feat: add shared pricing module with LiteLLM data

Create a unified pricing module in src/shared/utils/ that wraps
resources/pricing.json with typed lookup, tiered cost calculation,
and display pricing helpers. This is the foundation for consolidating
the dual cost calculation systems (main jsonl.ts + renderer sessionAnalyzer).

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

src/shared/utils/pricing.ts

@@ -0,0 +1,111 @@
+import pricingData from '../../../resources/pricing.json';
+
+export interface LiteLLMPricing {
+  input_cost_per_token: number;
+  output_cost_per_token: number;
+  cache_creation_input_token_cost?: number;
+  cache_read_input_token_cost?: number;
+  input_cost_per_token_above_200k_tokens?: number;
+  output_cost_per_token_above_200k_tokens?: number;
+  cache_creation_input_token_cost_above_200k_tokens?: number;
+  cache_read_input_token_cost_above_200k_tokens?: number;
+  [key: string]: unknown;
+}
+
+export interface DisplayPricing {
+  input: number;
+  output: number;
+  cache_read: number;
+  cache_creation: number;
+}
+
+const TIER_THRESHOLD = 200_000;
+
+const pricingMap = pricingData as Record<string, unknown>;
+
+function tryGetPricing(key: string): LiteLLMPricing | null {
+  const entry = pricingMap[key];
+  if (
+    entry &&
+    typeof entry === 'object' &&
+    'input_cost_per_token' in entry &&
+    'output_cost_per_token' in entry
+  ) {
+    return entry as LiteLLMPricing;
+  }
+  return null;
+}
+
+export function getPricing(modelName: string): LiteLLMPricing | null {
+  const exact = tryGetPricing(modelName);
+  if (exact) return exact;
+
+  const lowerName = modelName.toLowerCase();
+  const lower = tryGetPricing(lowerName);
+  if (lower) return lower;
+
+  for (const key of Object.keys(pricingMap)) {
+    if (key.toLowerCase() === lowerName) {
+      const match = tryGetPricing(key);
+      if (match) return match;
+    }
+  }
+
+  return null;
+}
+
+export function calculateTieredCost(tokens: number, baseRate: number, tieredRate?: number): number {
+  if (tokens <= 0) return 0;
+  if (!tieredRate || tokens <= TIER_THRESHOLD) {
+    return tokens * baseRate;
+  }
+  const costBelow = TIER_THRESHOLD * baseRate;
+  const costAbove = (tokens - TIER_THRESHOLD) * tieredRate;
+  return costBelow + costAbove;
+}
+
+export function calculateMessageCost(
+  modelName: string,
+  inputTokens: number,
+  outputTokens: number,
+  cacheReadTokens: number,
+  cacheCreationTokens: number
+): number {
+  const pricing = getPricing(modelName);
+  if (!pricing) return 0;
+
+  const inputCost = calculateTieredCost(
+    inputTokens,
+    pricing.input_cost_per_token,
+    pricing.input_cost_per_token_above_200k_tokens
+  );
+  const outputCost = calculateTieredCost(
+    outputTokens,
+    pricing.output_cost_per_token,
+    pricing.output_cost_per_token_above_200k_tokens
+  );
+  const cacheCreationCost = calculateTieredCost(
+    cacheCreationTokens,
+    pricing.cache_creation_input_token_cost ?? 0,
+    pricing.cache_creation_input_token_cost_above_200k_tokens
+  );
+  const cacheReadCost = calculateTieredCost(
+    cacheReadTokens,
+    pricing.cache_read_input_token_cost ?? 0,
+    pricing.cache_read_input_token_cost_above_200k_tokens
+  );
+
+  return inputCost + outputCost + cacheCreationCost + cacheReadCost;
+}
+
+export function getDisplayPricing(modelName: string): DisplayPricing | null {
+  const pricing = getPricing(modelName);
+  if (!pricing) return null;
+
+  return {
+    input: pricing.input_cost_per_token * 1_000_000,
+    output: pricing.output_cost_per_token * 1_000_000,
+    cache_read: (pricing.cache_read_input_token_cost ?? 0) * 1_000_000,
+    cache_creation: (pricing.cache_creation_input_token_cost ?? 0) * 1_000_000,
+  };
+}

test/shared/utils/pricing.test.ts

@@ -0,0 +1,80 @@
+import { describe, it, expect } from 'vitest';
+import {
+  getPricing,
+  calculateTieredCost,
+  calculateMessageCost,
+  getDisplayPricing,
+} from '@shared/utils/pricing';
+
+describe('Shared Pricing Module', () => {
+  describe('getPricing', () => {
+    it('should find pricing by exact model name', () => {
+      const pricing = getPricing('claude-3-5-sonnet-20241022');
+      expect(pricing).not.toBeNull();
+      expect(pricing!.input_cost_per_token).toBeGreaterThan(0);
+      expect(pricing!.output_cost_per_token).toBeGreaterThan(0);
+    });
+
+    it('should find pricing case-insensitively', () => {
+      const pricing = getPricing('Claude-3-5-Sonnet-20241022');
+      expect(pricing).not.toBeNull();
+    });
+
+    it('should return null for unknown models', () => {
+      const pricing = getPricing('totally-fake-model-xyz');
+      expect(pricing).toBeNull();
+    });
+  });
+
+  describe('calculateTieredCost', () => {
+    it('should use base rate for tokens below 200k', () => {
+      const cost = calculateTieredCost(100_000, 0.000003);
+      expect(cost).toBeCloseTo(0.3, 6);
+    });
+
+    it('should apply tiered rate above 200k', () => {
+      const cost = calculateTieredCost(250_000, 0.000003, 0.000006);
+      expect(cost).toBeCloseTo(0.9, 6);
+    });
+
+    it('should use base rate when no tiered rate provided', () => {
+      const cost = calculateTieredCost(250_000, 0.000015);
+      expect(cost).toBeCloseTo(3.75, 6);
+    });
+
+    it('should return 0 for zero or negative tokens', () => {
+      expect(calculateTieredCost(0, 0.000003)).toBe(0);
+      expect(calculateTieredCost(-100, 0.000003)).toBe(0);
+    });
+  });
+
+  describe('calculateMessageCost', () => {
+    it('should compute cost for a known model', () => {
+      const cost = calculateMessageCost('claude-3-5-sonnet-20241022', 1000, 500, 0, 0);
+      expect(cost).toBeCloseTo(0.0105, 6);
+    });
+
+    it('should return 0 for unknown models', () => {
+      const cost = calculateMessageCost('unknown-model', 1000, 500, 0, 0);
+      expect(cost).toBe(0);
+    });
+
+    it('should include cache token costs', () => {
+      const cost = calculateMessageCost('claude-3-5-sonnet-20241022', 1000, 500, 300, 200);
+      expect(cost).toBeGreaterThan(0.0105);
+    });
+  });
+
+  describe('getDisplayPricing', () => {
+    it('should return per-million rates for a known model', () => {
+      const dp = getDisplayPricing('claude-3-5-sonnet-20241022');
+      expect(dp).not.toBeNull();
+      expect(dp!.input).toBeCloseTo(3.0, 1);
+      expect(dp!.output).toBeCloseTo(15.0, 1);
+    });
+
+    it('should return null for unknown models', () => {
+      expect(getDisplayPricing('unknown-model')).toBeNull();
+    });
+  });
+});