fix(broadcast): OFFSEC-015 — scope recipients to sender's org

Previously POST /workspaces/:id/broadcast collected every non-removed
workspace in the database, allowing a workspace in Org-A to broadcast to
every workspace in Org-B, Org-C, etc.

Fix: walk parent_id chain with a recursive CTE to find the sender's org
root, then filter recipients to workspaces sharing that root. Same
isolation pattern as hotfix #1157 (staging) — port to this main-target
PR so the cherry-pick doesn't ship the vulnerable original.

Adds workspace_broadcast_test.go from #1157 with:
- TestBroadcast_OrgScopedRecipients (cross-org isolation regression)
- TestBroadcast_OrgScoped_OrgRootSender
- TestBroadcast_OrgScoped_ChildWorkspaceSender
- + NotFound / Disabled / EmptyOrg / InvalidID coverage

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

workspace-server/internal/handlers/workspace_broadcast.go

@@ -3,7 +3,7 @@ package handlers
 // workspace_broadcast.go — POST /workspaces/:id/broadcast
 //
 // Allows a workspace with broadcast_enabled=true to send a message to every
-// non-removed agent workspace in the org.  The message is:
+// non-removed agent workspace in the SAME ORG.  The message is:
 //
 //   • Persisted in each recipient's activity_logs (type='broadcast_receive')
 //     so poll-mode agents pick it up via GET /activity.
@@ -16,6 +16,11 @@ package handlers
 // Auth: WorkspaceAuth (the agent triggers this with its own bearer token).
 // The handler re-validates broadcast_enabled inside the DB lookup to prevent
 // TOCTOU — the middleware only proved the token is valid, not the ability.
+//
+// Org isolation (OFFSEC-015): recipients are scoped to the sender's org using
+// a recursive CTE that walks the parent_id chain to find the org root. This
+// prevents a compromised or misconfigured workspace from broadcasting to
+// workspaces in other tenants' orgs.
 
 import (
 	"log"
@@ -74,11 +79,49 @@ func (h *BroadcastHandler) Broadcast(c *gin.Context) {
 		return
 	}
 
-	// Collect all non-removed agent workspaces (excludes the sender itself).
-	rows, err := db.DB.QueryContext(ctx,
-		`SELECT id FROM workspaces WHERE status != 'removed' AND id != $1`,
-		senderID,
-	)
+	// Find the sender's org root by walking the parent_id chain.
+	// Workspaces with parent_id = NULL are org roots; every other workspace
+	// belongs to the org identified by its topmost ancestor.
+	var orgRootID string
+	err = db.DB.QueryRowContext(ctx, `
+		WITH RECURSIVE org_chain AS (
+			SELECT id, parent_id, id AS root_id
+			FROM workspaces
+			WHERE id = $1
+			UNION ALL
+			SELECT w.id, w.parent_id, c.root_id
+			FROM workspaces w
+			JOIN org_chain c ON w.id = c.parent_id
+		)
+		SELECT root_id FROM org_chain WHERE parent_id IS NULL LIMIT 1
+	`, senderID).Scan(&orgRootID)
+	if err != nil {
+		log.Printf("Broadcast: org root lookup for %s: %v", senderID, err)
+		c.JSON(http.StatusInternalServerError, gin.H{"error": "internal error"})
+		return
+	}
+
+	// Collect all non-removed agent workspaces in the SAME ORG (same root_id),
+	// excluding the sender itself.
+	rows, err := db.DB.QueryContext(ctx, `
+		WITH RECURSIVE org_chain AS (
+			SELECT id, parent_id, id AS root_id
+			FROM workspaces
+			WHERE parent_id IS NULL
+			UNION ALL
+			SELECT w.id, w.parent_id, c.root_id
+			FROM workspaces w
+			JOIN org_chain c ON w.parent_id = c.id
+		)
+		SELECT c.id
+		FROM org_chain c
+		WHERE c.root_id = $1
+		  AND c.id != $2
+		  AND EXISTS (
+			  SELECT 1 FROM workspaces w
+			  WHERE w.id = c.id AND w.status != 'removed'
+		  )
+	`, orgRootID, senderID)
 	if err != nil {
 		log.Printf("Broadcast: recipient query failed for %s: %v", senderID, err)
 		c.JSON(http.StatusInternalServerError, gin.H{"error": "internal error"})

workspace-server/internal/handlers/workspace_broadcast_test.go

@@ -0,0 +1,428 @@
+package handlers
+
+import (
+	"bytes"
+	"context"
+	"encoding/json"
+	"errors"
+	"net/http"
+	"net/http/httptest"
+	"testing"
+
+	"github.com/DATA-DOG/go-sqlmock"
+	"github.com/gin-gonic/gin"
+)
+
+// -------- Org-scoped recipient query tests (OFFSEC-015) --------
+
+// TestBroadcast_OrgScopedRecipients verifies that a broadcast from Org-A does
+// NOT reach workspaces belonging to Org-B. This is the core regression test
+// for OFFSEC-015: the original query had no org filter, so a workspace in
+// Org-A could broadcast to every non-removed workspace in the entire DB,
+// including workspaces owned by other tenants.
+func TestBroadcast_OrgScopedRecipients(t *testing.T) {
+	mock := setupTestDB(t)
+	broadcaster := newTestBroadcaster()
+	handler := NewBroadcastHandler(broadcaster)
+
+	// Org-A structure:
+	//   org-a-root  (parent_id = NULL)  ← sender
+	//   ├── ws-a-child
+	// Org-B structure:
+	//   org-b-root  (parent_id = NULL)
+	//   └── ws-b-child
+	senderID := "00000000-0000-0000-0000-000000000001" // org-a-root
+	wsAChild := "00000000-0000-0000-0000-000000000002"
+	// ws-b-child is in Org-B (different root); the org-scoped query MUST NOT include it.
+
+	// 1. Sender lookup
+	mock.ExpectQuery(`SELECT name, broadcast_enabled FROM workspaces WHERE id = \$1 AND status != 'removed'`).
+		WithArgs(senderID).
+		WillReturnRows(sqlmock.NewRows([]string{"name", "broadcast_enabled"}).AddRow("Org-A Root", true))
+
+	// 2. Org root lookup — sender is its own root (parent_id = NULL)
+	mock.ExpectQuery(`WITH RECURSIVE org_chain AS`).
+		WithArgs(senderID).
+		WillReturnRows(sqlmock.NewRows([]string{"root_id"}).AddRow(senderID))
+
+	// 3. Org-scoped recipient query — MUST include org filter so ws-b-child is NOT included.
+	// The query joins on org_chain.root_id = orgRootID, which scopes to Org-A only.
+	mock.ExpectQuery(`WITH RECURSIVE org_chain AS`).
+		WithArgs(senderID, senderID). // orgRootID, senderID (EXCLUDED)
+		WillReturnRows(sqlmock.NewRows([]string{"id"}).AddRow(wsAChild)) // only Org-A child
+
+	// Activity log inserts
+	mock.ExpectExec(`INSERT INTO activity_logs`).WithArgs(wsAChild, senderID, sqlmock.AnyArg()).WillReturnResult(sqlmock.NewResult(0, 1))
+	mock.ExpectExec(`INSERT INTO activity_logs`).WithArgs(senderID, sqlmock.AnyArg()).WillReturnResult(sqlmock.NewResult(0, 1))
+
+	w := httptest.NewRecorder()
+	c, _ := gin.CreateTestContext(w)
+	c.Params = gin.Params{{Key: "id", Value: senderID}}
+	body := `{"message":"hello from org-a"}`
+	c.Request = httptest.NewRequest("POST", "/workspaces/"+senderID+"/broadcast", bytes.NewBufferString(body))
+	c.Request.Header.Set("Content-Type", "application/json")
+
+	handler.Broadcast(c)
+
+	if w.Code != http.StatusOK {
+		t.Errorf("expected 200, got %d: %s", w.Code, w.Body.String())
+	}
+
+	var resp map[string]interface{}
+	if err := json.Unmarshal(w.Body.Bytes(), &resp); err != nil {
+		t.Fatalf("failed to unmarshal response: %v", err)
+	}
+	if resp["status"] != "sent" {
+		t.Errorf("expected status 'sent', got %v", resp["status"])
+	}
+	// ws-b-child is in a DIFFERENT org — the org-scoped query MUST NOT include it.
+	// If it were included, the mock would have an unmet expectation.
+	if err := mock.ExpectationsWereMet(); err != nil {
+		t.Errorf("unmet mock expectations — cross-org workspace was included in broadcast: %v", err)
+	}
+}
+
+// TestBroadcast_OrgScoped_OrgRootSender verifies that when the sender IS the
+// org root (parent_id = NULL), broadcasts still reach sibling workspaces.
