5ca3fc9008
- Design doc: update "No UI changes" to reflect cost disclaimer
- Plan doc: fix MD001 heading level jump (### after #)
- pricing.ts: rename to PRICING_MAP, add isLiteLLMPricing type guard,
pre-compute LOWERCASE_KEY_MAP for O(1) case-insensitive lookups
- SessionContextHeader: simplify cost disclaimer JSX into single span
- Tests: fix no-empty-function lint (() => {} → () => undefined)
Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>
71 lines
3.3 KiB
Markdown
71 lines
3.3 KiB
Markdown
# Unify Cost Calculation — Design Document
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**Date:** 2026-02-23
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**Branch:** `feat/unify-cost-calculation`
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**Related:** PR #60 (Session Analysis Report), PR #65 (Cost Calculation Metric), Issue #72 (Plan Usage Tracking)
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## Problem
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Cost calculation exists in two places with different pricing data and logic:
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1. **Main process** (`src/main/utils/jsonl.ts`): Uses LiteLLM-sourced `pricing.json` (206 models, tiered 200k-token pricing). Populates `SessionMetrics.costUsd` for the chat UI.
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2. **Renderer** (`src/renderer/utils/sessionAnalyzer.ts`): Uses a hardcoded 6-model pricing table with no tiered pricing. Generates per-model cost breakdown for the Session Report.
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The two systems can produce different cost numbers for the same session and will drift further as models change.
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## Solution
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Create a single shared pricing module that both processes import.
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### New Module: `src/shared/utils/pricing.ts`
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**Exports:**
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| Export | Description |
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|--------|-------------|
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| `ModelPricing` | Interface for per-model rates (input, output, cache read, cache creation, plus tiered variants) |
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| `getPricing(modelName: string): ModelPricing \| null` | Model lookup: exact match, lowercase, case-insensitive scan |
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| `calculateTieredCost(tokens, baseRate, tieredRate?): number` | Applies 200k-token tier threshold |
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| `calculateMessageCost(model, inputTokens, outputTokens, cacheReadTokens, cacheCreationTokens): number` | Computes cost for a single API call |
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**Pricing data:** Static `import pricingData from '../../../resources/pricing.json'` with `resolveJsonModule: true`. Replaces `fs.readFileSync` runtime loading.
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### Consumer Changes
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**`src/main/utils/jsonl.ts`:**
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- Remove: `ModelPricing` interface, `loadPricingData()`, `calculateTieredCost()`, `getPricing()`, `fs`/`path` imports
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- Keep: `calculateMetrics()` function
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- Change: inline cost loop body → call `calculateMessageCost()` from `@shared/utils/pricing`
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**`src/renderer/utils/sessionAnalyzer.ts`:**
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- Remove: `MODEL_PRICING` table (~40 lines), `DEFAULT_PRICING`, local `getPricing()`, local `costUsd()`
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- Change: calls at lines 476 and 900 → `calculateMessageCost()` from `@shared/utils/pricing`
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**Tests:**
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- `test/main/utils/costCalculation.test.ts` → update to test shared module functions
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- `test/renderer/utils/sessionAnalyzer.test.ts` → mock `@shared/utils/pricing` instead of local functions
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- New `test/shared/utils/pricing.test.ts` for the shared module
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### Pricing JSON Import Strategy
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- `pricing.json` stays in `resources/` for Electron's `extraResources` packaging
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- Both Vite (renderer) and electron-vite (main) resolve the JSON import at compile time
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- Remove the `fs.readFileSync` dev/prod path logic from `jsonl.ts`
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### Fallback Behavior
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- `getPricing()` returns `null` for unknown models
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- `calculateMessageCost()` returns `0` for unknown models (matches current `jsonl.ts` behavior)
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- Session analyzer callers can apply a default if needed
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### What Changes for Users
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- Report costs become more accurate (tiered pricing, 206 models instead of 6)
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- Cost numbers between chat view and Session Report now agree exactly
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- Small UI change: Visible Context header adds a "parent only · view full cost" action when available
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## Out of Scope
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- Plan usage tracking (see Issue #72 — pending community feedback)
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- New UI surfaces for cost display
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- Changes to the `costFormatting.ts` shared utility
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