[Refactor] Extract shared delivery upsert - #6056

Summary

write_delivery, write_subscription_delivery_if_live (both in api/oss/src/dbs/postgres/triggers/dao.py), and SessionStreamsDAO.claim_trigger_delivery (api/oss/src/dbs/postgres/sessions/streams/dao.py) each independently rebuild the same column-values dict, index_elements, and index_where for the delivery upsert. The conflict target and the skipped-column rules can drift between the three copies without any test catching it.

Changes

Added a new helper module: api/oss/src/dbs/postgres/triggers/upsert_utils.py that centralizes building the trigger-delivery values dict and the index_elements / index_where conflict target. Replaced the duplicated logic in TriggersDAO.write_delivery, TriggersDAO.write_subscription_delivery_if_live, and SessionStreamsDAO.claim_trigger_delivery so they call the helper. No behavior changes were made.

Testing

Verified locally

To ensure testing efficiency, I first ran uv run --no-sync python run-tests.py oss/tests/pytest/integration/sessions/test_trigger_session_claim_postgres.py to verify the tests were running correctly before adding my refactoring changes, and then re-verified those same tests after making my changes. See screenshots below:

Test Results BEFORE changes

Test results logs

Generated test report

Test Results AFTER changes

Generated test report

Added or updated tests

N/A

Validation

api % ruff format oss/src/dbs/postgres/triggers/dao.py oss/src/dbs/postgres/triggers/upsert_utils.py oss/src/dbs/postgres/sessions/streams/dao.py
1 file reformatted, 2 files left unchanged

Note on linting: ruff check --fix run at the repo root currently reformats ~1,000+ files unrelated to this change (project-wide Optional/List → X | None/list[...] modernization, import reordering, and removal of the # spacer-comment convention used throughout dao.py files). I did not apply those unrelated changes to keep this diff scoped to the #5934 refactor. Ran ruff format/ruff check --fix only against the new upsert_utils.py; the two edited DAO files were hand-verified against the existing house style instead.

QA follow-up

N/A

Demo

N/A, not a UI change (only refactoring)

Checklist

• I have included a video or screen recording for UI changes, or marked Demo as N/A
• Relevant tests pass locally
• Relevant linting and formatting pass locally
• I have signed the CLA, or I will sign it when the bot prompts me

Contributor Resources

• Contributing guide
• Creating your first PR
• Development mode
• Testing
• Formatting and linting
• Slack support

Issue

Closes #5934