fix(agents): keep fallback routes account-bound

src/utils/delivery-context.shared.ts

@@ -243,17 +243,20 @@ export function mergeDeliveryContext(
     normalizedPrimary?.channel &&
     normalizedFallback?.channel &&
     normalizedPrimary.channel !== normalizedFallback.channel;
+  const accountsConflict =
+    normalizedPrimary?.accountId &&
+    normalizedFallback?.accountId &&
+    normalizedPrimary.accountId !== normalizedFallback.accountId;
+  const routesConflict = channelsConflict || accountsConflict;
   return normalizeDeliveryContext({
     channel: normalizedPrimary?.channel ?? normalizedFallback?.channel,
     // Keep route fields paired to their channel; avoid crossing fields between
     // unrelated channels during session context merges.
-    to: channelsConflict
-      ? normalizedPrimary?.to
-      : (normalizedPrimary?.to ?? normalizedFallback?.to),
-    accountId: channelsConflict
+    to: routesConflict ? normalizedPrimary?.to : (normalizedPrimary?.to ?? normalizedFallback?.to),
+    accountId: routesConflict
       ? normalizedPrimary?.accountId
       : (normalizedPrimary?.accountId ?? normalizedFallback?.accountId),
-    threadId: channelsConflict
+    threadId: routesConflict
       ? normalizedPrimary?.threadId
       : (normalizedPrimary?.threadId ?? normalizedFallback?.threadId),
   });

src/utils/delivery-context.test.ts

@@ -53,6 +53,20 @@ describe("delivery context helpers", () => {
     });
   });
 
+  it("does not inherit route fields from a different account on the same channel", () => {
+    const merged = mergeDeliveryContext(
+      { channel: "telegram", accountId: "bot-a" },
+      { channel: "telegram", to: "123", accountId: "bot-b", threadId: "99" },
+    );
+
+    expect(merged).toEqual({
+      channel: "telegram",
+      to: undefined,
+      accountId: "bot-a",
+    });
+    expect(merged?.threadId).toBeUndefined();
+  });
+
   it("uses fallback route fields when fallback has no channel", () => {
     const merged = mergeDeliveryContext(
       { channel: "demo-channel" },