[codex] harden runtime safety and audit paths

[Arbousier1]

Summary

• make live reload transactional and reject startup-only configuration changes
• validate scheduler, queue, pool, timeout, snapshot, and allocation bounds
• enforce snapshot backup frequency with concurrency-safe reservations
• harden operation-log initialization, queue saturation, file access, and shutdown completion
• remove misleading/dead proxy handoff settings and validate backend message identity/payloads
• fix partial-startup cleanup, runtime debug toggles, periodic-save rescheduling, and CI task ordering
• add regression coverage for config reload/ranges, snapshot rate limiting, operation-log saturation, and Velocity protocol/config handling

Verification

• ./gradlew clean ci --no-daemon --stacktrace
• ./gradlew stressTest --no-daemon --stacktrace
• ./gradlew jmhBenchmark --no-daemon --stacktrace
• JDK 25 + Paper 26.2.build.40-alpha: clean compileJava compileTestJava verifyJava21Bytecode

All checks passed locally. The Paper 26.2 compile still emits Java 21 bytecode (class major 65).