🤖 feat: show model pricing on hover in chat-input picker

[Neppkun]

Summary

Hovering a model row in the chat-input picker now shows a tooltip with that model's pricing (input / output / cache-read / cache-write per 1M tokens), context window, and max output. No delay — the tooltip appears as soon as the cursor lands on a row.

Background

Users frequently want to know what a model costs before they pick it, but today that info is only available two extra clicks away in Settings → Models. Surfacing it right in the picker turns "switch model" into a decision that includes cost without any context switch.

Implementation

• Extracted the existing per-model tooltip body from ModelRow.tsx into a new shared component ModelPricingTooltip (src/browser/components/ModelPricingTooltip/ModelPricingTooltip.tsx). The markup, Tailwind classes, and formatCostPerMillion / formatTokenCount helpers are moved verbatim so the Settings tooltip is byte-identical to before.
• Wrapped each picker row in ModelSelector.tsx with a Radix Tooltip (delayDuration={0}, portaled TooltipContent on side="right" with collisionPadding={12} so it flips at the viewport edge). Pricing is looked up inline with the existing pure, renderer-local getModelStats(model) — no IPC, no prop threading, no async loading.
• Pre-existing intra-row tooltips on the Eye and Star buttons are untouched and continue to take precedence when the cursor is over them.
• When getModelStats returns null (e.g. Ollama, custom providers with no metadata) the shared component renders the existing "No pricing data available" copy.

Net product LoC: roughly +25 (most of the new file is text moved from ModelRow.tsx).

Validation

• make typecheck — clean on both project configs.
• make lint — ESLint checks passed!.
• bun test src/browser/features/Settings/Sections/ — 65 pass / 0 fail (covers ModelRow and the suites that mock ModelSelector).
• bun test src/common/utils/tokens/modelStats.test.ts — 19 pass (pricing data layer untouched, sanity check).
• Local sandbox: confirmed the tooltip appears on hover, flips sides near the viewport edge, falls back to "No pricing data available", and the Settings → Models info popover renders identically to before the refactor.

Risks

Low. The Settings tooltip is the same JSX with the same classes, just imported from a new module; the new picker tooltip is additive and uses the same Radix primitive already in use inside this scrollable list for the Eye/Star buttons. If anything goes wrong the visible blast radius is "tooltip doesn't appear" rather than anything affecting model selection.

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Generated with mux • Model: anthropic:claude-opus-4-7 • Thinking: high • Cost: $4.36