+func TestBroadcast_OrgScoped_OrgRootSender(t *testing.T) {
+	mock := setupTestDB(t)
+	broadcaster := newTestBroadcaster()
+	handler := NewBroadcastHandler(broadcaster)
+
+	senderID := "00000000-0000-0000-0000-000000000001" // org-a-root
+	siblingID := "00000000-0000-0000-0000-000000000002"
+
+	mock.ExpectQuery(`SELECT name, broadcast_enabled FROM workspaces WHERE id = \$1 AND status != 'removed'`).
+		WithArgs(senderID).
+		WillReturnRows(sqlmock.NewRows([]string{"name", "broadcast_enabled"}).AddRow("Root Agent", true))
+
+	// Sender is the org root — CTE returns sender's own ID as root
+	mock.ExpectQuery(`WITH RECURSIVE org_chain AS`).
+		WithArgs(senderID).
+		WillReturnRows(sqlmock.NewRows([]string{"root_id"}).AddRow(senderID))
+
+	// Recipients in same org, excluding sender
+	mock.ExpectQuery(`WITH RECURSIVE org_chain AS`).
+		WithArgs(senderID, senderID).
+		WillReturnRows(sqlmock.NewRows([]string{"id"}).AddRow(siblingID))
+
+	mock.ExpectExec(`INSERT INTO activity_logs`).WithArgs(siblingID, senderID, sqlmock.AnyArg()).WillReturnResult(sqlmock.NewResult(0, 1))
+	mock.ExpectExec(`INSERT INTO activity_logs`).WithArgs(senderID, sqlmock.AnyArg()).WillReturnResult(sqlmock.NewResult(0, 1))
+
+	w := httptest.NewRecorder()
+	c, _ := gin.CreateTestContext(w)
+	c.Params = gin.Params{{Key: "id", Value: senderID}}
+	body := `{"message":"hello siblings"}`
+	c.Request = httptest.NewRequest("POST", "/workspaces/"+senderID+"/broadcast", bytes.NewBufferString(body))
+	c.Request.Header.Set("Content-Type", "application/json")
+
+	handler.Broadcast(c)
+
+	if w.Code != http.StatusOK {
+		t.Errorf("expected 200, got %d: %s", w.Code, w.Body.String())
+	}
+	if err := mock.ExpectationsWereMet(); err != nil {
+		t.Errorf("unmet expectations: %v", err)
+	}
+}
+
+// TestBroadcast_OrgScoped_ChildWorkspaceSender verifies that a non-root child
+// workspace can broadcast to siblings in the same org.
+func TestBroadcast_OrgScoped_ChildWorkspaceSender(t *testing.T) {
+	mock := setupTestDB(t)
+	broadcaster := newTestBroadcaster()
+	handler := NewBroadcastHandler(broadcaster)
+
+	orgRootID := "00000000-0000-0000-0000-000000000001"
+	senderID := "00000000-0000-0000-0000-000000000002" // child workspace
+	siblingID := "00000000-0000-0000-0000-000000000003"
+
+	mock.ExpectQuery(`SELECT name, broadcast_enabled FROM workspaces WHERE id = \$1 AND status != 'removed'`).
+		WithArgs(senderID).
+		WillReturnRows(sqlmock.NewRows([]string{"name", "broadcast_enabled"}).AddRow("Child Agent", true))
+
+	// Org root lookup — walk up to find org-a-root
+	mock.ExpectQuery(`WITH RECURSIVE org_chain AS`).
+		WithArgs(senderID).
+		WillReturnRows(sqlmock.NewRows([]string{"root_id"}).AddRow(orgRootID))
+
+	// Recipients: same org, excluding sender
+	mock.ExpectQuery(`WITH RECURSIVE org_chain AS`).
+		WithArgs(orgRootID, senderID).
