feat(pulse): abstract PulseDatabase interface from bun:sqlite

Phase 1 of pulseflare migration: decouple core logic from bun:sqlite.

- Add PulseDatabase/PulseStatement interfaces in database.ts
- Replace 'import { Database } from bun:sqlite' with PulseDatabase alias
  in defs.ts, projection-engine.ts, guard-projection.ts
- Update PulseStore.getDatabase() and ScopedStore.scopeDatabase() return
  types to PulseDatabase
- store.ts retains bun:sqlite as concrete implementation
- Export PulseDatabase/PulseStatement from package index
- All existing tests pass unchanged

packages/pulse/src/database.ts

@@ -0,0 +1,21 @@
+/**
+ * Abstract database interface for Pulse.
+ *
+ * Decouples core logic from bun:sqlite so alternative backends
+ * (e.g. Cloudflare D1) can provide their own implementation.
+ */
+
+export interface PulseStatement {
+  get(...params: any[]): any;
+  all(...params: any[]): any[];
+  run(...params: any[]): { changes: number; lastInsertRowid: number | bigint };
+}
+
+export interface PulseDatabase {
+  exec(sql: string): void;
+  prepare(sql: string): PulseStatement;
+  run(sql: string, ...params: any[]): void;
+  transaction<T>(fn: () => T): (...args: any[]) => T;
+  close(): void;
+  readonly inTransaction: boolean;
+}

packages/pulse/src/defs.d.ts

@@ -4,7 +4,7 @@
  * Append-only definition tables for objects, events, and projections.
  * Content-addressed versioning with code_rev binding.
  */
-import type { Database } from 'bun:sqlite';
+import type { PulseDatabase as Database } from './database.js';
 export interface ObjectDef {
   name: string;
   codeRev: string;

packages/pulse/src/defs.ts

@@ -5,9 +5,9 @@
  * Content-addressed versioning with code_rev binding.
  */
 
-import type { Database } from 'bun:sqlite';
 import { createHash } from 'node:crypto';
 import jsonata from 'jsonata';
+import type { PulseDatabase as Database } from './database.js';
 
 // ── Types ──────────────────────────────────────────────────────
 

packages/pulse/src/guard-projection.ts

@@ -3,7 +3,7 @@
  * Core logic delegated to guard-core.ts (pure, portable).
  */
 
-import type { Database } from 'bun:sqlite';
+import type { PulseDatabase as Database } from './database.js';
 import {
   checkGuardsCore,
   clearGuardExpressionCache as clearCoreCache,

packages/pulse/src/index.ts

@@ -899,6 +899,10 @@ export function createRule<S, E, T>(
   return (prev, curr, inner) => logic(accessor(prev), accessor(curr), inner);
 }
 
+// ── Database Abstraction ────────────────────────────────────────
+
+export type { PulseDatabase, PulseStatement } from './database.js';
+
 // ── Storage ────────────────────────────────────────────────────
 
 export {

packages/pulse/src/projection-engine.d.ts

@@ -4,7 +4,7 @@
  * Incremental fold engine for projections with JSONata expressions.
  * Projections are first-class citizens with their own state table.
  */
-import type { Database } from 'bun:sqlite';
+import type { PulseDatabase as Database } from './database.js';
 /** Clear the compiled expression cache (useful for testing). */
 export declare function clearExpressionCache(): void;
 export interface ProjectionState {

packages/pulse/src/projection-engine.ts

@@ -5,7 +5,7 @@
  * Projections are first-class citizens with their own state table.
  */
 
-import type { Database } from 'bun:sqlite';
+import type { PulseDatabase as Database } from './database.js';
 import jsonata, { type Expression } from 'jsonata';
 import { getProjectionDef } from './defs.js';
 

packages/pulse/src/store.d.ts

@@ -5,6 +5,7 @@
  * content-addressed object store (CAS) on disk via SHA-256 hashes.
  */
 import { Database } from 'bun:sqlite';
+import type { PulseDatabase } from './database.js';
 export interface EventRecord {
   id: number;
   occurredAt: number;
@@ -99,8 +100,8 @@ export interface CreateScopedStoreOptions {
 export interface ScopedStore {
   scope(name: string): PulseStore;
   listScopes(): string[];
-  /** Get underlying Database for scope (used by projection engine) */
-  scopeDatabase(name: string): Database;
+  /** Get underlying database for scope (used by projection engine) */
+  scopeDatabase(name: string): PulseDatabase;
   putObject(data: unknown): Promise<string>;
   getObject(hash: string): Promise<unknown | null>;
   close(): Promise<void>;

packages/pulse/src/store.ts

@@ -6,6 +6,7 @@
  */
 
 import { Database } from 'bun:sqlite';
+import type { PulseDatabase } from './database.js';
 import { createHash } from 'node:crypto';
 import {
   existsSync,
@@ -108,8 +109,8 @@ export interface PulseStore {
   /** Read data from CAS store by hash. Returns null if not found. */
   getObject(hash: string): Promise<unknown | null>;
 
-  /** Get the underlying bun:sqlite Database handle (for guard projections etc.) */
-  getDatabase(): Database;
+  /** Get the underlying database handle (for guard projections etc.) */
+  getDatabase(): PulseDatabase;
 
   /** Close the database */
   close(): Promise<void>;
@@ -544,8 +545,8 @@ export interface ScopedStore {
   scope(name: string): PulseStore;
   listScopes(): string[];
 
-  /** Get underlying Database for scope (used by projection engine) */
-  scopeDatabase(name: string): Database;
+  /** Get underlying database for scope (used by projection engine) */
+  scopeDatabase(name: string): PulseDatabase;
 
   putObject(data: unknown): Promise<string>;
   getObject(hash: string): Promise<unknown | null>;