This skill.
User guide: docs/user-guide/how-to-guides/publish-external-source-adapter.md
Canonical contract: docs/user-guide/microservices/controller/data_formats.md (section External Source Input Message Format and its subsections).
When validating payloads against schema definitions: controller/src/schema/metadata.schema.json (external_source, external_pose, external_detection).
If an example adapter already exists for the protocol or a close cousin, read it before inventing a new layout: tools/external_source_adapters/ (for example mavlink_to_external_source.py).

Architecture background (optional): docs/adr/0016-unified-external-source-ingestion.md.

Hard Rule — No Contract Duplication

The field tables, required-field lists, pose-trust rules, identity/collision guidance, rejection reasons, and full JSON examples are defined only in data_formats.md (backed by the schema).

Do not copy those tables, field lists, or examples into this skill, into generated code comments, or into new documentation pages.
Cite the relevant data_formats.md anchors (or the how-to checklist) instead.
If the contract and a snippet appear to disagree, trust data_formats.md / the schema and fix the snippet.

Preferred Layout

Put runnable example adapters under tools/external_source_adapters/.
Keep protocol-specific dependencies in that directory's requirements.txt (for example pymavlink). Do not add them to core Scenescape runtime requirements unless the product explicitly adopts the protocol.
Follow the how-to's SCENESCAPE_* environment-variable naming for source id, broker, MQTT auth, and root cert. Topic path uses SCENESCAPE_SOURCE_ID.
Reuse scene_common.mqtt.PubSub and PubSub.DATA_EXTERNAL rather than a one-off MQTT client, unless the user requires otherwise.
When adding or renaming an example adapter, update tools/external_source_adapters/README.md and add a See Also link from the how-to — do not paste the script into data_formats.md.

Agent Checklist When Writing a Converter

Publish to external/{source_id}/{thing_type} with matching payload source_id. Do not put a scene uid in the topic path. Prefer wgs84 for mobile agents (geospatial auto-attach); use CONTROLLER_EXTERNAL_SOURCE_BINDINGS for scene-frame poses.
Choose a persistent source_id and per-object id (see Choosing a source_id in data_formats.md); never mint fresh UUIDs on each restart.
Map native observations into source-local translation (metres) relative to the source origin described by pose.
Choose reference_frame (wgs84 vs scene) correctly; honor CONTROLLER_TRUSTED_POSITIONING_SOURCES for scene poses.
Convert the source's native orientation (euler, DCM, etc.) into the contract's quaternion (x, y, z, w). Do not invent alternate rotation field shapes.
Use ISO 8601 UTC timestamps (scene_common.timestamp.get_iso_time is fine).
Pose-only sources (GNSS/attitude with no separate detections): either publish pose with an empty objects array (cache refresh), or report the platform itself as one object at [0, 0, 0] using the same persistent id as source_id — see Choosing a source_id in data_formats.md. Do not mint a second identity for "the vehicle."
Publish over authenticated MQTT with the Scenescape CA cert (see the how-to skeleton using scene_common.mqtt.PubSub and PubSub.DATA_EXTERNAL).
Keep credentials in environment variables or secret files — never hard-code and never ship default passwords.
Do not add controller-side ID remapping, lookup caches, or identity allowlists; translation belongs in the adapter.
Prefer linking readers to data_formats.md examples over inventing new sample payloads.

Out of Scope (Refuse / Defer)

Do not implement or imply as part of an adapter task:

Footprint handoff / overlap policy for the spatial binder (ADR 14 Future Work)
Cross-source fusion or camera/external deduplication
Per-source identity trust allowlists (identity is trusted by default with collision detection — see data_formats.md)
Changes to Scene Controller pose cache, identity registry, or schema unless the user explicitly requested a contract change
Broker mTLS/ACL binding of credentials to publisher ids, or other trust-domain hardening beyond same-authority certs (ADR 14 Future Work)
Promoting a protocol library into core Scenescape dependencies "for convenience"

Maintenance (Anti-Drift)

When the external-source contract changes:

Update controller/src/schema/metadata.schema.json and the External Source section of docs/user-guide/microservices/controller/data_formats.md first.
Then only adjust broken links, checklist wording, or the how-to MQTT skeleton in docs/user-guide/how-to-guides/publish-external-source-adapter.md and this skill.
If example adapters under tools/external_source_adapters/ break against the new contract, fix their mapping code and README pointers — still without copying field tables into the README.
Do not re-document fields here. This skill stays a thin procedure + pointer document.

external-source-adapter

External-Source Adapter Skill

Mandatory Reads (In Order)