FEATURE: Add MCP support for Flow's request handling cycle

[nezaniel]

This adjusts the RequestBodyParsingMiddleware so that the request body can be processed by an MCP server.

Upgrade instructions

none

Review instructions

this should not have any side effects on anything, but I'm not sure

Checklist

• Code follows the PSR-12 coding style
• Tests have been created, run and adjusted as needed
• The PR is created against the 8.3 branch (https://www.neos.io/features/release-roadmap.html)
• Reviewer - PR Title is brief but complete and starts with FEATURE|TASK|BUGFIX
• Reviewer - The first section explains the change briefly for change-logs
• Reviewer - Breaking Changes are marked with !!! and have upgrade-instructions

[kdambekalns]

To be honest: The explanation does not explain why this is needed. Could you elaborate on that a bit more?

Maybe even in a way that is more generic? Because, why should we do this only for MCP? Surely it's not MCP-specific?

[nezaniel]

Converting to draft as there are more things to be considered as well.

As far as I understood it, the mcp/sdk server uses the request body in a way that also supports streaming, meaning it cannot consume an already resolved request body. My interpretation (not knowledge) would be that this affects everything of (potential) content-type "text/event-stream", whether MCP or not.

I'm not exactly sure whether this belongs on framework level as I can do the rewind in my MCP base controller as well with the same working result.

[nezaniel]

I've managed to get streaming working with our base MCP controller (see https://github.com/sitegeist/Sitegeist.Pandora). The handling of "text/event-stream" must imho be done by Flow's request handler (we currently use a custom one). I'd like to discuss a possible implementation (it might be enough to just check the response content type) and target version. As this is a new feature, I guess it would go to 9.2?