From c569e5faba0509ead67a24373b6cb77690491b2e Mon Sep 17 00:00:00 2001
From: Peter Steinberger <steipete@gmail.com>
Date: Tue, 7 Apr 2026 12:50:59 +0800
Subject: [PATCH] Sessions: split chat type derivation seam

---
 src/routing/session-key.test.ts          |  6 +--
 src/sessions/session-chat-type-shared.ts | 67 +++++++++++++++++++++++
 src/sessions/session-chat-type.ts        | 68 +++++++-----------------
 3 files changed, 89 insertions(+), 52 deletions(-)
 create mode 100644 src/sessions/session-chat-type-shared.ts

diff --git a/src/routing/session-key.test.ts b/src/routing/session-key.test.ts
index bfe3ab50261..56cbdd234a9 100644
--- a/src/routing/session-key.test.ts
+++ b/src/routing/session-key.test.ts
@@ -1,5 +1,5 @@
 import { describe, expect, it } from "vitest";
-import { deriveSessionChatType } from "../sessions/session-chat-type.js";
+import { deriveSessionChatTypeFromKey } from "../sessions/session-chat-type-shared.js";
 import {
   getSubagentDepth,
   isCronSessionKey,
@@ -70,7 +70,7 @@ describe("isCronSessionKey", () => {
   });
 });
 
-describe("deriveSessionChatType", () => {
+describe("deriveSessionChatTypeFromKey", () => {
   it.each([
     { key: "agent:main:discord:direct:user1", expected: "direct" },
     { key: "agent:main:telegram:group:g1", expected: "group" },
@@ -83,7 +83,7 @@ describe("deriveSessionChatType", () => {
     { key: "agent:main", expected: "unknown" },
     { key: "", expected: "unknown" },
   ] as const)("derives chat type for %j => $expected", ({ key, expected }) => {
-    expect(deriveSessionChatType(key)).toBe(expected);
+    expect(deriveSessionChatTypeFromKey(key)).toBe(expected);
   });
 });
 
diff --git a/src/sessions/session-chat-type-shared.ts b/src/sessions/session-chat-type-shared.ts
new file mode 100644
index 00000000000..92c6566683d
--- /dev/null
+++ b/src/sessions/session-chat-type-shared.ts
@@ -0,0 +1,67 @@
+import { parseAgentSessionKey } from "./session-key-utils.js";
+
+export type SessionKeyChatType = "direct" | "group" | "channel" | "unknown";
+
+function deriveBuiltInLegacySessionChatType(
+  scopedSessionKey: string,
+): SessionKeyChatType | undefined {
+  if (/^group:[^:]+$/.test(scopedSessionKey)) {
+    return "group";
+  }
+  if (/^[0-9]+(?:-[0-9]+)*@g\.us$/.test(scopedSessionKey)) {
+    return "group";
+  }
+  if (/^whatsapp:(?!.*:group:).+@g\.us$/.test(scopedSessionKey)) {
+    return "group";
+  }
+  if (/^discord:(?:[^:]+:)?guild-[^:]+:channel-[^:]+$/.test(scopedSessionKey)) {
+    return "channel";
+  }
+  return undefined;
+}
+
+export function deriveSessionChatTypeFromScopedKey(
+  scopedSessionKey: string,
+  deriveLegacySessionChatTypes: Array<
+    (scopedSessionKey: string) => SessionKeyChatType | undefined
+  > = [],
+): SessionKeyChatType {
+  const tokens = new Set(scopedSessionKey.split(":").filter(Boolean));
+  if (tokens.has("group")) {
+    return "group";
+  }
+  if (tokens.has("channel")) {
+    return "channel";
+  }
+  if (tokens.has("direct") || tokens.has("dm")) {
+    return "direct";
+  }
+  const builtInLegacy = deriveBuiltInLegacySessionChatType(scopedSessionKey);
+  if (builtInLegacy) {
+    return builtInLegacy;
+  }
+  for (const deriveLegacySessionChatType of deriveLegacySessionChatTypes) {
+    const derived = deriveLegacySessionChatType(scopedSessionKey);
+    if (derived) {
+      return derived;
+    }
+  }
+  return "unknown";
+}
+
+/**
+ * Best-effort chat-type extraction from session keys across canonical and legacy formats.
+ */
+export function deriveSessionChatTypeFromKey(
+  sessionKey: string | undefined | null,
+  deriveLegacySessionChatTypes: Array<
+    (scopedSessionKey: string) => SessionKeyChatType | undefined
+  > = [],
+): SessionKeyChatType {
+  const raw = (sessionKey ?? "").trim().toLowerCase();
+  if (!raw) {
+    return "unknown";
+  }
+  const scoped = parseAgentSessionKey(raw)?.rest ?? raw;
+  return deriveSessionChatTypeFromScopedKey(scoped, deriveLegacySessionChatTypes);
+}
diff --git a/src/sessions/session-chat-type.ts b/src/sessions/session-chat-type.ts
index 01f533ba38e..febdfb9579c 100644
--- a/src/sessions/session-chat-type.ts
+++ b/src/sessions/session-chat-type.ts
@@ -1,54 +1,24 @@
 import { iterateBootstrapChannelPlugins } from "../channels/plugins/bootstrap-registry.js";
-import { parseAgentSessionKey } from "./session-key-utils.js";
+import {
+  deriveSessionChatTypeFromKey,
+  type SessionKeyChatType,
+} from "./session-chat-type-shared.js";
 
