fix(net): validate block delivery before provider credit

[317787106]

What does this PR do?

Block responses currently clear fetch requests before validation and can receive activity or contribution credit without useful delivery. Validate the parent hash and height relationship, retain request responsibility through preliminary validation, and distinguish accepted, sync-required, ignored, and state-failed processing outcomes. Credit broadcast and sync providers only at the appropriate validated/useful stage, including shutdown guards.

Keep broadcasting after validation and parent checks but before full execution. Keep the release branch's sync BAD_BLOCK penalties.

Why?

Invalid data must remain recoverable through disconnect handling, and peer-quality timestamps should reflect validated interaction and useful block delivery.

Split scope

Independent split 1 of #91, based directly on release_v4.8.3. It does not require the inventory activity or scheduling PR. INV confirmation and download retry/recovery are separate changes; the retry PR will follow after the first three splits merge. Existing public signatures, wire/storage formats, configuration, and dependency versions are unchanged.

Validation

• ARM64/JDK 17: 36 focused and existing regression tests passed.
• checkstyleMain checkstyleTest passed.
• Semgrep: no findings in changed files.
• Repository-wide test: 3,470 tests, 26 skipped, zero failures/errors.
• FindSecBugs: no new security findings versus the release base (25 existing logging warnings).
• Local integration rehearsal of all three independent splits: 159 networking tests and Checkstyle passed after reconciling the overlapping handlers, peer-method insertion, and sync test fixture.
• Local worktree commands skip :framework:generateGitProperties because the existing metadata plugin cannot resolve linked worktrees.

CI status

Linux JDK 8/17 builds, coverage gate, Checkstyle, and the JDK 8 smoke test passed. The first macOS run exited with Gradle Test Executor 11 status 1 without a reported failing assertion; all 22 new tests passed in that run. A single rerun of the failed macOS job has been requested; its root cause is not established.

Related split PRs

• fix(net): validate block delivery before provider credit #97: block validation and provider accounting
• fix(net): confirm block inventory activity after processing #98: validated block inventory activity
• fix(net): separate block fetch eligibility and scheduling #99: block provider selection and scheduling

All three target release_v4.8.3 independently. The fourth retry/recovery PR will be proposed only after these three merge.