feat(zsh): add currency conversion support for cost display

[tusharmath]

Summary

Add configurable currency conversion support to zsh rprompt cost display, enabling users to view costs in their preferred currency and exchange rate.

Context

The zsh rprompt previously displayed costs only in USD with a hardcoded "$" symbol. Users in different regions needed to mentally convert costs to their local currency, which was inconvenient and error-prone. This change allows users to configure their preferred currency symbol and conversion rate via environment variables.

Changes

• Added currency_symbol and conversion_ratio fields to ZshRPrompt struct
• Added environment variable support for FORGE_CURRENCY_SYMBOL (defaults to "$")
• Added environment variable support for FORGE_CURRENCY_CONVERSION_RATE (defaults to 1.0)
• Updated cost display logic to apply conversion ratio and use custom currency symbol
• Added comprehensive tests for currency conversion (INR and EUR examples)

Key Implementation Details

• Currency configuration is read from environment variables at rprompt initialization
• Conversion ratio multiplies the base USD cost to get the displayed value
• Currency symbol can be any string (e.g., "INR", "€", "£", "¥")
• Backward compatible: defaults to USD with "$" symbol if no configuration provided

Use Cases

• View costs in INR for Indian users: export FORGE_CURRENCY_SYMBOL=INR FORGE_CURRENCY_CONVERSION_RATE=83.5
• View costs in EUR for European users: export FORGE_CURRENCY_SYMBOL=€ FORGE_CURRENCY_CONVERSION_RATE=0.92
• View costs in GBP for UK users: export FORGE_CURRENCY_SYMBOL=£ FORGE_CURRENCY_CONVERSION_RATE=0.79

Testing

# Run unit tests for rprompt
cargo test -p forge_main zsh::rprompt

# Test with custom currency
export FORGE_CURRENCY_SYMBOL=INR
export FORGE_CURRENCY_CONVERSION_RATE=83.5
# Verify rprompt displays converted costs

Links

• Related files: crates/forge_main/src/zsh/rprompt.rs, crates/forge_main/src/ui.rs

[CLAassistant]

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1 out of 3 committers have signed the CLA.

✅ tusharmath
❌ Tushar Mathur
❌ forge-code-agent

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[graphite-app]

Test expectation is mathematically incorrect. The calculation 0.01 * 83.5 = 0.835 will round to 0.84 when formatted with {:.2}, not 0.83. This test will fail.

let expected = " %B%F{15}\u{f167a} FORGE%f%b %B%F{15}1.5k%f%b %B%F{2}INR0.84%f%b %F{134}\u{ec19} gpt-4%f";

Suggested change

	let expected = " %B%F{15}\u{f167a} FORGE%f%b %B%F{15}1.5k%f%b %B%F{2}INR0.83%f%b %F{134}\u{ec19} gpt-4%f";
	let expected = " %B%F{15}\u{f167a} FORGE%f%b %B%F{15}1.5k%f%b %B%F{2}INR0.84%f%b %F{134}\u{ec19} gpt-4%f";

Spotted by Graphite Agent



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[graphite-app]

Inconsistent default currency symbol. The Default impl sets currency_symbol to "\u{f155}" (a Nerd Font icon), but the UI code in ui.rs defaults to "$" when FORGE_CURRENCY_SYMBOL is not set, and all documentation states the default is "$". This creates inconsistent behavior depending on how ZshRPrompt is instantiated.

// Should be:
currency_symbol: "$".to_string(),

This ensures consistency with the documented behavior and the UI code path. The Nerd Font icon \u{f155} should only be used when explicitly configured via the environment variable or builder method.

Suggested change

	currency_symbol: "\u{f155}".to_string(),
	currency_symbol: "$".to_string(),

Spotted by Graphite Agent



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