fix(ag-ui): keep empty confirm_changes resumes unseeded

Generic/predictive resumes with messages:[] must not prepend stored history into the turn input — confirm_changes synthesizes only the resume tool message and short-circuits without another model call. Seeding that history caused approval mismatch warnings and an extra stream invocation (test_agent_endpoint_confirm_changes_clears_persisted_interrupt). Only non-empty client-replayed generic resumes go through reconcile_resume_messages + seeded_resume_from_snapshot. Approval and workflow/checkpoint paths still seed empty via reconcile.
Evan Mattson (moonbox3) · Sep 14, 2026 · Sep 8, 2026 · Sep 8, 2026 · Sep 9, 2026 · Sep 9, 2026
commit e6820218139be57f3fefff0e3a533e1456e6d28b
@@ -2493,9 +2493,12 @@ async def run_agent_stream(
                 )
                 raw_messages = provider_suffix
         elif not config.use_service_session:
-            if resume_payload is not None:
-                # Predictive-state / generic resumes also merge history here; mark seeded
-                # so save-time resume_seeded_messages does not prepend again (#8140).
+            if resume_payload is not None and raw_messages:
+                # Client-replayed transcript on predictive/generic resume: overlap-merge
+                # and mark seeded so save-time resume_seeded_messages does not prepend
+                # again (#8140). Empty interrupt-only resumes (e.g. confirm_changes)
+                # must stay empty so synthesized resume tool messages are the only
+                # turn input; history is restored at save when this flag stays false.
                 seeded_resume_from_snapshot = True
                 raw_messages = snapshot_session.reconcile_resume_messages(raw_messages)
             else:

@@ -144,9 +144,14 @@ def resume_seeded_messages(self, incoming: list[dict[str, Any]]) -> list[dict[st
     def reconcile_resume_messages(self, incoming: list[dict[str, Any]]) -> list[dict[str, Any]]:
         """Merge stored history with resume messages without double-persisting.
 
-        Empty incoming (interrupt-only / checkpoint resume) prepends stored
-        history. Non-empty incoming is overlapped via the thread-snapshot
-        reconstructor so a client that replays its transcript is not duplicated.
+        Empty incoming prepends stored history (approval / checkpoint builders that
+        need history in the provider or snapshot input). Non-empty incoming is
+        overlapped via the thread-snapshot reconstructor so a client that replays
+        its transcript is not duplicated.
+
+        Agent confirm_changes resumes that synthesize the tool result separately
+        should keep empty incoming as empty and call this only for non-empty
+        client-replayed transcripts.
         """
         if self._stored is None:
             return incoming