[chrisbutler]

Unicode reactions need a verified helper capability and a single validation/serialization contract across REST, Socket.IO, and the private API. Without that, a server can accept a reaction its running helper cannot send, or serialize an unrelated classic reaction incorrectly when an emoji field is present.

This is a draft follow-up stacked on #839 (head 68b72b9897c574c44bd41bf79556c99695407ec7). Zach Garcia's original advanced-Tapbacks commits remain the foundation and retain their authorship. Merge/rebase #839 first; the incremental contribution to review here is commit 6c16e45 relative to that head. GitHub's full development comparison currently includes #839's changes and its existing helper resources; this follow-up adds source/tests only and does not replace helper binaries.

• Read the strict boolean capability from the active Messages helper's ping, clear it when that helper disconnects, and expose it in server metadata.
• Share bounded, single-grapheme Unicode validation across REST, the shared send interface, and private-API dispatch. Preserve the existing six classic reaction names and their removal forms.
• Preserve ZWJ, modifier, flag, keycap, and variation-selector sequences in the helper payload. Only emoji Tapback types use the emoji field during serialization; classic types remain classic.

Validation: node --test tests/emoji-reactions.test.cjs passes all eight tests. These run production TypeScript with explicit boundary mocks, covering classic/Unicode add/remove, invalid payloads, exact helper dispatch, disconnect/legacy-helper capability behavior, REST and Socket.IO/direct-call rejection, and metadata. Tests do not launch Electron, connect to Messages, or use a live database.

The full TS check with the installed compiler and --ignoreDeprecations 5.0 remains blocked by the existing ScheduledService.ts NodeJS.Timer/clearInterval type mismatch outside this diff. This is the same baseline limitation documented in the contact PRs.

Depends on the companion helper capability PR: BlueBubblesApp/bluebubbles-helper#78 . Older helpers omit the flag and retain classic reactions; Unicode requests fail closed. Draft review items include agreement on the metadata contract, full server/client integration with #839, and cross-macOS runtime testing. The deployed predecessor stack has user-confirmed Unicode delivery, but these isolated review branches have not been installed over it.

ChatKit delayed loading remains an alternative review branch outside this PR's incremental diff: https://github.com/chrisbutler/bluebubbles-server/tree/review/delayed-helper-loader . Implementation and tests were developed with Codex assistance. No personal messages, contacts, room selections, credentials, or deployment version bumps are added.

Bridge companion: mautrix/imessage#241 . Integration requires rebuilding the helper from #78 and coordinating the bundled helper resource/MD5 refresh through the normal release process; the resources currently inherited from #839 do not advertise the new capability.