Feature: Add Note to Budget Command

[CarolGitonga]

The Kujali backend follows a CQRS (Command Query Responsibility Segregation) pattern built on top of Firebase Cloud Functions. Each business operation is expressed as a Command and a Handler.

Design Choices

AddNoteToBudgetCommand (add-note.command.ts)
A plain class with readonly fields: orgId, budgetId, content, createdBy, createdAt
orgId is included because all Firestore data in this project is multi-tenant, scoped under orgs/{orgId}/.... Without it, the handler cannot construct the correct Firestore path.
createdAt defaults to Date.now() so callers don't have to provide it explicitly.

BudgetNote (budget-note.interface.ts)
Extends IObject, which provides the auto-generated id field.
Keeps the model in the model/budgetting library, consistent with how all other domain interfaces are structured in the monorepo.

AddNoteToBudgetHandler (add-note.handler.ts)
Extends FunctionHandler<AddNoteToBudgetCommand, AddNoteToBudgetResult>

add-budget-note.function.ts
Uses RestRegistrar, the same registrar used by promoteBudget and other command functions. This makes the function callable from the Angular frontend using AngularFire's httpsCallable.
Registered under the name addNoteToBudget and exported from main.ts so Firebase picks it up at deploy time.

Serverless Deployment & Scaling
What is Serverless?
Serverless means the infrastructure (servers, OS, runtime) is fully managed by the cloud provider. You deploy code (a function), define a trigger, and the platform handles provisioning, scaling, and availability. Firebase Cloud Functions run on Google Cloud Functions, which is a fully serverless compute platform.

Trade-offs to be aware of
Cold starts can affect UX if the function is rarely called. Mitigation: Cloud Scheduler keep-alive pings, or migrating to Cloud Run (which supports min-instances).
No long-running processes — serverless functions have a max timeout (9 minutes on Gen 1). addNoteToBudget is a fast write operation so this is not a concern here.

The screenshot below shows addNoteToBudget on the emulator

[CarolGitonga]

"Latest changes pushed — refactored handler placement to follow the libs/functions/finance/budgeting pattern consistent with the rest of the codebase."