Add Platform Data Flow explanation page

src/content/docs/explanations/platform/data-flow.mdx

@@ -0,0 +1,101 @@
+---
+title: Platform Data Flow
+---
+
+This page explains what data flows between a
+[Tenzir Node](/explanations/node) and the
+[Tenzir Platform](/explanations/platform), so you can reason about
+privacy, compliance, and what an operator of the Tenzir Platform can see.
+
+When a Tenzir Node starts, it opens a single outbound, TLS-encrypted
+WebSocket connection to the Tenzir Platform. All communication between
+the two travels over that connection.
+
+For the bigger picture on TLS termination and trust boundaries, see the
+[FAQ entry on data privacy](/explanations/faqs#can-tenzir-see-my-data).
+
+## The connection is a tunnel, not a feed
+
+The Tenzir Node does not push state to the Tenzir Platform. It opens the
+WebSocket, authenticates, and then waits. The Tenzir Platform — and
+through it, the app — uses this connection as a reverse tunnel to call
+the [node API](/reference/node/api) on demand.
+
+In other words: whatever the app shows you about a Tenzir Node was
+pulled from that node at the moment you asked for it. The Tenzir
+Platform does not maintain a continuously updated mirror of the
+Tenzir Node's state.
+
+The Tenzir Node initiates the connection — the Tenzir Platform never
+connects to it. For nodes registered with the hosted Tenzir Platform,
+the endpoint defaults to `wss://ws.tenzir.app:443/production`. See
+<Guide>node-setup/configure-tls</Guide> for the TLS options.
+
+## What the app pulls on demand
+
+Anything you can retrieve via the [node API](/reference/node/api), the
+Tenzir Platform can retrieve on behalf of an authenticated user in your
+workspace. In practice this means:
+
+- The list of **pipelines** on the Tenzir Node, their TQL source,
+  labels, and lifecycle state.
+- **Pipeline metrics** such as ingress/egress event and byte counters.
+- **Diagnostics** (warnings and errors) emitted by pipelines.
+- **Contexts** — their names, types, and, if you open them in the app,
+  their contents.
+- **Packages** installed on the Tenzir Node and their configuration.
+- **Schemas** the Tenzir Node has seen.
+
+These are fetched when a page or component in the app needs them. Close
+the page and the requests stop.
+
+## Pipeline data does not flow through the Tenzir Platform
+
+Pipelines run entirely on the Tenzir Node. The events flowing through a
+pipeline's operators are **not** routed through the Tenzir Platform,
+regardless of where the pipeline was created.
+
+The single exception is a pipeline you run interactively from the app
+(for example, in the Explorer). In that case the results stream
+Tenzir Node → Tenzir Platform → browser for as long as the view is
+open, so the app can render them. They are not persisted on the
+Tenzir Platform.
+
+## Secrets
+
+When a pipeline accesses a secret, the Tenzir Node requests its value
+from the Tenzir Platform over the same encrypted channel, and the
+Tenzir Platform replies with the resolved value. See
+<Explanation>secrets</Explanation>.
+
+## What is *not* sent
+
+The Tenzir Platform does **not** receive:
+
+- The **events stored in the Tenzir Node** (Parquet partitions, the
+  catalog, or query results) — unless you explicitly query them from
+  the app.
+- The **raw bytes** ingested from your sources.
+- **Pipeline payloads** for pipelines that aren't being viewed live in
+  the app.
+- **Configuration files**, environment variables, or secret values
+  defined locally on the Tenzir Node.
+- **Operating system logs** or anything outside the `tenzir-node`
+  process.
+
+## Encryption and trust
+
+The WebSocket is TLS-encrypted and terminates at the Tenzir Platform.
+In the editions where Tenzir hosts the Tenzir Platform, Tenzir is
+therefore technically able to observe data that traverses it during
+interactive use. If this is unacceptable, host the Tenzir Platform
+yourself with the [Sovereign Edition](https://tenzir.com/pricing) — see
+<Guide>platform-setup</Guide>.
+
+## See Also
+
+- <Guide>node-setup/configure-tls</Guide>
+- <Explanation>platform</Explanation>
+- <Explanation>node</Explanation>
+- <Explanation>secrets</Explanation>
+- <Explanation>faqs</Explanation>

src/sidebar.ts

@@ -260,6 +260,7 @@ export const explanations = [
       "explanations/pipeline",
       "explanations/node",
       "explanations/platform",
+      "explanations/platform/data-flow",
       "explanations/language",
     ],
     "architecture",