diff --git a/application/account_facts_publisher.py b/application/account_facts_publisher.py
index 1d99102..ce91173 100644
--- a/application/account_facts_publisher.py
+++ b/application/account_facts_publisher.py
@@ -216,10 +216,6 @@ def build_firstrade_account_snapshot(
     if not isinstance(balances, Mapping):
         raise AccountFactsPublishError("snapshot_invalid")
     currency = balances.get("currency")
-    # Firstrade US equity balance payloads often omit an ISO currency field; the
-    # rest of this platform already treats Firstrade cash as USD.
-    if currency is None:
-        currency = "USD"
     if not isinstance(currency, str) or not _CURRENCY_RE.fullmatch(currency):
         raise AccountFactsPublishError("provider_currency_unavailable")
     provider_equity = balances.get("provider_equity")
@@ -232,10 +228,6 @@ def build_firstrade_account_snapshot(
         raise AccountFactsPublishError("snapshot_time_invalid")
 
     cash_balance = balances.get("cash_balance")
-    # Use exact available_cash only when cash_balance is absent — still a real
-    # provider cash figure, never synthesized from equity or buying power.
-    if cash_balance is None:
-        cash_balance = balances.get("available_cash")
     cash: list[dict[str, str]] = []
     if cash_balance is not None:
         cash.append({
diff --git a/application/session_check_service.py b/application/session_check_service.py
index 549718d..aac53f7 100644
--- a/application/session_check_service.py
+++ b/application/session_check_service.py
@@ -388,6 +388,7 @@ def archive_cached_account_facts(
         "source": "cached_account_facts",
         "balance_metrics": {
             "total_equity": balances.get("provider_equity"),
+            "currency": balances.get("currency"),
             "cash_balance": balances.get("cash_balance"),
             "available_cash": balances.get("available_cash"),
             "buying_power": balances.get("buying_power"),
diff --git a/docs/account-archive-history.md b/docs/account-archive-history.md
index a81081a..170c42e 100644
--- a/docs/account-archive-history.md
+++ b/docs/account-archive-history.md
@@ -127,6 +127,27 @@ unchanged. Existing conflicting records are rejected; unknown POST outcomes are
 not automatically retried. A successful exact history-only ACK is not a logged-in
 API or page acceptance result.
 
+## Cached observation cash and currency
+
+For forward observations from 2026-11-03, the cached account-facts publisher
+uses only exact `balances.cash_balance` for `cash[].cash_balance`, tagged
+`provider.cash_balance`. Missing exact cash produces an empty `cash` list;
+`available_cash` and `buying_power` never replace it. Decimal text, including
+zero and negative cash, is preserved without conversion.
+
+Published balance and cash rows require an explicit native `balances.currency`.
+Missing or invalid currency fails with `provider_currency_unavailable` before
+archive or publication; neither USD nor configured position currency supplies
+that native fact. The existing payload schema is unchanged.
+
+The cached archive independently retains `balance_metrics.currency`, including
+JSON null when the native currency is absent. Exact/null cash, available cash
+and buying power remain separate fields in both existing latest and history
+records. Original observation times and storage paths are unchanged. This is
+an additive archive field for new writes, with no history backfill or rewrite.
+The two archive writes remain non-atomic. Older saved-history projection above
+is a separate route and retains its existing currency policy.
+
 ## Cached account-history source inspection
 
 Cached-only account facts and history reads use the shared session cache as the
diff --git a/tests/test_account_facts_publisher.py b/tests/test_account_facts_publisher.py
index c3a1691..34a838d 100644
--- a/tests/test_account_facts_publisher.py
+++ b/tests/test_account_facts_publisher.py
@@ -73,13 +73,15 @@ def test_builds_fixed_snapshot_with_only_provider_equity_and_cash():
     assert "buying_power" not in repr(payload)
 
 
-def test_defaults_missing_provider_currency_to_usd():
+@pytest.mark.parametrize("missing_key", [False, True])
+def test_rejects_missing_native_currency_even_with_configured_position_currency(missing_key):
     data = observation()
     data["balances"]["currency"] = None
-    payload = build_firstrade_account_snapshot(
-        data, load_account_facts_publish_config(config()), account_scope="us"
-    )
-    assert payload["broker_reported_balances"][0]["currency"] == "USD"
+    if missing_key:
+        del data["balances"]["currency"]
+    cfg = load_account_facts_publish_config(config(FIRSTRADE_ACCOUNT_FACTS_POSITION_CURRENCY="EUR"))
+    with pytest.raises(AccountFactsPublishError, match="^provider_currency_unavailable$"):
+        build_firstrade_account_snapshot(data, cfg, account_scope="us")
 
