This is the first independently tested slice of the Jev feature in #241. It adds a bounded Jev client, exact Chat-source validation, quote extraction, and shared conversation types. The application does not call these modules yet.

The source check compares the quoted UTF-16 range, message identity, and author with the saved Chat entry. Provider responses must match the requested answer types and keys; requests support cancellation and timeouts. A review fix also caps the entire serialized request at 256 KiB of UTF-8 before transport, so many individually valid questions cannot create an oversized call.

**Review scope:** 10 files; 1,109 source lines and 522 test lines. This layer is based on main. Event replay follows in the next PR; decision records, interpretation, and application wiring follow later.

**Validation:** 25 focused tests pass on the updated head, full workspace/E2E types pass, repository CI and formatting pass locally. All three required GitHub checks pass on the updated head. Provider responses are controlled fixtures; this does not establish live model quality.


### Review fix: total request bound


Temporarily closing and reopening to retrigger required CI on the updated head; the PR remains intended for merge.