IssueCoreRestSink.emit() passed task_spec.triggering_event_id straight
into the httpx json= payload. When the field is a UUID object (rather
than a string), httpx's JSON encoder raised
"TypeError: Object of type UUID is not JSON serializable", failing the
emission. Guard with str(), preserving None for optional event ids.
Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
Issue-core requires a shared ingestion key on POST /issues/. The REST sink
now sends Authorization: Bearer using ISSUE_CORE_API_KEY and fails fast
when the key is missing under ISSUE_SINK_TYPE=rest.
Updates .env.example, emission boundary docs, and unit tests for the
header contract and missing-key error.