Add BACnet read-only adapter foundation

docs/LEARNING_LOG.md

@@ -22,6 +22,60 @@ This file should be updated by Codex after each meaningful change.
 ### What to learn next
 ```
 
+## 2026-05-25 - BACnet Read-Only Adapter Foundation
+
+### What changed
+
+Added a read-only BACnet adapter foundation that loads enabled BACnet
+connection profiles, polls configured object references through an injected
+object reader, and emits normalized `process.measurement.recorded`
+FactoryEvents.
+
+### Why it matters
+
+This completes the first foundation pass for the three protocol families in the
+connection-management epic. BACnet data can now follow the same safe path as
+OPC-UA and MQTT: configured source reads become FactoryEvents without adding
+write operations, commandable-property changes, arbitrary object discovery, or
+UI ingestion controls.
+
+### How it works
+
+`load_enabled_bacnet_profiles()` reads the local connection profile store and
+filters to enabled BACnet profiles. `run_bacnet_read_only_adapter()` passes each
+profile to a `BacnetObjectReader`, which reads only configured object
+references for the configured device address, device instance, optional network
+number, and polling interval. Each numeric object reading becomes a process
+measurement event whose source metadata includes the profile ID, device/network
+descriptor, object reference, and poll index. Unavailable devices, missing
+objects, unconfigured objects, stale readings, and nonnumeric values raise clear
+adapter errors.
+
+### How to run it
+
+The foundation is currently exercised from Python code and tests. It reads the
+same local profile store used by the connection profile API and writes to the
+same event store interface used by ingestion.
+
+### How to test it
+
+```bash
+.venv/bin/python -m pytest services/ingestion/tests/test_bacnet_read_only_adapter.py
+```
+
+### Key files
+
+- `services/ingestion/factory_ingestion/bacnet_read_only_adapter.py`
+- `services/ingestion/tests/test_bacnet_read_only_adapter.py`
+- `services/ingestion/README.md`
+
+### What to learn next
+
+Add a real BACnet/IP object reader only after connector runtime orchestration,
+network approval, and object mapping rules are defined. Keep BACnet writes and
+commandable-property changes out of this path unless a dedicated ADR approves
+them.
+
 ## 2026-05-25 - MQTT Read-Only Adapter Foundation
 
 ### What changed

services/ingestion/README.md

@@ -272,6 +272,63 @@ configuration access, Sparkplug-style JSON payload mapping, broker-unavailable
 errors, malformed payload errors, unmapped topic errors, and the absence of a
 publish/writeback surface.
 
+## BACnet Read-Only Adapter Foundation
+
+The read-only BACnet adapter foundation reads enabled BACnet
+`ProtocolConnectionProfile` records from the local connection profile store,
+uses an injected object reader to poll configured object references, and emits
+normalized `process.measurement.recorded` FactoryEvents into an event store.
+
+This foundation does not add a BACnet/IP runtime, object discovery, write path,
+commandable-property changes, or UI ingestion controls. Until a connector ADR
+explicitly expands the behavior, the adapter is limited to:
+
+- enabled profiles where `protocol = "bacnet"`;
+- the configured device address in `endpoint`;
+- configured `device_instance` and optional `network_number`;
+- configured object references such as `analogInput:1.presentValue`;
+- the configured polling interval in `acquisition.poll_interval_seconds`;
+- read-only object polling through an injected reader.
+
+Each object reading supplies the object reference, numeric present value, unit,
+optional object name, quality, and optional read timestamp. The adapter maps
+each reading into a process measurement event and captures source metadata:
+
+- `source.system` is `bacnet:<connection-profile-id>`;
+- `source.adapter` is `bacnet-read-only-adapter`;
+- `source.source_event_id` includes the connection profile ID, network/device
+  descriptor, object reference, and poll index;
+- `payload.tag_name` stores the configured BACnet object reference.
+
+Stale readings can be rejected by passing `max_reading_age_seconds`; stale
+flags from the object reader are rejected immediately. Unavailable devices,
+missing objects, unconfigured objects, stale readings, and nonnumeric values
+raise clear adapter errors.
+
+### Docker Desktop BACnet demo limitations
+
+Local BACnet/IP demos are UDP based and can behave differently under Docker
+Desktop networking than they do on a real plant network. Broadcast discovery,
+BBMD/foreign-device registration, host networking, routing between VLANs, and
+UDP port exposure can all vary by host OS and Docker configuration. Treat any
+Docker Desktop BACnet demo as a local smoke path only.
+
+Production BACnet/IP expectations are separate: configured devices and objects
+should be read through network-approved routes, with explicit device addressing,
+object mapping, polling intervals, and operations approval. This foundation does
+not claim production readiness and does not write BACnet properties.
+
+Run the focused tests:
+
+```bash
+.venv/bin/python -m pytest services/ingestion/tests/test_bacnet_read_only_adapter.py
+```
+
+The test suite covers fake BACnet clients, device address/network handling,
+object references, polling interval access, units/object mapping,
+device-unavailable errors, missing object errors, stale reading errors, and the
+absence of write or commandable-property surfaces.
+
 ## Accepted Event Storage
 
 Accepted events are written to the local JSONL event store: