Add signed x402 paid-action example endpoint and tests

[GsCommand]

Motivation

• Provide a server-side example that demonstrates the correct trust boundary between x402 payment acceptance and CommandLayer execution attestation.
• Show how to capture a paid-action request, execute a deterministic local action, and produce a CLAS-style signed receipt without performing real x402 settlement.

Description

• Add POST /api/examples/x402-paid-action implemented in api/examples/x402-paid-action.js with strict method/body validation and explicit JSON error statuses.
• Validate x402 payment envelope (payment.protocol === 'x402', payment.status === 'accepted', and payment.payment_id), support only action === 'summarize.text', and enforce input length limits.
• Execute a deterministic local summary via buildDeterministicSummary, deduplicate by request_id::payment_id using an in-memory seenReceipts map, and return the same receipt for duplicates.
• Sign CLAS-style receipts by reusing lib/receiptSigning.js (signReceipt, resolveReceiptSigningConfigFromEnv, hasValidSigningConfig) and include metadata.trace and metadata.proof fields; update docs with a short example and trust-boundary reminder in docs/integrations/x402-commandlayer-receipts.md.

Testing

• Add tests in tests/api-x402-paid-action.test.js covering method checks, malformed body, missing/invalid payment, unsupported action, signing-unavailable behavior, successful signing, duplicate idempotency, and local receipt verification.
• Run npm test, which passed all tests (87 passed, 0 failed) including the new suite.
• Verify that returned receipts include metadata.trace and metadata.proof.hash, contain an Ed25519 signature, and verify locally via verifyReceipt with an injected ENS text resolver.

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Codex Task

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Project	Deployment	Actions	Updated (UTC)
commandlayer-commandlayer-org	Ready	Preview, Comment	May 23, 2026 9:17pm
commandlayer-org	Ready	Preview, Comment	May 23, 2026 9:17pm
commandlayer-org111	Ready	Preview, Comment	May 23, 2026 9:17pm