Add Vibes-Coded Observer middleware example (x402 guard gates before settle)

[doteyeso-ops]

Summary

Adds examples/vibes_coded_observer.py — a drop-in Observer that screens an agent's irreversible actions (payments, transfers, stateful writes) against Vibes-Coded's hosted x402 pay-per-call guard APIs before ag402 settles them.

Because ag402_core.enable() already auto-pays any HTTP 402, the guard calls need zero payment code — ag402 transparently settles the tiny per-call USDC fee.

How it fits the ag402 / Observer split

• ag402 = Money Layer (deterministic settlement)
• Observer = Trust Layer (pre-action reliability + replay protection)
• Vibes-Coded guards = the evidence source a governance/observer stack calls per action

Guard mapping (all live endpoints):

Action intent	Guard
payment_or_transfer / idempotent_call	idempotency-guard
stateful_action	agent-state-guard
external_write	memory-exfil-guard
value_transfer	rate-limit-guard

A guard returning allowed: false blocks the action (fail-closed). Uses the sandbox key from AG402_SANDBOX_KEY (thanks @BTCBoyd for the key in #4).

Test plan

• Syntax valid; all referenced guard slugs verified against the live catalog
• pip install ag402-core httpx && AG402_SANDBOX_KEY=... python examples/vibes_coded_observer.py

Happy to adjust the guard→intent mapping or wire it into the existing integration examples (LangChain/CrewAI/Autogen) if you'd like it as a first-class reference integration.

[doteyeso-ops]

@AetherCore-Dev @BTCBoyd @0xAllenDev — bumping for review. This adds examples/vibes_coded_observer.py: an ag402 Observer middleware that wraps gateway actions and routes irreversible ones (payment/transfer/stateful) through an external reliability layer before settle. It's a concrete integration showing how ag402 handles settlement while a peer handles trust — the synergy you described. The example is self-contained, references only public endpoints, and the sandbox key from BTCBoyd can be wired via env. Happy to adjust style/scope to match the repo. Merging this gives ag402 users a drop-in trust gate.