feat: integrate chat credits handling into chat stream processing

[pradipthaadhi]

• Added handleChatCredits function to manage usage tracking for chat sessions.
• Updated the chat stream execution to include credit handling after processing messages.
• Ensured compatibility with the existing chat completion handling logic.
• test(api): mock handleChatCredits and DEFAULT_MODEL in handleChatStream tests

Summary by CodeRabbit

• Bug Fixes
  • Chat completions now reliably apply credit charges when a conversation finishes.
  • Charges are enforced to deduct at least one credit even if reported usage is zero.
  • Credit calculations now use a sensible model fallback when the model isn't specified.

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[coderabbitai]

No actionable comments were generated in the recent review. 🎉

ℹ️ Recent review info

⚙️ Run configuration

Configuration used: Path: .coderabbit.yaml

Review profile: CHILL

Plan: Pro

Run ID: c94e6fd3-9ae5-493c-b7be-d3bbe850a867

📥 Commits

Reviewing files that changed from the base of the PR and between 12e6797 and a600ead.

📒 Files selected for processing (1)

• lib/credits/handleChatCredits.ts

🚧 Files skipped from review as they are similar to previous changes (1)

• lib/credits/handleChatCredits.ts

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📝 Walkthrough

Walkthrough

Captured and retained the streaming result in lib/chat/handleChatStream.ts, used it for UI streaming and invoked handleChatCredits on completion; lib/credits/handleChatCredits.ts now always computes and deducts at least 1 credit (removed usageCost > 0 guard).

Changes

Cohort / File(s)	Summary
Stream result & credit invocation lib/chat/handleChatStream.ts	Store agent.stream(chatConfig) as streamResult; use streamResult.toUIMessageStream() for UI merge; on onFinish call handleChatCredits with await streamResult.usage, model: body.model ?? DEFAULT_MODEL, and accountId: body.accountId.
Credits deduction logic lib/credits/handleChatCredits.ts	Removed if (usageCost > 0) check. Always compute creditsToDeduct = Math.max(1, Math.round(usageCost * 100)) and call deductCredits unconditionally, ensuring a minimum deduction of 1 credit even when usageCost ≤ 0.

Sequence Diagram(s)

sequenceDiagram
  actor Client
  participant Handler as "handleChatStream"
  participant Agent
  participant UI as "UI Stream"
  participant Credits as "handleChatCredits"
  participant Billing as "Billing Service"

  Client->>Handler: start chat request
  Handler->>Agent: agent.stream(chatConfig)
  Agent-->>Handler: streamResult
  Handler->>UI: streamResult.toUIMessageStream() (merge)
  UI-->Client: incremental messages
  UI->>Handler: onFinish event
  Handler->>Handler: handleChatCompletion(...)
  Handler->>Credits: handleChatCredits(usage=await streamResult.usage, model, accountId)
  Credits->>Billing: deductCredits(accountId, creditsToDeduct)
  Billing-->>Credits: deduction result
  Credits-->>Handler: completion

Loading

Estimated code review effort

🎯 3 (Moderate) | ⏱️ ~25 minutes

Poem

A stream retained, the tokens told,
Completion rings where numbers fold,
One credit kept as minimum due,
Ledger whispers, balances true. ✨

🚥 Pre-merge checks | ✅ 1

✅ Passed checks (1 passed)

Check name	Status	Explanation
Solid & Clean Code	✅ Passed	Pull request demonstrates strong adherence to SOLID principles, clean code practices, and maintainable architecture with proper separation of concerns, clear dependency flow, comprehensive error handling, and well-structured code organization.

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✨ Finishing Touches

🧪 Generate unit tests (beta)

• Create PR with unit tests

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Project	Deployment	Actions	Updated (UTC)
recoup-api	Ready	Preview	Mar 30, 2026 3:00am

[coderabbitai]

Actionable comments posted: 1

🤖 Prompt for all review comments with AI agents

Verify each finding against the current code and only fix it if needed.

Inline comments:
In `@lib/credits/handleChatCredits.ts`:
- Around line 30-35: The current logic in handleChatCredits.ts always converts
zero-cost events into a 1-credit charge (creditsToDeduct) and unconditionally
calls deductCredits, causing non-billable sessions to consume credits; update
handleChatCredits so you only call deductCredits(accountId, creditsToDeduct)
when an explicit "billable usage happened" condition from the chat/session is
true (derive this from the same signal used in lib/chat/handleChatStream.ts for
real completions), and keep the Math.max(1, Math.round(usageCost * 100)) minimum
calculation only for those billable cases; ensure you still compute
creditsToDeduct the same way but gate the call to deductCredits(...) behind that
billable flag so cached/provider-failed/non-aborted-but-non-billable flows do
not mutate balance or throw.

🪄 Autofix (Beta)

Fix all unresolved CodeRabbit comments on this PR:

• Push a commit to this branch (recommended)
• Create a new PR with the fixes

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ℹ️ Review info

⚙️ Run configuration

Configuration used: Path: .coderabbit.yaml

Review profile: CHILL

Plan: Pro

Run ID: 56727693-526b-4be3-bf48-8df898f150c3

📥 Commits

Reviewing files that changed from the base of the PR and between 1433341 and 12e6797.

⛔ Files ignored due to path filters (3)

• lib/chat/__tests__/handleChatStream.test.ts is excluded by !**/*.test.*, !**/__tests__/** and included by lib/**
• lib/chat/__tests__/integration/chatEndToEnd.test.ts is excluded by !**/*.test.*, !**/__tests__/** and included by lib/**
• lib/credits/__tests__/handleChatCredits.test.ts is excluded by !**/*.test.*, !**/__tests__/** and included by lib/**

📒 Files selected for processing (1)

• lib/credits/handleChatCredits.ts