diff --git a/CHANGELOG.md b/CHANGELOG.md
index 0b692fc4..2ef35594 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -3,6 +3,10 @@
 
 ## [Unreleased]
 
+### Fixed
+
+- New WebUI sessions no longer persist `display.personality` into per-session `Session.personality`; only explicit personality changes remain durable, preventing stale global display defaults from overriding profile-scoped session behavior. Closes #2845.
+
 ## [v0.51.130] — 2026-05-24 — Release DB (stage-batch12 — 3-PR profile-isolation + boot-precedence + workspace Artifacts tab)
 
 ### Fixed
diff --git a/api/models.py b/api/models.py
index 3c8d895d..0a734bc5 100644
--- a/api/models.py
+++ b/api/models.py
@@ -1945,18 +1945,6 @@ def new_session(workspace=None, model=None, profile=None, model_provider=None, p
         if model_provider:
             effective_model_provider = model_provider
 
-    # Read default personality from config display.personality
-    _default_personality = None
-    try:
-        from api.config import get_config as _get_cfg_for_personality
-        _cfg_personality = (_get_cfg_for_personality().get('display') or {}).get('personality')
-        if _cfg_personality and isinstance(_cfg_personality, str):
-            _cfg_personality = _cfg_personality.strip().lower()
-            if _cfg_personality and _cfg_personality not in ('default', 'none', 'neutral'):
-                _default_personality = _cfg_personality
-    except Exception:
-        pass
-
     wt = worktree_info if isinstance(worktree_info, dict) else None
     workspace_path = (wt.get('path') if wt and wt.get('path') else workspace) if wt else workspace
     s = Session(
@@ -1965,7 +1953,7 @@ def new_session(workspace=None, model=None, profile=None, model_provider=None, p
         model_provider=effective_model_provider,
         profile=profile,
         project_id=project_id,
-        personality=_default_personality,
+        personality=None,
         worktree_path=wt.get('path') if wt else None,
         worktree_branch=wt.get('branch') if wt else None,
         worktree_repo_root=wt.get('repo_root') if wt else None,
diff --git a/tests/test_default_personality.py b/tests/test_default_personality.py
index 28169a0a..98d4c920 100644
--- a/tests/test_default_personality.py
+++ b/tests/test_default_personality.py
@@ -1,123 +1,48 @@
-"""Test that new_session() reads display.personality from config and uses it as default.
+"""Regression coverage for display.personality not becoming durable session state.
 
-Regression test for the feature that makes /personality taleb sticky across
-new sessions — when display.personality is set in config.yaml, every new
-session should inherit it without requiring an explicit /personality command.
+Issue #2845: display.personality is a display/default hint, but new_session()
+previously copied it into Session.personality. That made cosmetic config durable
+per-session state and could override profile-scoped behavior later. Only an
+explicit /api/personality/set call should persist Session.personality.
 """
 
-import pytest
 from unittest.mock import patch
 
 
-# ---------------------------------------------------------------------------
-# R1: new_session() inherits display.personality from config
-# ---------------------------------------------------------------------------
-
-def test_new_session_reads_default_personality_from_config():
-    """When display.personality is set to 'taleb', new_session() should
-    create a Session with personality='taleb'."""
+def test_new_session_does_not_inherit_display_personality_from_config():
+    """display.personality='taleb' must not stamp Session.personality."""
     import api.models as m
     import api.config as cfg_mod
 
-    _cfg = {
+    cfg = {
         "display": {"personality": "taleb"},
         "agent": {"personalities": {"taleb": {"system_prompt": "Be like Taleb", "tone": "blunt"}}},
     }
 
-    with patch.object(cfg_mod, "get_config", return_value=_cfg), \
+    with patch.object(cfg_mod, "get_config", return_value=cfg), \
          patch.object(m.Session, "save", return_value=None):
         s = m.new_session(workspace="/tmp/test-personality")
 
-    assert s.personality == "taleb", (
-        f"Expected personality='taleb', got {s.personality!r}"
-    )
+    try:
+        assert s.personality is None
+    finally:
+        with m.LOCK:
+            m.SESSIONS.pop(s.session_id, None)
 
 
-# ---------------------------------------------------------------------------
-# R2: 'none', 'default', 'neutral' are treated as no personality
-# ---------------------------------------------------------------------------
-
-@pytest.mark.parametrize("personality_value", ["none", "default", "neutral", ""])
-def test_new_session_ignores_neutral_personality_values(personality_value):
-    """Values like 'none', 'default', 'neutral', and '' should NOT be set as
-    the session personality — they mean 'no personality overlay'."""
-
+def test_new_session_still_defaults_to_no_personality_when_config_missing():
+    """Missing display.personality continues to produce personality=None."""
     import api.models as m
     import api.config as cfg_mod
 
