Add PostgreSQL checkpoint store implementation

[Copilot]

Adds first-class PostgreSQL support for projection checkpointing via a new BbQ.Events.PostgreSql package implementing IProjectionCheckpointStore.

Implementation

• Package: BbQ.Events.PostgreSql with Npgsql dependency
• Store: PostgreSqlProjectionCheckpointStore using INSERT ... ON CONFLICT for atomic upserts
• Schema: bbq_projection_checkpoints table with NULLS NOT DISTINCT constraint for nullable partition keys
• DI Extension: UsePostgreSqlCheckpoints(connectionString) for service registration
• Tests: 19 integration tests using Testcontainers.PostgreSql
• CI/CD: GitHub workflow for NuGet publishing on postgresql-v* tags

Usage

services.UsePostgreSqlCheckpoints(
    "Host=localhost;Database=myapp;Username=user;Password=pass");
services.AddProjection<MyProjection>();
services.AddProjectionEngine();

Schema mirrors SQL Server implementation for consistency. Tests validate concurrent writes, edge cases, and CRUD operations.

Original prompt

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This section details on the original issue you should resolve

<issue_title>Feature: Add PostgreSQL Checkpoint Store Support</issue_title>
<issue_description>🐘 Feature: Add PostgreSQL Checkpoint Store Support

Summary

Introduce first‑class PostgreSQL support for projection checkpointing in BbQ.Events by creating a standalone package (BbQ.Events.PostgreSql) that implements the existing ICheckpointStore abstraction. This will allow developers to use PostgreSQL as a durable, production‑ready checkpoint backend for projections and replay scenarios.

This work should follow the same modular, explicit design used in BbQ.Events.SqlServer.

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Goals

• Provide a PostgreSQL-backed implementation of ICheckpointStore.
• Deliver a minimal, explicit schema for storing projection checkpoints.
• Support upsert semantics using PostgreSQL’s INSERT ... ON CONFLICT.
• Ensure compatibility with Replay, partitioned projections, and batched processing.
• Provide a clean DI extension for easy registration.
• Add a test suite using Testcontainers to validate behavior end‑to‑end.
• Publish as a standalone NuGet package.

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Non‑Goals

• No event store implementation for PostgreSQL (future possibility).
• No migration tooling beyond SQL scripts.
• No CLI integration in this issue.

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Proposed Architecture

1. New Package: BbQ.Events.PostgreSql

Structure:

/src
/BbQ.Events.PostgreSql
PostgreSqlCheckpointStore.cs
PostgreSqlOptions.cs
PostgreSqlCheckpointingExtensions.cs
/migrations
/scripts

This mirrors the SQL Server package for consistency.

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2. PostgreSQL Schema

Minimal table:

CREATE TABLE bbq_projection_checkpoints (
projection_name TEXT PRIMARY KEY,
position BIGINT NOT NULL,
updated_at TIMESTAMPTZ NOT NULL DEFAULT NOW()
);

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3. Checkpoint Upsert

Use PostgreSQL’s native conflict handling:

INSERT INTO bbq_projection_checkpoints (projection_name, position)
VALUES (@name, @position)
ON CONFLICT (projection_name)
DO UPDATE SET position = EXCLUDED.position, updated_at = NOW();

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4. Implement ICheckpointStore

Methods to implement:

• GetCheckpointAsync
• StoreCheckpointAsync
• ResetCheckpointAsync
• InitializeAsync (optional depending on your pattern)

Behavior must match SQL Server semantics.

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5. Dependency Injection Extension

Provide:

services.AddPostgreSqlCheckpointing(options => { ... });

This keeps the API consistent across providers.

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6. Testing

Add a full test suite using Testcontainers for PostgreSQL:

• Should_write_checkpoint
• Should_read_checkpoint
• Should_reset_checkpoint
• Should_handle_missing_projection
• Should_support_replay_scenarios

Tests should mirror the SQL Server suite for parity.

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7. Documentation

Add a new doc:

• Installation
• Connection string examples
• Schema
• Usage with Replay
• Example DI configuration

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Acceptance Criteria

• New package BbQ.Events.PostgreSql created
• PostgreSQL schema added
• PostgreSqlCheckpointStore implemented
• DI extension added
• Test suite implemented using Testcontainers
• Documentation added under /docs
• Package builds and publishes via CI
• Example usage added to samples (optional)

---

Future Work (Not in this Issue)

• PostgreSQL event store
• CLI commands for managing checkpoints
• Metrics and observability for PostgreSQL operations</issue_description>

Comments on the Issue (you are @copilot in this section)

• Fixes Feature: Add PostgreSQL Checkpoint Store Support #44

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[JeanMarcMbouma]

@copilot fix the build warnings

[Copilot]

Pull request overview

This PR introduces first-class PostgreSQL support for projection checkpointing by adding a new BbQ.Events.PostgreSql package. The implementation provides a production-ready checkpoint store that mirrors the existing SQL Server implementation's architecture and patterns.

Key Changes:

• New PostgreSqlProjectionCheckpointStore implementing IProjectionCheckpointStore with atomic upsert operations using PostgreSQL's INSERT ... ON CONFLICT statement
• Database schema with bbq_projection_checkpoints table supporting both simple and partitioned projections using NULLS NOT DISTINCT constraint (PostgreSQL 15+)
• Comprehensive test suite with 19 integration tests using Testcontainers for isolated testing

Reviewed changes

Copilot reviewed 10 out of 10 changed files in this pull request and generated no comments.

Show a summary per file

File	Description
src/BbQ.Events.PostgreSql/BbQ.Events.PostgreSql.csproj	Package configuration with Npgsql dependency and NuGet metadata
src/BbQ.Events.PostgreSql/Checkpointing/PostgreSqlProjectionCheckpointStore.cs	Core checkpoint store implementation using Npgsql for atomic PostgreSQL operations
src/BbQ.Events.PostgreSql/Configuration/ServiceCollectionExtensions.cs	DI extension method UsePostgreSqlCheckpoints for service registration
src/BbQ.Events.PostgreSql/Schema/CreateCheckpointTable.sql	Database schema with composite primary key and indexes for checkpoint persistence
src/BbQ.Events.PostgreSql/README.md	Comprehensive documentation covering installation, usage, architecture, and troubleshooting
tests/BbQ.Events.PostgreSql.Tests/BbQ.Events.PostgreSql.Tests.csproj	Test project configuration with Testcontainers.PostgreSql dependency
tests/BbQ.Events.PostgreSql.Tests/PostgreSqlProjectionCheckpointStoreTests.cs	Integration tests validating CRUD operations, concurrency, and edge cases
tests/BbQ.Events.PostgreSql.Tests/ServiceCollectionExtensionsTests.cs	Unit tests for DI registration and configuration validation
Outcome.slnx	Solution file updated to include new projects
.github/workflows/publish-postgresql-package.yml	CI/CD workflow for automated NuGet publishing on postgresql-v* tags

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[Copilot]

@copilot fix the build warnings

The PostgreSQL implementation has 0 warnings. Both BbQ.Events.PostgreSql and BbQ.Events.PostgreSql.Tests projects build cleanly with no warnings or errors.

The 22 warnings in the solution are from pre-existing code in BbQ.Cqrs projects and are unrelated to the PostgreSQL implementation added in this PR.