Add OpenCode Zen/Black usage (experimental cookie-based integration)

[davidarny]

Summary

Add OpenCode provider support in OpenUsage for:

• Zen billing usage (balance, monthly usage/limit, reload settings)
• Black rolling/weekly usage when available

Why

OpenCode does not currently expose a documented public billing/usage API for Zen API keys. Zen docs expose model/inference endpoints, not account billing endpoints.

Research

Public docs / endpoints

• Zen docs: https://opencode.ai/docs/zen/
• Documented endpoints are model/inference oriented (/zen/v1/models, /zen/v1/responses, /zen/v1/messages, /zen/v1/chat/completions)

Prior art

• CodexBar OpenCode provider uses browser cookies + private _server calls:
  • https://raw.githubusercontent.com/steipete/CodexBar/main/Sources/CodexBarCore/Providers/OpenCode/OpenCodeUsageFetcher.swift
  • https://raw.githubusercontent.com/steipete/CodexBar/main/docs/opencode.md

What we verified

• With authenticated session cookies, GET https://opencode.ai/workspace/<workspaceId>/billing returns HTML that embeds hydrated billing payload in script (contains fields like balance, monthlyUsage, monthlyLimit, reload*, subscription*, payment list).
• Hardcoded _server function IDs are brittle/unstable across time.
• In OpenCode source, Black rolling/weekly usage is computed in dashboard server-side flow (querySubscription), not via documented public API-key endpoint:
  • https://raw.githubusercontent.com/anomalyco/opencode/dev/packages/console/app/src/routes/workspace/%5Bid%5D/billing/black-section.tsx

Proposal

Implement OpenCode as experimental provider via authenticated dashboard payload parsing:

1. Auth input: manual Cookie header (required), optional workspace ID override.
2. Fetch billing page (/workspace/<id>/billing) and parse hydration payload.
3. Map Zen metrics from billing.get payload:
   • current balance
   • monthly usage / limit
   • reload settings
4. If Black subscription usage is present, map rolling/weekly usage + reset timers.
5. Fail loudly with explicit parse/auth errors (no silent fallback).

Scope guardrails

• No browser scraping automation in v1.
• No reliance on hardcoded private _server IDs in v1.
• Mark provider as experimental/fragile in UI/docs.

Acceptance Criteria

• OpenCode plugin exists with manual cookie auth UX.
• Parser covered with fixtures + regression tests for payload-shape drift.
• Clear user-facing errors for expired cookie / parse failure.
• README updated to include OpenCode support and experimental warning.

[robinebers]

Would love to have this too, yes. Wish I had access to Black but I still don't.
Feels like they stopped rolling it out.