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perf(ui): parallelize session decryption on cold start #124

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8ef72d3
perf(ui): parallelize session decryption on cold start
lucharo Mar 10, 2026
27d1646
fix(ui): isolate per-session errors in parallel decryption
lucharo Mar 11, 2026
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149 changes: 84 additions & 65 deletions apps/ui/sources/sync/engine/sessions/sessionSnapshot.ts
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Original file line number Diff line number Diff line change
Expand Up @@ -70,83 +70,102 @@ export async function fetchAndApplySessions(params: {
cursor = nextCursor;
}

// Initialize all session encryptions first
// Decrypt all session keys in parallel
const sessionKeys = new Map<string, Uint8Array | null>();
for (const session of sessions) {
if (session.dataEncryptionKey) {
const decrypted = await encryption.decryptEncryptionKey(session.dataEncryptionKey);
if (!decrypted) {
console.error(`Failed to decrypt data encryption key for session ${session.id}`);
sessionKeys.set(session.id, null);
sessionDataKeys.delete(session.id);
continue;
const keyResults = await Promise.all(
sessions.map(async (session) => {
try {
if (session.dataEncryptionKey) {
const decrypted = await encryption.decryptEncryptionKey(session.dataEncryptionKey);
return { id: session.id, decrypted, hasKey: true };
}
return { id: session.id, decrypted: null, hasKey: false };
} catch (err) {
console.error(`Failed to decrypt encryption key for session ${session.id}`, err);
return { id: session.id, decrypted: null, hasKey: true };
}
sessionKeys.set(session.id, decrypted);
sessionDataKeys.set(session.id, decrypted);
}),
);
for (const { id, decrypted, hasKey } of keyResults) {
if (hasKey && !decrypted) {
console.error(`Failed to decrypt data encryption key for session ${id}`);
sessionKeys.set(id, null);
sessionDataKeys.delete(id);
} else if (hasKey && decrypted) {
sessionKeys.set(id, decrypted);
sessionDataKeys.set(id, decrypted);
} else {
sessionKeys.set(session.id, null);
sessionDataKeys.delete(session.id);
sessionKeys.set(id, null);
sessionDataKeys.delete(id);
}
}
await encryption.initializeSessions(sessionKeys);

// Decrypt sessions
const decryptedSessions: (Omit<Session, 'presence'> & { presence?: 'online' | number })[] = [];
for (const session of sessions) {
const encryptionMode: 'e2ee' | 'plain' = session.encryptionMode === 'plain' ? 'plain' : 'e2ee';

const sessionEncryption = encryption.getSessionEncryption(session.id);
if (encryptionMode === 'e2ee' && !sessionEncryption) {
console.error(`Session encryption not found for ${session.id} - this should never happen`);
continue;
// Decrypt all sessions in parallel
const parsePlainMetadata = (value: string): Metadata | null => {
try {
const parsedJson = JSON.parse(value);
const parsed = MetadataSchema.safeParse(parsedJson);
return parsed.success ? parsed.data : null;
} catch {
return null;
}
};

const parsePlainAgentState = (value: string | null): unknown => {
if (!value) return {};
try {
const parsedJson = JSON.parse(value);
const parsed = AgentStateSchema.safeParse(parsedJson);
return parsed.success ? parsed.data : {};
} catch {
return {};
}
};

const parsePlainMetadata = (value: string): Metadata | null => {
const decryptedSessionResults = await Promise.all(
sessions.map(async (session) => {
try {
const parsedJson = JSON.parse(value);
const parsed = MetadataSchema.safeParse(parsedJson);
return parsed.success ? parsed.data : null;
} catch {
const encryptionMode: 'e2ee' | 'plain' = session.encryptionMode === 'plain' ? 'plain' : 'e2ee';

const sessionEncryption = encryption.getSessionEncryption(session.id);
if (encryptionMode === 'e2ee' && !sessionEncryption) {
console.error(`Session encryption not found for ${session.id} - this should never happen`);
return null;
}

const metadata =
encryptionMode === 'plain'
? parsePlainMetadata(session.metadata)
: await sessionEncryption!.decryptMetadata(session.metadataVersion, session.metadata);

const agentState =
encryptionMode === 'plain'
? parsePlainAgentState(session.agentState)
: await sessionEncryption!.decryptAgentState(session.agentStateVersion, session.agentState);

const accessLevel = session.share?.accessLevel;
const normalizedAccessLevel =
accessLevel === 'view' || accessLevel === 'edit' || accessLevel === 'admin' ? accessLevel : undefined;
return {
...session,
encryptionMode,
thinking: false,
thinkingAt: 0,
metadata,
agentState,
accessLevel: normalizedAccessLevel,
canApprovePermissions: session.share?.canApprovePermissions ?? undefined,
};
} catch (err) {
console.error(`Failed to decrypt session ${session.id}`, err);
return null;
}
};

const parsePlainAgentState = (value: string | null): unknown => {
if (!value) return {};
try {
const parsedJson = JSON.parse(value);
const parsed = AgentStateSchema.safeParse(parsedJson);
return parsed.success ? parsed.data : {};
} catch {
return {};
}
};

const metadata =
encryptionMode === 'plain'
? parsePlainMetadata(session.metadata)
: await sessionEncryption!.decryptMetadata(session.metadataVersion, session.metadata);

const agentState =
encryptionMode === 'plain'
? parsePlainAgentState(session.agentState)
: await sessionEncryption!.decryptAgentState(session.agentStateVersion, session.agentState);

// Put it all together
const accessLevel = session.share?.accessLevel;
const normalizedAccessLevel =
accessLevel === 'view' || accessLevel === 'edit' || accessLevel === 'admin' ? accessLevel : undefined;
decryptedSessions.push({
...session,
encryptionMode,
thinking: false,
thinkingAt: 0,
metadata,
agentState,
accessLevel: normalizedAccessLevel,
canApprovePermissions: session.share?.canApprovePermissions ?? undefined,
});
}
}),
);
const decryptedSessions = decryptedSessionResults.filter(
(s): s is NonNullable<typeof s> => s !== null,
);

// Apply to storage
applySessions(decryptedSessions);
Expand Down