Add PostgreSQL implementations for EventStore, APIKeyStore, IdempotencyStore, and DLQStore

[Copilot]

• Create store/pg_event_store.go - PostgreSQL EventStore using pgxpool
• Create store/pg_api_keys.go - PostgreSQL APIKeyStore using pgxpool
• Create store/pg_idempotency.go - PostgreSQL IdempotencyStore using pgxpool
• Create store/pg_dlq.go - PostgreSQL DLQStore using pgxpool
• Fix buildPGDLQQuery: remove dead idx++ after ErrorType
• Fix PGEventStore.Append concurrency: use pg_advisory_xact_lock keyed on execution UUID to serialize per-execution appends
• Add store/pg_stores_test.go: integration tests for all four PG stores, gated by PG_URL
• Fix idempotency test cleanup: replace prefix-based DELETE WHERE key LIKE $1 with DELETE FROM idempotency_keys so fixed keys used by runIdempotencyTests ("order-123-step-validate", "expired-key", "dup-key", etc.) are properly cleaned up between runs
• All tests pass, linter clean

Original prompt

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This section details on the original issue you should resolve

<issue_title>Add PostgreSQL support for SQLite-only stores (EventStore, APIKeyStore, IdempotencyStore, DLQStore)</issue_title>
<issue_description>## Problem

Four core subsystems in store/ package only have SQLite implementations (plus InMemory for testing). This forces deployments to include SQLite even when PostgreSQL is the primary database.

Store	File	Interface
Event Store	store/event_store.go	EventStore
API Key Store	store/api_keys.go	APIKeyStore
Idempotency Store	store/idempotency.go	IdempotencyStore
Dead Letter Queue	store/dlq.go	DLQStore

All four use database/sql with modernc.org/sqlite driver and SQLite-specific DDL. The database.workflow module already supports both PostgreSQL (pgx) and SQLite, but these operational stores don't.

Proposed Solution

Follow the pattern already established in platform/state/ which has both sqlite_store.go and postgres_store.go:

1. Create store/pg_event_store.go, store/pg_api_keys.go, store/pg_idempotency.go, store/pg_dlq.go
2. Use PostgreSQL-compatible SQL (parameter placeholders $1, TIMESTAMPTZ, JSONB, UUID)
3. Accept a *sql.DB or *pgxpool.Pool connection
4. Add a factory function that selects the right implementation based on driver/config
5. Use build tags or runtime detection to choose implementation

Key SQL Differences to Handle:

• Parameter placeholders: ? (SQLite) → $1, $2, ... (PostgreSQL)
• DDL: INTEGER PRIMARY KEY AUTOINCREMENT → BIGSERIAL PRIMARY KEY
• JSON columns: TEXT → JSONB
• Timestamps: TEXT → TIMESTAMPTZ
• UUIDs: TEXT → UUID

Context

BuyMyWishlist and other PostgreSQL-first deployments shouldn't need SQLite as a dependency. The database.workflow module (module/database.go) already supports pgx driver — these stores should leverage it.</issue_description>

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

• Fixes Add PostgreSQL support for SQLite-only stores (EventStore, APIKeyStore, IdempotencyStore, DLQStore) #213

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[Copilot]

Pull request overview

Adds PostgreSQL-backed implementations for four core store/ subsystems (EventStore, APIKeyStore, IdempotencyStore, DLQStore) so PostgreSQL-first deployments aren’t forced to depend on SQLite for these operational stores.

Changes:

• Introduces PGEventStore, PGAPIKeyStore, PGIdempotencyStore, and PGDLQStore using *pgxpool.Pool and PostgreSQL-native types (UUID, JSONB, TIMESTAMPTZ).
• Creates required tables/indexes on construction via CREATE TABLE IF NOT EXISTS.
• Updates go.mod to make github.com/xdg-go/scram a direct dependency.

Reviewed changes

Copilot reviewed 5 out of 5 changed files in this pull request and generated 6 comments.

Show a summary per file

File	Description
store/pg_event_store.go	New Postgres event store implementation (append-only execution event log).
store/pg_api_keys.go	New Postgres API key store implementation (CRUD + validation).
store/pg_idempotency.go	New Postgres idempotency key store implementation (check/store/cleanup).
store/pg_dlq.go	New Postgres DLQ store implementation (entry lifecycle + filtering).
go.mod	Promotes xdg-go/scram to a direct dependency.

[intel352]

@copilot apply changes based on the comments in this thread

[intel352]

@copilot address this issue. #216 (comment)

[Copilot]

@copilot address this issue. #216 (comment)

Fixed in 7eabfa3 — removed the dead idx++ (and its nolint comment) from the ErrorType block in buildPGDLQQuery. The placeholder numbering is unchanged; idx simply isn't needed after the last condition.

[Copilot]

Pull request overview

Copilot reviewed 6 out of 6 changed files in this pull request and generated 1 comment.

[intel352]

@copilot apply changes based on the comments in this thread

[Copilot]

@copilot apply changes based on the comments in this thread

Applied in 359e6fb — the idempotency subtest cleanup now uses DELETE FROM idempotency_keys instead of a prefix filter, ensuring all rows created by runIdempotencyTests (including hardcoded keys) are removed after each run.