docs(traces): document trace context propagation controls

detect/synthetic-monitoring/browser-checks/playwright-support.mdx

@@ -111,6 +111,8 @@ We currently support the following configuration options. We will update this li
   </Tab>
 </Tabs>
 
+To disable automatic trace header injection for Browser checks that use the Playwright Test Runner, define `use.extraHTTPHeaders` in the Playwright configuration. An empty object also disables injection. Checkly preserves the headers that you define, and the [built-in trace environment variables](/detect/synthetic-monitoring/browser-checks/mac-structure#built-in-runtime-variables) remain available.
+
 
 <Warning>
 A check using [the Playwright Test Runner (`@playwright/test`)](https://playwright.dev/docs/intro) will currently run around 30-50% longer than [a regular Playwright check (`playwright`)](https://playwright.dev/docs/library). This is caused by the automatic creation of trace and video assets. We are aware of this and are investigating solutions. If this is significantly degrading the performance of your check, we recommend to divide longer tests into multiple checks.

detect/synthetic-monitoring/playwright-checks/configuration.mdx

@@ -131,6 +131,8 @@ Checkly enforces these options for every run. User configuration does not overri
 
 Checkly supports Playwright's [`globalTimeout`](https://playwright.dev/docs/api/class-testconfig#test-config-global-timeout). Use it to control the maximum duration of the Playwright suite after `npx playwright test` starts.
 
+To disable automatic trace header injection, define `use.extraHTTPHeaders` in your Playwright configuration. A top-level value disables injection for the whole suite. A project-level value disables it only for that project. An empty object also disables injection. Checkly preserves the headers that you define, and the [built-in trace environment variables](/detect/synthetic-monitoring/playwright-checks/environment-variables#built-in-variables-in-playwright-check-suites) remain available.
+
 Playwright Check Suites also provide specific configuration for your Playwright monitoring.
 
 * `installCommand:` Override the command to install dependencies. `npm install --dev` is used by default.

snippets/generic-runtime-variables-table.mdx

@@ -7,7 +7,9 @@
 | `CHECK_RUN_ID`    | The UUID of the check run execution.        | Only available on scheduled runs.    |
 | `CHECK_TYPE`      | The type of the check, e.g. `BROWSER`.      |                                      |
 | `CHECKLY_TRACE_ID` | The OpenTelemetry trace ID of the check run. Use it to correlate the run with the trace in your own observability backend. | Only in Browser and Multistep checks and API setup & teardown scripts, and only when [Traces](/resolve/traces/overview) is active for the check; unset otherwise. |
+| `CHECKLY_TRACEPARENT` | The W3C `traceparent` header value of the check run's trace. Use it to propagate the trace context to your own tooling. | Only in Browser and Multistep checks, and only when [Traces](/resolve/traces/overview) is active for the check; unset otherwise. |
+| `CHECKLY_TRACESTATE` | The W3C `tracestate` header value of the check run's trace. Use it with `CHECKLY_TRACEPARENT` to propagate the full trace context. | Only in Browser and Multistep checks, and only when [Traces](/resolve/traces/overview) is active for the check; unset otherwise. |
 | `PUBLIC_IP_V4`    | The IPv4 of the check run execution.        |                                      |
 | `PUBLIC_IP_V6`    | The IPv6 of the check run execution.        |                                      |
 | `REGION`          | The current region, e.g. `us-west-1`.       |                                      |
-| `RUNTIME_VERSION` | The version of the runtime, e.g, `2023.09`. | Only in Browser, Multistep, and API setup/teardown scripts. |
+| `RUNTIME_VERSION` | The version of the runtime, e.g, `2023.09`. | Only in Browser, Multistep, and API setup/teardown scripts. |