fix(line): keep group allowlists scoped (#106056)

Prevent LINE group allowlist policy from inheriting DM allowFrom entries, so open DMs do not broaden group access. Keep group-specific allowlists and per-group overrides as the only group admission sources, and document the scoped behavior.

Co-authored-by: pgondhi987 <pgondhi987@users.noreply.github.com>

docs/channels/line.md

@@ -140,8 +140,9 @@ Allowlists and policies:
 - `channels.line.dmPolicy`: `pairing | allowlist | open | disabled` (default `pairing`)
 - `channels.line.allowFrom`: allowlisted LINE user IDs for DMs; `dmPolicy: "open"` requires `["*"]`
 - `channels.line.groupPolicy`: `allowlist | open | disabled` (default `allowlist`)
-- `channels.line.groupAllowFrom`: allowlisted LINE user IDs for groups
-- Per-group overrides: `channels.line.groups.<groupId>.allowFrom` (plus `enabled`, `requireMention`, `systemPrompt`, `skills`)
+- `channels.line.groupAllowFrom`: allowlisted LINE user IDs for groups; DM `allowFrom` entries do not admit group senders
+- Per-group overrides: `channels.line.groups.<groupId>.allowFrom` (plus `enabled`, `requireMention`, `systemPrompt`, `skills`). With
+  `groupPolicy: "allowlist"`, set `groupAllowFrom` or the per-group `allowFrom`; an empty group allowlist blocks group messages even when DMs are open.
 - Static sender access groups can be referenced from `allowFrom`, `groupAllowFrom`, and per-group `allowFrom` with `accessGroup:<name>`; see [Access groups](/channels/access-groups).
 - Runtime note: if `channels.line` is completely missing, runtime falls back to `groupPolicy="allowlist"` for group checks (even if `channels.defaults.groupPolicy` is set).
 

extensions/line/src/bot-handlers.test.ts

@@ -524,6 +524,28 @@ describe("handleLineWebhookEvents", () => {
     expect(readAllowFromStoreMock).not.toHaveBeenCalled();
   });
 
+  it("does not use the DM allowlist when group allowlist policy has no group entries", async () => {
+    const processMessage = vi.fn();
+    await expectGroupMessageBlocked({
+      processMessage,
+      event: createReplayMessageEvent({
+        messageId: "m5c",
+        groupId: "group-1",
+        userId: "user-open-dm",
+        webhookEventId: "evt-5c",
+        isRedelivery: false,
+      }),
+      context: createLineWebhookTestContext({
+        processMessage,
+        dmPolicy: "open",
+        allowFrom: ["*"],
+        groupPolicy: "allowlist",
+        requireMention: false,
+      }),
+    });
+    expect(readAllowFromStoreMock).not.toHaveBeenCalled();
+  });
+
   it("blocks group messages without sender id when groupPolicy is allowlist", async () => {
     const processMessage = vi.fn();
     const event = {

extensions/line/src/bot-handlers.ts

@@ -253,12 +253,10 @@ async function shouldProcessLineEvent(
       : groupConfig?.allowFrom !== undefined
         ? "allowlist"
         : runtimeGroupPolicy;
+  // LINE group allowlists are scoped separately from DM allowFrom.
+  // The shared ingress policy below intentionally keeps fallback disabled.
   const groupAllowFrom = normalizeStringEntries(
-    firstDefined(
-      groupConfig?.allowFrom,
-      account.config.groupAllowFrom,
-      account.config.allowFrom?.length ? account.config.allowFrom : undefined,
-    ),
+    firstDefined(groupConfig?.allowFrom, account.config.groupAllowFrom),
   );
   const mentionFacts = (() => {
     if (!isGroup || event.type !== "message") {