Pete news: salted per-event GUID token + zone_clear taxonomy

Closes the two deferred code-review follow-ups on the adventure-news
seam, plus folds in two pre-committed WIP fixes.

A. Privacy — the public GUID no longer leaks a stable per-player id.
   Replaced userHash(userID)=sha256(userID)[:6] with
   eventToken(userID, discriminator)=HMAC-SHA256(salt, userID‖disc).
   The salt is 32 random bytes, auto-generated once and persisted in the
   durable news_config table (cached via sync.Once). Because each event
   uses a distinct HMAC message, tokens are a PRF output and are BOTH
   uncomputable from a Matrix handle (no enumeration of a player's
   events, incl. ones anonymized after !news optout) AND mutually
   unlinkable (a named event can't be walked back to a player's other,
   anonymized events). Updated all emit sites: pete.go zone, dnd_combat
   death, adventure_duel rival, dnd_setup arrival, achievements
   milestone, bootstrap x3.

B. Taxonomy — repeat zone clears were mislabeled zone_first. Now emit
   zone_clear (bulletin) vs zone_first (realm-first, priority). Adopted
   the invariant GUID-prefix == event_type, which also fixes latent
   permalink mislabels (achv->milestone, rival->rival_result rendered a
   neutral "Dispatch" on their permalink pages).

Folded-in WIP fixes: create the news_config table b42beec's
newsEmissionOn reads but never created; reap sent pete_emit_queue rows
in RunMaintenance; don't burn a retry attempt when shutdown cancels an
in-flight send.

Tests: TestEventToken (salted/stable/per-event/persisted),
TestEmitZoneClearTaxonomy (first->zone_first, repeat->zone_clear),
updated pete_test.go prefixes. Full internal suite + vet green.

Unshipped. Deploy Pete first (it must know zone_clear), then gogobee.

internal/plugin/pete_test.go

@@ -1,7 +1,10 @@
 package plugin
 
 import (
+	"crypto/sha256"
+	"encoding/hex"
 	"os"
+	"sync"
 	"testing"
 
 	"gogobee/internal/db"
@@ -98,10 +101,10 @@ func TestPeteNewsBackfill(t *testing.T) {
 	if got := queuedCount(t, "death:%"); got != 1 {
 		t.Errorf("death dispatches queued = %d, want 1", got)
 	}
-	if got := queuedCount(t, "achv:%"); got != 1 {
+	if got := queuedCount(t, "milestone:%"); got != 1 {
 		t.Errorf("achievement dispatches queued = %d, want 1", got)
 	}
-	if got := queuedCount(t, "zone:%"); got != 1 {
+	if got := queuedCount(t, "zone_first:%"); got != 1 {
 		t.Errorf("zone-first dispatches queued = %d, want 1", got)
 	}
 	// Realm-first ledger seeded so a later live clear tiers as a repeat.
@@ -116,6 +119,80 @@ func TestPeteNewsBackfill(t *testing.T) {
 	}
 }
 
+// TestEventToken: the public GUID token is salted (not a bare sha256 an attacker
+// can recompute from the handle), stable per logical event (idempotency), and
+// per-event so a user's tokens don't link to each other.
+func TestEventToken(t *testing.T) {
+	dir := t.TempDir()
+	db.Close()
+	if err := db.Init(dir); err != nil {
+		t.Fatalf("db.Init: %v", err)
+	}
+	t.Cleanup(db.Close)
+
+	// The salt is cached process-wide via sync.Once; reset it so it derives (and
+	// persists) against this test's fresh DB rather than an earlier test's.
+	guidSaltOnce = sync.Once{}
+	guidSalt = nil
+
+	u := id.UserID("@alice:example.org")
+
+	// Not the old unsalted digest: an attacker with the handle can't recompute it.
+	bare := sha256.Sum256([]byte(u))
+	if got := eventToken(u, "arrival"); got == hex.EncodeToString(bare[:9]) {
+		t.Error("token matches unsalted sha256(handle) — enumeration attack reopened")
+	}
+
+	// Stable for the same (user, discriminator): a re-emit dedups.
+	if eventToken(u, "arrival") != eventToken(u, "arrival") {
+		t.Error("token not stable for the same event — idempotency broken")
+	}
+
+	// Per-event: two different events for the same user yield unrelated tokens, so
+	// a named event can't be walked back to the user's anonymized events.
+	if eventToken(u, "arrival") == eventToken(u, "death:123") {
+		t.Error("tokens collide across events — linkage attack reopened")
+	}
+
+	// Different users, same discriminator, still differ.
+	if eventToken(u, "arrival") == eventToken(id.UserID("@bob:example.org"), "arrival") {
+		t.Error("token collides across users")
+	}
+
+	// The salt persisted, so it survives a restart (a re-emit after reboot dedups).
+	var salt string
+	if err := db.Get().QueryRow(`SELECT value FROM news_config WHERE key = ?`, newsGUIDSaltKey).Scan(&salt); err != nil || salt == "" {
+		t.Fatalf("guid salt not persisted: %v", err)
+	}
+}
+
+// TestEmitZoneClearTaxonomy: the realm's first clear of a zone emits a PRIORITY
+// zone_first; a later clear emits a BULLETIN zone_clear — distinct event_type and
+// GUID prefix, so Pete never files a repeat as a first-ever.
+func TestEmitZoneClearTaxonomy(t *testing.T) {
+	dir := t.TempDir()
+	db.Close()
+	if err := db.Init(dir); err != nil {
+		t.Fatalf("db.Init: %v", err)
+	}
+	t.Cleanup(db.Close)
+	enablePeteSeam(t)
+
+	db.Exec("seed player", `INSERT INTO player_meta (user_id, display_name) VALUES (?, ?)`,
+		"@zapp:x", "Zapp")
+	exp := &Expedition{ZoneID: "goblin_warren"}
+
+	emitZoneClearNews(id.UserID("@zapp:x"), exp) // realm-first
+	emitZoneClearNews(id.UserID("@zapp:x"), exp) // repeat
+
+	if got := queuedCount(t, "zone_first:%"); got != 1 {
+		t.Errorf("zone_first queued = %d, want 1 (the realm-first)", got)
+	}
+	if got := queuedCount(t, "zone_clear:%"); got != 1 {
+		t.Errorf("zone_clear queued = %d, want 1 (the repeat)", got)
+	}
+}
+
 // TestNewsEmissionKillSwitch: the runtime flag defaults on and persists a flip.
 func TestNewsEmissionKillSwitch(t *testing.T) {
 	dir := t.TempDir()