Description

Even when isReady() returns true, the servlet container may still be processing a previous write internally. Always set readyAndDrained to false after a direct write in runOrBuffer() to ensure subsequent writes go through the container thread via onWritePossible(), matching the servlet spec requirement.

Tomcat throws:

java.lang.IllegalStateException: In non-blocking mode you may not write to the ServletOutputStream until the previous write has completed and isReady() returns true

Testing

Validated by running servlet tests locally. TomcatTransportTest.clientChecksInboundMetadataSize_header passes.

Fixes

Fixes #12723