chore(unit tests): failing disk_v2 bug demonstrations

[blt]

Summary

Seven vector-buffers tests that assert the correct invariant and therefore
fail against current Vector, each reproducing a real disk buffer v2 data-loss
or accounting defect. The failures are the demonstration — CI on this PR is
expected to be red on these tests until the underlying bugs are fixed.

Test	Bug
drop_newest_drops_should_increment_component_discarded_metric_issue_24606	#24606 — drops never hit component_discarded_events_total
ledger_total_buffer_size_decrement_should_saturate_not_underflow_issue_21683	#21683 — unsaturated decrement wraps → writer deadlock
get_total_records_should_be_zero_on_drained_buffer_issue_21683_metrics	get_total_records 0-1 underflow on a drained buffer
writer_drop_without_flush_should_not_lose_buffered_events_issue_24948	#24948 — writer Drop without flush loses buffered events
rejected_delivery_should_not_advance_acks_finalizer_status_discard	finalizer discards BatchStatus; a rejected delivery still advances acks
file_id_rollover_compare_should_be_wrap_aware_reader_932	reader.rs:932 file-id comparison not wrap-aware
delete_completed_data_file_size_delta_should_saturate_reader_524	reader.rs:524 metadata.len() - bytes_read underflow

Stack (Antithesis-driven disk buffer v2 data-loss investigation):

• docs(buffers): disk_v2 data-loss research scratchbook #25524 — research scratchbook (docs)
• chore(unit tests): failing disk_v2 bug demonstrations #25525 — failing bug-demonstration tests
• feat(buffers): SUT-side antithesis underflow assertions #25526 — SUT-side assertions
• chore(tests): disk_v2 antithesis test harness + exercisers #25527 — test harness + exercisers

How did you test this PR?

cargo nextest run -p vector-buffers → exactly these 7 fail (78 pass), each for the
documented reason. Independent of the rest of the stack (no Antithesis deps needed).

Change Type

• Bug fix
• New feature
• Dependencies
• Non-functional (chore, refactoring, docs) — tests only
• Performance

Is this a breaking change?

• Yes
• No

Does this PR include user facing changes?

• Yes.
• No. A maintainer will apply the no-changelog label to this PR.

References

• Related: buffer_byte_size has value 18446744073709548000 #21683, vector_component_discarded_events_total metric not showing/incrementing for gcp_pubsub sink when disk buffer is full (drop_newest) #24606, Sinks configured with disk buffers cause partial stall of pipeline on config reload #24948

[blt]

Warning

This pull request is not mergeable via GitHub because a downstack PR is open. Once all requirements are satisfied, merge this PR as a stack on Graphite.
Learn more

• chore(tests): disk_v2 antithesis test harness + exercisers #25527
• feat(buffers): SUT-side antithesis underflow assertions #25526
• chore(unit tests): failing disk_v2 bug demonstrations #25525 👈 (View in Graphite)
• docs(buffers): disk_v2 data-loss research scratchbook #25524
• master

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[datadog-vectordotdev]

✨ Fix all issues with Cursor

⚠️ Warnings

🧪 7 Tests failed

buffer_usage_data::tests::drop_newest_drops_should_increment_component_discarded_metric_issue_24606 from vector-buffers     (Fix with Cursor)

Test has failed

variants::disk_v2::tests::acknowledgements::rejected_delivery_should_not_advance_acks_finalizer_status_discard from vector-buffers     (Fix with Cursor)

Test has failed

variants::disk_v2::tests::invariants::delete_completed_data_file_size_delta_should_saturate_reader_524 from vector-buffers     (Fix with Cursor)

Test has failed

View all

ℹ️ Info

No other issues found (see more)

❄️ No new flaky tests detected

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