Close #29: the v1 rate structure types

Price is a rate function, not a scalar (#22), and #15 bars any model from
evaluating one — so the shapes have to be closed AND computable. This replaces
the src/pricing seam with a composition rather than an enumeration: one base
schedule deciding unit price, plus closed modifiers, plus an optional floor.
Three vendors on one small RFP already produced five cells of the alternative
cross-product, and two of the three are the same object wearing different
decoration.

The scenario vocabulary is closed too, and published with the RFP, so every bid
in a field is priced against identical assumptions. A structure reading a
variable the RFP never declared is rejected at submission, while the vendor can
still fix it.

Abstention is typed. `input_missing` is separated from `shape_unsupported`
because Chesapeake's shape is fully supported and its unit price simply is not
in the document — that is recoverable by asking, and collapsing the two throws
away the only actionable fact. Null is never zero, never the vendor's stated
figure, and never a partial sum.

The derivation is the record. A bare scalar can only assert; a protest asks why
a bid ranked where it did. Lines accumulate as exact rationals in bigint and
round once, half-up. A scenario amendment voids derived costs rather than
recomputing them.

Exceptions carry a closed consequence union. Anacostia's EX-3 says the vendor
cannot bid produce at all if declined — a nullable price delta reads that as "no
cost impact", the inverse of the truth, on the most consequential of the three.

Two defects the corpus check caught that review would not have:

  - The band ladder priced two ways depending on a flag. `to` is inclusive, and
    subtracting those bounds in the marginal path lost the unit between bands —
    one in 21,400, invisible in the total and wrong in the record.

  - The published scenario was quantizing the price before the evaluator saw it.
    Twelve basis-point shares moved the seasonal factor by 3e-5, about $19 on a
    $624,000 line. Weights, not shares: a school calendar publishes instructional
    days, an exact integer, and the ratio is taken last.

  npm run check:pricing

Potomac computes $589,570.00 and not the stated $589,970.00; Chesapeake abstains
naming base.unitPrice; Anacostia is $649,792.00 with the calendar and unpriceable
without it; a 3-of-4-line bid withholds its total.

Migrations generated in two passes so drizzle-kit never needed the interactive
rename prompt. No SQL hand-edited.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>

package.json

@@ -3,13 +3,14 @@
   "version": "0.0.0",
   "private": true,
   "type": "module",
-  "description": "Retail RFP transmission system — v1 code layout",
+  "description": "Retail RFP transmission system \u2014 v1 code layout",
   "scripts": {
     "typecheck": "tsc --noEmit",
     "generate": "drizzle-kit generate",
     "generate:custom": "drizzle-kit generate --custom",
     "migrate": "drizzle-kit migrate",
-    "seams": "grep -rn 'new Seam(' src/ --include=*.ts"
+    "seams": "grep -rn 'new Seam(' src/ --include=*.ts",
+    "check:pricing": "tsx src/pricing/corpus-check.ts"
   },
   "dependencies": {
     "drizzle-orm": "^0.45.2",
@@ -18,6 +19,7 @@
   "devDependencies": {
     "@types/node": "^22.10.0",
     "drizzle-kit": "^0.31.10",
+    "tsx": "^4.23.5",
     "typescript": "^5.7.0"
   }
 }