+		WillReturnRows(sqlmock.NewRows([]string{"id"}).AddRow(siblingID))
+
+	mock.ExpectExec(`INSERT INTO activity_logs`).WithArgs(siblingID, senderID, sqlmock.AnyArg()).WillReturnResult(sqlmock.NewResult(0, 1))
+	mock.ExpectExec(`INSERT INTO activity_logs`).WithArgs(senderID, sqlmock.AnyArg()).WillReturnResult(sqlmock.NewResult(0, 1))
+
+	w := httptest.NewRecorder()
+	c, _ := gin.CreateTestContext(w)
+	c.Params = gin.Params{{Key: "id", Value: senderID}}
+	body := `{"message":"child broadcasting"}`
+	c.Request = httptest.NewRequest("POST", "/workspaces/"+senderID+"/broadcast", bytes.NewBufferString(body))
+	c.Request.Header.Set("Content-Type", "application/json")
+
+	handler.Broadcast(c)
+
+	if w.Code != http.StatusOK {
+		t.Errorf("expected 200, got %d: %s", w.Code, w.Body.String())
+	}
+	if err := mock.ExpectationsWereMet(); err != nil {
+		t.Errorf("unmet expectations: %v", err)
+	}
+}
+
+// -------- Non-regression cases --------
+
+func TestBroadcast_NotFound(t *testing.T) {
+	mock := setupTestDB(t)
+	broadcaster := newTestBroadcaster()
+	handler := NewBroadcastHandler(broadcaster)
+
+	senderID := "00000000-0000-0000-0000-000000000099"
+	// UUID is valid, but no workspace row matches
+	mock.ExpectQuery(`SELECT name, broadcast_enabled FROM workspaces WHERE id = \$1 AND status != 'removed'`).
+		WithArgs(senderID).
+		WillReturnError(errors.New("workspace not found"))
+
+	w := httptest.NewRecorder()
+	c, _ := gin.CreateTestContext(w)
+	c.Params = gin.Params{{Key: "id", Value: senderID}}
+	body := `{"message":"test"}`
+	c.Request = httptest.NewRequest("POST", "/workspaces/"+senderID+"/broadcast", bytes.NewBufferString(body))
+	c.Request.Header.Set("Content-Type", "application/json")
+
+	handler.Broadcast(c)
+
+	if w.Code != http.StatusNotFound {
+		t.Errorf("expected 404, got %d: %s", w.Code, w.Body.String())
+	}
+	if err := mock.ExpectationsWereMet(); err != nil {
+		t.Errorf("unmet expectations: %v", err)
+	}
+}
+
+func TestBroadcast_Disabled(t *testing.T) {
+	mock := setupTestDB(t)
+	broadcaster := newTestBroadcaster()
+	handler := NewBroadcastHandler(broadcaster)
+
+	senderID := "00000000-0000-0000-0000-000000000001"
+	mock.ExpectQuery(`SELECT name, broadcast_enabled FROM workspaces WHERE id = \$1 AND status != 'removed'`).
+		WithArgs(senderID).
+		WillReturnRows(sqlmock.NewRows([]string{"name", "broadcast_enabled"}).AddRow("Disabled Agent", false))
+
+	w := httptest.NewRecorder()
+	c, _ := gin.CreateTestContext(w)
+	c.Params = gin.Params{{Key: "id", Value: senderID}}
+	body := `{"message":"should not send"}`
+	c.Request = httptest.NewRequest("POST", "/workspaces/"+senderID+"/broadcast", bytes.NewBufferString(body))
+	c.Request.Header.Set("Content-Type", "application/json")
+
+	handler.Broadcast(c)
+
+	if w.Code != http.StatusForbidden {
+		t.Errorf("expected 403, got %d: %s", w.Code, w.Body.String())
+	}
+	var resp map[string]interface{}
+	if err := json.Unmarshal(w.Body.Bytes(), &resp); err != nil {
+		t.Fatalf("failed to unmarshal: %v", err)
+	}
+	if resp["error"] != "broadcast_disabled" {
+		t.Errorf("expected error 'broadcast_disabled', got %v", resp["error"])
+	}
+}
+
+func TestBroadcast_EmptyOrg_NoRecipients(t *testing.T) {
+	mock := setupTestDB(t)
+	broadcaster := newTestBroadcaster()
+	handler := NewBroadcastHandler(broadcaster)
+
+	senderID := "00000000-0000-0000-0000-000000000001" // org root, only workspace in org
+
+	mock.ExpectQuery(`SELECT name, broadcast_enabled FROM workspaces WHERE id = \$1 AND status != 'removed'`).
+		WithArgs(senderID).
+		WillReturnRows(sqlmock.NewRows([]string{"name", "broadcast_enabled"}).AddRow("Lone Root", true))
+
+	mock.ExpectQuery(`WITH RECURSIVE org_chain AS`).
+		WithArgs(senderID).
+		WillReturnRows(sqlmock.NewRows([]string{"root_id"}).AddRow(senderID))
+
+	// No other workspaces in this org
+	mock.ExpectQuery(`WITH RECURSIVE org_chain AS`).
+		WithArgs(senderID, senderID).
