Task #6: Cost-based work fee pricing with BTC oracle

- btc-oracle.ts: CoinGecko BTC/USD fetch (60s cache), usdToSats() helper,
  fallback to BTC_PRICE_USD_FALLBACK env var (default $100k), 5s abort timeout
- pricing.ts: Full rewrite — per-model token rates (Haiku/Sonnet, env-var
  overridable), DO infra amortisation, originator margin %, estimateInputTokens(),
  estimateOutputTokens() by request tier, calculateActualCostUsd() for post-work ledger,
  async calculateWorkFeeSats() → WorkFeeBreakdown
- agent.ts: WorkResult now includes inputTokens + outputTokens from Anthropic usage;
  workModel/evalModel exposed as readonly public; EVAL_MODEL/WORK_MODEL env var support
- jobs.ts: Work invoice creation calls pricingService.calculateWorkFeeSats() async;
  stores estimatedCostUsd/marginPct/btcPriceUsd on job; after executeWork stores
  actualInputTokens/actualOutputTokens/actualCostUsd; GET response includes
  pricingBreakdown (awaiting_work_payment) and costLedger (complete)
- lib/db/src/schema/jobs.ts: 6 new real/integer columns for cost tracking; schema pushed
- openapi.yaml: PricingBreakdown + CostLedger schemas added to JobStatusResponse
- replit.md: 17 new env vars documented in Cost-based work fee pricing section

artifacts/api-server/src/lib/agent.ts

@@ -7,6 +7,8 @@ export interface EvalResult {
 
 export interface WorkResult {
   result: string;
+  inputTokens: number;
+  outputTokens: number;
 }
 
 export interface AgentConfig {
@@ -15,12 +17,12 @@ export interface AgentConfig {
 }
 
 export class AgentService {
-  private readonly evalModel: string;
-  private readonly workModel: string;
+  readonly evalModel: string;
+  readonly workModel: string;
 
   constructor(config?: AgentConfig) {
-    this.evalModel = config?.evalModel ?? "claude-haiku-4-5";
-    this.workModel = config?.workModel ?? "claude-sonnet-4-6";
+    this.evalModel = config?.evalModel ?? process.env.EVAL_MODEL ?? "claude-haiku-4-5";
+    this.workModel = config?.workModel ?? process.env.WORK_MODEL ?? "claude-sonnet-4-6";
   }
 
   async evaluateRequest(requestText: string): Promise<EvalResult> {
@@ -64,7 +66,11 @@ Fulfill it thoroughly and helpfully. Be concise yet complete.`,
       throw new Error("Unexpected non-text response from work model");
     }
 
-    return { result: block.text };
+    return {
+      result: block.text,
+      inputTokens: message.usage.input_tokens,
+      outputTokens: message.usage.output_tokens,
+    };
   }
 }