fix: secure temporary files and resource lookups

[FrankChen021]

What

• replace insecure default temporary-file creation with owner-private NIO or test-managed temporary locations
• make test resource lookup use declaring-class literals and close resource streams
• preserve portable getconf PATH lookup with a narrow CodeQL suppression and rationale
• strengthen temporary archive cleanup in the OSS, S3, and Cassandra segment pushers

Why

This addresses the 55 CodeQL warnings in the temporary-file and resource-lookup group:

• 46 java/local-temp-file-or-directory-information-disclosure
• 8 java/unsafe-get-resource
• 1 java/relative-path-command

Impact

Temporary files are created with restrictive permissions or inside managed private directories. Resource lookup no longer depends on runtime subclass dispatch, and affected tests can load resources when packaged in JARs.

Root cause

The affected code used legacy File.createTempFile, runtime-class resource lookup, and one intentionally portable executable lookup that CodeQL could not distinguish from an attacker-controlled command.

Checks

• affected 21-module reactor test compilation and Checkstyle passed
• production-focused tests: 24 passed
• processing-focused tests: 174 passed
• cross-module focused tests: 100 passed
• git diff --check

Created by GPT-5.6-Sol.