chore(historian): batch-era defaults + appsettings/doc alignment

src/Server/ZB.MOM.WW.OtOpcUa.Host/appsettings.json

@@ -43,10 +43,17 @@
     "OutboxPath": "",
     "_OutboxPathComment": "Directory holding the FasterLog segment + commit files. Required when Enabled=true. In production set an ABSOLUTE path on durable storage.",
     "CommitMode": "PerEntry",
+    "_CommitModeComment": "PerEntry means one fsync per ingest BURST, not per value: the recorder appends a whole burst through AppendBatchAsync, which enqueues every entry and issues a single group commit. Periodic batches commits onto a timer every CommitIntervalMs (bounded loss window).",
     "CommitIntervalMs": 100,
-    "DrainBatchSize": 64,
+    "DrainBatchSize": 1024,
+    "_DrainBatchSizeComment": "Entries peeked + written per drain pass. Was 64 when a pass wrote its per-tag groups sequentially; the peek is an in-memory scan and the pass is now bounded-parallel over DrainConcurrency, so a wide batch is cheap — and 64 let the outbox fall permanently behind during any gateway hiccup.",
     "DrainIntervalSeconds": 2,
-    "Capacity": 0,
+    "DrainConcurrency": 8,
+    "_DrainConcurrencyComment": "Historian tags a single drain pass writes concurrently (one gateway round-trip per tag group). 1 restores the fully sequential drain. The ack is unchanged: still all-or-nothing after every group reports.",
+    "Capacity": 500000,
+    "_CapacityComment": "Max un-acked outbox entries before drop-oldest; 0 = unbounded. The Gitea #538 disk backstop for a historian refusing EVERY write — the one case the per-tag quarantine cannot resolve.",
+    "MaxWriteAttempts": 5,
+    "_MaxWriteAttemptsComment": "Gitea #538: consecutive failed drain passes one tag may accumulate — counted only across passes where OTHER tags wrote successfully — before its queued entries are abandoned so the FIFO head can advance.",
     "MinBackoffSeconds": 1,
     "MaxBackoffSeconds": 30
   },