diff --git a/docs/superpowers/specs/2026-07-02-cyclone-rendering-npi-extraction-design.md b/docs/superpowers/specs/2026-07-02-cyclone-rendering-npi-extraction-design.md
index e4f224c..6994fbf 100644
--- a/docs/superpowers/specs/2026-07-02-cyclone-rendering-npi-extraction-design.md
+++ b/docs/superpowers/specs/2026-07-02-cyclone-rendering-npi-extraction-design.md
@@ -62,14 +62,22 @@ Effective algorithm unchanged: 2-of-3 `{PCN, charge, NPI}` still fires when any
 
 New subcommand: `python -m cyclone.cli backfill-rendering-npi`.
 
-Behavior:
-1. For every `claim_batches.inbound_path`, re-parse the 837p file with the new parser; for every claim in the batch, write `Claim.rendering_provider_npi = parsed_value` **only when the column is currently `NULL`** (idempotent).
-2. For every `remittances.inbound_path`, re-parse the 835 file with the new parser; for every remit, write both the per-segment NPIs (`ClaimPayment.service_provider_npi`) and the aggregated `Remittance.rendering_provider_npi`.
-3. Run `reconcile.run()` once over all open pairs at the end so the NPI arm can fire retroactively.
-4. Log per-batch counts (parsed, updated, skipped).
-5. Exit code 0 on success, 2 on file-level failure (no batch updated), 1 on unexpected exception.
+**Why explicit file args.** The `Batch` ORM does not retain a column for the original on-disk ingest path — the live ingest pipeline reads the upload body, parses, writes rows, and never persists the bytes. So there is no `claim_batches.inbound_path` / `remittances.inbound_path` to "look up" and re-parse from. The operator must point the CLI at the files (or the directory that holds them) that need backfill. Re-running ingest end-to-end would be the alternative, but it would re-`INSERT` claim rows and is a destructive operation; backfill is intentionally a read-reparse-targeted-`UPDATE`.
 
-Idempotent: re-running on a fully-populated DB is a no-op (typed columns not overwritten; reconcile already matched pairs skipped via `Claim.matched_remittance_id IS NOT NULL`).
+Flags:
+- `--file PATH` (repeatable) — one or more specific X12 files to re-parse. Each path is validated to exist before parsing.
+- `--input-dir DIR` — directory to scan one level deep for `*.txt` / `*.edi` / `*.x12` files. Falls back to `$CYCLONE_BACKFILL_INPUT_DIR` if neither `--file` nor `--input-dir` is passed.
+- `--type {837p,835}` (optional) — pin the parser. **When omitted, each file's transaction kind is auto-sniffed** (filename hint + ISA/ST prefix) so a mixed directory can be processed in one pass.
+
+Behavior:
+1. For each file resolved by `--file` / `--input-dir`, re-parse with the new parser (T4 wiring).
+2. **837p**: for every claim in the batch, write `Claim.rendering_provider_npi = parsed_value` **only when the column is currently `NULL`** (idempotent — already-populated rows are left alone).
+3. **835**: for every remit, write `Remittance.rendering_provider_npi` (typed column) **only when `NULL`**, and persist the per-segment `service_provider_npi` values into `Remittance.raw_json["service_provider_npis"]` (D5).
+4. After all files are processed, run `reconcile.run()` **once across every 835 Batch** so the D6 NPI arm can fire retroactively on newly-populated pairs.
+5. Log per-file counts (parsed, updated, skipped). Emit one-line summary to stdout: `claims_updated=N remits_updated=M files_processed=K files_skipped=J`.
+6. Exit code 0 on success (zero populated rows is still exit 0), 2 on file-level failure (no file processed), 1 on unexpected exception.
+
+Idempotent: re-running on a fully-populated DB is a no-op (typed columns not overwritten; reconcile skips already-matched pairs via `Claim.matched_remittance_id IS NOT NULL`).
 
 ### D8 — Backfill event emission
 
@@ -96,7 +104,8 @@ No `UPDATE` statements in the migration — backfill is a separate, deliberate s
 - `backend/src/cyclone/db.py` — `Claim.rendering_provider_npi`, `Remittance.rendering_provider_npi`. No claim_payments ORM — service_provider_npi persists only via `Remittance.raw_json["service_provider_npis"]` (D5).
 - `backend/src/cyclone/writer.py` / `writer_835.py` — set the new typed columns and the `raw_json` mirrors at write time. `writer_835.py` writes the per-CLP `service_provider_npi` into `Remittance.rendering_provider_npi` (D4, single value) and into `raw_json["service_provider_npis"]` (D5).
 - `backend/src/cyclone/reconcile.py` — extend `_content_keys_match` (D6).
-- `backend/src/cyclone/cli.py` — new `backfill-rendering-npi` subcommand.
+- `backend/src/cyclone/store/backfill.py` — **new helper module** owning `backfill_rendering_provider_npi(files, input_dir, transaction_type)`: file/CLI argument resolution, auto-sniffing (ISA/ST + filename hint), re-parse dispatch, idempotent typed-column writes, and the post-backfill `reconcile.run()` sweep. Returns a small summary dataclass for the CLI summary line.
+- `backend/src/cyclone/cli.py` — new `backfill-rendering-npi` subcommand (Click). Wires `--file` / `--input-dir` / `--type` / `--log-level`, delegates the heavy lifting to `store.backfill.backfill_rendering_provider_npi`, and prints the one-line summary.
 - `backend/src/cyclone/migrations/0019_add_rendering_and_service_provider_npis.sql` — D9.
 - `backend/tests/fixtures/` — new 837p fixture(s) with `NM1*82` and new 835 fixture(s) with `NM1*1P`.
 - `backend/tests/test_reconcile.py` — new tests for D6 (typed-column primary path, typed-column beats raw_json fallback, NPI arm fires when both sides populated).