-export type SessionKeyChatType = "direct" | "group" | "channel" | "unknown";
+export {
+  deriveSessionChatTypeFromKey,
+  type SessionKeyChatType,
+} from "./session-chat-type-shared.js";
 
-function deriveBuiltInLegacySessionChatType(
-  scopedSessionKey: string,
-): SessionKeyChatType | undefined {
-  if (/^group:[^:]+$/.test(scopedSessionKey)) {
-    return "group";
-  }
-  if (/^[0-9]+(?:-[0-9]+)*@g\.us$/.test(scopedSessionKey)) {
-    return "group";
-  }
-  if (/^whatsapp:(?!.*:group:).+@g\.us$/.test(scopedSessionKey)) {
-    return "group";
-  }
-  if (/^discord:(?:[^:]+:)?guild-[^:]+:channel-[^:]+$/.test(scopedSessionKey)) {
-    return "channel";
-  }
-  return undefined;
-}
-
-/**
- * Best-effort chat-type extraction from session keys across canonical and legacy formats.
- */
 export function deriveSessionChatType(sessionKey: string | undefined | null): SessionKeyChatType {
-  const raw = (sessionKey ?? "").trim().toLowerCase();
-  if (!raw) {
-    return "unknown";
-  }
-  const scoped = parseAgentSessionKey(raw)?.rest ?? raw;
-  const tokens = new Set(scoped.split(":").filter(Boolean));
-  if (tokens.has("group")) {
-    return "group";
-  }
-  if (tokens.has("channel")) {
-    return "channel";
-  }
-  if (tokens.has("direct") || tokens.has("dm")) {
-    return "direct";
-  }
-  const builtInLegacy = deriveBuiltInLegacySessionChatType(scoped);
-  if (builtInLegacy) {
-    return builtInLegacy;
-  }
-  for (const plugin of iterateBootstrapChannelPlugins()) {
-    const derived = plugin.messaging?.deriveLegacySessionChatType?.(scoped);
-    if (derived) {
-      return derived;
-    }
-  }
-  return "unknown";
+  return deriveSessionChatTypeFromKey(
+    sessionKey,
+    iterateBootstrapChannelPlugins()
+      .map((plugin) => plugin.messaging?.deriveLegacySessionChatType)
+      .filter(
+        (
+          deriveLegacySessionChatType,
+        ): deriveLegacySessionChatType is NonNullable<typeof deriveLegacySessionChatType> =>
+          Boolean(deriveLegacySessionChatType),
+      ),
+  );
 }