-    _cfg = {
-        "display": {"personality": personality_value},
-        "agent": {"personalities": {}},
-    }
+    cfg = {"agent": {"personalities": {}}}
 
-    with patch.object(cfg_mod, "get_config", return_value=_cfg), \
-         patch.object(m.Session, "save", return_value=None):
-        s = m.new_session(workspace="/tmp/test-personality-neutral")
-
-    assert s.personality is None, (
-        f"Expected None for display.personality={personality_value!r}, "
-        f"got {s.personality!r}"
-    )
-
-
-# ---------------------------------------------------------------------------
-# R3: Missing display.personality → personality=None
-# ---------------------------------------------------------------------------
-
-def test_new_session_no_personality_when_config_missing():
-    """When config has no display.personality (or display section is absent),
-    new_session() should set personality=None."""
-
-    import api.models as m
-    import api.config as cfg_mod
-
-    _cfg = {"agent": {"personalities": {}}}  # No display section at all
-
-    with patch.object(cfg_mod, "get_config", return_value=_cfg), \
+    with patch.object(cfg_mod, "get_config", return_value=cfg), \
          patch.object(m.Session, "save", return_value=None):
         s = m.new_session(workspace="/tmp/test-personality-missing")
 
-    assert s.personality is None
-
-
-# ---------------------------------------------------------------------------
-# R4: Config exception is handled gracefully → personality=None
-# ---------------------------------------------------------------------------
-
-def test_new_session_handles_config_exception_gracefully():
-    """If get_config() raises, we should still get a valid session with
-    personality=None (the try/except should swallow the error)."""
-
-    import api.models as m
-    import api.config as cfg_mod
-
-    def _boom():
-        raise RuntimeError("config exploded")
-
-    with patch.object(cfg_mod, "get_config", side_effect=_boom), \
-         patch.object(m.Session, "save", return_value=None):
-        s = m.new_session(workspace="/tmp/test-personality-boom")
-
-    assert s.personality is None
-
-
-# ---------------------------------------------------------------------------
-# R5: display.personality is case-insensitive
-# ---------------------------------------------------------------------------
-
-def test_new_session_personality_is_case_insensitive():
-    """display.personality='Taleb' should be normalized to 'taleb'."""
-
-    import api.models as m
-    import api.config as cfg_mod
-
-    _cfg = {
-        "display": {"personality": "Taleb"},
-        "agent": {"personalities": {"taleb": {"system_prompt": "Be like Taleb"}}},
-    }
-
-    with patch.object(cfg_mod, "get_config", return_value=_cfg), \
-         patch.object(m.Session, "save", return_value=None):
-        s = m.new_session(workspace="/tmp/test-personality-case")
-
-    assert s.personality == "taleb"
\ No newline at end of file
+    try:
+        assert s.personality is None
+    finally:
+        with m.LOCK:
+            m.SESSIONS.pop(s.session_id, None)
diff --git a/tests/test_issue798.py b/tests/test_issue798.py
index 5f5fd6a1..7957570e 100644
--- a/tests/test_issue798.py
+++ b/tests/test_issue798.py
@@ -290,6 +290,24 @@ def test_new_session_uses_explicit_profile_default_model_and_provider(tmp_path,
             m.SESSIONS.pop(s.session_id, None)
 
 
+def test_new_session_does_not_persist_display_personality(monkeypatch, tmp_path):
+    """display.personality is a UI/default hint, not durable per-session state."""
+    import api.config as c
+    import api.models as m
+
+    monkeypatch.setattr(c, "get_config", lambda: {"display": {"personality": "kawaii"}})
+    with patch.object(m.Session, 'save', return_value=None):
+        s = m.new_session(workspace=str(tmp_path), profile="default")
+    try:
+        assert s.personality is None, (
+            "new_session() must not stamp display.personality into the persistent "
+            "Session.personality field; only explicit /api/personality/set should."
+        )
+    finally:
+        with m.LOCK:
+            m.SESSIONS.pop(s.session_id, None)
+
+
 def test_get_hermes_home_for_profile_rejects_path_traversal():
     """R19j: get_hermes_home_for_profile() must reject names that don't match
     _PROFILE_ID_RE (e.g. path traversal like '../../etc') and return the base