docs: Query page output dot notation and metadata availability (#3132)

Clarifies in the Query docs that run metadata is not available on the
Query page and that the output column is JSON, so dot notation (e.g.
output.externalId) should be used for selecting and filtering. Adds an
example that filters by an output field in WHERE

docs/insights/query.mdx

@@ -5,7 +5,7 @@ description: "Query allows you to write custom queries against your data using T
 
 ### Available tables
 
-- `runs`: contains all task run data including status, timing, costs, and metadata
+- `runs`: contains all task run data including status, timing, costs, and task output. Run metadata (key-value set in your task) is not available on the Query page.
 - `metrics`: contains metrics data for your runs including CPU, memory, and your custom metrics
 
 ### `metrics` table columns
@@ -388,16 +388,19 @@ WHERE notEmpty(tags)
 
 ### JSON functions
 
-Extract data from JSON columns (like runs.output, runs.error, metrics.attributes, etc.):
+The `output`, `error`, and `metrics.attributes` columns are already JSON, so use dot notation to read or filter on them. You don't need `JSONExtract*` for these (those are for string columns).
 
 ```sql
 SELECT
   run_id,
   output.message AS output_message,
   output.count AS count,
-  output.error != NULL AS has_error
+  output.externalId AS external_id
 FROM runs
-WHERE output IS NOT NULL
+WHERE task_identifier = 'my-task'
+  AND output.externalId = 'something'
+ORDER BY triggered_at DESC
+LIMIT 100
 ```
 
 ## Query scopes