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Fix UNIQUE constraint on events.sequence during concurrent tool calls #139

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Fix UNIQUE constraint on events.sequence during concurrent tool calls #139

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36 changes: 30 additions & 6 deletions mcp/src/server/events.ts
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Original file line number Diff line number Diff line change
Expand Up @@ -47,6 +47,9 @@ class EventBus {

/**
* Emit an event to all subscribers.
* Assigns a sequence number and immediately notifies subscribers.
* For SQLite-backed stores, use nextSequence() + notify() instead
* to ensure the sequence is persisted before subscribers see it.
*/
emit(
type: AFSEventType,
Expand All @@ -61,6 +64,22 @@ class EventBus {
payload,
};

this.notify(event);
return event;
}

/**
* Get the next unique sequence number.
*/
nextSequence(): number {
return ++globalSequence;
}

/**
* Notify all subscribers of an event.
* The event must already have a valid sequence assigned.
*/
notify(event: AFSEvent): void {
// Notify global subscribers
for (const handler of this.handlers) {
try {
Expand All @@ -71,7 +90,7 @@ class EventBus {
}

// Notify session-specific subscribers
const sessionHandlers = this.sessionHandlers.get(sessionId);
const sessionHandlers = this.sessionHandlers.get(event.sessionId);
if (sessionHandlers) {
for (const handler of sessionHandlers) {
try {
Expand All @@ -81,8 +100,6 @@ class EventBus {
}
}
}

return event;
}

/**
Expand Down Expand Up @@ -188,6 +205,15 @@ class UserEventBus {
payload,
};

this.notifyForUser(userId, event);
return event;
}

/**
* Notify all subscribers for a specific user of an event.
* The event must already have a valid sequence assigned.
*/
notifyForUser(userId: string, event: AFSEvent): void {
// Notify user-specific global subscribers
const userHandlers = this.userHandlers.get(userId);
if (userHandlers) {
Expand All @@ -203,7 +229,7 @@ class UserEventBus {
// Notify user-specific session subscribers
const userSessions = this.userSessionHandlers.get(userId);
if (userSessions) {
const sessionHandlers = userSessions.get(sessionId);
const sessionHandlers = userSessions.get(event.sessionId);
if (sessionHandlers) {
for (const handler of sessionHandlers) {
try {
Expand All @@ -214,8 +240,6 @@ class UserEventBus {
}
}
}

return event;
}

/**
Expand Down
114 changes: 83 additions & 31 deletions mcp/src/server/sqlite.ts
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Original file line number Diff line number Diff line change
Expand Up @@ -18,6 +18,7 @@ import type {
Annotation,
AnnotationStatus,
ThreadMessage,
ActionRequest,
Organization,
User,
UserRole,
Expand Down Expand Up @@ -305,14 +306,43 @@ export function createSQLiteStore(dbPath?: string): AFSStore {
const cutoff = new Date(Date.now() - retentionDays * 24 * 60 * 60 * 1000).toISOString();
stmts.pruneOldEvents.run(cutoff);

function persistEvent(event: AFSEvent): void {
stmts.insertEvent.run({
type: event.type,
timestamp: event.timestamp,
sessionId: event.sessionId,
sequence: event.sequence,
payload: JSON.stringify(event.payload),
});
/**
* Persist an event to SQLite and notify subscribers.
* Assigns a unique sequence number with retry on UNIQUE constraint violation.
* Persists BEFORE notifying so SSE subscribers see the correct sequence.
*/
function emitAndPersist(
type: AFSEventType,
sessionId: string,
payload: Annotation | Session | ThreadMessage | ActionRequest
): void {
const MAX_RETRIES = 5;
for (let attempt = 0; attempt < MAX_RETRIES; attempt++) {
const event: AFSEvent = {
type,
timestamp: new Date().toISOString(),
sessionId,
sequence: eventBus.nextSequence(),
payload,
};
try {
stmts.insertEvent.run({
type: event.type,
timestamp: event.timestamp,
sessionId: event.sessionId,
sequence: event.sequence,
payload: JSON.stringify(event.payload),
});
eventBus.notify(event);
return;
} catch (err: unknown) {
const message = err instanceof Error ? err.message : String(err);
if (message.includes("UNIQUE constraint failed: events.sequence") && attempt < MAX_RETRIES - 1) {
continue;
}
throw err;
}
}
}

