Add flag for HSUM Telecom fixes.

This CL adds a flag to use for adding support for HSUM in Telecom.

Test: ExtendedInCallServiceTest#testOnCannedTextResponsesLoaded
Flag: com.android.server.telecom.flags.telecom_main_user_in_get_respond_message_app
Bug: 358587742
Change-Id: I13babeb2b43cf202d3e4decf8043efaae6843377
diff --git a/flags/Android.bp b/flags/Android.bp
index e374a4d..501eba4 100644
--- a/flags/Android.bp
+++ b/flags/Android.bp
@@ -43,6 +43,7 @@
         "telecom_profile_user_flags.aconfig",
         "telecom_bluetoothdevicemanager_flags.aconfig",
         "telecom_non_critical_security_flags.aconfig",
+        "telecom_headless_system_user_mode.aconfig",
         "telecom_metrics_flags.aconfig",
     ],
 }
diff --git a/flags/telecom_headless_system_user_mode.aconfig b/flags/telecom_headless_system_user_mode.aconfig
new file mode 100644
index 0000000..f798733
--- /dev/null
+++ b/flags/telecom_headless_system_user_mode.aconfig
@@ -0,0 +1,14 @@
+package: "com.android.server.telecom.flags"
+container: "system"
+
+# OWNER=grantmenke TARGET=25Q1
+flag {
+    name: "telecom_main_user_in_get_respond_message_app"
+    is_exported: true
+    namespace: "telecom"
+    description: "Support HSUM mode by using the main user when getting respond via message app."
+    bug: "358587742"
+    metadata {
+        purpose: PURPOSE_BUGFIX
+      }
+}
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