Consolidate validated security and robustness fixes

[krotname]

Summary

• consolidate 20 independently green security/robustness PRs into one current-main integration branch
• preserve both Distances changes and combine Rail Fence validation with bounded decoding
• avoid 20 sequential branch-update builds while retaining the original focused commits

Supersedes #85, #86, #89, #90, #91, #92, #93, #95, #96, #97, #99, #100, #102, #103, #105, #106, #107, #109, #110, and #113.

Validation

• every source PR was rechecked at its exact head SHA: green checks and zero unresolved review threads
• mvn verify on the combined branch (Java 25): BUILD SUCCESS
• git diff --check