fix(pricing): support Gemini 3.8 Flash Cursor usage

[robinebers]

TL;DR

Cursor usage for gemini-3.8-flash-high now contributes to spend and token totals instead of appearing as an unknown model. Adds Gemini 3.8 Flash pricing and aliases that work offline and on first launch.

Approved issue

Fixes #1201. Maintainer PR.

What was happening

• Cursor's Gemini 3.8 Flash effort suffixes did not match a pricing alias.
• The bundled catalogs lack Gemini 3.8 Flash, and live models.dev only resolves exact model IDs, so the reported -high slug remained unpriced and its usage was excluded from totals.

What this changes

• Adds gemini-3.8-flash at $0.75 input, $0.75 cache writes, $0.075 cache reads, and $3.75 output per million tokens.
• Maps none, low, medium, high, and xhigh effort suffixes, optional preview suffixes, and Gemini 3.8 Flash (Auto…) Router labels to that entry, following existing Gemini alias patterns.
• Updates the supplement timestamp and pricing documentation.
• Adds regression coverage for aliases, offline resolution, unsupported suffixes, and CSV-to-spend totals without an unknown-model warning.

Heads-up

• Sources: Cursor models and pricing, Google Gemini API pricing, and models.dev, checked September 4, 2026.
• Cursor lists output at $3.50, while Google and models.dev list $3.75. Uses Google's API rate, following the Gemini 3.7 precedent in fix(pricing): price Gemini 3.7 Flash and refresh GPT-5.6 rates #1112. Cache writes default to input because no separate write rate is published.
• Google lists these introductory rates through December 31, 2026; the supplement will need a pricing refresh when they change.
• Merging publishes the supplement through the existing workflow; installed apps can receive the fix without an app release.

Tests

• Both new regression tests fail with the old supplement and pass with this fix.
• Supplement JSON, rates, regexes, and multipliers validated.
• swift test --filter 'ModelPricing|PricingBundledResource|CursorCSV|CursorSpend': 81 tests passed.
• CONFIG=debug script/build_and_run.sh verify: rebuilt, signed, relaunched, and confirmed running.
• This Mac's Xcode beta test runner needed the downloaded Sparkle framework linked into its local build directory before tests could load. No repository configuration changes were needed.

Screenshots

Not applicable; pricing data and aliases only.

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Note

Low Risk
Data-only pricing supplement and documentation with tests; no runtime logic changes beyond what the existing resolution pipeline already does for other Gemini Flash models.

Overview
Gemini 3.8 Flash Cursor usage (e.g. gemini-3.8-flash-high) is now priced and included in spend/token totals instead of showing as an unknown model.

The bundled pricing supplement adds a gemini-3.8-flash entry at Google’s introductory API rates ($0.75 input/cache write, $0.075 cache read, $3.75 output per million), bumps updated_at, and adds slug and Cursor Router alias rules for effort/preview variants—matching the existing Gemini 3.7 pattern (including $3.75 output vs Cursor’s $3.50 table).

Regression tests cover alias resolution (including offline/first launch), negative cases for bogus suffixes, and CSV → spend aggregation without unknown-model warnings. docs/pricing.md documents the new model and rates.

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