feat(r/sys/validators/v3): draft Phase B automated validator freeze

[moul]

Summary

Phase B of the validator freeze mechanism. Builds on Phase A (#5886) by adding an automated freeze path driven by registered off-chain monitors.

Draft — same intent as Phase A: open a design discussion before settling on anything.

What's added

• AutoFreezeValidator(cur, addr, reason, evidence) — callable by any registered monitor. Enforces four on-chain invariants before applying the freeze.
• ExpireAutoFrozen(cur) — sweeps auto-frozen entries whose TTL has elapsed and restores them to the effective valset. Callable by anyone.
• RegisterMonitor / DeregisterMonitor — GovDAO manages the monitor set.
• AddProtected / RemoveProtected — GovDAO manages a protected validator set that monitors cannot touch.
• autofreeze_test.gno — unit tests for state helpers and invariant arithmetic.
• Render extended with monitor list and auto-frozen validator table.

On-chain safety invariants (the monitor is untrusted)

#	Invariant	Value
1	Power floor	post-freeze live power ≥ 80% of total
2	Auto-frozen cap	at most 12% of total power auto-frozen at once
3	Protected set	GovDAO-designated validators immune to monitor freezes
4	Auto-expiry	auto-frozen entries expire after ~86400 blocks (~1 day)

A compromised monitor's worst case is bounded and time-limited by these invariants.

Open questions

1. Phase C: require N-of-M monitor attestation before a freeze fires (eliminates single-monitor risk entirely).
2. Per-monitor rate limiting: currently any registered monitor can fire unlimited freezes (invariant 2 caps total damage, but a single monitor could exhaust the cap quickly).
3. Auto-unfreeze on expiry: is automatic restore always safe, or should some cases require a human confirmation step?
4. Evidence format: currently a free-form string; should it be structured (e.g. signed double-sign proof)?

Files changed

• examples/gno.land/r/sys/validators/v3/autofreeze.gno — new, Phase B implementation
• examples/gno.land/r/sys/validators/v3/autofreeze_test.gno — new, unit tests
• examples/gno.land/r/sys/validators/v3/validators.gno — Render extended

[Gno2D2]

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