fix: preserve subagent thread routing (#1241)

Thanks @gnarco.

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

src/utils/delivery-context.test.ts

@@ -39,10 +39,13 @@ describe("delivery context helpers", () => {
   });
 
   it("builds stable keys only when channel and to are present", () => {
-    expect(deliveryContextKey({ channel: "whatsapp", to: "+1555" })).toBe("whatsapp|+1555|");
+    expect(deliveryContextKey({ channel: "whatsapp", to: "+1555" })).toBe("whatsapp|+1555||");
     expect(deliveryContextKey({ channel: "whatsapp" })).toBeUndefined();
     expect(deliveryContextKey({ channel: "whatsapp", to: "+1555", accountId: "acct-1" })).toBe(
-      "whatsapp|+1555|acct-1",
+      "whatsapp|+1555|acct-1|",
+    );
+    expect(deliveryContextKey({ channel: "slack", to: "channel:C1", threadId: "123.456" })).toBe(
+      "slack|channel:C1||123.456",
     );
   });
 
@@ -64,17 +67,24 @@ describe("delivery context helpers", () => {
       deliveryContextFromSession({
         channel: "telegram",
         lastTo: " 123 ",
+        lastThreadId: " 999 ",
       }),
     ).toEqual({
       channel: "telegram",
       to: "123",
       accountId: undefined,
+      threadId: "999",
     });
   });
 
   it("normalizes delivery fields and mirrors them on session entries", () => {
     const normalized = normalizeSessionDeliveryFields({
-      deliveryContext: { channel: " Slack ", to: " channel:1 ", accountId: " acct-2 " },
+      deliveryContext: {
+        channel: " Slack ",
+        to: " channel:1 ",
+        accountId: " acct-2 ",
+        threadId: " 444 ",
+      },
       lastChannel: " whatsapp ",
       lastTo: " +1555 ",
     });
@@ -83,9 +93,11 @@ describe("delivery context helpers", () => {
       channel: "whatsapp",
       to: "+1555",
       accountId: "acct-2",
+      threadId: "444",
     });
     expect(normalized.lastChannel).toBe("whatsapp");
     expect(normalized.lastTo).toBe("+1555");
     expect(normalized.lastAccountId).toBe("acct-2");
+    expect(normalized.lastThreadId).toBe("444");
   });
 });

src/utils/delivery-context.ts

@@ -5,6 +5,7 @@ export type DeliveryContext = {
   channel?: string;
   to?: string;
   accountId?: string;
+  threadId?: string | number;
 };
 
 export type DeliveryContextSessionSource = {
@@ -12,6 +13,7 @@ export type DeliveryContextSessionSource = {
   lastChannel?: string;
   lastTo?: string;
   lastAccountId?: string;
+  lastThreadId?: string | number;
   deliveryContext?: DeliveryContext;
 };
 
@@ -23,12 +25,22 @@ export function normalizeDeliveryContext(context?: DeliveryContext): DeliveryCon
       : undefined;
   const to = typeof context.to === "string" ? context.to.trim() : undefined;
   const accountId = normalizeAccountId(context.accountId);
-  if (!channel && !to && !accountId) return undefined;
-  return {
+  const threadId =
+    typeof context.threadId === "number" && Number.isFinite(context.threadId)
+      ? Math.trunc(context.threadId)
+      : typeof context.threadId === "string"
+        ? context.threadId.trim()
+        : undefined;
+  const normalizedThreadId =
+    typeof threadId === "string" ? (threadId ? threadId : undefined) : threadId;
+  if (!channel && !to && !accountId && normalizedThreadId == null) return undefined;
+  const normalized: DeliveryContext = {
     channel: channel || undefined,
     to: to || undefined,
     accountId,
   };
+  if (normalizedThreadId != null) normalized.threadId = normalizedThreadId;
+  return normalized;
 }
 
 export function normalizeSessionDeliveryFields(source?: DeliveryContextSessionSource): {
@@ -36,6 +48,7 @@ export function normalizeSessionDeliveryFields(source?: DeliveryContextSessionSo
   lastChannel?: string;
   lastTo?: string;
   lastAccountId?: string;
+  lastThreadId?: string | number;
 } {
   if (!source) {
     return {
@@ -43,6 +56,7 @@ export function normalizeSessionDeliveryFields(source?: DeliveryContextSessionSo
       lastChannel: undefined,
       lastTo: undefined,
       lastAccountId: undefined,
+      lastThreadId: undefined,
     };
   }
 
@@ -51,6 +65,7 @@ export function normalizeSessionDeliveryFields(source?: DeliveryContextSessionSo
       channel: source.lastChannel ?? source.channel,
       to: source.lastTo,
       accountId: source.lastAccountId,
+      threadId: source.lastThreadId,
     }),
     normalizeDeliveryContext(source.deliveryContext),
   );
@@ -61,6 +76,7 @@ export function normalizeSessionDeliveryFields(source?: DeliveryContextSessionSo
       lastChannel: undefined,
       lastTo: undefined,
       lastAccountId: undefined,
+      lastThreadId: undefined,
     };
   }
 
@@ -69,6 +85,7 @@ export function normalizeSessionDeliveryFields(source?: DeliveryContextSessionSo
     lastChannel: merged.channel,
     lastTo: merged.to,
     lastAccountId: merged.accountId,
+    lastThreadId: merged.threadId,
   };
 }
 
@@ -90,11 +107,14 @@ export function mergeDeliveryContext(
     channel: normalizedPrimary?.channel ?? normalizedFallback?.channel,
     to: normalizedPrimary?.to ?? normalizedFallback?.to,
     accountId: normalizedPrimary?.accountId ?? normalizedFallback?.accountId,
+    threadId: normalizedPrimary?.threadId ?? normalizedFallback?.threadId,
   });
 }
 
 export function deliveryContextKey(context?: DeliveryContext): string | undefined {
   const normalized = normalizeDeliveryContext(context);
   if (!normalized?.channel || !normalized?.to) return undefined;
-  return `${normalized.channel}|${normalized.to}|${normalized.accountId ?? ""}`;
+  const threadId =
+    normalized.threadId != null && normalized.threadId !== "" ? String(normalized.threadId) : "";
+  return `${normalized.channel}|${normalized.to}|${normalized.accountId ?? ""}|${threadId}`;
 }