diff --git a/goodwe_controller/app/inverter.py b/goodwe_controller/app/inverter.py
index 14b9540..f16f341 100644
--- a/goodwe_controller/app/inverter.py
+++ b/goodwe_controller/app/inverter.py
@@ -512,7 +512,7 @@ def build_roster(opts: dict, store, sign_cfg=None,
             soc_entity=opts.get("soc_entity", ""),
             batt_entity=opts.get("batt_entity", ""),
             batt_invert=bool(opts.get("batt_invert")),
-            max_w=float(opts.get("max_w", 2000)),
+            max_w=_flat_max_w(opts),
             # SAFETY-32. THE FLAT KEY, because this IS the single-inverter shape
             # - the one pack the flat options describe is the one pack whose
             # cut-out `bms_soc_floor` states. Defaulted from CFG-03's single
@@ -588,6 +588,36 @@ def _entry_bms_floor(entry: dict):
         return None
 
 
+def _flat_max_w(opts: dict) -> float:
+    """The single-inverter shape's cap, tolerating what rule 9 tolerates.
+
+    ⚠️ THIS USED TO BE A BARE `float(opts.get("max_w", 2000))` AND IT
+    DISAGREED WITH THE VALIDATOR. `validate.py`'s `_number()` reads `""` as
+    "use the default", so rule 9 looks at an empty `max_w` box, sees 2000 and
+    is content - while the bare `float("")` here raised ValueError from inside
+    `Controller.__init__`. Through UX-02's panel that surfaced as HTTP 500 on a
+    non-JSON body, which the page reported as "cannot reach the add-on": untrue,
+    and for the most prominent limit field's most likely transient state.
+
+    That inverted this module's own docstring rule - "keep the two in step: a
+    shape this tolerates that rule 9 does not name is a shape that runs" - in
+    the other direction: a shape rule 9 TOLERATED could not be composed at all.
+    The roster path never had the bug, because `_entry_max_w` below already
+    guards; only the flat path did.
+
+    Empty or absent is the default, exactly as `_number()` reads it.
+    Unparseable is 0.0, exactly as `_entry_max_w` reads it - and rule 9 refuses
+    it by name at line 790, with a sentence, before a control loop exists.
+    """
+    raw = opts.get("max_w", 2000)
+    if raw is None or raw == "":
+        return 2000.0
+    try:
+        return float(raw)
+    except (TypeError, ValueError):
+        return 0.0
+
+
 def _entry_max_w(entry: dict) -> float:
     """One entry's supervised cap, or 0.0 when it did not state a usable one.
 
diff --git a/goodwe_controller/app/selfconfig.py b/goodwe_controller/app/selfconfig.py
index c3e0f92..da5ad38 100644
--- a/goodwe_controller/app/selfconfig.py
+++ b/goodwe_controller/app/selfconfig.py
@@ -304,7 +304,36 @@ async def problems_and_ranges(opts: dict, hass=None):
     one. That was the first shape of this and it disagreed with itself.
     """
     flat = str(opts.get("setpoint_entity", "") or "").strip()
-    units = build_roster(opts, None)
+
+    # ⚠️ THE ROSTER IS BUILT BEFORE THE VALIDATOR RUNS, AND IT PARSES NUMBERS.
+    # `build_roster` reaches `inverter.py`'s `float(opts.get("max_w", 2000))`,
+    # which raises on a value the validator has a SENTENCE for. Cleared the
+    # `max_w` box and the panel answered HTTP 500 - not JSON, so the page said
+    # "cannot reach the add-on", which was untrue - while `validate.py`'s
+    # "max_w ... is not a number" was unreachable through the panel and reachable
+    # at startup, where `main.py` validates before it composes. That made this
+    # surface WEAKER than the startup gate for one field, which is the opposite
+    # of what this module claims below.
+    #
+    # A malformed scalar therefore falls back to validating WITHOUT device
+    # bounds. Those bounds come from the roster, and there is no roster; the
+    # validator's own complaint about the unparseable value is the answer the
+    # operator needs, and it is strictly more informative than a 500.
+    try:
+        units = build_roster(opts, None)
+    except (TypeError, ValueError) as exc:
+        # ⚠️ AND IT MUST NOT RETURN AN EMPTY LIST. An empty list means "no
+        # problems", and the page enables Save on it. If the roster could not be
+        # composed at all and the validator has nothing to say about why, that
+        # disagreement is itself the finding - so it is reported rather than
+        # swallowed. Returning `[]` here would turn a crash into a silent
+        # acceptance, which is worse than the 500 this replaced.
+        found = list(validate_startup_config(opts))
+        if not found:
+            found = [f"the configuration could not be composed ({type(exc).__name__}: "
+                     f"{exc}), and the validator did not name a reason. This is a "
+                     f"disagreement between the two and should be reported."]
+        return found, []
     if hass is not None:
         async def _limits(unit):
             if unit.setpoint_entity:
diff --git a/goodwe_controller/translations/en.yaml b/goodwe_controller/translations/en.yaml
index 30d7730..205e409 100644
--- a/goodwe_controller/translations/en.yaml
+++ b/goodwe_controller/translations/en.yaml
@@ -4,7 +4,7 @@
 # Without a `translations/` directory the Configuration tab renders the raw
 # option KEYS - `unit_sign_disagree_w`, `saturation_cycles`, `integrator_max_w`.
 # The frontend keeps a field when `e.name in options || e.required`, and all 71
-# keys are in `options:` (59 of them are `required` as well), so ALL SEVENTY are
+# keys are in `options:` (59 of them are `required` as well), so ALL SEVENTY-ONE are
 # rendered, always, in `schema:` order, with no description. This file is what
 # turns that into sentences.
 #