ADK agent that pays for a tool over x402 within an operator-set cap and verifies the receipt

[ShiftAboveCtrl]

A small ADK agent that buys a paid capability over x402 inside a spend cap the model cannot change, and verifies the signed receipt it gets back.

https://github.com/ShiftAboveCtrl/tollex/tree/main/examples/google-adk (root_agent with four function tools: tollex_plan (free), tollex_terms (free), tollex_buy, tollex_verify_receipt)

What may be useful beyond Tollex itself:

• Payments are off by default. tollex_buy only works when the operator sets TOLLEX_ALLOW_PAYMENTS=1, a per-call ceiling TOLLEX_MAX_ATOMIC_USDG and a session budget TOLLEX_MAX_SESSION_ATOMIC in the environment. They are never tool arguments, so the model cannot raise them.
• Rail pinned by config (TOLLEX_RAIL=base for USDC on Base, or robinhood): a 402 asking for another network, token or a higher amount is refused before anything is signed.
• Receipt verification as a tool: the agent checks the EIP-712 signature and the canonical content hash against a published key set before trusting the result.

cd examples/google-adk && pip install -r requirements.txt
adk run tollex_agent        # plans and reads prices freely; pays only with the env opt-in above

The capabilities are Robinhood Chain data (stock-token quotes and halts, chain reads, call simulation, x402 endpoint inspection), about 0.008 USD per call in USDC on Base. I'm from the Tollex team. Feedback on the tool shapes for ADK welcome.