fix: align compaction cuts and native usage accounting

src/server/pricing.ts

@@ -0,0 +1,50 @@
+/** Read-time API-dollar estimates. Pi owns both rates and arithmetic.
+ * Catalog resolution is key-independent; no provider dispatch/auth is needed.
+ * Never mutate saved native messages: calculateCost mutates its usage.cost.
+ */
+import { calculateCost, type Usage } from "@earendil-works/pi-ai";
+import { piModels } from "../agent/models.ts";
+import type { CallUsage, ChatRecord, JobRecord, TurnUsage } from "../core/contracts.ts";
+import { isChatGPTPlan, sessionCost as foldSessionCost, turnCost as foldTurnCost, jobCost as foldJobCost } from "../core/prices.ts";
+
+function catalogModel(id: string) {
+	const colon = id.indexOf(":");
+	if (colon < 0 || isChatGPTPlan(id)) return undefined;
+	return piModels().getModel(id.slice(0, colon), id.slice(colon + 1));
+}
+
+export function callCost(call: Partial<CallUsage>, modelId: string): number | null {
+	const model = catalogModel(modelId);
+	if (!model || call.inputTokens === undefined || call.outputTokens === undefined) return null;
+	const input = call.inputTokens;
+	const output = call.outputTokens;
+	const cacheRead = call.cacheReadTokens ?? 0;
+	const cacheWrite = call.cacheWriteTokens ?? 0;
+	const cacheWrite1h = call.cacheWrite1hTokens ?? 0;
+	if ([input, output, cacheRead, cacheWrite, cacheWrite1h].some((v) => !Number.isFinite(v) || v < 0) || cacheWrite1h > cacheWrite) return null;
+	// Old records discarded this split. Only price them if it cannot affect
+	// the result; do not invent short-retention precision from a missing field.
+	if (cacheWrite > 0 && call.cacheWrite1hTokens === undefined &&
+		[model.cost, ...(model.cost.tiers ?? [])].some((rate) => rate.cacheWrite !== 2 * rate.input)) return null;
+	const usage: Usage = {
+		input, output, cacheRead, cacheWrite, cacheWrite1h,
+		totalTokens: input + output + cacheRead + cacheWrite,
+		cost: { input: 0, output: 0, cacheRead: 0, cacheWrite: 0, total: 0 },
+	};
+	const total = calculateCost(model, usage).total;
+	return Number.isFinite(total) && total >= 0 ? total : null;
+}
+
+export function turnCost(turn: TurnUsage): number | null {
+	return foldTurnCost(turn, callCost);
+}
+export function sessionCost(record: Pick<ChatRecord, "turns">) {
+	return foldSessionCost(record, callCost);
+}
+export function jobCost(job: Pick<JobRecord, "usage">): number | null {
+	const usage = job.usage;
+	if (!usage || usage.steps < 1) return null;
+	const hasCalls = usage.calls?.length === usage.steps;
+	if (!hasCalls && usage.steps > 1 && catalogModel(usage.model)?.cost.tiers?.length) return null;
+	return foldJobCost(job, callCost);
+}