+		WillReturnRows(sqlmock.NewRows([]string{"id"}))
+
+	mock.ExpectExec(`INSERT INTO activity_logs`).WithArgs(senderID, sqlmock.AnyArg()).WillReturnResult(sqlmock.NewResult(0, 1))
+
+	w := httptest.NewRecorder()
+	c, _ := gin.CreateTestContext(w)
+	c.Params = gin.Params{{Key: "id", Value: senderID}}
+	body := `{"message":"hello org"}`
+	c.Request = httptest.NewRequest("POST", "/workspaces/"+senderID+"/broadcast", bytes.NewBufferString(body))
+	c.Request.Header.Set("Content-Type", "application/json")
+
+	handler.Broadcast(c)
+
+	if w.Code != http.StatusOK {
+		t.Errorf("expected 200, got %d: %s", w.Code, w.Body.String())
+	}
+	var resp map[string]interface{}
+	if err := json.Unmarshal(w.Body.Bytes(), &resp); err != nil {
+		t.Fatalf("failed to unmarshal: %v", err)
+	}
+	if resp["delivered"] != float64(0) {
+		t.Errorf("expected delivered=0, got %v", resp["delivered"])
+	}
+	if err := mock.ExpectationsWereMet(); err != nil {
+		t.Errorf("unmet expectations: %v", err)
+	}
+}
+
+func TestBroadcast_InvalidWorkspaceID(t *testing.T) {
+	setupTestDB(t)
+	broadcaster := newTestBroadcaster()
+	handler := NewBroadcastHandler(broadcaster)
+
+	w := httptest.NewRecorder()
+	c, _ := gin.CreateTestContext(w)
+	c.Params = gin.Params{{Key: "id", Value: "not-a-uuid"}}
+	body := `{"message":"test"}`
+	c.Request = httptest.NewRequest("POST", "/workspaces/not-a-uuid/broadcast", bytes.NewBufferString(body))
+	c.Request.Header.Set("Content-Type", "application/json")
+
+	handler.Broadcast(c)
+
+	if w.Code != http.StatusBadRequest {
+		t.Errorf("expected 400, got %d: %s", w.Code, w.Body.String())
+	}
+}
+
+func TestBroadcast_MissingMessage(t *testing.T) {
+	setupTestDB(t)
+	broadcaster := newTestBroadcaster()
+	handler := NewBroadcastHandler(broadcaster)
+
+	w := httptest.NewRecorder()
+	c, _ := gin.CreateTestContext(w)
+	c.Params = gin.Params{{Key: "id", Value: "00000000-0000-0000-0000-000000000001"}}
+	c.Request = httptest.NewRequest("POST", "/workspaces/00000000-0000-0000-0000-000000000001/broadcast", bytes.NewBufferString("{}"))
+	c.Request.Header.Set("Content-Type", "application/json")
+
+	handler.Broadcast(c)
+
+	if w.Code != http.StatusBadRequest {
+		t.Errorf("expected 400, got %d: %s", w.Code, w.Body.String())
+	}
+}
+
+// TestBroadcast_OrgRootLookupFails verifies that if the recursive CTE for
+// finding the org root errors, the handler returns 500 instead of proceeding
+// with an un-scoped query that would broadcast to all orgs.
+func TestBroadcast_OrgRootLookupFails(t *testing.T) {
+	mock := setupTestDB(t)
+	broadcaster := newTestBroadcaster()
+	handler := NewBroadcastHandler(broadcaster)
+
+	senderID := "00000000-0000-0000-0000-000000000001"
+
+	mock.ExpectQuery(`SELECT name, broadcast_enabled FROM workspaces WHERE id = \$1 AND status != 'removed'`).
+		WithArgs(senderID).
+		WillReturnRows(sqlmock.NewRows([]string{"name", "broadcast_enabled"}).AddRow("Root Agent", true))
+
+	// Org root CTE fails
+	mock.ExpectQuery(`WITH RECURSIVE org_chain AS`).
+		WithArgs(senderID).
+		WillReturnError(context.DeadlineExceeded)
+
+	w := httptest.NewRecorder()
+	c, _ := gin.CreateTestContext(w)
+	c.Params = gin.Params{{Key: "id", Value: senderID}}
+	body := `{"message":"should not broadcast"}`
+	c.Request = httptest.NewRequest("POST", "/workspaces/"+senderID+"/broadcast", bytes.NewBufferString(body))
+	c.Request.Header.Set("Content-Type", "application/json")
+
+	handler.Broadcast(c)
+
+	if w.Code != http.StatusInternalServerError {
+		t.Errorf("expected 500, got %d: %s", w.Code, w.Body.String())
+	}
+	// The recipient query MUST NOT be called — it would broadcast cross-org
+	// if the org root lookup failed silently.
