Harden resource cost evidence contract

README.md

@@ -54,6 +54,20 @@ month, and currency. Corrections are append-only: pass the current record ID
 to `ledger set-price --revision-of`; margin reports use the newest revision
 and preserve the earlier price for auditability.
 
+Ledger imports identify financial facts independently of filename and mtime.
+Duplicate, renamed, touched, and forced unchanged deliveries do not change
+totals. A changed row is rejected unless `force=True` explicitly appends a
+correction; reversals use `reverse_financial_fact` and retain their predecessor.
+All effective calculations use integer minor units with decimal
+round-half-even normalization.
+
+The executable resource-control exchange contract lives in
+`fin_hub.schemas.exchange`. `booked_cost_projection` emits current booked facts;
+`ingest_planning_evidence` stores typed forecasts, usage observations,
+allocations, optimization cases, and commitment candidates outside booked
+spend. `ingest_resource_forecast` adapts resource-control's v0.1 monthly backup
+forecast without inventing resource identity.
+
 ## Related Workplans
 
 - `the-custodian/workplans/CUST-WP-0025-fos-hub-bootstrap.md` — umbrella