Add EIA SEDS ingestion support

.claude/MONDAY_CHECKLIST.md

@@ -115,3 +115,42 @@ Update [`output/facility_fuel_pending_narrative.txt`](../output/facility_fuel_pe
 once facility-fuel is actually ingested. Replace the "Pending" framing with
 the real row count, period range, and any column-mapping notes from Step 3.
 Mirror the format of `operating_generator_capacity_sample.txt`.
+
+## New endpoint added — SEDS (State Energy Data System)
+
+Wired up 2026-05-17. Endpoint: `seds` (annual frequency,
+`https://api.eia.gov/v2/seds/data/`). Probed live, columns verified, smoke
+test of 50 rows landed in `public.energy_eia_seds_flat` with all typed
+columns populated.
+
+**Verified JSON keys** (no sector field — sector is encoded in `seriesId`):
+`period` (YYYY), `seriesId`, `seriesDescription`, `stateId`,
+`stateDescription`, `value`, `unit`.
+
+**Total volume:** ~2.57M rows across 65 years (1960–2024), ~40k rows/year.
+Ingested year-by-year via the generalized `fetch_eia_pages_by_period` to
+stay under EIA's 503 threshold (same pattern as the monthly endpoints).
+
+**What to verify Monday:**
+
+```sql
+-- Expected: ~2.5M+ rows, 1960 → 2024
+select count(*), min(year), max(year)
+from public.energy_eia_seds_flat;
+
+-- Spot-check that typed columns landed (not all NULL)
+select period, year, series_id, state_id, value, unit
+from public.energy_eia_seds_flat
+order by random()
+limit 5;
+```
+
+If row count is way under 2.5M, suspect a mid-run failure — check the log
+for `503` errors on the `seds` endpoint and re-run with
+`python3 ingest_eia_energy_layers.py --category state_energy --endpoint seds`.
+
+**Product/API docs for reference:**
+
+- Product page: https://www.eia.gov/state/seds/
+- Technical notes: https://www.eia.gov/state/seds/seds-technical-notes-complete.php
+- API documentation: https://www.eia.gov/opendata/documentation.php