Productize Switchboard Hosted: Standard + Pro billing surface

[abhicris]

Problem

The Switchboard 2-SKU economic model specifies Hosted Switchboard with two tiers (Standard, Pro) plus per-tx overage. Today the OSS lib is self-hostable but there is no managed control plane that a customer can point a checkout flow at. To onboard the first Hosted customers (IPTO PI per #82, Hanzo enterprise per #81, others), we need the billing surface live.

This issue tracks the productized billing surface itself, not any individual customer onboarding.

Proposed Approach

1. Customer onboarding flow:
   • Sign-up endpoint that issues an API key + endpoint URL
   • Tier selection (Standard / Pro) at sign-up; tier change requires support ticket (no self-serve downgrade)
   • Month-to-month default; annual option for Pro at a 10% discount
2. Metering:
   • Per-tx counter incremented on every x402_middleware.settle and AgentEscrow.release event
   • Overage line item: tx count above the included tier minute at $0.001/tx
3. Invoicing:
   • Monthly via Stripe (or a paid-billing provider already in the stack)
   • Pro annual customers get a single annual invoice with 10% off
4. Customer dashboard:
   • Tx count, gas spent, error rate
   • Realized 30d APY card if Lucidly adapter (Lucidly syUSD idle-balance adapter for agent wallets (refresh of #20) #80) is enabled
   • Budget headroom against the tier minute
5. No public pricing page. Per the kcolbchain pricing-private convention, prospects get pricing on application via the standard contact flow. The billing system enforces the tier numbers; the public surface does not display them.

Acceptance Criteria

• Sign-up flow live
• Stripe billing integrated; monthly invoices generated on test data
• Customer dashboard ships behind auth
• First customer onboarded successfully (likely IPTO PI per Tracking: IPTO PI as Switchboard Hosted Standard customer (arms-length) #82)
• Overage line item correctly billed on a synthetic over-tier workload
• No public pricing page; pricing visible only to authenticated customers + sales

References

• Issue Tracking: Hanzo hanzoai/agent reference integration (paid SOW) #81 — Hanzo agent reference integration (forward customer)
• Issue Tracking: IPTO PI as Switchboard Hosted Standard customer (arms-length) #82 — IPTO PI integration (first customer)
• internal: see project_switchboard_econ_model and SOPs at internal/ops/sops/switchboard/04-sop-hosted.md