feat(example): MockPendleRouter contract + deploy runbook (scenario A unblock)

[mike-diamond]

Summary

Makes the Buildathon demo's scenario A (Pendle yield swap) actually deployable + runnable, and pre-writes the full deploy runbook so the on-chain deploy (which needs Mike's funded key) is copy-paste.

The gap: the app already referenced MockPendleRouter (src/agent/envelope-builder.ts imports getMockPendleRouterAddress, holds MOCK_PENDLE_ROUTER_ABI, and comments point at contracts/src/MockPendleRouter.sol), but the contract and its deploy script did not exist. Scenario A could not be deployed end-to-end.

Changes

File	What
contracts/src/MockPendleRouter.sol	Deterministic 1:0.995 mock matching the exact ABI the app expects. Token-agnostic (no real transfers - so it runs on testnet without funding the caller), emits SwapExactTokenForPt, reverts InsufficientPtOut below minPtOut. Apache-2.0.
contracts/script/DeployMockPendleRouter.s.sol	Arbitrum Sepolia deploy script (the only chain the off-chain builder targets for the router).
contracts/test/MockPendleRouter.t.sol	5 tests incl. an end-to-end agent-signed envelope -> AgentPolicyGate -> router integration test proving the scenario A on-chain path.
DEPLOY.md	Full copy-paste deploy runbook: both chains, the easy-to-forget allow-list step, signer-pair pre-check, deployed.json + decoder-data wiring, post-deploy cast verification, smoke test.
contracts/README.md	Pointer to DEPLOY.md.

Verification

cd examples/arbitrum-london/contracts && forge test
# 20 passed (15 AgentPolicyGate + 5 MockPendleRouter), 0 failed

cd examples/arbitrum-london && npx tsc --noEmit
# clean, exit 0

Mock fidelity

The mock's fixed 995/1000 rate is exactly what buildPendleEnvelope assumes: it sets minPtOut = amountIn * (10000 - slippageBps) / 10000, so any declared slippage of 50 bps or looser succeeds and anything tighter reverts InsufficientPtOut - the same shape a real router would present. The integration test pins the 50 bps boundary.

What this does NOT do

• Deploy anything. Contracts still need a funded-key forge script run (Mike) - the whole point of DEPLOY.md.
• Touch scenario C (Robinhood RWA) - its buildRwaEnvelope still throws "not implemented" (Phase 2 Day 10). DEPLOY.md deploys the Robinhood gate only, for the multi-chain claim.
• Add real token custody / pricing / PT minting to the mock (deliberately out of scope; would obscure the review-and-sign flow).

Notes for review

• MockPendleRouter is intentionally stateless and token-free. If you want the demo to show a real ERC-20 pull (approve + transferFrom), that is a larger change and would need a mock input token + an approve leg in the envelope.
• DEPLOY.md flags the two silent-failure traps explicitly: skipping the allow-list, and a signer-pair mismatch. Both compile + deploy fine and only revert at execute time.

Leaving this open for your review - not merging.

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Project	Deployment	Actions	Updated (UTC)
txkit-docs	Ready	Preview, Comment	May 29, 2026 1:36pm
txkit-land	Ready	Preview, Comment	May 29, 2026 1:36pm
txkit-story	Ready	Preview, Comment	May 29, 2026 1:36pm