diff --git a/api/src/opentrons/protocol_engine/protocol_engine.py b/api/src/opentrons/protocol_engine/protocol_engine.py
index 7b2f8e76678..7c8db74ed06 100644
--- a/api/src/opentrons/protocol_engine/protocol_engine.py
+++ b/api/src/opentrons/protocol_engine/protocol_engine.py
@@ -242,6 +242,27 @@ def estop(self, maintenance_run: bool) -> None:
             return
         current_id = (
             # todo
+            #
+            ## Notes
+            # Reading:
+            # - Get single command by ID
+            # - Get all commands, ordered
+            # - Get slice of commands by integer index, potentially starting from "currently running or most recently executed" (but see confusing docs)
+            # - Get "current" (currently running, or most recently completed) command (but see confusing docs)
+            #   - May need to change for fixup commands
+            # - Get "next to execute" (first queued setup command or first queued protocol command)
+            #   - Will need to change for fixup commands
+            # == / !=, mostly for tests
+            # Writing:
+            # - Enqueue a new command
+            # - Update command for its new state
+            # Steps for this PR:
+            # 1. Naively move everything into this file
+            # ?. Resolve get_current()/get_slice() discrepancy
+            # ?. Add .tail to OrderedSet to support existing JSONv6 performance bug
+            # ?. General state deduplication and cleanup.
+            # "Most recently executed" unfortunately does not mean "most recent to have internally entered a completed state," because of mid-JSON-run failures.
+            # Resolve todo about separate actions for separate state transitions, instead of a single UpdateCommandAction
             self._state_store.commands.state.running_command_id
             or self._state_store.commands.state.queued_command_ids.head(None)
         )