fix(telegram): prevent channel-level groups from leaking to all accounts in multi-account setups

In multi-account Telegram configurations, `mergeTelegramAccountConfig()`
performs a shallow merge of channel-level config onto each account. This
causes channel-level `groups` to be inherited by ALL accounts, including
those whose bots are not members of the configured groups.

When a secondary bot attempts to handle group messages for a group it is
not in, the failure disrupts message delivery for all accounts — causing
silent message loss with no errors in logs.

Fix: exclude `groups` from the base spread (like `accounts` already is)
and only apply channel-level groups as fallback in single-account setups
for backward compatibility. Multi-account setups must use account-level
groups config.

Added 5 test cases covering single-account inheritance, multi-account
isolation, account-level priority, and backward compatibility.

Fixes #30673

src/telegram/accounts.test.ts

@@ -168,3 +168,104 @@ describe("resolveTelegramAccount allowFrom precedence", () => {
     expect(resolved.config.groupAllowFrom).toBeUndefined();
   });
 });
+
+describe("resolveTelegramAccount groups inheritance (#30673)", () => {
+  it("inherits channel-level groups in single-account setup", () => {
+    const resolved = resolveTelegramAccount({
+      cfg: {
+        channels: {
+          telegram: {
+            groups: { "-100123": { requireMention: false } },
+            accounts: {
+              default: { botToken: "123:default" },
+            },
+          },
+        },
+      },
+      accountId: "default",
+    });
+
+    expect(resolved.config.groups).toEqual({ "-100123": { requireMention: false } });
+  });
+
+  it("does NOT inherit channel-level groups to secondary account in multi-account setup", () => {
+    const resolved = resolveTelegramAccount({
+      cfg: {
+        channels: {
+          telegram: {
+            groups: { "-100123": { requireMention: false } },
+            accounts: {
+              default: { botToken: "123:default" },
+              dev: { botToken: "456:dev" },
+            },
+          },
+        },
+      },
+      accountId: "dev",
+    });
+
+    expect(resolved.config.groups).toBeUndefined();
+  });
+
+  it("does NOT inherit channel-level groups to default account in multi-account setup", () => {
+    const resolved = resolveTelegramAccount({
+      cfg: {
+        channels: {
+          telegram: {
+            groups: { "-100123": { requireMention: false } },
+            accounts: {
+              default: { botToken: "123:default" },
+              dev: { botToken: "456:dev" },
+            },
+          },
+        },
+      },
+      accountId: "default",
+    });
+
+    expect(resolved.config.groups).toBeUndefined();
+  });
+
+  it("uses account-level groups even in multi-account setup", () => {
+    const resolved = resolveTelegramAccount({
+      cfg: {
+        channels: {
+          telegram: {
+            groups: { "-100999": { requireMention: true } },
+            accounts: {
+              default: {
+                botToken: "123:default",
+                groups: { "-100123": { requireMention: false } },
+              },
+              dev: { botToken: "456:dev" },
+            },
+          },
+        },
+      },
+      accountId: "default",
+    });
+
+    expect(resolved.config.groups).toEqual({ "-100123": { requireMention: false } });
+  });
+
+  it("account-level groups takes priority over channel-level in single-account setup", () => {
+    const resolved = resolveTelegramAccount({
+      cfg: {
+        channels: {
+          telegram: {
+            groups: { "-100999": { requireMention: true } },
+            accounts: {
+              default: {
+                botToken: "123:default",
+                groups: { "-100123": { requireMention: false } },
+              },
+            },
+          },
+        },
+      },
+      accountId: "default",
+    });
+
+    expect(resolved.config.groups).toEqual({ "-100123": { requireMention: false } });
+  });
+});