Fix "MapStates replays stale sub-state on repeated invocations when parent has a cascading state_initializer"

[hippalectryon-0]

Fixes #761

Changes

Added sequence ID in the tasks keys

How I tested this

Tested against the MWE of the issue

Checklist

• PR has an informative and human-readable title (this will be pulled into the release notes)
• Changes are limited to a single goal (no scope creep)
• Code passed the pre-commit check & code is left cleaner/nicer than when first encountered.
• Any change in functionality is tested
• New functions are documented (with a description, list of inputs, and expected output)
• Placeholder code is flagged / future TODOs are captured in comments
• Project documentation has been updated if adding/changing functionality.

[skrawcz]

Good catch and clean fix! The root cause analysis in #761 is thorough and the fix is correct — including sequence_id in the sub-app key ensures repeated invocations with initialize_from get distinct sub-application IDs.

Backwards compatibility is fine here: if old persisted sub-app state exists, initialize_from simply falls back to default_state and the sub-apps run fresh, which is correct.

One ask before merge: please add a regression test in tests/core/test_parallelism.py. The MWE in #761 is a great template — something like:

• Create a MapStates action with cascade persistence (initialize_from on the parent)
• Run the parent app through the MapStates action twice (two steps)
• Assert the second invocation produces fresh results, not a replay of the first

Without an automated test, a future refactor could easily reintroduce this.

[hippalectryon-0]

I checked that the test passes with this PR and fails with the main branch.

[github-actions]

This PR has been inactive for 18 days after receiving review feedback.
Converting to draft.

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