diff --git a/CHANGELOG.md b/CHANGELOG.md
index 42919130..64d15ad9 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -3,6 +3,10 @@
 
 ## [Unreleased]
 
+### Fixed
+
+- Streaming checkpoint saves now run under the session's profile environment, so periodic background checkpoints no longer risk falling back to the process-global profile when a WebUI tab is using a non-default profile.
+
 ## [v0.51.134] — 2026-05-25 — Release DF (stage-batch16 — single-PR Windows path defaults)
 
 ### Fixed
diff --git a/api/streaming.py b/api/streaming.py
index e18e8792..fe59cfce 100644
--- a/api/streaming.py
+++ b/api/streaming.py
@@ -2557,6 +2557,18 @@ def _drop_checkpointed_current_user_from_context(messages, msg_text):
     return history
 
 
+def _save_streaming_checkpoint(session):
+    """Persist a streaming checkpoint under the session's profile context."""
+    from api import profiles as profiles_api
+
+    with profiles_api.profile_env_for_background_worker(
+        session,
+        "streaming checkpoint",
+        logger_override=logger,
+    ):
+        session.save(skip_index=True)
+
+
 def _normalize_fresh_chat_text(text):
     text = _strip_workspace_prefix(str(text or ''), include_legacy=True)
     text = re.sub(r"\s+", " ", text).strip().lower()
@@ -4552,7 +4564,7 @@ def _run_agent_streaming(
                         cur = _checkpoint_activity[0]
                         if cur > last_saved_activity:
                             with _agent_lock:
-                                s.save(skip_index=True)
+                                _save_streaming_checkpoint(s)
                             last_saved_activity = cur
                     except Exception as e:
                         logger.debug("Periodic checkpoint save failed: %s", e)
diff --git a/tests/test_issue2848_checkpoint_profile.py b/tests/test_issue2848_checkpoint_profile.py
new file mode 100644
index 00000000..f4792f78
--- /dev/null
+++ b/tests/test_issue2848_checkpoint_profile.py
@@ -0,0 +1,37 @@
+"""Regression coverage for #2848 checkpoint saves in background threads."""
+from __future__ import annotations
+
+from pathlib import Path
+
+
+def test_checkpoint_save_uses_session_profile_env(monkeypatch, tmp_path):
+    """Checkpoint saves run on their own thread, outside request TLS.
+
+    They must route profile-scoped helpers through the session's profile instead
+    of falling back to the process-global/default profile.
+    """
+    from api.models import Session
+    from api.streaming import _save_streaming_checkpoint
+    import api.config as config
+    import api.profiles as profiles
+
+    profile_home = tmp_path / "profiles" / "maiko"
+    profile_home.mkdir(parents=True)
+    captured = {}
+
+    monkeypatch.setattr(profiles, "get_hermes_home_for_profile", lambda profile: profile_home)
+    monkeypatch.setattr(profiles, "get_profile_runtime_env", lambda home: {"HERMES_CONFIG_PATH": str(Path(home) / "config.yaml")})
+
+    def fake_save(self, *args, **kwargs):
+        captured["kwargs"] = kwargs
+        captured["thread_env"] = dict(getattr(config._thread_ctx, "env", {}) or {})
+
+    monkeypatch.setattr(Session, "save", fake_save)
+
+    session = Session(session_id="issue2848", profile="maiko")
+
+    _save_streaming_checkpoint(session)
+
+    assert captured["kwargs"] == {"skip_index": True}
+    assert captured["thread_env"]["HERMES_HOME"] == str(profile_home)
+    assert captured["thread_env"]["HERMES_CONFIG_PATH"] == str(profile_home / "config.yaml")