fix: correct inverted native script timelock comparisons

[scarmuega]

Summary

eval_native_script in pallas-validate/src/phase1/shelley_ma.rs evaluated both native-script timelock opcodes with inverted comparisons:

• InvalidBefore(n) was satisfied when the transaction's validity interval started before slot n — it should be satisfied when it starts at or after n.
• InvalidHereafter(n) was satisfied when the validity interval ended after slot n — it should be satisfied when it ends at or before n.

This matches evalTimelock in the Mary/Allegra ledger spec (mary-ledger.pdf p.20). The result was consensus-relevant validation that both accepts invalid transactions and rejects valid ones.

The issue reporter spotted InvalidBefore; InvalidHereafter was inverted the same way and is fixed here too. The None (unbounded) arms were already correct and are unchanged.

Changes

• Flip the two comparison operators in eval_native_script.
• Add a #[cfg(test)] mod tests exercising the previously untested timelock branches: invalid_before, invalid_hereafter (after / exactly-at / before the lock, plus the missing-bound case), and nested_timelocks (ScriptAll / ScriptAny recursion).

Verification

• New unit tests: 3 passed
• Existing shelley_ma integration tests: 25 passed — no regression

Fixes #718

🤖 Generated with Claude Code

Summary by CodeRabbit

• Bug Fixes

  • Corrected timelock validation semantics: validity-interval bounds for before/after checks now evaluate in the intended direction, affecting when native scripts are considered satisfied.

• Tests

  • Added unit tests covering before/after bound checks and recursive propagation through combined timelock scripts to validate the updated behavior.

[coderabbitai]

No actionable comments were generated in the recent review. 🎉

ℹ️ Recent review info

⚙️ Run configuration

Configuration used: defaults

Review profile: CHILL

Plan: Pro

Run ID: f7af2664-2c99-4655-8190-84ad608c3703

📥 Commits

Reviewing files that changed from the base of the PR and between 6ee057b and 34a9f12.

📒 Files selected for processing (1)

• pallas-validate/src/phase1/shelley_ma.rs

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📝 Walkthrough

Walkthrough

This PR inverts the comparison logic for ShelleyMA native-script timelocks (InvalidBefore / InvalidHereafter) to match the spec and adds unit tests that exercise boundary and recursive composition behaviors.

Changes

ShelleyMA Timelock Semantics

Layer / File(s)	Summary
Timelock validity predicates pallas-validate/src/phase1/shelley_ma.rs	InvalidBefore(val) and InvalidHereafter(val) now check validity-interval bounds in the opposite direction, aligning with Shelley MA specification for native script evaluation.
Timelock validation tests pallas-validate/src/phase1/shelley_ma.rs	Unit tests cover InvalidBefore and InvalidHereafter satisfaction at/inside/outside bounds, and validate bounds threading through ScriptAll and ScriptAny compositions.

Estimated code review effort

🎯 3 (Moderate) | ⏱️ ~20 minutes

🐰 A little rabbit hops with glee,
I flipped the bounds so scripts agree.
Timelocks now read right, no more fright,
Tests hop in to prove the light.
Cheers for correctness — nibble of delight.

🚥 Pre-merge checks | ✅ 4 | ❌ 1

❌ Failed checks (1 warning)

Check name	Status	Explanation	Resolution
Docstring Coverage	⚠️ Warning	Docstring coverage is 0.00% which is insufficient. The required threshold is 80.00%.	Write docstrings for the functions missing them to satisfy the coverage threshold.

✅ Passed checks (4 passed)

Check name	Status	Explanation
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
Title check	✅ Passed	The title 'fix: correct inverted native script timelock comparisons' directly and clearly summarizes the main change: fixing inverted comparison logic in native script timelock evaluation.
Linked Issues check	✅ Passed	The code changes directly address all objectives from issue #718: flipping comparison operators for InvalidBefore and InvalidHereafter, aligning with the Mary/Allegra ledger spec, and adding comprehensive unit tests.
Out of Scope Changes check	✅ Passed	All changes are scoped to fixing the native script timelock evaluation logic and adding unit tests to validate the fix, with no unrelated modifications introduced.

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✨ 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/718-timelock-comparison

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