Add per-server telemetry request diagnostics

docs/beta-test-plans.md

@@ -94,6 +94,44 @@ and the limits of identifying matches from this protocol.
 The game scripts are uploaded artifacts, not source maintained in this
 repository. Their reporter should emit the three payloads above.
 
+### Telemetry diagnostics
+
+Open a server's **Diagnostics → Telemetry API requests** to inspect incoming
+`POST /api/telemetry` calls whose top-level `server` exactly matches its registered
+name. Each entry includes the Electric Cherry receipt time, HTTP result, error
+reason, event, map, round, player count, content type, and submitted JSON. Rejected
+reports are included, even when the content type is wrong but the body is readable
+JSON. Processing failures return 500 and record the internal error when diagnostic
+storage is available; failed database transactions do not update the scoreboard.
+
+The panel refreshes every five seconds while visible and has a manual refresh
+button. History is stored in SQLite starting with this version, with up to 200
+requests per server from the last seven days and a fleet-wide cap of 10,000
+requests. Old entries are pruned when new requests arrive, and expired entries
+are excluded from reads. Payload previews are limited to 16,384 characters and
+marked when truncated. Request headers other than content type are not stored.
+`GET /api/servers/{name}/telemetry-requests` returns the same recent history,
+newest first, with caching disabled.
+
+- **No entries:** no attributable requests are retained for this exact name.
+  Check the reporter's destination and server field. Calls that never reach
+  Electric Cherry, malformed JSON, and bodies without a usable server name
+  cannot appear in this server's log. Earlier requests are not backfilled.
+- **400 / 415:** inspect the error and payload. One invalid player's stats or a
+  duplicate GUID rejects the entire report. These requests do not update the
+  scoreboard.
+- **404:** the reported server was not registered or had been destroyed at the
+  time of the request.
+- **200:** Electric Cherry processed the report. An empty `players` array
+  produces an empty scoreboard, including when sent with `game_end`. If a
+  populated accepted report is missing from the scoreboard, investigate the
+  live update/browser path.
+- **500:** Electric Cherry failed to process the request. Inspect the recorded
+  error and the application log.
+
+RCON's online status and player count are separate from gameplay telemetry, so
+an occupied server can still have no scoreboard report.
+
 ## Requirements
 
 Requirements on a qualifying server are ANDed: