diff --git a/backend/app/routes/setup.py b/backend/app/routes/setup.py
index baca1135..9add89a0 100644
--- a/backend/app/routes/setup.py
+++ b/backend/app/routes/setup.py
@@ -96,6 +96,7 @@ def setup_config(settings_map: dict[str, Any], db: Session = Depends(require_set
         except (ValueError, RuntimeError) as exc:
             raise HTTPException(status_code=400, detail=str(exc))
         saved.append(key)
+    db.commit()  # sysconfig.set_value only flushes now — persist the wizard's config in one commit
     return {"saved": saved}
 
 
diff --git a/backend/app/state.py b/backend/app/state.py
index 3664783c..28dd3586 100644
--- a/backend/app/state.py
+++ b/backend/app/state.py
@@ -28,10 +28,12 @@ def is_sync_paused(db: Session) -> bool:
 
 
 def set_sync_paused(db: Session, paused: bool) -> None:
+    # Flushes, doesn't commit — the caller owns the transaction so the change lands with its audit
+    # row in one transaction (B-core-10).
     row = _row(db)
     row.sync_paused = paused
     db.add(row)
-    db.commit()
+    db.flush()
     log.info("Background sync %s", "paused" if paused else "resumed")
 
 
diff --git a/backend/app/sysconfig.py b/backend/app/sysconfig.py
index de23e9ee..13c25d2f 100644
--- a/backend/app/sysconfig.py
+++ b/backend/app/sysconfig.py
@@ -186,7 +186,9 @@ def get_bool(db: Session, key: str) -> bool:
 
 
 def set_value(db: Session, key: str, value) -> None:
-    """Validate, coerce, and persist a DB override for `key`. Secrets are encrypted."""
+    """Validate, coerce, and stage a DB override for `key` (secrets are encrypted). Flushes but does
+    NOT commit — the caller owns the transaction, so the change lands together with its audit row
+    (B-core-10). The staged value is visible to a same-session `get()` before the commit."""
     s = _BY_KEY[key]
     if s.type == "int":
         v = int(value)
@@ -212,15 +214,16 @@ def set_value(db: Session, key: str, value) -> None:
         db.add(row)
     row.value = stored
     row.encrypted = encrypted
-    db.commit()
+    db.flush()
 
 
 def reset(db: Session, key: str) -> None:
-    """Remove the DB override for `key` (fall back to the env/config default)."""
+    """Remove the DB override for `key` (fall back to the env/config default). Flushes but does NOT
+    commit — the caller owns the transaction (B-core-10)."""
     row = db.get(SystemConfig, key)
     if row is not None:
         db.delete(row)
-        db.commit()
+        db.flush()
 
 
 def describe(db: Session) -> dict:
diff --git a/backend/tests/test_config_commit_ownership.py b/backend/tests/test_config_commit_ownership.py
new file mode 100644
index 00000000..0cfbb814
--- /dev/null
+++ b/backend/tests/test_config_commit_ownership.py
@@ -0,0 +1,38 @@
+"""E3 S3 (B-core-10): the config/state mutators flush but do NOT self-commit, so the caller owns the
+transaction and a change lands together with its audit row. These lock that contract — a rollback
+before the caller commits discards the change (proving no hidden internal commit), while a same-session
+read still sees it (flush visibility). DB lane (`db` fixture) — skipped without Postgres.
+"""
+from app import state, sysconfig
+
+
+def test_set_value_flushes_but_leaves_the_commit_to_the_caller(db):
+    default = sysconfig.get_int(db, "quota_daily_budget")
+    new = default + 4321
+
+    sysconfig.set_value(db, "quota_daily_budget", new)
+    assert sysconfig.get_int(db, "quota_daily_budget") == new  # visible in-session (flushed)
+
+    db.rollback()  # the caller never committed
+    assert sysconfig.get_int(db, "quota_daily_budget") == default  # discarded — no hidden self-commit
+
+
+def test_reset_flushes_but_leaves_the_commit_to_the_caller(db):
+    default = sysconfig.get_int(db, "quota_daily_budget")
+    sysconfig.set_value(db, "quota_daily_budget", default + 10)
+    db.commit()  # a persisted override to reset
+
+    sysconfig.reset(db, "quota_daily_budget")
+    assert sysconfig.get_int(db, "quota_daily_budget") == default  # reset visible in-session
+    db.rollback()
+    assert sysconfig.get_int(db, "quota_daily_budget") == default + 10  # reset discarded until committed
+
+
+def test_set_sync_paused_flushes_but_leaves_the_commit_to_the_caller(db):
+    assert state.is_sync_paused(db) is False
+
+    state.set_sync_paused(db, True)
+    assert state.is_sync_paused(db) is True  # visible in-session
+
+    db.rollback()
+    assert state.is_sync_paused(db) is False  # discarded — the caller owns the commit