[0x5t4l1n]

Summary

Fix incorrect duplicate-check results for moved/deleted payload files and misleading PR line numbers. Compare complete merge-base/head contents so diff-like payload prefixes and truncated patches cannot hide additions.

Preserve whitespace in exact comparisons and report whitespace-only matches as advisory. Only exact duplicates fail the check and apply the duplicate label. Unreadable or incomplete payload data now causes an error instead of a successful partial scan.

Add an offline regression suite and a read-only CI workflow. Update contributor guidance and replace copied, unrelated instructions in eight category READMEs with context-specific validation guidance.

Motivation / Security-Research Context

Payload whitespace and protocol framing can affect behavior. Contributors need accurate locations and reliable duplicate checks without executing payloads.

Affected Category

Repository automation and documentation. No payload files changed.

Duplicate Check

Not applicable to payload additions: no payload entries were added or removed. Existing duplicate groups were left for contextual review.

Validation Performed

• python -m unittest discover -s scripts -p 'test_*.py' -v: 13 tests passed on Python 3.10.
• Covers real line numbers, diff-like prefixes, truncated patches, deleted-file moves, extension changes, file reordering, additional exact occurrences, whitespace advisory status/labels, diverged target branches, unreadable files and incomplete API content.
• git diff --cached --check: passed before commit.
• All tests use synthetic text and mocked GitHub responses; no payload execution or target interaction.
• Existing working-directory payload deletions were excluded by using a separate worktree.

The existing privileged duplicate-check workflow intentionally runs base-branch code, so this PR's new implementation is exercised by the new regression workflow and will take effect in that workflow after merge.

Source Attribution and References

N/A; fixes based on repository review and synthetic reproductions.

AI-Assisted Contribution Disclosure

• AI tools assisted with this contribution.
• Tool/model: Codex; exact model version unknown.
• Provider: OpenAI.
• What it helped with: Repository review, implementation, regression tests, documentation and PR preparation.
• Human validation performed: No human validation claimed; maintainer review is pending. Automated validation is listed above.

Licensing and Originality

Changes are original repository maintenance and contain no credentials, secrets, or private/customer data. Submitted under the repository's MIT License.

Responsible Use Confirmation

This change only reads synthetic or repository text and is consistent with the authorized-testing-only scope in DISCLAIMER.md.

[github-actions]

✅ No duplicate payload entries detected

Checked 0 normalized entries from added/modified payload files on the latest push.

Posted automatically by the Duplicate Payload Check workflow.