feat(warehouse): structured deltalite write stats + duration

[Gilbert09]

Problem

delta-rs's merge().execute() returned a rich stats dict that we logged as structured, parseable output (Delta Merge Stats: {json.dumps(...)}). The deltalite write path (#75884) instead logged a formatted string (deltalite write: committed v5 (+3 inserted / ~2 updated / …)) — human-readable but not parseable, and with no timing. deltalite's UpsertStats actually carries as much detail as delta-rs (and more: files_carried_over, files_probed, null_pk_rows) — we were just throwing the structure away.

Changes

• The commit log is now structured: ainfo("deltalite write: committed", duration_ms=…, version=…, rows_inserted=…, …) — every UpsertStats field becomes its own log key, so it's parseable again (parity with the old Delta Merge Stats line). The deltalite write: committed prefix is unchanged, so existing LogQL still matches.
• Total timing: the upsert is wall-clock timed and emitted as duration_ms on the log and a new warehouse_load_deltalite_write_duration_seconds histogram. (The log field is the cross-worker signal — the v2 worker's Prometheus isn't scraped.)
• _deltalite_write_stats enumerates the pyo3 getters rather than a fixed list, so fields added crate-side later flow through automatically — which is exactly what the follow-up deltalite PR (per-phase timings in UpsertStats) will add.

How did you test this code?

I'm an agent. TestDeltaliteWritePath — 7 pass — now also asserts the commit is logged with the UpsertStats fields as structured keys + a duration_ms, plus a unit test for _deltalite_write_stats (scalar getters only, methods/privates dropped). ruff clean.

Follow-up

A deltalite crate PR adds per-phase timers (probe / write / commit) to UpsertStats for full delta-rs-style timing breakdown; those fields will appear in this log automatically once the wheel is bumped.

[trunk-io]

😎 This pull request was merged.

[github-actions]

🤖 CI report

⚠️ Backend coverage — 93.0% of changed backend lines covered — 2 uncovered

🧪 Backend test coverage

Patch coverage — changed backend lines (products + core): ███████████████████░ 93.0% (29 / 31)

File	Patch	Uncovered changed lines
products/warehouse_sources/backend/temporal/data_imports/pipelines/core/delta_table_helper.py	87.5%	321–322

🤖 Agents: add a test covering the lines above, or note why under "How did you test this code?". Machine-readable gap list: the patch-coverage artifact on this run (gh run download 30633053487 -n patch-coverage), or the coverage-data block at the end of this comment.

Per-product line coverage (touched products)

Product	Coverage	Lines
demo	███████████░░░░░░░░░ 56.3%	1,497 / 2,661
tasks	██████████████░░░░░░ 70.1%	32,867 / 46,884
signals	████████████████░░░░ 81.3%	24,949 / 30,693
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	██████████████████░░ 87.8%	6,181 / 7,040
product_tours	██████████████████░░ 87.9%	1,303 / 1,482
exports	██████████████████░░ 88.2%	7,046 / 7,986
data_warehouse	██████████████████░░ 88.4%	12,192 / 13,798
engineering_analytics	██████████████████░░ 89.3%	6,529 / 7,309
conversations	██████████████████░░ 89.3%	17,600 / 19,701
dashboards	██████████████████░░ 89.5%	5,989 / 6,693
alerts	██████████████████░░ 90.2%	4,458 / 4,942
streamlit_apps	██████████████████░░ 90.7%	2,630 / 2,901
mcp_analytics	██████████████████░░ 90.9%	3,191 / 3,511
error_tracking	██████████████████░░ 91.0%	10,926 / 12,008
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	███████████████████░ 93.1%	5,771 / 6,197
posthog_ai	███████████████████░ 93.2%	1,326 / 1,422
web_analytics	███████████████████░ 93.3%	14,911 / 15,976
approvals	███████████████████░ 93.3%	3,437 / 3,682
reminders	███████████████████░ 93.4%	468 / 501
workflows	███████████████████░ 94.1%	7,241 / 7,698
endpoints	███████████████████░ 94.2%	8,655 / 9,192
review_hog	███████████████████░ 94.6%	8,101 / 8,563
skills	███████████████████░ 94.6%	3,158 / 3,337
experiments	███████████████████░ 95.5%	26,047 / 27,287
logs	███████████████████░ 95.5%	10,447 / 10,944
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%	16,081 / 16,679
user_interviews	███████████████████░ 96.5%	2,638 / 2,734
customer_analytics	███████████████████░ 97.1%	10,444 / 10,758
warehouse_sources	███████████████████░ 97.3%	359,337 / 369,337
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.

[deployment-status-posthog]

Deploy status

Environment	Status	Deployed At	Workflow
dev	✅ Deployed	2026-07-31 14:14 UTC	Run
prod-us	✅ Deployed	2026-07-31 14:30 UTC	Run
prod-eu	✅ Deployed	2026-07-31 14:29 UTC	Run