refactor(sessions): accurate scope wording for tip-only resume rejections

SessionResumeTooLargeError said 'across its lineage' even when the CLI
mid-setup path counted only the tip segment; the exception now takes a
scope phrase.

hermes_cli/cli_agent_setup_mixin.py

@@ -617,7 +617,9 @@ class CLIAgentSetupMixin:
                 try:
                     tip_check(self.session_id, max_messages=limit)
                 except SessionExportTooLargeError as exc:
-                    raise SessionResumeTooLargeError(exc.message_count, limit) from exc
+                    raise SessionResumeTooLargeError(
+                        exc.message_count, limit, scope="in its tip segment"
+                    ) from exc
             else:
                 safety_check = getattr(self._session_db, "assert_resume_safe", None)
                 if not callable(safety_check):

hermes_state.py

@@ -126,11 +126,16 @@ def resolved_max_export_messages() -> int:
 
 
 class SessionResumeTooLargeError(ValueError):
-    def __init__(self, message_count: int, limit: int = MAX_SAFE_RESUME_MESSAGES):
+    def __init__(
+        self,
+        message_count: int,
+        limit: int = MAX_SAFE_RESUME_MESSAGES,
+        scope: str = "across its lineage",
+    ):
         self.message_count = message_count
         self.limit = limit
         super().__init__(
-            f"session has at least {message_count} active messages across its lineage; "
+            f"session has at least {message_count} active messages {scope}; "
             f"safe resume limit is {limit}. Export the session instead, or set "
             "sessions.max_resume_messages: 0 in config.yaml to disable the guard."
         )