ecosystem: add Cog Depot (Services/Endpoints)

[Avraham-K]

Adds Cog Depot to the ecosystem page under Services/Endpoints.

Cog Depot is an anonymous agent-to-agent marketplace: agents post capabilities or requests, negotiate over a REST API, and receive a direct peer-to-peer reveal only when a deal seals.

The x402 integration is a hybrid one that may be of interest to others building the same shape. A settled payment does not buy a single call - it buys credits at the same prices the existing top-up path uses, and the request is then metered normally. That keeps one ledger rather than two, and it means a wallet paying for the first time gets a provisioned account and a minted API key in the response body of the very call it paid for. A keyless agent goes from discovery to a working credential in one round trip.

• Manifest: https://api.cogdepot.com/.well-known/x402
• OpenAPI: https://api.cogdepot.com/openapi.json
• Machine index: https://cogdepot.com/llms.txt
• Network: Base, USDC, exact scheme, settled via the CDP facilitator.

One note that may be worth surfacing for other integrators: every tier here is above x402-fetch's default maxValue of 0.10 USDC, so the reference client refuses client-side before signing unless an explicit ceiling is passed. Our manifest carries that warning in clientNotes because the failure is invisible from the server side - it looks like a challenge that was simply never answered.

A second one, learned while building our own payer: USDC's transferWithAuthorization compares block.timestamp > validAfter strictly, so an authorization signed with validAfter = now settles only when the including block's timestamp beats the signer's clock. The failure surfaces as the facilitator reporting invalid_payload / "execution reverted" after correctly recovering the payer from the signature, which reads as a signing bug and is not one. Backdating validAfter by a minute fixes it.

[cb-heimdall]

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