[P3] effectiveEffort preserves signed zero differently across platforms #37

Summary

Swift and Kotlin return different IEEE-754 zero signs for one effectiveEffort input ordering.

This was found by the Strain differential rollout tracked in #17.

Minimal reproduction

live = +0.0
stored = -0.0

Observed behavior

With the operands reversed, both implementations return +0.0.

Likely cause

The platforms use different maximum semantics for equal signed-zero operands: Swift preserves the second operand in this case, while kotlin.math.max canonicalizes the result to positive zero.

Impact

The numeric and displayed value remains zero. The difference matters only for exact serialization, hashing, or bit-level parity.

Severity: P3.

Acceptance criteria

• Decide whether effectiveEffort promises numeric equality or exact IEEE-754 parity.
• If exact parity is required, normalize signed zero identically on both platforms.
• Add mirrored deterministic tests for both operand orders.

No hardware testing is required; this is pure analytics behavior.