Wait for a deadline instead of polling for one

The timer thread promoted due work on a fixed one-second tick, so every
delayed item was 0-1000ms late whatever the load — measured on the house
at 705ms mean on a rollershutter stop, which is 2-4% of a 26-second
travel and accumulates in the position the motor node believes it is at.
It now sleeps to the soonest deadline and is woken when a nearer one is
scheduled, which measures 0.9ms end to end through Redis.

A promoted timer also went to the back of the queue. It goes into a due
lane of its own that `claim` reads first, so work that has waited out a
deadline is not held up by work that is merely queued.

Beside it, in the same code: seeding a message now bumps its version, so
a re-put flow's synchronous nodes no longer wait forever on a value that
is sitting in state; the consumer group drops the consumers of engines
that are gone (138 had accumulated on this installation); and the cast
that closes the long-standing `xclaim` mypy error.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>

backend/fluksio/flow/pipeline.py

@@ -395,13 +395,24 @@ class Pipeline:
         self.replace_flow(flow, [])
 
     def _seed(self, initial_values: dict[str, Any] | None) -> None:
-        """Give messages a starting value, without overwriting one already there."""
+        """Give messages a starting value, without overwriting one already there.
+
+        A seeded value counts as having arrived. Writing it without its version
+        left the value in state at version 0, which `_check_synchronous_ready`
+        reads as "never published" — so a flow that was dropped and recreated
+        came back with its synchronous nodes waiting on inputs that were sitting
+        right there, reporting `active` and `ok` and never running again.
+        """
         if not initial_values:
             return
+        seeded = []
         with self._state.lock():
             for name, value in initial_values.items():
                 if name not in self._state:
                     self._state[name] = value
+                    seeded.append(name)
+        if seeded:
+            self._state.increment_multi([self._version_key(name) for name in seeded])
 
     def get_node_by_id(self, nid: str) -> Node | None:
         return next((n for n in self._nodes if n.id == nid), None)