docs(influxdb3): document trigger logging behavior (#6804)

* docs(influxdb3): document trigger logging behavior

Add processing_engine_logs table documentation to system data reference,
explaining that logs are stored in both the trigger's database (primary)
and _internal. Update plugins error handling to specify trigger's database.

* Update content/shared/influxdb3-plugins/_index.md

content/shared/influxdb3-admin/query-system-data/_index.md

@@ -10,6 +10,7 @@ You can query the system tables for information about your running server, datab
     - [View column information for a table](#view-column-information-for-a-table)
     - [Recently executed queries](#recently-executed-queries)
     - [Query plugin files](#query-plugin-files)
+    - [Query trigger logs](#query-trigger-logs)
 
 ### Use the HTTP query API 
 
@@ -190,3 +191,47 @@ curl "http://localhost:8181/api/v3/query_sql" \
     "format": "jsonl"
   }'
 ```
+
+#### Query trigger logs
+
+The `system.processing_engine_logs` table stores log entries from Processing Engine triggers.
+
+Logs are stored in **two locations**:
+
+- The trigger's database (primary)--query here for trigger-specific debugging
+- The `_internal` database--contains logs from all triggers across all databases
+
+**Columns:**
+
+- `event_time` (Timestamp): When the log entry was recorded
+- `trigger_name` (String): Name of the trigger that generated the log
+- `log_level` (String): Log level (INFO, WARN, ERROR)
+- `log_text` (String): Log message content
+
+**Query logs for a specific trigger:**
+
+```bash { placeholders="DATABASE|TRIGGER" }
+influxdb3 query \
+  --database DATABASE \
+  "SELECT event_time, log_level, log_text
+   FROM system.processing_engine_logs
+   WHERE trigger_name = 'TRIGGER'
+   ORDER BY event_time DESC
+   LIMIT 20"
+```
+
+Replace the following:
+
+- {{% code-placeholder-key %}}`DATABASE`{{% /code-placeholder-key %}}: The database where you created the trigger
+- {{% code-placeholder-key %}}`TRIGGER`{{% /code-placeholder-key %}}: The name of your trigger
+
+**Query all trigger logs (from _internal):**
+
+```bash
+influxdb3 query \
+  --database _internal \
+  "SELECT event_time, trigger_name, log_level, log_text
+   FROM system.processing_engine_logs
+   ORDER BY event_time DESC
+   LIMIT 50"
+```

content/shared/influxdb3-plugins/_index.md

@@ -688,10 +688,12 @@ influxdb3 create trigger \
 
 To configure error handling behavior for a trigger, use the `--error-behavior <ERROR_BEHAVIOR>` CLI option with one of the following values:
 
-- `log` (default): Log all plugin errors to stdout and the `system.processing_engine_logs` system table.
+- `log` (default): Log all plugin errors to stdout and the `system.processing_engine_logs` table in the trigger's database.
 - `retry`: Attempt to run the plugin again immediately after an error.
 - `disable`: Automatically disable the plugin when an error occurs (can be re-enabled later via CLI).
 
+For more information, see how to [Query trigger logs](/influxdb3/version/admin/query-system-data/#query-trigger-logs).
+
 ```bash
 # Automatically retry on error
 influxdb3 create trigger \