Update changelog and mark ADR as accepted

Author: ch1bo

CHANGELOG.md

@@ -39,10 +39,17 @@ changes.
 - Add support for `Conway` in `hydra-chain-observer`.
 
 - **BREAKING** Change to the `hydra-node` logs, monitoring and removal of `log-filter` executable:
-  - We renamed the `Event` data types to `Input` and consequently log items like `BeginEvent` to `BeginInput`.
-  - In course of this, we also removed the `log-filter` executable as nobody is actively using it and we recommend using other off-the-shelf utilities to manipulate structured JSON logs (`jq` is already quite powerful).
+  - Renamed the `Event` data types to `Input` and consequently log items like `BeginEvent` to `BeginInput`.
+  - Changed structure of `LogicOutcome` entries.
+  - Added node-level log entry when an input was `DroppedFromQueue`.
+  - In course of this, the `log-filter` executable was removed as nobody is actively using it and other off-the-shelf utilities to manipulate structured JSON logs (`jq` is already quite powerful) are recommended.
   - Renamed prometheus metric `hydra_head_events -> hydra_head_inputs`.
 
+- Introduce `EventSource` and `EventSink` interfaces in `hydra-node`:
+  - These handles can now be used as "extension points" to make the `hydra-node` store and load its state differently or expose `StateEvent`s to other, external services.
+  - Internal refactoring of persistence mechanism as event source and sink in a backward-compatible way.
+  - More details can be found in [ADR21](https://hydra.family/head-protocol/adr/21/)
+
 ## [0.15.0] - 2024-01-18
 
 - Tested with `cardano-node 8.7.3` and `cardano-cli 8.17.0.0`.

docs/adr/2023-11-07_029-event-source-sink.md

@@ -3,11 +3,11 @@ slug: 29
 title: |
   29. EventSource & EventSink abstractions
 authors: [cardenaso11, quantumplation, ch1bo]
-tags: [Draft]
+tags: [Accepted]
 ---
 
 ## Status
-Draft
+Accepted
 
 ## Context
 
@@ -42,12 +42,12 @@ Draft
 ```hs
 data HydraNode tx m = HydraNode
   { -- ...
-  , eventSource :: EventSource (StateChanged tx) m
-  , eventSinks :: [EventSink (StateChanged tx) m]
+  , eventSource :: EventSource (StateEvent tx) m
+  , eventSinks :: [EventSink (StateEvent tx) m]
   }
 ```
 
-* The `hydra-node` will load events and __hydra_te its `HeadState` using `getEvents` of the single `eventSource`.
+* The `hydra-node` will load events and `hydrate` its `HeadState` using `getEvents` of the single `eventSource`.
 
 * The `stepHydraNode` main loop does call `putEvent` on all `eventSinks` in sequence. Any failure will make the `hydra-node` process terminate and require a restart.