Account for seller fees after selecting one price

.github/workflows/validate.yml

@@ -67,3 +67,13 @@ jobs:
           python-version: "3.12"
       - name: Check every field in the body appears in Appendix A
         run: python3 scripts/check_appendix.py
+
+  pricing-fixtures:
+    name: Pricing discussion fixtures
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v4
+      - uses: actions/setup-python@v5
+        with:
+          python-version: "3.12"
+      - run: python3 scripts/check_pricing_fixtures.py

docs/proposals/pricing-commitment-arithmetic.md

@@ -0,0 +1,117 @@
+# Account for seller fees after selecting one price
+
+Discussion wording for [#94](https://github.com/IABTechLab/OpenProposal/issues/94)
+and [#115](https://github.com/IABTechLab/OpenProposal/issues/115), against draft
+`44dfaaf618736219426c311ec997b6d37e94b950`. The arithmetic also exercises the
+final-rate reading discussed in [#30](https://github.com/IABTechLab/OpenProposal/issues/30).
+This is a proposed profile, not an adopted requirement or an OpenProposal wire
+validator. The normative specification is unchanged.
+
+## The fee interpretation changes the available media spend
+
+#94 treats `pricing[]` entries as alternatives. #115 adds seller fees as extra
+entries and includes them in `commitment.amount`. An extra alternative cannot
+simultaneously be an additive fee. Summing all entries instead loses the choice
+of cost method, currency and transaction mechanism.
+
+At USD 25 CPM, a USD 50,000 commitment containing a USD 2,500 production fee
+leaves USD 47,500 for media:
+
+```
+media_spend   = 50,000 - 2,500 = 47,500 USD
+derived_units = 47,500 / 25 * 1,000 = 1,900,000 impressions
+```
+
+Two million impressions would cost USD 50,000 before the fee, or USD 52,500
+in total. Therefore #115's statement that `derived_units` is unaffected needs
+revision if `amount` includes charges outside the unit rate.
+
+## Proposed wording for sections 3.1, 5.6 and 5.6.1
+
+This wording assumes adoption of the alternative-selection rule in #94.
+
+`pricing[]` entries are alternative prices. A commitment MUST resolve to
+exactly one entry under that rule. An implementation MUST NOT sum alternative
+entries to compute the buyer's charge.
+
+A selected option's `delta_flat` is a one-time seller charge for that line
+item commitment. It MUST NOT enter the unit rate or become another pricing
+alternative solely to make it additive. A cost already included in the unit
+rate MUST NOT also be added as a flat charge. Each selected option that is not
+already included contributes its charge once.
+
+For `basis = spend`, `amount` is the total pre-tax amount payable to the seller
+for this line item, including applicable seller flat charges. It excludes
+amounts payable by the buyer to other parties. For a selected unit-rate method:
+
+```
+flat_charges  = sum of applicable one-time seller charges
+media_spend   = commitment.amount - flat_charges
+derived_units = media_spend / agreed_rate * rate_per
+```
+
+`rate_per` is 1,000 for CPM and CPMV, and 1 for CPC. The agreed rate MUST be
+positive. Flat charges MUST NOT exceed the spend commitment. Zero remaining
+media spend yields zero informative units and still has to satisfy any
+applicable minimum-unit requirement.
+
+For `basis = units`, the committed units remain binding:
+
+```
+media_spend   = commitment.amount / rate_per * agreed_rate
+seller_total  = media_spend + flat_charges
+```
+
+`min_spend` and budget bounds apply to the seller total on the same pre-tax
+basis. The selected entry's currency applies to rates, flat charges and budget
+bounds. No currency conversion is implied. Informative unit estimates MUST NOT
+be rounded in a way that changes the committed amount or authorizes extra spend.
+
+## Arithmetic inputs do not establish acceptance
+
+The adapter consumes resolved, field-qualified adjustments that are not already
+included. Its provisional #30 calculation starts with the chosen `gross_rate`,
+adds applicable `delta_cpm`, then multiplies by `(1 + delta_pct)` factors.
+`0.20` means a 20 percent increase. Flat charges remain separate.
+
+If the caller supplies an already accepted final-rate counter, that rate replaces
+the composed rate without applying option rate deltas again. The caller must
+have established acceptance for the bound proposal revision and selection.
+`selection_key` is an opaque fixture binding, not an acceptance protocol.
+
+The adapter does not evaluate floor eligibility. Every successful result carries
+`floor_check: not_checked`. A posted floor is checked only for numeric shape and
+nonnegativity. In particular, an explicitly accepted USD 19 rate against a posted
+USD 20 floor remains USD 19 in the calculation. The floor does not veto acceptance
+already established by the caller.
+
+How a counter resolves automatically, how selected adjustments compose the floor,
+and how seller assent is authenticated remain in #30. That discussion proposes
+applying rate adjustments to the base floor. This profile neither adopts that
+proposal nor silently compares a final rate with an uncomposed floor. A successful
+calculation never authorizes a commitment, reservation or agreed order.
+
+## Scope and reproduction
+
+```
+python3 scripts/check_pricing_fixtures.py
+python3 scripts/check_pricing_fixtures.py --json
+```
+
+[`fixtures/pricing/cases.json`](../../fixtures/pricing/cases.json) contains fixed
+expected outcomes independent of the calculator. Decimal strings and rational
+outputs avoid binary floating point rounding. `"1000/3"` is an exact informative
+quantity, not a proposed JSON wire type. Currency checks cover agreement and
+shape, not ISO-4217 membership. The caller supplies a mechanism-eligible choice.
+
+The profile implements CPM, CPMV and CPC only. It rejects unsupported tax-inclusive
+inputs, #103 print adjustments and flat credits. It cannot infer a mandatory fee
+that is not represented by the resolved options. General fee objects, tax amounts,
+invoice rounding and cost-method extensions need separate decisions. Impression
+bounds are checked only for CPM; clicks and viewable impressions are not silently
+treated as the same quantity. Unsupported cases are not declarations that an
+OpenProposal document is invalid.
+
+If the fee wording is adopted, update the affected body sections, field
+descriptions in Appendices A and B, and committed examples together. The executable
+profile is supporting discussion evidence, not a replacement for those changes.