feat: Add RequestId filter

[patel-vansh]

Description
This PR adds RequestId filter which will improve debugging, traceability, as well as better logging for each request.

This filter is fully opt-in, that means there's no BC here. The filter line is commented so that users can easily add if needed.

Request id is generated during early lifecycle. Incoming header X-Request-ID will be prioritized over auto generation of request ids, so that CDN/web server/load balancer can generate request id for better traceability.

If the header is not present, the framework will create request id via bin2hex(random_bytes(16)) function, that means the framework-generated ids will be of length 32.

Why only bin2hex?
I initially thought of UUID v4, but due to lack of in-built support for UUID, I changed that to bin2hex. Adding a new external dependency for just this one thing would be less feasible, IMO. And also random_bytes(16) should provide enough randomness so collision would be highly unlikely.

If there is some other better way to generate id, then I would surely change to that.

Checklist:

• Securely signed commits
• Component(s) with PHPDoc blocks, only if necessary or adds value (without duplication)
• Unit testing, with >80% coverage
• User guide updated
• Conforms to style guide

[michalsn]

Thanks for working on this. I agree that having a request ID can be useful. However, I am not sure we should add this directly to IncomingRequest. I would prefer to see this as documentation only, or provide an opt-in filter that's disabled by default. This is a path similar to those followed by Symfony and Laravel.

If we provide an example or filter, it should store the value in context()->set('request_id', $id) so $logGlobalContext can pick it up, set X-Request-ID on the response in after(), and validate incoming IDs: non-empty, bounded length, and safe characters only.

Let's see what others think.

[memleakd]

Thanks for working on this. I agree that having a request ID is useful.

I also use this in my projects, but with a filter-based approach, and it has worked well in practice. I think that shape fits better here than adding it directly to IncomingRequest.

The filter can resolve or generate the ID early, validate any incoming X-Request-ID, store it in context()->set('request_id', $id) so $logGlobalContext can include it in logs, and expose the same ID back on the response as X-Request-ID.

This avoids keeping separate request-id state on the request object, keeps the feature opt-in, and makes the ID useful for logs, response headers, and support/debug workflows.

[patel-vansh]

Thanks @michalsn and @memleakd for your reviews. I've changed the implementation. Added a filter which is completely opt-in, so there's no BC. This filter will set request_id key in Context class so that $logGlobalContext can automatically log request IDs.

[memleakd]

Thanks for updating this. I think the filter direction is much better. I added a few comments on things that still look worth checking.

[memleakd]

Thanks for the updates. This looks much better now. Just two small things left for me:

[memleakd]

I noticed one last thing with the filter ordering. I think requestid should stay after pagecache in after. PageCache::after() stores response headers, so if requestid runs first, we may accidentally cache X-Request-ID.

[memleakd]

LGTM

[michalsn]

Looks good, thanks! You can rebase to resolve the PHPStan error.

[datamweb]

Since Context is still a relatively new feature in CodeIgniter, I wonder if it would be helpful to include a small code example showing how to access the request ID from the context.

Something along the lines of:

$requestId = service('context')->get('request_id');

This might make the feature easier to discover for users who are not yet familiar with the Context API.