chore: import upstream snapshot with attribution

docs/md/how_to/javascript/virtual_server/clickhouse.md

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+# ClickHouse Virtual Server
+
+Perspective provides a built-in virtual server for
+[ClickHouse](https://clickhouse.com/), allowing `<perspective-viewer>` to query
+ClickHouse tables directly from the browser.
+
+For server-side Python usage, see the
+[Python ClickHouse guide](../../python/virtual_server/clickhouse.md).
+
+## Installation
+
+```bash
+npm install @perspective-dev/client @perspective-dev/viewer @clickhouse/client-web
+```
+
+## Usage
+
+Connect to a ClickHouse instance and bind it to a Perspective viewer:
+
+```javascript
+import perspective from "@perspective-dev/client";
+import "@perspective-dev/viewer";
+import { createClient } from "@clickhouse/client-web";
+
+// Connect to ClickHouse
+const clickhouseClient = createClient({
+    url: "http://localhost:8123",
+    database: "default",
+});
+
+// Create a Perspective virtual server backed by ClickHouse
+const handler = perspective.ClickhouseHandler(clickhouseClient);
+const messageHandler = perspective.createMessageHandler(handler);
+
+// Connect a viewer
+const client = await perspective.worker(messageHandler);
+const table = await client.open_table("my_table");
+document.getElementById("viewer").load(table);
+```
+
+## Examples
+
+- [Browser ClickHouse example](https://github.com/perspective-dev/perspective/tree/master/examples/esbuild-clickhouse-virtual)

docs/md/how_to/javascript/virtual_server/custom.md

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+# Implementing a custom Virtual Server
+
+You can connect Perspective to any data source by implementing the
+`VirtualServerHandler` interface and passing it to `createMessageHandler()`.
+
+For background on virtual servers, see the
+[Virtual Servers overview](../../../explanation/virtual_servers.md).
+
+## Example
+
+```typescript
+import perspective from "@perspective-dev/client";
+import type {
+    VirtualServerHandler,
+    ColumnType,
+    ViewConfig,
+    ViewWindow,
+    VirtualDataSlice,
+} from "@perspective-dev/client";
+
+const handler = {
+    async getHostedTables(): Promise<string[]> {
+        return ["my_table"];
+    },
+
+    async tableSchema(tableId: string): Promise<Record<string, ColumnType>> {
+        return { name: "string", price: "float", date: "date" };
+    },
+
+    async tableSize(tableId: string): Promise<number> {
+        return 1000;
+    },
+
+    async tableMakeView(
+        tableId: string,
+        viewId: string,
+        config: ViewConfig,
+    ): Promise<void> {
+        // Translate `config` (group_by, sort, filter, etc.) into a query
+        // against your data source. Store the query keyed by `viewId`
+        // for later data retrieval.
+    },
+
+    async viewDelete(viewId: string): Promise<void> {
+        // Clean up resources for this view
+    },
+
+    async viewGetData(
+        viewId: string,
+        config: ViewConfig,
+        schema: Record<string, ColumnType>,
+        viewport: ViewWindow,
+        dataSlice: VirtualDataSlice,
+    ): Promise<void> {
+        // Query your data source using `config` and `viewport` for the
+        // row/column window. Push columnar results via `dataSlice.setCol()`.
+    },
+
+    getFeatures() {
+        return {
+            group_by: true,
+            sort: true,
+            filter_ops: {
+                string: ["==", "!=", "contains", "is null", "is not null"],
+                float: ["==", "!=", ">", "<", ">=", "<="],
+            },
+            aggregates: {
+                float: ["sum", "avg", "count", "min", "max"],
+                string: ["count", "any"],
+            },
+        };
+    },
+} satisfies VirtualServerHandler;
+
+// Create a message handler and use it like a worker
+const messageHandler = perspective.createMessageHandler(handler);
+const client = await perspective.worker(messageHandler);
+const table = await client.open_table("my_table");
+document.getElementById("viewer").load(table);
+```

docs/md/how_to/javascript/virtual_server/duckdb.md

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+# DuckDB Virtual Server
+
+Perspective provides a built-in virtual server for
+[DuckDB](https://duckdb.org/), allowing `<perspective-viewer>` to query
+DuckDB-WASM databases directly in the browser.
+
+For server-side Python usage, see the
+[Python DuckDB guide](../../python/virtual_server/duckdb.md).
+
+## Installation
+
+```bash
+npm install @perspective-dev/client @perspective-dev/viewer @duckdb/duckdb-wasm
+```
+
+## Usage
+
+Initialize DuckDB-WASM, load data, and connect it to a Perspective viewer:
+
+```javascript
+import perspective from "@perspective-dev/client";
+import "@perspective-dev/viewer";
+import * as duckdb from "@duckdb/duckdb-wasm";
+
+// Initialize DuckDB-WASM
+const DUCKDB_BUNDLES = duckdb.getJsDelivrBundles();
+const bundle = await duckdb.selectBundle(DUCKDB_BUNDLES);
+const worker = await duckdb.createWorker(bundle.mainWorker);
+const logger = new duckdb.ConsoleLogger();
+const db = new duckdb.AsyncDuckDB(logger, worker);
+await db.instantiate(bundle.mainModule);
+
+// Load data into DuckDB
+const conn = await db.connect();
+await conn.query(`CREATE TABLE my_table AS SELECT * FROM 'data.parquet'`);
+
+// Create a Perspective virtual server backed by DuckDB
+const handler = perspective.DuckDBHandler(db);
+const messageHandler = perspective.createMessageHandler(handler);
+
+// Connect a viewer
+const client = await perspective.worker(messageHandler);
+const table = await client.open_table("my_table");
+document.getElementById("viewer").load(table);
+```
+
+## Examples
+
+- [Browser DuckDB example](https://github.com/perspective-dev/perspective/tree/master/examples/esbuild-duckdb-virtual)