Add diagnostic redaction regression tests

[fengyangxxx]

Summary

Fixes #1.

Adds focused diagnostic redaction regression coverage and the small build-script guards needed to keep diagnostic metadata reviewable: repository-relative paths, host identifier redaction, JSON-to-.logd pairing validation, chunked artifact validation, and deterministic missing-tool diagnostics.

This PR is scoped only to the diagnostic redaction/regression bounty.

Changes

• Redacts local repository, home, temp, username, and machine identifiers from diagnostic metadata.
• Normalizes diagnostic artifact references to repository-relative forward-slash paths.
• Rejects absolute Windows and POSIX diagnostic_logd references.
• Validates that generated diagnostic metadata references existing matching .logd artifacts, including chunked .logd parts.
• Keeps missing npm and cmake tools as module failures instead of crashing diagnostic generation.
• Adds 14 Python regression tests for redaction, path normalization, artifact pairing, chunked log references, non-UTF-8 console fallbacks, and missing-tool handling.
• Includes script-generated diagnostic artifacts for code commit 0c8d9252.

Diagnostic artifacts

• diagnostic/build-0c8d9252.json
• diagnostic/build-0c8d9252.logd

The diagnostic bundle was generated by running python3 build.py in a clean Linux container using the committed tools/encryptly/linux-x64/encryptly binary. The JSON reports diagnostic_logd=diagnostic/build-0c8d9252.logd, chunked=false, no diagnostic_logd_error, and no message_blocker.

Testing

• python3 -m unittest discover -s tests
  • PASS: 14 tests.
• python3 build.py --list
  • PASS: command completed successfully.
• python3 build.py
  • Generated the matching JSON and encrypted .logd bundle.
  • Diagnostic summary: 10 modules total, 7 passed, 3 failed.
  • Passing modules: backend, frontend, market, compliance, v2-market-stream, nfc-scanner, openapi-tools.
• git diff --check
  • PASS.

Notes

• The generated diagnostic password is intentionally not copied into this PR body.
• Maintainers may remove diagnostic artifacts before merging if desired.