Fix disk state manager debounced writes

[harsh21234i]

Fixes #6806

Summary

Fixes a disk state manager bug where debounced set_state() calls for non-BaseState tokens could return stale in-
memory values and flush the wrong value to disk.

Problem

When StateManagerDisk used _write_debounce_seconds > 0, set_state() only queued the first value for a token. A
later set_state() before the debounce flush did not update the queued item, so close() or the background flush
could persist stale data.

Also, non-BaseState values were not updated in the in-memory cache while the write was pending, so get_state()
could return the default/old value before the disk flush completed.

Changes

• Update the in-memory cache immediately for non-BaseState tokens.
• Replace existing queued write payloads with the latest value.
• Preserve the original queue timestamp so repeated updates do not indefinitely delay the flush.
• Add regression tests for pending read-after-write behavior and latest-value flushing.

Testing

• uv run pytest tests/units/test_state.py::test_state_manager_disk_debounced_set_state_updates_non_base_state_cache tests/units/test_state.py::test_state_manager_disk_debounced_set_state_flushes_latest_non_base_state -q
• uv run pytest tests/units/test_state.py -k "deserialize_gc_state_disk or state_manager_disk_close_resets_write_queue_task or state_manager_disk_debounced_set_state" -q
• uv run ruff check reflex/istate/manager/disk.py tests/units/test_state.py
• uv run ruff format --check reflex/istate/manager/disk.py tests/units/test_state.py
• uv run pyright reflex/istate/manager/disk.py tests/units/test_state.py

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[codspeed-hq]

Merging this PR will not alter performance

✅ 26 untouched benchmarks
⏩ 8 skipped benchmarks¹

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_{Comparing harsh21234i:fix/disk-state-manager-debounced-writes (5094278) with main (9854a3a)}

Footnotes

1. 8 benchmarks were skipped, so the baseline results were used instead. If they were deleted from the codebase, click here and archive them to remove them from the performance reports. ↩

[greptile-apps]

Greptile Summary

This PR fixes cache coherence and queued writes in the disk state manager. The main changes are:

• Updates pending non-BaseState values in memory.
• Replaces queued payloads with the latest value.
• Preserves the original debounce timestamp.
• Keeps the previous cache value when an immediate write fails.
• Adds tests for pending reads, flushing, and write failures.

Confidence Score: 5/5

No additional blocking issue was found in this follow-up.

• The immediate failure path now updates the cache only after persistence succeeds.
• The new tests cover the intended successful write behavior and immediate write failure.

Important Files Changed

Filename	Overview
reflex/istate/manager/disk.py	Updates cache ordering and queued payload replacement for immediate and debounced disk writes.
tests/units/test_state.py	Adds tests for pending cache reads, latest-value flushing, and immediate write failures.
news/6807.bugfix.md	Documents the disk state manager bug fix.

_{Reviews (3): Last reviewed commit: "Add changelog fragment for disk state fi..." | Re-trigger Greptile}