#613 release: charge credits per chat turn (#612)

Summary

Releases PR #612 from `test` → `main`.

• Closes the silent revenue-loss gap: every successful chat workflow turn now atomically debits the account wallet AND records a `usage_events` audit row
• Refactors to consolidate billing into the existing `handleChatCredits` orchestrator (one path for both `/api/chat` and `/api/chat/workflow`)
• Switches `recordCreditDeduction` to the atomic `deduct_credits_with_audit` Postgres RPC (recoupable/database#26) — eliminates wallet/meter drift for ALL callers, including the 3 research handlers
• Closes #605 chat-workflow billing gap

Test plan

• 3195 unit tests passing
• Lint / format / tsc clean
• E2E preview verification: wallet 998c → 997c, audit row `PenhKC1lRbdzyRQjcaSH0` landed with correct fields (`source='api'`, `agent_type='main'`, `model_id='anthropic/claude-haiku-4.5'`, `credits_deducted_cents=1`)
• Post-merge: sanity check on `sandbox.recoupable.com` against `https://api.recoupable.com\` — trigger a chat and confirm wallet drops

🤖 Generated with Claude Code

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Summary by cubic

Charges credits for every successful chat workflow turn with an atomic wallet debit + audit, closing the chat-workflow billing gap. Consolidates billing for both /api/chat and /api/chat/workflow; closes #605.

• New Features

  • Atomic debit + audit via deduct_credits_with_audit Postgres RPC for each turn (no wallet/meter drift).
  • runAgentWorkflow persists the assistant message, then bills using handleChatCredits with accountId, model, gateway cost, and token usage from message metadata.
  • getCreditUsage accepts a gateway-reported USD cost and short-circuits token math; 1¢ minimum still applies.
  • Source tagging on audit rows: workflow path uses source="api"; streaming path defaults to source="web".

• Refactors

  • Unified billing through handleChatCredits for /api/chat and /api/chat/workflow.
  • Replaced deductCredits + insertUsageEvent with a single RPC wrapper: lib/supabase/credits_usage/deductCreditsWithAudit.
  • Threaded validated accountId into the workflow; updated tests and Supabase RPC types.