fix(etl): guard daily_diffs schema on Postgres

[stranske]

Summary

• fail fast in daily_diff_flow when daily_diffs is missing on Postgres, instead of executing SQLite-only assumptions later in the flow
• keep SQLite behavior unchanged (create table on demand for local/test use)
• add regression assertions that Postgres path does not emit SQLite DDL

Testing

• pytest -q tests/test_daily_diff.py

[agents-workflows-bot]

⚠️ Action Required: Unable to determine source issue for PR #737. The PR title, branch name, or body must contain the issue number (e.g. #123, branch: issue-123, or the hidden marker ).

[stranske-keepalive]

🤖 Keepalive Loop Status

PR #737 | Agent: Codex | Iteration 0/5

Current State

Metric	Value
Iteration progress	[----------] 0/5
Action	wait (missing-agent-label)
Disposition	skipped (transient)
Gate	success
Tasks	0/4 complete
Timeout	45 min (default)
Timeout usage	2m elapsed (5%, 43m remaining)
Keepalive	❌ disabled
Autofix	❌ disabled

🔍 Failure Classification

| Error type | infrastructure |
| Error category | resource |
| Suggested recovery | Confirm the referenced resource exists (repo, PR, branch, workflow, or file). |

[stranske-keepalive]

Keepalive Work Log (click to expand)

#	Time (UTC)	Agent	Action	Result	Files	Tasks	Progress	Commit	Gate
0	2026-03-02 03:49:22	Codex	wait (missing-agent-label-transient)	skipped	—	0	0/4	—	success
0	2026-03-02 04:18:13	Codex	wait (missing-agent-label-transient)	skipped	—	0	0/4	—	success
0	2026-03-02 04:31:44	Codex	wait (missing-agent-label-transient)	skipped	—	0	0/4	—	success
0	2026-03-02 04:34:13	Codex	wait (missing-agent-label-transient)	skipped	—	0	0/4	—	success

[Copilot]

Pull request overview

Updates the daily diff ETL flow to avoid running SQLite-only DDL against Postgres by validating the daily_diffs table early, while preserving the existing “create on demand” behavior for SQLite dev/test runs.

Changes:

• Updated _ensure_daily_diffs_table() to create daily_diffs only for SQLite and to fail fast on non-SQLite connections.
• Added regression assertions to ensure the Postgres path does not emit SQLite-specific DDL (e.g., AUTOINCREMENT, CREATE TABLE IF NOT EXISTS).

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated 1 comment.

File	Description
etl/daily_diff_flow.py	Adds Postgres-side existence check for daily_diffs and keeps SQLite table creation behavior.
tests/test_daily_diff.py	Strengthens the Postgres-flow test to assert the new guard query runs and SQLite DDL is not emitted.