diff --git a/scripts/asvs/apply.py b/scripts/asvs/apply.py
index d4960afe..29248423 100644
--- a/scripts/asvs/apply.py
+++ b/scripts/asvs/apply.py
@@ -82,10 +82,20 @@ def render(cell: dict[str, Any], live: dict[str, Any] | None = None) -> str:
     out.append(f'verified_at = "{cell["verified_at"]}"')
     if cell.get("reviewed_by"):
         out.append(f"reviewed_by = {toml_str(cell['reviewed_by'])}")
-    # Carry through every other scalar the live cell had -- decision_closed and friends, and anything
-    # a future schema adds that this writer has never heard of.
-    for key, value in (live or {}).items():
-        if key in _ORDERED or key in _SUBTABLES or key in cell:
+    # Carry through every other scalar from BOTH SOURCES -- decision_closed and friends off the live
+    # cell, and anything a future schema adds that this writer has never heard of, from either side.
+    #
+    # The source is the UNION deliberately. Walking `live` alone meant a key arriving on the PAYLOAD
+    # and absent from the vault was never iterated, so the `key in cell` skip never even evaluated for
+    # it and the value was dropped -- the same silent loss as the allowlist incident above, one
+    # direction over, and equally invisible downstream because an absent field reads as a valid
+    # default. `cell` wins on a collision: the payload is the update.
+    #
+    # Skipping ONLY _ORDERED and _SUBTABLES keeps the rule the header states -- enumerate what you
+    # ORDER, never what you KEEP. The old `key in cell` clause was an enumeration of the second kind
+    # wearing a de-duplication's clothes: every key it legitimately suppressed is already in _ORDERED.
+    for key, value in {**(live or {}), **cell}.items():
+        if key in _ORDERED or key in _SUBTABLES:
             continue
         out.append(_scalar(key, value))
     for a in cell.get("evidence") or []:
diff --git a/tests/test_asvs_apply.py b/tests/test_asvs_apply.py
index 7ee2ec61..465797e0 100644
--- a/tests/test_asvs_apply.py
+++ b/tests/test_asvs_apply.py
@@ -20,7 +20,7 @@
 
 import pytest
 
-from scripts.asvs.apply import _BANNED, main
+from scripts.asvs.apply import _BANNED, main, render
 
 #: A two-cell record. `5.4.3` is owner-CLOSED, mirroring the real one, because the closed-cell guards
 #: are the ones with the worst failure mode: an un-closing is invisible to every downstream check.
@@ -163,6 +163,49 @@ def test_omitted_keys_are_carried_through_rather_than_dropped(tmp_path: Path) ->
     assert got["decision_closed_by"] == "owner"
 
 
+def test_a_payload_only_unknown_key_survives_too() -> None:  # #1242
+    """The INVERSE of the 7818991d incident, and the direction the carry-through never covered.
+
+    The preservation loop's SOURCE was the LIVE cell, so a key the writer has never heard of survived
+    only if it was ALREADY in the vault. A key arriving on the PAYLOAD and absent from live was never
+    iterated at all -- the `key in cell` skip the design relies on never even evaluated for it, because
+    the key was not in the source being walked.
+
+    That is the same silent-drop shape as the incident, one direction over: a NEW schema field applied
+    to a cell that predates it would vanish on write, and an absent field reads as a valid default, so
+    no gate downstream can tell PRESERVED from DROPPED.
+
+    The module comment already states the governing rule -- the writer enumerates only what it ORDERS,
+    and everything else survives by default. This asserts that rule holds for BOTH sources.
+    """
+    cell = {
+        "id": "1.2.3",
+        "level": 1,
+        "verdict": "Pass",
+        "last_verified": "2026-08-13",
+        "verified_at": "0" * 40,
+        "a_future_scalar": "must survive",
+        "a_future_flag": True,
+        "a_future_count": 7,
+    }
+    # live has NONE of the future keys -- so a live-sourced loop can never reach them.
+    out = render(cell, {"id": "1.2.3", "level": 1, "verdict": "Pass"})
+    assert 'a_future_scalar = "must survive"' in out
+    assert "a_future_flag = true" in out
+    assert "a_future_count = 7" in out
+
+
+def test_live_only_keys_still_survive_after_the_payload_fix() -> None:  # #1242
+    """Negative control for the test above: widening the source must not LOSE the direction that
+    already worked. A key present only on the live cell is still carried."""
+    out = render(
+        {"id": "1.2.3", "level": 1, "verdict": "Pass", "last_verified": "x", "verified_at": "y"},
+        {"id": "1.2.3", "decision_closed": True, "decision_closed_by": "owner"},
+    )
+    assert "decision_closed = true" in out
+    assert 'decision_closed_by = "owner"' in out
+
+
 def test_the_preservation_backstop_fires_when_carry_through_is_broken(
     tmp_path: Path, monkeypatch: pytest.MonkeyPatch, capsys: pytest.CaptureFixture[str]
 ) -> None: