fix: bound resident finding evidence

[sylvesterkaczmarek]

Summary

Make the protected post-job hook reject resident network-finding evidence that the Rust producer cannot emit.

Problem

The Rust resident retains at most 1024 network findings. It also records a truncation flag and a lifetime sampled count with a strict relationship to the retained list.

The Action already independently validates the analogous critical-finding bound, but ordinary findings were only consumed or sliced downstream. A malformed report could therefore present a non-array, more than 1024 retained findings, or an impossible retained/truncated/sample-count combination without failing the protected post hook.

Evidence / reproduction

• The Rust resident owns a bounded FindingCollection; the reporting path copies its retained list into evidence.findings, copies its truncation state into evidence.findings_truncated, and copies its lifetime sample count into counters.sampled_violations.
• The producer retains at most 1024 findings. Before that boundary, every sampled finding is retained, so sampled_violations == findings.length. Once the retained list is full, further samples set truncation and increase the sampled count, so valid truncated evidence has exactly 1024 retained findings and sampled_violations > 1024.
• On the base Action code, the protected report validator independently bounds critical_findings, but it has no equivalent producer-contract validation for ordinary findings.
• Downstream consumers even use defensive report.findings.slice(0, 1024) in places. That limits presentation work but does not make an impossible report invalid; extra or inconsistent evidence can be silently ignored rather than rejected.
• Minimal invalid states accepted by the old validation boundary include a non-array findings value, 1025 retained findings, findings_truncated: true with only 1023 retained rows, or a non-truncated list whose sampled count exceeds its retained length.
• action/finding-evidence-bounds.test.cts pins valid producer boundaries at 0, 1, 1024, and first truncation (1024 retained / 1025 sampled), then verifies those impossible combinations are rejected.

This is the same trust-boundary principle already applied to critical findings: the protected post hook should accept only evidence states the resident producer can legitimately create.

Change

• enforce the 1024 retained-finding producer bound in the protected post hook
• require findings_truncated to match the producer state
• require the sampled count to equal retained findings before truncation and exceed the retained count after truncation
• validate before DNS correlation, summaries, and structured reporting
• add boundary regressions for 0, 1, 1024, first truncation, and impossible combinations

No firewall, DNS authorization, or report schema behavior changes.