[Bug]: SIST silently replaces NaN values

[harryswift01]

Bug Report

SIST currently appears to replace some NaN values with zero.

This can hide a numerical problem and make an unreliable result look valid.

To Reproduce

Add the smallest known input that produces a NaN value.

Finding a reproducible example is part of this issue.

YAML configuration

# Add the configuration here.

CLI command used

# Add the command here.

Actual output

The calculation may continue after an invalid value has been replaced, without clearly identifying the affected result or whether the output remains reliable.

Expected output

SIST should either warn clearly and mark the affected result, or stop with a useful error.

NaN values should not be silently converted to zero or infinity.

Proposed Work

• Find where NaN and infinity are produced or replaced.
• Identify the affected scientific quantities.
• Define recoverable and fatal cases.
• Remove silent replacement.
• Include useful context in warnings and errors.
• Record warnings in structured results.
• Add tests for warning and failure paths.

Done When

• NaN values are no longer silently replaced.
• Diagnostics identify the affected calculation stage.
• Fatal cases stop safely.
• Recoverable cases are recorded in the result.
• Partial or unreliable results are clearly marked.
• The behaviour is covered by automated tests.