refactor(security): make empty allowlist behavior explicit

extensions/bluebubbles/src/targets.test.ts

@@ -1,5 +1,6 @@
 import { describe, expect, it } from "vitest";
 import {
+  isAllowedBlueBubblesSender,
   looksLikeBlueBubblesTargetId,
   normalizeBlueBubblesMessagingTarget,
   parseBlueBubblesTarget,
@@ -181,3 +182,21 @@ describe("parseBlueBubblesAllowTarget", () => {
     });
   });
 });
+
+describe("isAllowedBlueBubblesSender", () => {
+  it("denies when allowFrom is empty", () => {
+    const allowed = isAllowedBlueBubblesSender({
+      allowFrom: [],
+      sender: "+15551234567",
+    });
+    expect(allowed).toBe(false);
+  });
+
+  it("allows wildcard entries", () => {
+    const allowed = isAllowedBlueBubblesSender({
+      allowFrom: ["*"],
+      sender: "+15551234567",
+    });
+    expect(allowed).toBe(true);
+  });
+});

src/plugin-sdk/allow-from.test.ts

@@ -37,6 +37,18 @@ describe("isAllowedParsedChatSender", () => {
     expect(allowed).toBe(false);
   });
 
+  it("can explicitly allow when allowFrom is empty", () => {
+    const allowed = isAllowedParsedChatSender({
+      allowFrom: [],
+      sender: "+15551234567",
+      emptyAllowFrom: "allow",
+      normalizeSender: (sender) => sender,
+      parseAllowTarget,
+    });
+
+    expect(allowed).toBe(true);
+  });
+
   it("allows wildcard entries", () => {
     const allowed = isAllowedParsedChatSender({
       allowFrom: ["*"],

src/plugin-sdk/allow-from.ts

@@ -21,12 +21,15 @@ export function isAllowedParsedChatSender<TParsed extends ParsedChatAllowTarget>
   chatId?: number | null;
   chatGuid?: string | null;
   chatIdentifier?: string | null;
+  emptyAllowFrom?: "deny" | "allow";
   normalizeSender: (sender: string) => string;
   parseAllowTarget: (entry: string) => TParsed;
 }): boolean {
   const allowFrom = params.allowFrom.map((entry) => String(entry).trim());
   if (allowFrom.length === 0) {
-    return false;
+    // Fail closed by default. Callers can opt into legacy "empty = allow all"
+    // behavior explicitly when a surface intentionally treats an empty list as open.
+    return params.emptyAllowFrom === "allow";
   }
   if (allowFrom.includes("*")) {
     return true;