feat(alpha): complete hardening backlog

Complete the alpha-hardening Ralph task set, including tracker billing/accounting guards, validator fraud-audit primitives, wallet binding proof support, documentation runbooks, and updated tests.

Verification: .venv/bin/python -m compileall -q packages tests; .venv/bin/python -m pytest -q --tb=short (313 passed, 3 skipped, 1 failed: tests/test_mining_cli.py::test_legacy_start_without_port_uses_next_available_port because meshnet-node pid 1263451 is already listening on port 7000).

packages/validator/meshnet_validator/tripwire.py

@@ -0,0 +1,36 @@
+"""Passive output-quality tripwires (ADR-0018 §7).
+
+Cheap heuristics over every completed request's text -- no model access, no
+extra inference -- that flag likely-degenerate output (repetition loops,
+truncation) so ``AdaptiveAuditSampler`` can bump that single request's audit
+probability. A flag never strikes or bans a wallet by itself; it only raises
+the odds that request gets a real audit (research §8 layer 5).
+
+True perplexity scoring needs the serving model's logits, which the validator
+does not have outside an audit call, so it stays roadmap-only (ADR-0018 §8);
+this covers the repetition/truncation half of the passive-tripwire layer.
+"""
+
+from __future__ import annotations
+
+
+def detect_output_tripwire(
+    text: str,
+    *,
+    min_words: int = 4,
+    repetition_threshold: float = 0.4,
+) -> bool:
+    """Flag empty output or a single word/token dominating the response."""
+    if not text or not text.strip():
+        return True
+    words = text.split()
+    if len(words) < min_words:
+        return False
+    counts: dict[str, int] = {}
+    for word in words:
+        counts[word] = counts.get(word, 0) + 1
+    most_common = max(counts.values())
+    return (most_common / len(words)) >= repetition_threshold
+
+
+__all__ = ["detect_output_tripwire"]