return {
Expand All @@ -335,8 +365,7 @@ export function createSQLiteStore(dbPath?: string): AFSStore {
metadata: null,
});

const event = eventBus.emit("session.created", session.id, session);
persistEvent(event);
emitAndPersist("session.created", session.id, session);

return session;
},
Expand Down Expand Up @@ -366,8 +395,7 @@ export function createSQLiteStore(dbPath?: string): AFSStore {
const session = this.getSession(id);
if (session) {
const eventType: AFSEventType = status === "closed" ? "session.closed" : "session.updated";
const event = eventBus.emit(eventType, id, session);
persistEvent(event);
emitAndPersist(eventType, id, session);
}
return session;
},
Expand Down Expand Up @@ -425,8 +453,7 @@ export function createSQLiteStore(dbPath?: string): AFSStore {
authorId: annotation.authorId ?? null,
});

const event = eventBus.emit("annotation.created", sessionId, annotation);
persistEvent(event);
emitAndPersist("annotation.created", sessionId, annotation);

return annotation;
},
Expand Down Expand Up @@ -457,8 +484,7 @@ export function createSQLiteStore(dbPath?: string): AFSStore {

const updated = this.getAnnotation(id);
if (updated && existing.sessionId) {
const event = eventBus.emit("annotation.updated", existing.sessionId, updated);
persistEvent(event);
emitAndPersist("annotation.updated", existing.sessionId, updated);
}
return updated;
},
Expand Down Expand Up @@ -495,8 +521,7 @@ export function createSQLiteStore(dbPath?: string): AFSStore {
const updated = this.updateAnnotation(annotationId, { thread });

if (updated && existing.sessionId) {
const event = eventBus.emit("thread.message", existing.sessionId, message);
persistEvent(event);
emitAndPersist("thread.message", existing.sessionId, message);
}

return updated;
Expand All @@ -519,8 +544,7 @@ export function createSQLiteStore(dbPath?: string): AFSStore {
stmts.deleteAnnotation.run(id);

if (existing.sessionId) {
const event = eventBus.emit("annotation.deleted", existing.sessionId, existing);
persistEvent(event);
emitAndPersist("annotation.deleted", existing.sessionId, existing);
}

return existing;
Expand Down Expand Up @@ -659,15 +683,44 @@ export function createTenantStore(dbPath?: string): TenantStore {
const cutoff = new Date(Date.now() - retentionDays * 24 * 60 * 60 * 1000).toISOString();
tenantStmts.pruneOldEvents.run(cutoff);

function persistEventForUser(event: AFSEvent, userId: string): void {
tenantStmts.insertEvent.run({
type: event.type,
timestamp: event.timestamp,
sessionId: event.sessionId,
sequence: event.sequence,
payload: JSON.stringify(event.payload),
userId,
});
/**
* Persist a user-scoped event to SQLite and notify subscribers.
* Assigns a unique sequence number with retry on UNIQUE constraint violation.
*/
function emitAndPersistForUser(
userId: string,
type: AFSEventType,
sessionId: string,
payload: Annotation | Session | ThreadMessage | ActionRequest
): void {
const MAX_RETRIES = 5;
for (let attempt = 0; attempt < MAX_RETRIES; attempt++) {
const event: AFSEvent = {
type,
timestamp: new Date().toISOString(),
sessionId,
sequence: eventBus.nextSequence(),
payload,
};
try {
tenantStmts.insertEvent.run({
type: event.type,
timestamp: event.timestamp,
sessionId: event.sessionId,
sequence: event.sequence,
payload: JSON.stringify(event.payload),
userId,
});
eventBus.notify(event);
return;
} catch (err: unknown) {
const message = err instanceof Error ? err.message : String(err);
if (message.includes("UNIQUE constraint failed: events.sequence") && attempt < MAX_RETRIES - 1) {
continue;
}
throw err;
}
}
}

return {
Expand Down Expand Up @@ -801,8 +854,7 @@ export function createTenantStore(dbPath?: string): TenantStore {
userId,
});

const event = eventBus.emit("session.created", session.id, session);
persistEventForUser(event, userId);
emitAndPersistForUser(userId, "session.created", session.id, session);

return session;
},
Expand Down