What ProtoCore has actually shipped, kept as a feature-level record.

This exists because ROADMAP.md is for work that is not done yet. Mixing the two made the roadmap unreadable: 14 of its 17 sections held no open items at all, so the plan was buried under its own history.

Two neighboring documents cover different questions, and this one should not duplicate either:

FEATURES.md - what the library does, as a reference grid. The answer to "can it do X".
CHANGELOG.md - when each change landed, generated per commit. The answer to "when did X change".
This file - what was undertaken and finished, at the granularity a roadmap item was written in. The answer to "was X ever built, and what did it involve".

Sections below are moved verbatim from the roadmap, so the wording is as it was written while the work was planned and then marked done.