Remember missing actor state keys instead of re-reading them

[CasperGN]

Based on the PR for fix/actor-refresh-default-tracker (#1237, which is itself based on #1227). Merge it after that. Until then this diff also shows the earlier commits; this PR's own commits are 02f0066 ("feat(actor): cache state that is not found in the default state tracker") and b491245 ("test(actor): run the nested reentrant test on Python 3.10").

Description

What was wrong. Reading an actor state key that does not exist went to the state store every time, because the state manager did not remember misses. Code that checks for a key and then creates it (contains_state then set_state, get_or_add_state, try_add_state) paid for an extra store read each time.

What changed. When try_get_state finds a key missing, it now stores a "not found" entry in the default state tracker (the one activation, reminders and timers use). Later calls use it with no store read:

• try_get_state, get_state, contains_state report the key as absent (get_state raises KeyError).
• try_remove_state / remove_state have nothing to remove (return False / raise KeyError).
• try_add_state, set_state, set_state_ttl, get_or_add_state, add_or_update_state turn the entry into an add, keeping the ttl. add_or_update_state does not call its update function.
• get_state_names leaves the key out, is_state_marked_for_remove returns False, and save_state never sends the entry.

After a reentrant save, the default-tracker refresh from #1237 treats a "not found" entry like a clean one: a reentrant write replaces it with the saved value, and a reentrant remove drops it. Without this, a reminder that saw a key as missing would keep seeing it as missing after a reentrant call created it.

Design choices.

• No new member on the public StateChangeKind enum (the .NET SDK added NotFound). A new member would break user code that matches on every value, and the change-kind-to-operation map in _state_provider.py would raise KeyError if it ever reached a save. The entry is a private StateMetadata subclass that reports the existing none change kind, so any code that does not know about it treats it as clean and never saves it. Public types, ActorStateChange and subclasses of ActorStateManager are unchanged.
• Misses are cached only in the default tracker, not in the per-call trackers used under reentrancy. Only the default tracker is refreshed after a reentrant save. If an outer reentrant call cached a miss and a nested reentrant call on the same actor (A -> B -> A) then created the key, the outer call would still see it as missing, and get_or_add_state / try_add_state would overwrite the nested call's value. A test covers this case. As far as I can tell, dotnet-sdk#1913 caches misses in the per-call tracker too and may have the same gap.

Behaviour change. Missing keys read through the default tracker now stay cached until the actor deactivates or clear_cache() is called. An actor that reads many distinct missing keys (for example names built from input) keeps one small entry per key for its lifetime. The .NET SDK behaves the same way.

This ports dapr/dotnet-sdk#1913 and its follow-up fix dapr/dotnet-sdk#1916. Thanks to @olitomlinson for pointing out the .NET changes on #1227.

Issue reference

Related to dapr/dapr#10532 (reminders miss state saved by reentrant calls) and #1227.

Checklist

• Code compiles correctly
• Created/updated tests
• Extended the documentation (no public API change)

Ran: pytest tests/actor (205 passed, 10 new), ruff check, ruff format --check, mypy (all clean).

🤖 Generated with Claude Code

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 84.01%. Comparing base (fb229bc) to head (b491245).

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #1238      +/-   ##
==========================================
+ Coverage   83.89%   84.01%   +0.11%     
==========================================
  Files         123      123              
  Lines       10265    10301      +36     
==========================================
+ Hits         8612     8654      +42     
+ Misses       1653     1647       -6     

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