Retain existing leveraged ETF shares for small accounts

[Pigbibi]

Summary

• keep an existing whole share for TQQQ/SOXL when the positive target is below one share price
• preserve existing cash-substitution behavior for other unbuyable sleeves
• add regression coverage for the sell-all-then-cannot-buy-back case

Tests

• python -m py_compile application/execution_service.py tests/test_execution_service.py
• git diff --check
• timeout 120 python -m pytest tests/test_execution_service.py -k 'existing_whole_share or uses_sellable_quantity or insufficient_cash_for_whole_share or leaves_small_safe_haven' -q

[chatgpt-codex-connector]

💡 Codex Review

Here are some automated review suggestions for this pull request.

Reviewed commit: e41c65c8b4

ℹ️ About Codex in GitHub

Your team has set up Codex to review pull requests in this repo. Reviews are triggered when you

• Open a pull request for review
• Mark a draft as ready
• Comment "@codex review".

If Codex has suggestions, it will comment; otherwise it will react with 👍.

Codex can also answer questions or update the PR. Try commenting "@codex address that feedback".

[chatgpt-codex-connector]

Account for the trade threshold when retaining one share

When the default $100 min-trade floor is used and TQQQ is below $100, an account holding exactly two TQQQ shares with a positive sub-share target gets its target raised to one quote here; the later threshold check then sees only a one-share delta (<$100) and skips the sell, leaving two leveraged shares instead of the intended single retained share. The added regression sets current_min_trade to 10, so it misses this production-default path.

Useful? React with 👍 / 👎.