/api/v3/actions?mc_seqno=... returns 500 timeout on testnet for all seqno values

[jessicawch]

Description

The /api/v3/actions endpoint on testnet (testnet.toncenter.com) consistently returns 500 Internal Server Error with "timeout: context deadline exceeded" when filtering by mc_seqno. This affects every mc_seqno value. The same endpoint works correctly on mainnet (toncenter.com).

Steps to Reproduce

# Testnet — FAILS (any mc_seqno value)
curl "https://testnet.toncenter.com/api/v3/actions?mc_seqno=48106165&limit=10&sort=asc&action_type=ton_transfer"
# Response: {"error":"timeout: context deadline exceeded"}  HTTP 500

# Mainnet — WORKS (same query structure)
curl "https://toncenter.com/api/v3/actions?mc_seqno=45000000&limit=10&sort=asc&action_type=ton_transfer"
# Response: 200 OK with actions data

What works on testnet

• GET /api/v3/masterchainInfo — ✅ Works
• GET /api/v3/actions (without mc_seqno) — ✅ Works
• GET /api/v3/transactions?mc_seqno=... — ✅ Works
• GET /api/v3/actions?mc_seqno=... — ❌ 500 timeout

Expected Behavior

/api/v3/actions?mc_seqno=... should return actions for the given masterchain seqno on testnet, as it does on mainnet.

Possible Root Cause

This appears similar to toncenter/ton-indexer#90, where mc_block_seqno-based queries timed out due to missing PostgreSQL indexes on the testnet indexer database.

Environment

• Endpoint: https://testnet.toncenter.com/api/v3
• Date observed: 2026-03-24
• API key: provided via X-API-Key header