Improve We can't get valid state history. logging

[MadLittleMods]

Improve We can't get valid state history. logging. Add event_id so you can actually correlate everything together in the logs.

Spawning from @jakobrss asking about what to look for when someone encounters this error

Dev notes

These logs originate from matrix-org/synapse#3904 where they used to have the room_id and event_id included directly but then was updated in matrix-org/synapse#9596 to rely on the log context holding this info.

Pull Request Checklist

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[MadLittleMods]

These log messages can be refactored to not use the _compute_event_context_with_maybe_missing_prevs prefix if there is a strong preference.

Being able to search for _compute_event_context_with_maybe_missing_prevs sounds nice to me.

[MadLittleMods]

Example logs:

SYNAPSE_TEST_LOG_LEVEL=DEBUG poetry run trial tests.handlers.test_federation_event.FederationEventHandlerTests.test_process_pulled_event_records_failed_backfill_attempts

_trial_temp/test.log

2026-05-08 07:18:38-0500 [-] synapse.handlers.federation_event - 1168 - INFO - test - _compute_event_context_with_maybe_missing_prevs(event_id=$C9yIQdfmuUAMM7Iziu5xft5kkFCRXdjPsBleizH0MBU): Event in room !tZrGbzfBcdXoJtzfLn:test is missing prev_events ['$fake_prev_event']: calculating state for a backwards extremity
2026-05-08 07:18:38-0500 [-] synapse.handlers.federation_event - 1191 - INFO - test - _compute_event_context_with_maybe_missing_prevs(event_id=$C9yIQdfmuUAMM7Iziu5xft5kkFCRXdjPsBleizH0MBU): Requesting state from other.example.com for missing prev_event $fake_prev_event
2026-05-08 07:18:38-0500 [-] synapse.handlers.federation_event - 1233 - WARNING - test - _compute_event_context_with_maybe_missing_prevs(event_id=$C9yIQdfmuUAMM7Iziu5xft5kkFCRXdjPsBleizH0MBU): Error attempting to resolve state from other.example.com for missing prev_events: Unable to get missing prev_event $fake_prev_event

[erikjohnston]

Seems like decent improvements

[MadLittleMods]

Thanks for the review @erikjohnston 🐩