fix: correct P&L calculation in ton_trading_record_trade (issue #129)

[konard]

Root Cause

The exit_price_usd parameter in ton_trading_record_trade was documented as "USD price of to_asset at exit", but entry_price_usd is "USD price of from_asset at entry". This asymmetry caused a double-counting bug when closing TON→USDT positions.

For a trade like 10 TON → USDT at entry $1.240, exit $1.249:

• The user passes amount_out=12.49 (USDT received) and exit_price_usd=1.249 (TON exit price, from market data)
• Old formula: usdOut = amount_out × exit_price_usd = 12.49 × 1.249 = 15.60 ❌
• New formula: usdOut = amount_in × exit_price_usd = 10 × 1.249 = 12.49 ✅

Fix

Changed exit_price_usd semantics to consistently refer to the from_asset price (same as entry_price_usd):

usdIn  = amount_in × entry_price_usd
usdOut = amount_in × exit_price_usd
pnl    = usdOut − usdIn

This matches the formula requested in the issue:

pnl_usd = (amount_in × exit_price_usd) - (amount_in × entry_price_usd)
pnl_pct = ((exit_price - entry_price) / entry_price) × 100

Reproducing Tests Added

Two regression tests for the exact positions from the issue report:

Position	amount_in	entry_price	exit_price	Expected P&L	Old (buggy)
#28	10 TON	$1.240	$1.249	+$0.09 / +0.73%	+$3.20 / +25.8%
#29	50 TON	$1.252	$1.251	−$0.05 / −0.08%	+$15.65 / +25.0%

All 108 tests pass.

Parameter Description Updated

exit_price_usd now reads:

"USD price of from_asset at trade exit. Must match the same asset as entry_price_usd (e.g. if you sold TON, provide TON's USD price at the time of closing)."

Closes #129

[konard]

🤖 Solution Draft Log

This log file contains the complete execution trace of the AI solution draft process.

💰 Cost estimation:

• Public pricing estimate: $1.277680
• Calculated by Anthropic: $1.277680 USD
• Difference: $0.000000 (0.00%)

📊 Context and tokens usage:

• Context window: 71.9K / 1M (7%) input tokens, 23.3K / 64K (36%) output tokens

Total: (61.9K + 2.3M cached) input tokens, 23.3K output tokens, $1.277680 cost

🤖 Models used:

• Tool: Anthropic Claude Code
• Requested: sonnet
• Model: Claude Sonnet 4.6 (claude-sonnet-4-6)

📎 Log file uploaded as Gist (1465KB)

• View complete solution draft log

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[konard]

✅ Ready to merge

This pull request is now ready to be merged:

• All CI checks have passed
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• No pending changes

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