fix: validate minimum margin for position opens

[rdave8]

Summary

• Add reusable opening-margin validation for maker and taker positions.
• Check scaled margin against MIN_OPENING_MARGIN.
• Return ValidationError::InvalidMargin before transaction handling when margin is below the protocol minimum.

Context

The contracts require both openMaker and openTaker margins to be at least 5 USDC. Previously, the SDK only required a positive margin, allowing invalid parameters to reach contract simulation and revert with MarginTooLow.

Testing

• Added boundary coverage immediately below, at, and above the minimum.

Summary by CodeRabbit

• Bug Fixes
  • Enforced the protocol’s minimum opening margin when opening maker and taker positions.
  • Updated margin validation to reject values below the required threshold (around the 5.0 USDC boundary), preventing invalid position-opening requests.
  • Made margin handling consistent across maker and taker openings.
• Tests
  • Added a unit test covering failure below the minimum and success at/above it.

[coderabbitai]

No actionable comments were generated in the recent review. 🎉

ℹ️ Recent review info

⚙️ Run configuration

Configuration used: defaults

Review profile: CHILL

Plan: Pro Plus

Run ID: 5d13450f-b485-45c2-aa59-02ed29fba252

📥 Commits

Reviewing files that changed from the base of the PR and between 62514b6 and 8409527.

📒 Files selected for processing (1)

• src/client/trades.rs

🚧 Files skipped from review as they are similar to previous changes (1)

• src/client/trades.rs

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📝 Walkthrough

Walkthrough

Opening margin handling scales values to six decimals and enforces the protocol minimum for taker and maker position openings, with boundary-focused unit tests.

Changes

Opening Margin Validation

Layer / File(s)	Summary
Margin validation helper src/client/trades.rs	Adds scale_opening_margin and imports the protocol minimum and six-decimal scaling helpers.
Trade entrypoint enforcement src/client/trades.rs	Updates taker and maker opening paths to use minimum-margin validation and tests values below, at, and near the 5.0 boundary.

Estimated code review effort: 2 (Simple) | ~10 minutes

🚥 Pre-merge checks | ✅ 5

✅ Passed checks (5 passed)

Check name	Status	Explanation
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
Title check	✅ Passed	The title clearly matches the main change: enforcing a minimum margin when opening positions.
Docstring Coverage	✅ Passed	Docstring coverage is 100.00% which is sufficient. The required threshold is 80.00%.
Linked Issues check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check	✅ Passed	Check skipped because no linked issues were found for this pull request.

✨ 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/min-opening-margin-validation

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[Praz314159]

Thanks for the dedup