25-2: DataShard: don't leave processed checkpoints in the buffer

[snaury]

Changelog entry

Don't leave processed checkpoints in the buffer. Fixes #24779.

Changelog category

• Bugfix

Description for reviewers

[github-actions]

🟢 2025-09-12 14:50:14 UTC The validation of the Pull Request description is successful.

[github-actions]

⚪ 2025-09-12 14:51:13 UTC Pre-commit check linux-x86_64-relwithdebinfo for 7bd6915 has started.
⚪ 2025-09-12 14:51:26 UTC Artifacts will be uploaded here
⚪ 2025-09-12 14:54:23 UTC ya make is running...
🟡 2025-09-12 15:42:56 UTC Some tests failed, follow the links below. Going to retry failed tests...

Test history | Ya make output | Test bloat

TESTS	PASSED	ERRORS	FAILED	SKIPPED	MUTED?
26974	25693	0	6	1227	48

⚪ 2025-09-12 15:45:19 UTC ya make is running... (failed tests rerun, try 2)
🟢 2025-09-12 15:58:23 UTC Tests successful.

Test history | Ya make output | Test bloat | Test bloat

TESTS	PASSED	ERRORS	FAILED	SKIPPED	MUTED?
103 (only retried tests)	58	0	0	4	41

🟢 2025-09-12 15:58:30 UTC Build successful.
🟢 2025-09-12 15:58:49 UTC ydbd size 2.2 GiB changed* by +48 Bytes, which is < 100.0 KiB vs stable-25-2: OK

ydbd size dash	stable-25-2: 1c9de78	merge: 7bd6915	diff	diff %
ydbd size	2 324 850 336 Bytes	2 324 850 384 Bytes	+48 Bytes	+0.000%
ydbd stripped size	487 260 648 Bytes	487 260 712 Bytes	+64 Bytes	+0.000%

^{*please be aware that the difference is based on comparing your commit and the last completed build from the post-commit, check comparation}

[github-actions]

⚪ 2025-09-12 14:51:27 UTC Pre-commit check linux-x86_64-release-asan for 7bd6915 has started.
⚪ 2025-09-12 14:51:40 UTC Artifacts will be uploaded here
⚪ 2025-09-12 14:54:49 UTC ya make is running...
🟡 2025-09-12 16:06:21 UTC Some tests failed, follow the links below. This fail is not in blocking policy yet Going to retry failed tests...

Test history | Ya make output | Test bloat

TESTS	PASSED	ERRORS	FAILED	SKIPPED	MUTED?
12791	12581	0	45	125	40

⚪ 2025-09-12 16:07:35 UTC ya make is running... (failed tests rerun, try 2)
🟡 2025-09-12 16:32:56 UTC Some tests failed, follow the links below. This fail is not in blocking policy yet Going to retry failed tests...

Test history | Ya make output | Test bloat | Test bloat

TESTS	PASSED	ERRORS	FAILED	SKIPPED	MUTED?
264 (only retried tests)	203	0	5	23	33

⚪ 2025-09-12 16:33:06 UTC ya make is running... (failed tests rerun, try 3)
🟡 2025-09-12 16:46:13 UTC Some tests failed, follow the links below. This fail is not in blocking policy yet

Test history | Ya make output | Test bloat | Test bloat | Test bloat

TESTS	PASSED	ERRORS	FAILED	SKIPPED	MUTED?
90 (only retried tests)	33	0	4	22	31

🟢 2025-09-12 16:46:21 UTC Build successful.
🟢 2025-09-12 16:46:46 UTC ydbd size 3.8 GiB changed* by +752 Bytes, which is < 100.0 KiB vs stable-25-2: OK

ydbd size dash	stable-25-2: 1c9de78	merge: 7bd6915	diff	diff %
ydbd size	4 045 787 600 Bytes	4 045 788 352 Bytes	+752 Bytes	+0.000%
ydbd stripped size	1 408 532 120 Bytes	1 408 532 248 Bytes	+128 Bytes	+0.000%

^{*please be aware that the difference is based on comparing your commit and the last completed build from the post-commit, check comparation}