Fix: rrdtool DS names must be <= 19 chars

sanitizeName now keeps the first 15 chars plus a 3-hex hash suffix
for names longer than 19 chars (rrdtool's hard limit on DS name
length). The previous replace-dots-only version produced names up to
31 chars, which rrdtool rejected with 'invalid DS format'.

src/HomeAssistant/Runtime/Metrics.hs

@@ -15,11 +15,13 @@ module HomeAssistant.Runtime.Metrics
 
 import Control.Concurrent (threadDelay)
 import Control.Monad (forever, unless)
+import Data.Char (ord)
 import Data.Int (Int64)
 import Data.List (intercalate, sortBy)
 import Data.Ord (comparing)
 import Data.Text (Text)
 import Data.Void (Void)
+import Numeric (showHex)
 import qualified Data.Text as T
 import qualified Data.HashMap.Strict as HM
 import qualified System.Metrics as M (Value (..), Sample, Store, sampleAll)
@@ -41,8 +43,16 @@ dsTypeOf (M.Counter _) = Just Derive
 dsTypeOf (M.Gauge _)   = Just Gauge
 dsTypeOf _             = Nothing
 
+-- | Maps an ekg metric label to a valid rrd DS name (≤19 chars, [A-Za-z0-9_]).
+-- Long names keep the first 15 chars plus a 3-hex hash suffix for uniqueness.
 sanitizeName :: Text -> String
-sanitizeName = T.unpack . T.replace "." "_"
+sanitizeName name
+  | length sanitized <= 19 = sanitized
+  | otherwise = take 15 sanitized ++ "_" ++ paddedHash
+  where
+    sanitized = T.unpack (T.replace "." "_" name)
+    paddedHash = let h = showHex (sum (map ord sanitized) `mod` 4096) ""
+                 in replicate (3 - length h) '0' ++ h
 
 buildSchema :: M.Sample -> [DsSpec]
 buildSchema sample =