feat(toncenter): document Streaming API v2

docs.json

@@ -133,6 +133,16 @@
                       "directory": "ecosystem/api/toncenter/v3"
                     }
                   },
+                  {
+                    "group": "Streaming API",
+                    "tag": "v2",
+                    "pages": [
+                      "ecosystem/api/toncenter/streaming/overview",
+                      "ecosystem/api/toncenter/streaming/sse",
+                      "ecosystem/api/toncenter/streaming/wss",
+                      "ecosystem/api/toncenter/streaming/reference"
+                    ]
+                  },
                   {
                     "group": "Nominator Pools API",
                     "openapi": {

ecosystem/api/toncenter/introduction.mdx

@@ -4,7 +4,7 @@ title: Introduction
 
 TON Center HTTP APIs: read blockchain data, query smart contracts, send transactions.
 
-<Columns cols={2}>
+<Columns cols={3}>
   <Card
     title="API v2"
     icon="bolt"
@@ -20,4 +20,12 @@ TON Center HTTP APIs: read blockchain data, query smart contracts, send transact
   >
     Indexed database for traces, Jettons, NFTs, and historical queries.
   </Card>
+
+  <Card
+    title="Streaming API v2"
+    icon="signal-stream"
+    href="/ecosystem/api/toncenter/streaming/overview"
+  >
+    Low-latency updates on subscriptions through SSE or WebSockets.
+  </Card>
 </Columns>

ecosystem/api/toncenter/streaming/overview.mdx

@@ -0,0 +1,106 @@
+---
+title: "Streaming API overview"
+sidebarTitle: "Overview"
+---
+
+import { Aside } from '/snippets/aside.jsx';
+
+The TON Center **Streaming API** (v2) provides developer access to TON Blockchain through [Server-Sent Events (SSE)](https://en.wikipedia.org/wiki/Server-sent_events) and [WebSockets](https://en.wikipedia.org/wiki/WebSocket). It delivers low-latency, real-time updates on transactions and actions observed on the TON blockchain. Clients can subscribe to updates for monitoring a wallet, some contract addresses, or a specific trace of transactions.
+
+Streaming API serves as a real-time, streaming version of the [indexed access layer (API v3)](/ecosystem/api/toncenter/v3/overview). Use it when building wallets, explorers, monitoring systems, or automation tools.
+
+<Aside
+  type="caution"
+  title="Gap recovery"
+>
+  The Streaming API does not recover past events; it only tracks current ones. As such, network interruptions, client restarts, or brief service downtime can cause missed events.
+
+  When application state or business logic depends on a complete event sequence, resynchronize with historical data by polling [API v3](/ecosystem/api/toncenter/v3/overview) after reconnecting.
+</Aside>
+
+<Aside
+  type="note"
+  title="Version naming"
+>
+  The [API v2](/ecosystem/api/toncenter/v2/overview) and [API v3](/ecosystem/api/toncenter/v3/overview) include their major version numbers in their product names. For the Streaming API, `v2` means the current protocol version and doesn't refer to different APIs.
+</Aside>
+
+## Event groups
+
+The Streaming API emits the following event groups:
+
+- Trace-based events: `transactions`, `actions`, `trace`
+- State updates: `account_state_change` and `jettons_change`
+- Invalidation signal: `trace_invalidated`
+
+The [event types section](/ecosystem/api/toncenter/streaming/reference#event-types) and [notification schemas section](/ecosystem/api/toncenter/streaming/reference#notification-schemas) provide the exact payload structure for each event.
+
+## Finality model
+
+Trace-based events carry a `finality` field according to their finality level:
+
+```json
+"finality": "pending" | "confirmed" | "finalized"
+```
+
+Each trace moves through the following monotonic lifecycle:
+
+```mermaid
+flowchart LR
+  pending --> confirmed --> finalized
+  pending --> trace_invalidated
+  confirmed --> trace_invalidated
+```
+
+- `pending` — result of emulation or speculative execution. This state can be invalidated (`trace_invalidated`).
+- `confirmed` — trace or transactions are included in a candidate shard block. Rollback chance is very small, but still possible.
+- `finalized` — committed in the masterchain and will not be updated nor invalidated.
+
+Non-trace events behave differently:
+
+- `account_state_change` and `jettons_change` are emitted only when `finality` field is set to either `confirmed` or `finalized`.
+- `trace_invalidated` applies to previously emitted trace-based data and is not emitted after `finalized`.
+
+## Delivery behavior
+
+The `min_finality` field is used to control how early the server emits trace-based updates:
+
+- `pending` — receive every trace snapshot as it moves from `pending` to `confirmed` to `finalized`.
+- `confirmed` — skip pure emulation results and start at `confirmed` or later.
+- `finalized` — receive only finalized trace-based events.
+
+Choose the setting based on the tolerance for speculative data:
+
+- Use `pending` for the lowest latency.
+- Use `confirmed` for lower rollback risk with near-real-time delivery.
+- Use `finalized` when only settled data is acceptable.
+
+The [delivery semantics section](/ecosystem/api/toncenter/streaming/reference#delivery-semantics) and [event invalidation section](/ecosystem/api/toncenter/streaming/reference#event-invalidation) document the exact behavior for each event type.
+
+## Supported interfaces
+
+The Streaming API exposes two transports: SSE and a WebSocket. Choose either of the transports to proceed with its usage:
+
+<Columns cols={2}>
+  <Card
+    title="SSE: Server-Sent Events"
+    icon="server"
+    href="/ecosystem/api/toncenter/streaming/sse"
+  >
+    Recommended for browser environments or clients that prefer HTTP streaming and a fixed subscription.
+  </Card>
+
+  <Card
+    title="WebSocket"
+    icon="signal-stream"
+    href="/ecosystem/api/toncenter/streaming/wss"
+  >
+    Preferred for persistent, bidirectional communication with dynamic subscription patterns.
+  </Card>
+</Columns>
+
+## See also
+
+- [Notification reference](/ecosystem/api/toncenter/streaming/reference)
+- [API key](/ecosystem/api/toncenter/get-api-key)
+- [API authentication](/ecosystem/api/toncenter/v3-authentication)