fix(data-imports): retry delta vacuum on commit conflict

[Gilbert09]

Problem

An error tracking issue surfaced a CommitFailedError during delta maintenance, on the _vacuum frame in maintenance.py:

Failed to commit transaction: Commit failed: a concurrent transaction deleted data this operation read.
Help: This transaction's query must be rerun to exclude the removed data.

The call path: run_scheduled -> run_maintenance -> compact_if_fragmented -> _vacuum -> delta-rs's table.vacuum().

vacuum() commits a REMOVE of tombstoned files, so it's subject to delta-rs's conflict checker exactly like merge and optimize.compact — delta-rs doesn't retry this itself (see the comment on DELTA_MERGE_CONFLICT_RETRIES), because resolving it safely means re-reading the table and re-running the operation. _compact already routes through execute_with_conflict_retry for this reason, but _vacuum called table.vacuum() directly, so a concurrent maintenance pass touching the same table (e.g. a second Temporal activity attempt still finishing a compact after the first attempt's heartbeat timed out) made the CommitFailedError propagate straight out instead of retrying with a refreshed table.

This is best-effort maintenance code — the exception was already caught by run_scheduled's try/except and never re-raised, so no sync was ever at risk. This only affects whether a self-healing race gets reported as a defect.

Changes

• Route _vacuum's table.vacuum() call through execute_with_conflict_retry, matching _compact.
• Generalize execute_with_conflict_retry's return type (it was typed dict, matching optimize.compact()'s stats, but vacuum() returns a list of removed file paths).

How did you test this code?

• Added TestVacuum.test_retries_on_commit_conflict_then_succeeds in test_maintenance.py, mirroring the existing compact regression test — asserts _vacuum retries once with a refreshed table on CommitFailedError instead of raising immediately.
• Ran the full delta/test/ suite (51 tests) and mypy --cache-fine-grained repo-wide — both clean.

Docs update

N/A — internal maintenance-code fix, no user-facing or API surface change.

🤖 Agent context

Autonomy: Fully autonomous

Triaged from a live PostHog error-tracking issue (webhook-delivered) using Claude Code. Pulled the stack trace and warehouse_sources_* event properties via the PostHog MCP tools to confirm the failing frame and reproduction context (an Intercom incremental sync), then traced the call path into delta/maintenance.py and compared _vacuum against _compact's existing conflict-retry handling.

Searched open PRs (by exception type, message phrase, module path, and the maintainer's own open PRs) before starting. Found related-but-distinct open/merged work on the same maintenance code (#75240, #73454, #74541, #74594) — all address different DeltaError signatures or a different re-fetch bug, none add commit-conflict retry to vacuum.

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[github-actions]

Hey @Gilbert09! 👋

It looks like your git author email on this PR isn't your @posthog.com address (owerstom@gmail.com). Since you're on the PostHog team, it's worth pointing your local git author email at your @posthog.com address. Why it matters:

• Consistent work identity in git history — internal tooling that attributes commits to team members keys off your @posthog.com address.
• Keeps team contributions easy to tell apart from external community ones when scanning history.

You can fix it for this repo with:

git config user.email "you@posthog.com"

Or set it globally with git config --global user.email "you@posthog.com". No need to redo this PR — just a nudge for next time. 🙂

[github-actions]

🤖 CI report

✅ Backend coverage — all changed backend lines covered

🧪 Backend test coverage

Patch coverage — changed backend lines (products + core): ████████████████████ 100.0% (11 / 11)

All changed backend lines are covered ✅

Per-product line coverage (touched products)

Product	Coverage	Lines
demo	███████████░░░░░░░░░ 56.3%	1,497 / 2,661
tasks	██████████████░░░░░░ 70.3%	33,203 / 47,255
signals	████████████████░░░░ 81.4%	25,289 / 31,055
cdp	████████████████░░░░ 82.1%	3,285 / 3,999
data_modeling	█████████████████░░░ 85.7%	7,716 / 9,008
notebooks	█████████████████░░░ 86.0%	7,794 / 9,060
actions	█████████████████░░░ 86.6%	717 / 828
cohorts	█████████████████░░░ 87.5%	6,393 / 7,309
exports	██████████████████░░ 87.9%	7,078 / 8,054
product_tours	██████████████████░░ 87.9%	1,303 / 1,482
data_warehouse	██████████████████░░ 88.4%	12,264 / 13,870
engineering_analytics	██████████████████░░ 89.3%	6,529 / 7,309
conversations	██████████████████░░ 89.5%	17,667 / 19,746
dashboards	██████████████████░░ 89.5%	5,989 / 6,693
alerts	██████████████████░░ 90.3%	4,482 / 4,966
streamlit_apps	██████████████████░░ 90.7%	2,630 / 2,901
mcp_analytics	██████████████████░░ 90.9%	3,191 / 3,511
error_tracking	██████████████████░░ 91.0%	10,928 / 12,010
slack_app	██████████████████░░ 91.1%	9,664 / 10,610
marketing_analytics	██████████████████░░ 91.2%	12,092 / 13,265
stamphog	██████████████████░░ 91.3%	4,505 / 4,936
product_analytics	███████████████████░ 92.5%	5,849 / 6,321
early_access_features	███████████████████░ 92.6%	1,287 / 1,390
ai_observability	███████████████████░ 92.8%	15,618 / 16,821
surveys	███████████████████░ 93.2%	5,853 / 6,281
posthog_ai	███████████████████░ 93.2%	1,326 / 1,422
approvals	███████████████████░ 93.3%	3,437 / 3,682
web_analytics	███████████████████░ 93.4%	15,047 / 16,112
reminders	███████████████████░ 93.4%	468 / 501
workflows	███████████████████░ 94.1%	7,251 / 7,707
endpoints	███████████████████░ 94.2%	8,655 / 9,192
review_hog	███████████████████░ 94.6%	8,101 / 8,563
skills	███████████████████░ 94.6%	3,158 / 3,337
logs	███████████████████░ 95.4%	10,487 / 10,987
experiments	███████████████████░ 95.5%	26,047 / 27,287
annotations	███████████████████░ 96.2%	732 / 761
revenue_analytics	███████████████████░ 96.3%	1,887 / 1,960
feature_flags	███████████████████░ 96.4%	17,488 / 18,144
replay_vision	███████████████████░ 96.4%	16,286 / 16,891
user_interviews	███████████████████░ 96.5%	2,638 / 2,734
customer_analytics	███████████████████░ 97.1%	10,463 / 10,777
warehouse_sources	███████████████████░ 97.3%	359,901 / 369,906
data_catalog	████████████████████ 97.7%	2,588 / 2,648
pulse	████████████████████ 98.4%	2,017 / 2,049

Report-only. Patch coverage = changed backend lines covered vs origin/master. Sorted lowest first.
Known gaps: lines covered only by Temporal tests show as uncovered; core line numbers may drift if master changed the same file.

[stamphog]

Contained internal retry-logic fix for delta-lake vacuum maintenance, author is on the owning team, change is well-tested and generalizes an existing helper already used for compact — no risky territory touched.

• 👍 on the PR from hex-security-app[bot].

Gate mechanics and policy version

Gate		Result
prerequisites	✓	all clear
deny-list	✓	no deny categories matched
size	✓	25L, 2F substantive, 48L/3F incl. docs/generated/snapshots — within ceiling
tier	✓	T1-agent / T1b-small (48L, 3F, single-area, fix)
stamphog 2.0.0b4		.stamphog/policy.yml @ 34c5044 · reviewed head ccc808c