diff --git a/packages/cli/src/repowise/cli/commands/update_cmd/persistence.py b/packages/cli/src/repowise/cli/commands/update_cmd/persistence.py
index 2adb77fd9..ae546be59 100644
--- a/packages/cli/src/repowise/cli/commands/update_cmd/persistence.py
+++ b/packages/cli/src/repowise/cli/commands/update_cmd/persistence.py
@@ -16,7 +16,7 @@
 
 import structlog
 
-from repowise.cli.helpers import console, head_commit_ts, run_async, save_state
+from repowise.cli.helpers import console, err_console, head_commit_ts, run_async, save_state
 from repowise.core.analysis.health import HEALTH_ANALYZER_VERSION
 
 from .incremental import _build_repo_graph
@@ -1251,14 +1251,27 @@ def _run_full_health_rescore(
 # REPOWISE_GIT_WINDOW_ANCHOR / historical checkouts; override for tests.
 _FULL_RESCORE_INTERVAL_DAYS = 7.0
 
+# The malformed-value warning is global, not per-repo. `_full_rescore_interval_days`
+# is consulted once per repo in a workspace fan-out, `repowise watch` and post-commit
+# hook updates, so a naive warn-in-except would spam the terminal once per repo. Hoist
+# the once-per-invocation guarantee into a module-level guard (#1371).
+_FULL_RESCORE_WARNING_SENT = False
+
 
 def _full_rescore_interval_days() -> float:
+    global _FULL_RESCORE_WARNING_SENT
     raw = os.environ.get("REPOWISE_FULL_RESCORE_INTERVAL_DAYS", "").strip()
     if raw:
         try:
             return max(0.0, float(raw))
         except ValueError:
-            pass
+            if not _FULL_RESCORE_WARNING_SENT:
+                _FULL_RESCORE_WARNING_SENT = True
+                err_console.print(
+                    "[yellow]Warning:[/yellow] "
+                    f"REPOWISE_FULL_RESCORE_INTERVAL_DAYS must be a number "
+                    f"(got '{raw}'); using {_FULL_RESCORE_INTERVAL_DAYS:.0f}-day default"
+                )
     return _FULL_RESCORE_INTERVAL_DAYS
 
 
diff --git a/tests/unit/cli/test_health_rescore_gate.py b/tests/unit/cli/test_health_rescore_gate.py
index 2a5482fde..1f966d541 100644
--- a/tests/unit/cli/test_health_rescore_gate.py
+++ b/tests/unit/cli/test_health_rescore_gate.py
@@ -10,6 +10,7 @@
 import pytest
 
 from repowise.cli.commands.update_cmd.persistence import (
+    _full_rescore_interval_days,
     full_rescore_due,
     health_analyzer_changed,
 )
@@ -161,3 +162,71 @@ def test_init_never_stamps_the_cadence_for_a_run_that_scored_nothing(module_name
             f"{module_name} resolves the cadence stamp without checking that this "
             f"run produced a health report: {line.strip()}"
         )
+
+
+def _capture_warnings(monkeypatch) -> list[str]:
+    """Collect what ``_full_rescore_interval_days`` warns, via the shared err_console."""
+    from repowise.cli import helpers
+
+    printed: list[str] = []
+    monkeypatch.setattr(
+        helpers.err_console, "print", lambda *a, **k: printed.append(" ".join(str(x) for x in a))
+    )
+    return printed
+
+
+class TestFullRescoreIntervalWarningOnce:
+    """#1371: a malformed REPOWISE_FULL_RESCORE_INTERVAL_DAYS must warn once per invocation.
+
+    ``_full_rescore_interval_days`` is consulted once per repo in a workspace
+    fan-out, ``repowise watch`` and post-commit hook updates. A naive warn-in-
+    except spams one line per repo; the module-level guard collapses it to a
+    single warning.
+    """
+
+    def test_warns_once_across_many_repos(self, monkeypatch):
+        monkeypatch.setenv("REPOWISE_FULL_RESCORE_INTERVAL_DAYS", "not-a-number")
+        monkeypatch.setattr(
+            "repowise.cli.commands.update_cmd.persistence._FULL_RESCORE_WARNING_SENT", False
+        )
+        printed = _capture_warnings(monkeypatch)
+
+        # Simulate the per-repo fan-out: many independent reads in one invocation.
+        for _ in range(5):
+            assert _full_rescore_interval_days() == 7.0
+
+        (line,) = printed
+        assert "REPOWISE_FULL_RESCORE_INTERVAL_DAYS" in line
+        assert "not-a-number" in line
+        assert len(printed) == 1  # not once per repo
+
+    def test_valid_value_stays_silent(self, monkeypatch):
+        monkeypatch.setenv("REPOWISE_FULL_RESCORE_INTERVAL_DAYS", "7")
+        monkeypatch.setattr(
+            "repowise.cli.commands.update_cmd.persistence._FULL_RESCORE_WARNING_SENT", False
+        )
+        printed = _capture_warnings(monkeypatch)
+
+        assert _full_rescore_interval_days() == 7.0
+        assert printed == []
+
+    def test_default_is_unchanged(self, monkeypatch):
+        monkeypatch.delenv("REPOWISE_FULL_RESCORE_INTERVAL_DAYS", raising=False)
+        monkeypatch.setattr(
+            "repowise.cli.commands.update_cmd.persistence._FULL_RESCORE_WARNING_SENT", False
+        )
+        assert _full_rescore_interval_days() == 7.0
+
+    def test_warning_survives_valid_reads_after_invalid(self, monkeypatch):
+        """A valid read after the invalid one must not re-arm the guard."""
+        monkeypatch.setenv("REPOWISE_FULL_RESCORE_INTERVAL_DAYS", "oops")
+        monkeypatch.setattr(
+            "repowise.cli.commands.update_cmd.persistence._FULL_RESCORE_WARNING_SENT", False
+        )
+        printed = _capture_warnings(monkeypatch)
+
+        assert _full_rescore_interval_days() == 7.0
+        # Valid now: still no re-warning.
+        monkeypatch.setenv("REPOWISE_FULL_RESCORE_INTERVAL_DAYS", "7")
+        assert _full_rescore_interval_days() == 7.0
+        assert len(printed) == 1