write negative cache ONLY on permanent provider failure so transient errors retry

src/service.zig

@@ -1003,11 +1003,16 @@ pub const DataService = struct {
                 }
                 return DataError.TransientError;
             }
-            // NotFound, ParseError, InvalidResponse, AuthError -
-            // symbol genuinely has no candle data on Tiingo (the only
-            // provider for historical candles since the 2026-05
-            // audit). Negative-cache so we don't keep retrying.
-            s.writeNegative(symbol, .candles_daily);
+            // Only a genuine NotFound means "this symbol has no candle
+            // data on Tiingo" (the sole historical-candle provider since
+            // the 2026-05 audit) and earns a sticky negative-cache entry.
+            // Unauthorized / InvalidResponse / PaymentRequired and the
+            // like are not permanent facts about the symbol (transient
+            // auth misconfig, a malformed response) - fail this call but
+            // stay retryable, matching fetchCached's policy. This matters
+            // now that the candle negative cache is actually honored: a
+            // bad negative would otherwise stick until --refresh.
+            if (isPermanentProviderFailure(err)) s.writeNegative(symbol, .candles_daily);
             return DataError.FetchFailed;
         };
         // populateAllFromTiingo writes all three caches itself; we