 
 @pytest.mark.parametrize("value", ["", "usd", "US", "USDX", "USD "])
@@ -125,20 +127,20 @@ def test_allows_cash_to_be_absent_without_synthesizing_it():
     assert payload["cash"] == []
 
 
-def test_falls_back_to_available_cash_when_cash_balance_absent():
+@pytest.mark.parametrize("missing_key", [False, True])
+def test_available_cash_never_replaces_missing_exact_cash(missing_key):
     data = observation()
     data["balances"]["cash_balance"] = None
     data["balances"]["available_cash"] = "240.00"
+    if missing_key:
+        del data["balances"]["cash_balance"]
 
     payload = build_firstrade_account_snapshot(
         data, load_account_facts_publish_config(config()), account_scope="us"
     )
 
-    assert payload["cash"] == [{
-        "currency": "USD",
-        "cash_balance": "240.00",
-        "source_tag": "provider.cash_balance",
-    }]
+    assert payload["cash"] == []
+    assert payload["broker_reported_balances"] == [{"currency": "USD", "net_assets": "1234.50"}]
 
 
 @pytest.mark.parametrize(
@@ -383,3 +385,16 @@ def test_opt_in_reports_ambiguous_long_stock_value_distinctly():
     with pytest.raises(AccountFactsPublishError, match="long_stock_value_ambiguous"):
         build_firstrade_account_snapshot(
             data, cfg, account_scope="us", include_valuation_basis=True)
+
+
+@pytest.mark.parametrize("cash_balance", ["0.00", "-12.34567890", "250.25000000"])
+def test_preserves_exact_cash_and_native_currency_separately(cash_balance):
+    data = observation()
+    data["balances"].update(currency="EUR", cash_balance=cash_balance)
+    cfg = load_account_facts_publish_config(config(FIRSTRADE_ACCOUNT_FACTS_POSITION_CURRENCY="USD"))
+    data.update(positions_status="available", positions=[])
+    payload = build_firstrade_account_snapshot(data, cfg, account_scope="us")
+    assert payload["cash"] == [{
+        "currency": "EUR", "cash_balance": cash_balance, "source_tag": "provider.cash_balance",
+    }]
+    assert payload["broker_reported_balances"] == [{"currency": "EUR", "net_assets": "1234.50"}]
diff --git a/tests/test_cached_funds_archive.py b/tests/test_cached_funds_archive.py
index a7f5c90..2d6d73c 100644
--- a/tests/test_cached_funds_archive.py
+++ b/tests/test_cached_funds_archive.py
@@ -109,3 +109,48 @@ def test_unrequested_positions_stay_absent(archive_route):
     observation.update(positions_status="not_requested", positions=None)
     assert invoke().status_code == 200
     assert "positions" not in writes[1][1]
+
+
+@pytest.mark.parametrize("currency", ["USD", "EUR", None, "missing"])
+def test_cached_archive_retains_native_currency_in_both_json_records(archive_route, currency):
+    import json
+
+    observation, writes, publishes, _, service = archive_route
+    observation["observed_started_at"] = "2026-11-03T23:59:59+00:00"
+    observation["observed_finished_at"] = "2026-11-04T00:00:03+00:00"
+    observation["balances"].update(currency=currency, cash_balance="0.00000000")
+    if currency == "missing":
+        del observation["balances"]["currency"]
+    expected = observation["balances"].get("currency")
+    # Exercise the archive independently: unknown currency is retained as null,
+    # even though the publisher rejects it before the endpoint archives anything.
+    service.archive_cached_account_facts(observation)
+    assert len(writes) == 2
+    for key, value in writes:
+        saved = json.loads(json.dumps(value))
+        assert saved["balance_metrics"] == {
+            "total_equity": "100.123456", "cash_balance": "0.00000000",
+            "available_cash": "25.01", "buying_power": None, "currency": expected,
+        }
+        assert saved["as_of"] == observation["observed_started_at"]
+        assert saved["observed_finished_at"] == observation["observed_finished_at"]
+    assert writes[0][0].endswith("/funds/latest.json")
+    assert writes[1][0].endswith("/funds/history/2026/11/03/20261103T235959Z.json")
+    assert publishes == []
+
+
+@pytest.mark.parametrize("currency", [None, "", "usd"])
+def test_unknown_or_invalid_currency_blocks_archive_and_publish(archive_route, currency):
+    observation, writes, publishes, client, _ = archive_route
+    observation["balances"]["currency"] = currency
+    response = invoke()
+    assert response.status_code == 503
+    assert response.json == {"ok": False, "error": "provider_currency_unavailable"}
+    assert writes == publishes == []
+    assert client.closed
+
+
+def test_endpoint_does_not_publish_available_cash_as_exact_cash(archive_route):
+    _, _, publishes, _, _ = archive_route
+    assert invoke().status_code == 200
+    assert publishes[0][0]["cash"] == []