[bug][runtime] Derive durable-state action UUID from the plan-unique action name

[purushah]

Linked issue: N/A (bug found during recovery testing)

Purpose of change

ActionStateUtil.generateUUIDForAction derives the durable-state key from Action.hashCode(). Action's hash folds in JavaFunction's Class[] parameterTypes, and Class.hashCode() is the per-JVM identity hash — so every durable-state key silently changes when the JVM restarts. After any failure recovery, lookups can never hit: every action re-executes instead of replaying, which breaks the exactly-once contract of the action-state store (and re-bills every LLM call in agent workloads).

This PR derives the UUID from action.getName(), which is unique within a plan and stable across processes.

How it was found

Kill/restore recovery experiments with a deliberately non-deterministic agent and the Kafka action-state store: 0/134 re-processed actions replayed from the store before this fix; 90/90 replayed with 0% divergence after. The existing test suite doesn't catch it because all tests run inside a single JVM, where identity hashes are stable.

Compatibility note

The key format changes, so state written by prior versions won't be found on restore. Those keys were already unreadable across restarts (that's the bug), so no working deployment regresses; single-process re-reads within one JVM lifetime are unaffected in practice because recovery is the only reader.

Tests

• Two new regression tests in ActionStateUtilTest: (1) the action-UUID key segment equals UUID.nameUUIDFromBytes(action.getName()) — pins the derivation, so any future key-format change is a conscious, reviewed break of cross-restart state compatibility (verified to FAIL against the pre-fix code); (2) two separately constructed Action instances with the same name — what "the same action, after a JVM restart" looks like — produce identical state keys.
• mvn test -pl runtime -am -Dtest='*ActionState*' — 129 tests, 0 failures (includes ActionStateUtilTest, KafkaActionStateStoreTest, Fluss store integration tests), on current main (rebased over [Bug] Recovered Durable ActionState for keys owned by other subtasks is never pruned #1024).
• Cross-JVM behavior additionally validated by the kill/restore experiment above.

API

No public API changes.

Documentation

• doc-needed
• doc-not-needed
• doc-included

Was this patch authored or co-authored using generative AI tooling?

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