feat: Deduplicate coin list at startup with warning log

[keitaj]

Summary

• Detect and remove duplicate coins in the trading list at startup, logging a WARNING with the duplicates
• Prevents issues like the TSLA duplication bug where .env.farming and start_farming_us.sh both added TSLA, causing XYZ_COINS=...,TSLA,TSLA,...
• Extracted as _deduplicate_coins() static method for testability

Motivation

A real bug was discovered where TSLA appeared twice in the US session coin list. This caused the bot to allocate double position slots to TSLA and potentially worsened cost efficiency ($/1K went from $0.058 to $0.202). This validation catches such configuration errors at startup.

Changes

• bot.py: Add _deduplicate_coins() static method and call it during coin list assembly. Logs WARNING with duplicate names.
• tests/test_deduplicate_coins.py: 8 tests covering no-dups, single/multi dups, order preservation, empty list, mixed HL/HIP-3, case sensitivity.

Test plan

• Unit tests added (8 new tests)
• flake8 passes
• pytest passes (744 tests, 0 failures)
• No regressions in existing tests

🤖 Generated with Claude Code

[keitaj]

Review: Deduplicate coin list at startup

Simple, well-tested defensive validation. Addresses a real bug (TSLA duplication in US session).

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1. Return type annotation (nit)

bot.py L253:

-> tuple could be more specific: -> Tuple[List[str], List[str]]. Minor readability improvement.

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Verdict: LGTM

• No blockers or should-fix items
• 8 tests with real assertions covering all edge cases
• Additive-only change, fully backward compatible
• Static method is clean and testable
• One nit (return type annotation) — optional

Merging after CI check.