-		if body.AnnounceGuildBaseURL == "" || body.AnnounceChannelID == "" {
-			http.Error(w, "announce_guild_base_url and announce_channel_id must both be set (or both empty for no broadcasts)", http.StatusBadRequest)
-			return
-		}
-		g, c := body.AnnounceGuildBaseURL, body.AnnounceChannelID
-		aGuild, aChannel = &g, &c
-	}
-
 	created, err := h.store.Create(r.Context(), store.CreateTopicInput{
-		Title:                body.Title,
-		Summary:              body.Summary,
-		Visibility:           models.Visibility(body.Visibility),
-		VerdictSchemaID:      body.VerdictSchemaID,
-		SignupOpenAt:         parsed[0],
-		SignupCloseAt:        parsed[1],
-		DebateStartAt:        parsed[2],
-		DebateEndAt:          parsed[3],
-		CreatorUserID:        caller.ID,
-		AnnounceGuildBaseURL: aGuild,
-		AnnounceChannelID:    aChannel,
+		Title:           body.Title,
+		Summary:         body.Summary,
+		Visibility:      models.Visibility(body.Visibility),
+		VerdictSchemaID: body.VerdictSchemaID,
+		SignupOpenAt:    parsed[0],
+		SignupCloseAt:   parsed[1],
+		DebateStartAt:   parsed[2],
+		DebateEndAt:     parsed[3],
+		CreatorUserID:   caller.ID,
 	})
 	if err != nil {
 		http.Error(w, "create failed: "+err.Error(), http.StatusInternalServerError)

internal/httpapi/handlers/verdict.go

@@ -1,30 +1,26 @@
 package handlers
 
 import (
-	"context"
 	"encoding/json"
 	"errors"
-	"fmt"
 	"net/http"
 	"time"
 
 	"github.com/go-chi/chi/v5"
 
 	"git.hangman-lab.top/hzhang/Dialectic.Backend/internal/auth"
-	"git.hangman-lab.top/hzhang/Dialectic.Backend/internal/fabric"
 	"git.hangman-lab.top/hzhang/Dialectic.Backend/internal/models"
 	"git.hangman-lab.top/hzhang/Dialectic.Backend/internal/store"
 )
 
 type VerdictHandler struct {
-	topics    *store.TopicStore
-	camps     *store.CampStore
-	verdicts  *store.VerdictStore
-	announcer *fabric.Announcer // optional; nil-safe via Enabled() check
+	topics   *store.TopicStore
+	camps    *store.CampStore
+	verdicts *store.VerdictStore
 }
 
-func NewVerdictHandler(t *store.TopicStore, c *store.CampStore, v *store.VerdictStore, ann *fabric.Announcer) *VerdictHandler {
-	return &VerdictHandler{topics: t, camps: c, verdicts: v, announcer: ann}
+func NewVerdictHandler(t *store.TopicStore, c *store.CampStore, v *store.VerdictStore) *VerdictHandler {
+	return &VerdictHandler{topics: t, camps: c, verdicts: v}
 }
 
 type submitVerdictBody struct {
@@ -117,24 +113,6 @@ func (h *VerdictHandler) Submit(w http.ResponseWriter, r *http.Request) {
 		w.Header().Set("x-warn", "verdict saved but status update failed: "+err.Error())
 	}
 
-	// Lifecycle broadcast — completed event. Best-effort; runs async
-	// outside the request context so a slow Fabric doesn't slow the
-	// judge's response. Target is per-topic (nil announcer or nil
-	// target on topic → silently skipped by announcer).
-	if h.announcer != nil {
-		var tgt fabric.Target
-		if topic.AnnounceGuildBaseURL != nil && topic.AnnounceChannelID != nil {
-			tgt = fabric.Target{
-				GuildBaseURL: *topic.AnnounceGuildBaseURL,
-				ChannelID:    *topic.AnnounceChannelID,
-			}
-		}
-		go func(t *fabric.Announcer, tID, title, judge string, target fabric.Target) {
-			summary := fmt.Sprintf("verdict published by judge=%s. Use dialectic_view_verdict to see the structured result.", judge)
-			_ = t.PostLifecycleEvent(context.Background(), target, tID, title, "completed", summary)
-		}(h.announcer, verdict.TopicID, topic.Title, caller.ID, tgt)
-	}
-
 	writeJSON(w, http.StatusCreated, map[string]any{
 		"id":             verdict.ID,
 		"topic_id":       verdict.TopicID,

internal/httpapi/routes.go

@@ -11,7 +11,6 @@ import (
 
 	"git.hangman-lab.top/hzhang/Dialectic.Backend/internal/auth"
 	"git.hangman-lab.top/hzhang/Dialectic.Backend/internal/config"
-	"git.hangman-lab.top/hzhang/Dialectic.Backend/internal/fabric"
 	"git.hangman-lab.top/hzhang/Dialectic.Backend/internal/httpapi/handlers"
 	"git.hangman-lab.top/hzhang/Dialectic.Backend/internal/store"
 )
@@ -63,8 +62,7 @@ func Mount(cfg *config.Config, db *sqlx.DB, version string) http.Handler {
 	topicsH := handlers.NewTopicsHandler(topicStore, campStore)
 	signupsH := handlers.NewSignupsHandler(topicStore, signupStore)
 	argsH := handlers.NewArgumentsHandler(topicStore, campStore, roundStore, argStore)
-	announcer := fabric.NewAnnouncer(cfg.FabricSystemAPIKey)
-	verdictH := handlers.NewVerdictHandler(topicStore, campStore, verdictStore, announcer)
+	verdictH := handlers.NewVerdictHandler(topicStore, campStore, verdictStore)
 	adminH := handlers.NewAdminHandler(db, cfg.AgentAPIKeyPepper, cfg.DialecticAdminAPIKey)
 
 	// Routes.