fix(lightyear): parse FX conversions as CASH trades for FX FIFO engine

[GeiserX]

Summary

• FX Conversion rows were incorrectly skipped, causing detectAutoConvert() to assume the account uses auto-convert (no manual CASH trades → broker does it)
• This meant FX gains/losses on manual EUR↔FCY conversions were never computed per Art. 37.1.l LIRPF (DGT V2324-10)
• Now emits assetCategory=CASH trades for non-EUR conversion legs, enabling the FX FIFO engine to track lots and compute taxable FX gains
• EUR legs are skipped (the FX engine only needs the FCY side)

Test plan

• Non-EUR conversion leg emitted as CASH BUY trade (USD +64.50)
• EUR leg of conversion pair skipped
• Negative gross (FCY→EUR) emits SELL CASH
• Presence of CASH trades enables FX FIFO detection (autoConvert=false)
• All 1019 existing tests pass

Summary by CodeRabbit

• New Features

  • FX conversions now tracked as taxable trade events for accurate tax and P&L calculations.
  • Fractional currency codes (GBX, ZAC, ILA) automatically normalized to base currencies with proper amount scaling.

• Bug Fixes

  • Improved handling of non-EUR currency conversions in import processing.

[coderabbitai]

Caution

Review failed

The pull request is closed.

ℹ️ Recent review info

⚙️ Run configuration

Configuration used: Path: .coderabbit.yaml

Review profile: CHILL

Plan: Pro

Run ID: 7d9dcfdc-b0ae-4be6-8116-f02e0b513bba

📥 Commits

Reviewing files that changed from the base of the PR and between 25a8241 and 80cd600.

📒 Files selected for processing (4)

• src/parsers/lightyear.ts
• src/parsers/trading212.ts
• tests/parsers/lightyear.test.ts
• tests/parsers/trading212.test.ts

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📝 Walkthrough

Walkthrough

Two independent parser improvements: Lightyear now emits CASH FX trades for non-EUR conversions instead of skipping them, with FIFO fields populated for downstream processing. Trading 212 normalizes fractional currencies (GBX, ZAC, ILA) to base ISO codes by scaling all monetary amounts by ÷100.

Changes

Lightyear FX Conversion Handling

Layer / File(s)	Summary
Skip Set Removal src/parsers/lightyear.ts	conversion removed from non-taxable skip set, enabling conversion rows to be processed as taxable transactions.
Conversion Logic src/parsers/lightyear.ts	Adds explicit handling for conversion rows that emits CASH-category FX trade records for non-EUR legs, mapping grossAmount sign to BUY/SELL semantics with FIFO fields populated.
Test Updates & Coverage tests/parsers/lightyear.test.ts	Inline test updated to expect CASH BUY trade for USD conversion leg; new "FX conversions" section verifies non-EUR CASH emission, EUR leg skipping, FCY→EUR SELL trades, and FX FIFO detection; overall trade count increased from 5 to 6.

Trading 212 Fractional Currency Normalization

Layer / File(s)	Summary
Normalization Helper src/parsers/trading212.ts	Introduces FRACTIONAL_CURRENCIES set (GBX, ZAC, ILA) and normalizeCurrency() function that returns base ISO currency and Decimal divisor for amount scaling.
Currency Resolution src/parsers/trading212.ts	CSV column initialization resolves both instrument price currency and cash "Total" currency via normalization, storing priceDivisor and cashDivisor instead of raw codes.
Cash Transaction Scaling src/parsers/trading212.ts	Withholding Tax, Dividends, and Interest-on-cash amounts now scaled by dividing absolute CSV total by cashDivisor before emission.
Trade Monetary Scaling src/parsers/trading212.ts	Trade price and total amounts normalized by dividing priceStr by priceDivisor and totalStr by cashDivisor, affecting downstream money, cost, and proceeds calculations.
Fractional Currency Tests tests/parsers/trading212.test.ts	New test suite verifies GBX→GBP normalization (÷100) for buy/sell trades, dividends, and withholding tax; includes guard test for unchanged GBP inputs.

Estimated code review effort

🎯 3 (Moderate) | ⏱️ ~25 minutes

Possibly related PRs

• GeiserX/DeclaRenta#146: Modifies Trading 212 parser; this PR's fractional currency scaling is a direct enhancement to that parser.
• GeiserX/DeclaRenta#117: Modifies Lightyear conversion handling; this PR changes how conversions are processed into CASH FX trades.
• GeiserX/DeclaRenta#124: This PR's CASH FX trade emissions for conversions directly interact with FXCONV detection and auto-convert account suppression in that PR.

✨ Finishing Touches

📝 Generate docstrings

• Create stacked PR
• Commit on current branch

🧪 Generate unit tests (beta)

• Create PR with unit tests
• Commit unit tests in branch fix/lightyear-fx-conversions

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[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 97.65%. Comparing base (8f6bef2) to head (80cd600).
⚠️ Report is 9 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #161      +/-   ##
==========================================
+ Coverage   97.63%   97.65%   +0.01%     
==========================================
  Files          38       38              
  Lines        7622     7669      +47     
  Branches     1549     1563      +14     
==========================================
+ Hits         7442     7489      +47     
  Misses        179      179              
  Partials        1        1              

Files with missing lines	Coverage Δ
src/parsers/lightyear.ts	99.06% <100.00%> (+0.16%)	⬆️
src/parsers/trading212.ts	97.71% <100.00%> (+0.16%)	⬆️

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