Java files in mixed Maven projects could not resolve Kotlin types from the same module or upstream reactor modules, because Kotlin compiler output never reached JDT's Java model.
A per-project bridge compiles saved Kotlin sources with the project's own Maven setup into private staging output (a bundled Maven extension redirects outputs and records each module's Kotlin compile result) and mounts the Kotlin classes as marked libraries through a bundled JDT command, leaving m2e/JRE containers and other entries untouched. The last successful snapshot stays mounted while rebuilding; a new one is published when every Kotlin target compiles, even if javac fails, so Java callers of a renamed or removed Kotlin API show their errors in the editor. Kotlin compile failures keep the previous API and are reported under the kotlin-bridge Problems source. Removing the last Kotlin file withdraws the libraries. Changes under build outputs and excluded directories never trigger a rebuild.
Part of #428