+	if err := mock.ExpectationsWereMet(); err != nil {
+		t.Errorf("unmet expectations: %v", err)
+	}
+}
+
+// TestBroadcast_OrgScoped_SelfBroadcastExcluded verifies that broadcasting
+// from a workspace does not send a broadcast_receive to the sender itself
+// (the sender logs broadcast_sent, not broadcast_receive).
+func TestBroadcast_OrgScoped_SelfBroadcastExcluded(t *testing.T) {
+	mock := setupTestDB(t)
+	broadcaster := newTestBroadcaster()
+	handler := NewBroadcastHandler(broadcaster)
+
+	senderID := "00000000-0000-0000-0000-000000000001"
+	peerID := "00000000-0000-0000-0000-000000000002"
+
+	mock.ExpectQuery(`SELECT name, broadcast_enabled FROM workspaces WHERE id = \$1 AND status != 'removed'`).
+		WithArgs(senderID).
+		WillReturnRows(sqlmock.NewRows([]string{"name", "broadcast_enabled"}).AddRow("Root Agent", true))
+
+	mock.ExpectQuery(`WITH RECURSIVE org_chain AS`).
+		WithArgs(senderID).
+		WillReturnRows(sqlmock.NewRows([]string{"root_id"}).AddRow(senderID))
+
+	// Recipient query MUST exclude sender via id != senderID
+	mock.ExpectQuery(`WITH RECURSIVE org_chain AS`).
+		WithArgs(senderID, senderID).
+		WillReturnRows(sqlmock.NewRows([]string{"id"}).AddRow(peerID))
+
+	// Peer receives broadcast_receive
+	mock.ExpectExec(`INSERT INTO activity_logs`).WithArgs(peerID, senderID, sqlmock.AnyArg()).WillReturnResult(sqlmock.NewResult(0, 1))
+	// Sender logs broadcast_sent (NOT broadcast_receive)
+	mock.ExpectExec(`INSERT INTO activity_logs`).WithArgs(senderID, sqlmock.AnyArg()).WillReturnResult(sqlmock.NewResult(0, 1))
+
+	w := httptest.NewRecorder()
+	c, _ := gin.CreateTestContext(w)
+	c.Params = gin.Params{{Key: "id", Value: senderID}}
+	body := `{"message":"no echo to self"}`
+	c.Request = httptest.NewRequest("POST", "/workspaces/"+senderID+"/broadcast", bytes.NewBufferString(body))
+	c.Request.Header.Set("Content-Type", "application/json")
+
+	handler.Broadcast(c)
+
+	if w.Code != http.StatusOK {
+		t.Errorf("expected 200, got %d: %s", w.Code, w.Body.String())
+	}
+	if err := mock.ExpectationsWereMet(); err != nil {
+		t.Errorf("unmet expectations: %v", err)
+	}
+}
+
+// TestBroadcast_Truncate tests that messages are truncated with the Unicode ellipsis
+// TestBroadcast_Truncate tests that messages are truncated with the Unicode ellipsis
+// character (U+2026) when len(msg) > max. The truncated output is max runes + "…",
+// so truncating a 48-char string at max=20 produces 21 characters (20 runes + "…").
+func TestBroadcast_Truncate(t *testing.T) {
+	cases := []struct {
+		msg    string
+		max    int
+		expect string
+	}{
+		{"short", 120, "short"}, // under max — no truncation
+		// exactly120chars (15) + 105 ones = 120 chars; at max=120 → unchanged
+		{"exactly120chars1111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111", 120, "exactly120chars111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111…"},
+		// "this is a longer mes" = 20 runes; + "…" = 21 chars
+		{"this is a longer message that needs truncating", 20, "this is a longer mes…"},
+		// at-max boundary: 20 chars at max=20 → no truncation
+		{"exactly twenty chars", 20, "exactly twenty chars"},
+		// over max: 11 chars at max=10 → 10 + "…" = 11
+		{"hello world!", 10, "hello worl…"},
+	}
+	for _, tc := range cases {
+		result := broadcastTruncate(tc.msg, tc.max)
+		if result != tc.expect {
+			t.Errorf("broadcastTruncate(%q, %d) = %q; want %q", tc.msg, tc.max, result, tc.expect)
+		}
+	}
+}