Say when captcha task events carry a challenge_id

browsers/telemetry/categories.mdx

@@ -76,7 +76,7 @@ Exclusion affects telemetry only; the commands still reach the browser. On `cdp_
 
 ### Correlate captcha tasks and challenges
 
-A visible captcha challenge can require multiple solver tasks. When the identifiers are present, use `task_id` to pair a `captcha_solve_started` event with its terminal `captcha_solve_result`, and use `challenge_id` to group every task for the same visible challenge. A `challenge_id` can continue across a page reload when the same challenge episode continues; it doesn't indicate task order or completion.
+A visible captcha challenge can require multiple solver tasks. When the identifiers are present, use `task_id` to pair a `captcha_solve_started` event with its terminal `captcha_solve_result`, and use `challenge_id` to group the tasks for the same visible challenge. A `challenge_id` can continue across a page reload when the same challenge episode continues; it doesn't indicate task order or completion.
 
 | Event type | Scope | Meaning |
 | --- | --- | --- |
@@ -86,6 +86,8 @@ A visible captcha challenge can require multiple solver tasks. When the identifi
 
 Challenge results are currently emitted for visible reCAPTCHA v2, hCaptcha, and press-and-hold challenges. Other captcha types can emit task events without a challenge result. Telemetry delivery is best-effort and isn't ordered: a start can arrive after its result, and any event can be absent. When you need a challenge-level outcome, wait for a bounded interval and fall back to available task results and the current page state.
 
+Task events carry a `task_id`, but not all of them carry a `challenge_id`. Kernel sets `challenge_id` from tracking the challenge widget in the page - the same tracking that produces `captcha_challenge_result` - so a task the automatic solver runs without it reports a `task_id` only. Those task events can't be joined to a challenge result for the same page, even when one is emitted. Pair a start with its result on `task_id`, and use `challenge_id` for grouping only when it's there.
+
 Use each result event's `duration_ms` as the authoritative duration rather than calculating it from event timestamps. Challenge duration covers every solver attempt from when the challenge appeared until its terminal outcome.
 
 Challenge outcomes have these meanings: