if (features.newThing) {
  doNewThing();
}

order_id,customer_id,customer_name,sku,quantity,event_at
o-100,c-7,Ada,rail-pass,2,2026-09-24T10:00:00Z
o-100,c-7,Ada,seat-upgrade,1,2026-09-24T10:00:00Z
o-101,c-8,Grace,rail-pass,1,2026-09-24T10:01:00Z

immutable CSV in object storage
            |
       batch worker
            |
     tenant route snapshot
       /           \
  Databricks     PostgreSQL data API
  COPY INTO       validate + transaction
  bronze/curated  customers/orders/items
       \           /
       read adapter for the tenant

// pipeline/route.ts
export type PipelinePath = "databricks" | "postgres";
export interface RouteSnapshot {
  version: number;
  defaultPath: PipelinePath;
  tenants: Record<string, PipelinePath>;
}
export interface BatchRef {
  tenantId: string;
  batchId: string;
  fileName: string; // a basename under the tenant's immutable S3 prefix
  sha256: string;   // digest of the file's bytes, recorded when uploaded
}
export function choosePath(
  config: RouteSnapshot,
  tenantId: string,
): { path: PipelinePath; configVersion: number } {
  return {
    path: config.tenants[tenantId] ?? config.defaultPath,
    configVersion: config.version,
  };
}
export function checkBatchRef(batch: BatchRef): void {
  if (!/^[a-z0-9-]{1,64}$/.test(batch.tenantId) ||
      !/^[a-zA-Z0-9-]{1,100}$/.test(batch.batchId) ||
      !/^[a-zA-Z0-9-]+\.csv$/.test(batch.fileName) ||
      !/^[a-f0-9]{64}$/.test(batch.sha256)) {
    throw new Error("Invalid batch reference");
  }
}

CREATE TABLE IF NOT EXISTS main.orders.order_rows_bronze (
  order_id STRING,
  customer_id STRING,
  customer_name STRING,
  sku STRING,
  quantity STRING,
  event_at STRING
) USING DELTA;
CREATE TABLE IF NOT EXISTS main.orders.order_rows_current (
  order_id STRING,
  customer_id STRING,
  customer_name STRING,
  sku STRING,
  quantity INT,
  event_at TIMESTAMP
) USING DELTA;

// pipeline/databricks.ts
type StatementResult = {
  statement_id?: string;
  status: { state: string; error?: { message: string } };
  result?: { data_array?: string[][] };
};
export class DatabricksSql {
  constructor(
    private readonly host: string,
    private readonly token: string,
    private readonly warehouseId: string,
  ) {}
  private async request(path: string, init?: RequestInit): Promise<StatementResult> {
    const response = await fetch(`${this.host}${path}`, {
      ...init,
      headers: {
        Authorization: `Bearer ${this.token}`,
        "Content-Type": "application/json",
        ...init?.headers,
      },
    });
    if (!response.ok) throw new Error(`Databricks HTTP ${response.status}`);
    return response.json() as Promise<StatementResult>;
  }
  async execute(statement: string, parameters: { name: string; value: string }[] = []) {
    let result = await this.request("/api/2.0/sql/statements", {
      method: "POST",
      body: JSON.stringify({
        warehouse_id: this.warehouseId,
        statement,
        parameters,
        wait_timeout: "10s",
        disposition: "INLINE",
        format: "JSON_ARRAY",
      }),
    });
    const deadline = Date.now() + 120_000;
    while (result.status.state === "PENDING" || result.status.state === "RUNNING") {
      if (!result.statement_id || Date.now() > deadline) {
        throw new Error("Databricks statement exceeded worker deadline");
      }
      await new Promise(resolve => setTimeout(resolve, 1_000));
      result = await this.request(`/api/2.0/sql/statements/${result.statement_id}`);
    }
    if (result.status.state !== "SUCCEEDED") {
      throw new Error(result.status.error?.message ?? `Statement ${result.status.state}`);
    }
    return result.result?.data_array ?? [];
  }
}
export async function loadDatabricksBatch(
  sql: DatabricksSql,
  batch: BatchRef,
): Promise<void> {
  checkBatchRef(batch);
  const prefix = `s3://example-order-feed/${batch.tenantId}/`;
  // Only the basename is interpolated; checkBatchRef restricts its alphabet.
  await sql.execute(`
    COPY INTO main.orders.order_rows_bronze
    FROM '${prefix}'
    FILEFORMAT = CSV
    FILES = ('${batch.fileName}')
    FORMAT_OPTIONS ('header' = 'true')
  `);
  // The source file is a complete order snapshot. Deduplicate source rows
  // before MERGE: two matching source rows for one target key are ambiguous.
  await sql.execute(`
    MERGE INTO main.orders.order_rows_current AS target
    USING (
      SELECT order_id, customer_id, customer_name, sku,
             CAST(quantity AS INT) AS quantity,
             CAST(event_at AS TIMESTAMP) AS event_at
      FROM main.orders.order_rows_bronze
      QUALIFY ROW_NUMBER() OVER (
        PARTITION BY order_id, sku ORDER BY CAST(event_at AS TIMESTAMP) DESC
      ) = 1
    ) AS source
    ON target.order_id = source.order_id AND target.sku = source.sku
    WHEN MATCHED AND source.event_at >= target.event_at THEN UPDATE SET
      customer_id = source.customer_id,
      customer_name = source.customer_name,
      quantity = source.quantity,
      event_at = source.event_at
    WHEN NOT MATCHED THEN INSERT
      (order_id, customer_id, customer_name, sku, quantity, event_at)
      VALUES (source.order_id, source.customer_id, source.customer_name,
              source.sku, source.quantity, source.event_at)
  `);
}

CREATE TABLE customers (
  tenant_id text NOT NULL,
  customer_id text NOT NULL,
  customer_name text NOT NULL,
  PRIMARY KEY (tenant_id, customer_id)
);
CREATE TABLE orders (
  tenant_id text NOT NULL,
  order_id text NOT NULL,
  customer_id text NOT NULL,
  event_at timestamptz NOT NULL,
  PRIMARY KEY (tenant_id, order_id),
  FOREIGN KEY (tenant_id, customer_id)
    REFERENCES customers (tenant_id, customer_id)
);
CREATE TABLE order_items (
  tenant_id text NOT NULL,
  order_id text NOT NULL,
  sku text NOT NULL,
  quantity integer NOT NULL CHECK (quantity > 0),
  PRIMARY KEY (tenant_id, order_id, sku),
  FOREIGN KEY (tenant_id, order_id)
    REFERENCES orders (tenant_id, order_id) ON DELETE CASCADE
);
CREATE TABLE ingestion_batches (
  tenant_id text NOT NULL,
  batch_id text NOT NULL,
  sha256 char(64) NOT NULL,
  committed_at timestamptz NOT NULL DEFAULT now(),
  PRIMARY KEY (tenant_id, batch_id)
);

// pipeline/postgres-path.ts
import { S3Client, GetObjectCommand } from "@aws-sdk/client-s3";
import { parse } from "csv-parse/sync";
import { createHash } from "node:crypto";
export type OrderRow = {
  order_id: string;
  customer_id: string;
  customer_name: string;
  sku: string;
  quantity: number;
  event_at: string;
};
const s3 = new S3Client({});
export async function loadPostgresBatch(
  batch: BatchRef,
  apiBase: string,
  serviceToken: string,
): Promise<void> {
  checkBatchRef(batch);
  const key = `${batch.tenantId}/${batch.fileName}`;
  const object = await s3.send(new GetObjectCommand({
    Bucket: "example-order-feed", Key: key,
  }));
  if (!object.Body) throw new Error("Empty object body");
  const bytes = await object.Body.transformToByteArray();
  const digest = createHash("sha256").update(bytes).digest("hex");
  if (digest !== batch.sha256) throw new Error("Batch content changed");
  const records = parse(Buffer.from(bytes), {
    columns: true, skip_empty_lines: true, bom: true,
  }) as Record<string, string>[];
  if (records.length === 0 || records.length > 10_000) {
    throw new Error("Batch size outside accepted range");
  }
  const rows: OrderRow[] = records.map(row => ({
    order_id: row.order_id,
    customer_id: row.customer_id,
    customer_name: row.customer_name,
    sku: row.sku,
    quantity: Number(row.quantity),
    event_at: row.event_at,
  }));
  const response = await fetch(`${apiBase}/v1/batches`, {
    method: "POST",
    headers: {
      Authorization: `Bearer ${serviceToken}`,
      "Content-Type": "application/json",
    },
    body: JSON.stringify({ ...batch, rows }),
  });
  if (!response.ok) throw new Error(`Data API rejected batch: ${response.status}`);
}

// data-api/batches.ts (Fastify + pg + zod)
import Fastify from "fastify";
import pg from "pg";
import { z } from "zod";
const pool = new pg.Pool({ connectionString: process.env.DATABASE_URL });
const app = Fastify();
const rowSchema = z.object({
  order_id: z.string().min(1).max(100),
  customer_id: z.string().min(1).max(100),
  customer_name: z.string().min(1).max(200),
  sku: z.string().min(1).max(100),
  quantity: z.number().int().positive(),
  event_at: z.string().datetime({ offset: true }),
});
const batchSchema = z.object({
  tenantId: z.string().regex(/^[a-z0-9-]{1,64}$/),
  batchId: z.string().min(1).max(100),
  fileName: z.string().endsWith(".csv"),
  sha256: z.string().regex(/^[a-f0-9]{64}$/),
  rows: z.array(rowSchema).min(1).max(10_000),
});
app.post("/v1/batches", async (request, reply) => {
  const parsed = batchSchema.safeParse(request.body);
  if (!parsed.success) {
    return reply.code(400).send({ error: "Invalid batch payload" });
  }
  const input = parsed.data;
  // Gateway auth must bind this tenantId to the authenticated caller.
  const byOrder = new Map<string, typeof input.rows>();
  for (const row of input.rows) {
    const group = byOrder.get(row.order_id) ?? [];
    group.push(row);
    byOrder.set(row.order_id, group);
  }
  for (const rows of byOrder.values()) {
    const first = rows[0];
    const skus = new Set<string>();
    for (const row of rows) {
      if (row.customer_id !== first.customer_id ||
          row.customer_name !== first.customer_name ||
          row.event_at !== first.event_at || skus.has(row.sku)) {
        return reply.code(400).send({ error: "Inconsistent order snapshot" });
      }
      skus.add(row.sku);
    }
  }
  const client = await pool.connect();
  try {
    await client.query("BEGIN");
    const inserted = await client.query(
      `INSERT INTO ingestion_batches (tenant_id, batch_id, sha256)
       VALUES ($1, $2, $3) ON CONFLICT DO NOTHING RETURNING batch_id`,
      [input.tenantId, input.batchId, input.sha256],
    );
    if (inserted.rowCount === 0) {
      const existing = await client.query(
        `SELECT sha256 FROM ingestion_batches
         WHERE tenant_id = $1 AND batch_id = $2`,
        [input.tenantId, input.batchId],
      );
      await client.query("COMMIT");
      if (existing.rows[0]?.sha256 !== input.sha256) {
        return reply.code(409).send({ error: "Batch ID reused with new bytes" });
      }
      return reply.send({ status: "already-committed" });
    }
    for (const [orderId, rows] of byOrder) {
      const first = rows[0];
      await client.query(
        `INSERT INTO customers (tenant_id, customer_id, customer_name)
         VALUES ($1, $2, $3)
         ON CONFLICT (tenant_id, customer_id)
         DO UPDATE SET customer_name = EXCLUDED.customer_name`,
        [input.tenantId, first.customer_id, first.customer_name],
      );
      await client.query(
        `INSERT INTO orders (tenant_id, order_id, customer_id, event_at)
         VALUES ($1, $2, $3, $4)
         ON CONFLICT (tenant_id, order_id) DO UPDATE SET
           customer_id = EXCLUDED.customer_id,
           event_at = EXCLUDED.event_at
         WHERE orders.event_at <= EXCLUDED.event_at`,
        [input.tenantId, orderId, first.customer_id, first.event_at],
      );
      const current = await client.query(
        `SELECT event_at FROM orders WHERE tenant_id = $1 AND order_id = $2
         FOR UPDATE`,
        [input.tenantId, orderId],
      );
      if (new Date(current.rows[0].event_at).toISOString() !==
          new Date(first.event_at).toISOString()) continue; // stale snapshot
      await client.query(
        `DELETE FROM order_items WHERE tenant_id = $1 AND order_id = $2`,
        [input.tenantId, orderId],
      );
      for (const row of rows) {
        await client.query(
          `INSERT INTO order_items (tenant_id, order_id, sku, quantity)
           VALUES ($1, $2, $3, $4)`,
          [input.tenantId, orderId, row.sku, row.quantity],
        );
      }
    }
    await client.query("COMMIT");
    return reply.send({ status: "committed", orders: byOrder.size });
  } catch (error) {
    await client.query("ROLLBACK");
    throw error;
  } finally {
    client.release();
  }
});

app.get<{ Params: { orderId: string } }>(
  "/v1/orders/:orderId",
  async (request, reply) => {
    // tenantId comes from authenticated gateway context, never a query param.
    const tenantId = request.headers["x-verified-tenant-id"] as string;
    const order = await pool.query(
      `SELECT o.order_id, o.event_at, c.customer_id, c.customer_name
       FROM orders o JOIN customers c
         ON c.tenant_id = o.tenant_id AND c.customer_id = o.customer_id
       WHERE o.tenant_id = $1 AND o.order_id = $2`,
      [tenantId, request.params.orderId],
    );
    if (order.rowCount === 0) return reply.code(404).send();
    const items = await pool.query(
      `SELECT sku, quantity FROM order_items
       WHERE tenant_id = $1 AND order_id = $2 ORDER BY sku`,
      [tenantId, request.params.orderId],
    );
    return { ...order.rows[0], items: items.rows };
  },
);

// pipeline/read-order.ts
export type OrderView = {
  orderId: string;
  customerId: string;
  customerName: string;
  eventAt: string;
  items: { sku: string; quantity: number }[];
};
export async function getOrder(
  config: RouteSnapshot,
  tenantId: string,
  orderId: string,
  deps: { databricks: DatabricksSql; apiBase: string; serviceToken: string },
): Promise<OrderView | null> {
  if (choosePath(config, tenantId).path === "postgres") {
    const response = await fetch(
      `${deps.apiBase}/v1/orders/${encodeURIComponent(orderId)}`,
      { headers: { Authorization: `Bearer ${deps.serviceToken}` } },
    );
    if (response.status === 404) return null;
    if (!response.ok) throw new Error(`Data API HTTP ${response.status}`);
    const row = await response.json() as {
      order_id: string; customer_id: string; customer_name: string;
      event_at: string; items: { sku: string; quantity: number }[];
    };
    return {
      orderId: row.order_id, customerId: row.customer_id,
      customerName: row.customer_name, eventAt: row.event_at,
      items: row.items,
    };
  }
  const rows = await deps.databricks.execute(`
    SELECT order_id, customer_id, customer_name, sku,
           CAST(quantity AS STRING), CAST(event_at AS STRING)
    FROM main.orders.order_rows_current WHERE order_id = :order_id
    ORDER BY sku
  `, [{ name: "order_id", value: orderId }]);
  if (rows.length === 0) return null;
  return {
    orderId: rows[0][0], customerId: rows[0][1],
    customerName: rows[0][2], eventAt: rows[0][5],
    items: rows.map(row => ({ sku: row[3], quantity: Number(row[4]) })),
  };
}

// pipeline/worker.ts
export async function processBatch(
  config: RouteSnapshot,
  batch: BatchRef,
  deps: { databricks: DatabricksSql; apiBase: string; serviceToken: string },
) {
  checkBatchRef(batch);
  const decision = choosePath(config, batch.tenantId);
  // Persist {batchId, sha256, path, configVersion} in your job ledger.
  if (decision.path === "databricks") {
    await loadDatabricksBatch(deps.databricks, batch);
  } else {
    await loadPostgresBatch(batch, deps.apiBase, deps.serviceToken);
  }
  return decision;
}

// checkout/expedited.ts
export type ShippingFlag = {
  enabled: boolean;
  killSwitch: boolean;
  rolloutPercent: number; // integer 0..100
  revision: string;
};
export type QuoteInput = {
  accountId: string;
  subtotalCents: number;
  region: "US-LOWER-48" | "US-OTHER" | "INTERNATIONAL";
};
export type ShippingQuote = {
  standardCents: number;
  expeditedCents: number | null;
  decision: {
    offered: boolean;
    flagRevision: string;
    reason: string;
  };
};
export function bucket(accountId: string): number {
  let hash = 0x811c9dc5;
  for (const byte of new TextEncoder().encode(accountId)) {
    hash ^= byte;
    hash = Math.imul(hash, 0x01000193) >>> 0;
  }
  return hash % 100;
}
export function quoteShipping(input: QuoteInput, flag: ShippingFlag): ShippingQuote {
  if (!Number.isSafeInteger(input.subtotalCents) || input.subtotalCents < 0 ||
      !Number.isInteger(flag.rolloutPercent) ||
      flag.rolloutPercent < 0 || flag.rolloutPercent > 100) {
    throw new Error("Invalid quote input or flag configuration");
  }
  const reason = !flag.enabled || flag.killSwitch ? "disabled"
    : bucket(input.accountId) >= flag.rolloutPercent ? "outside-rollout"
    : input.region !== "US-LOWER-48" ? "unsupported-region"
    : input.subtotalCents < 7_500 ? "below-minimum"
    : "eligible";
  return {
    standardCents: 799,
    expeditedCents: reason === "eligible" ? 1499 : null,
    decision: {
      offered: reason === "eligible",
      flagRevision: flag.revision,
      reason,
    },
  };
}
// At checkout creation, persist the quoted cents and decision with the order.
// At payment confirmation, charge that stored quote after its normal expiry
// and inventory checks. Do not ask the flag again halfway through checkout.

package shipping
import (
    "errors"
    "hash/fnv"
)
type Flag struct {
    Enabled        bool
    KillSwitch     bool
    RolloutPercent int
    Revision       string
}
type Input struct {
    AccountID     string
    SubtotalCents int64
    Region        string
}
type Decision struct {
    Offered      bool
    FlagRevision string
    Reason       string
}
type Quote struct {
    StandardCents  int64
    ExpeditedCents *int64
    Decision       Decision
}
func Bucket(accountID string) int {
    h := fnv.New32a()
    _, _ = h.Write([]byte(accountID)) // UTF-8 bytes, as in TextEncoder
    return int(h.Sum32() % 100)
}
func QuoteShipping(in Input, flag Flag) (Quote, error) {
    if in.SubtotalCents < 0 || flag.RolloutPercent < 0 ||
        flag.RolloutPercent > 100 {
        return Quote{}, errors.New("invalid quote input or flag configuration")
    }
    reason := "eligible"
    switch {
    case !flag.Enabled || flag.KillSwitch:
        reason = "disabled"
    case Bucket(in.AccountID) >= flag.RolloutPercent:
        reason = "outside-rollout"
    case in.Region != "US-LOWER-48":
        reason = "unsupported-region"
    case in.SubtotalCents < 7500:
        reason = "below-minimum"
    }
    result := Quote{
        StandardCents: 799,
        Decision: Decision{
            Offered: reason == "eligible", FlagRevision: flag.Revision,
            Reason: reason,
        },
    }
    if result.Decision.Offered {
        expedited := int64(1499)
        result.ExpeditedCents = &expedited
    }
    return result, nil
}

{
  "savedFilters": true,
  "revision": "ui-2026-09-24-3"
}

// SavedFiltersFeature.tsx
import { useEffect, useState } from "react";
type Capabilities = { savedFilters: boolean; revision: string };
type Filter = { id: string; name: string; query: string };
export function SavedFiltersFeature() {
  const [capability, setCapability] = useState<Capabilities | null>(null);
  const [filters, setFilters] = useState<Filter[]>([]);
  const [open, setOpen] = useState(
    () => localStorage.getItem("saved-filters-open") === "true",
  );
  const [error, setError] = useState<string | null>(null);
  useEffect(() => {
    const controller = new AbortController();
    fetch("/v1/me/features", { signal: controller.signal, credentials: "include" })
      .then(response => {
        if (!response.ok) throw new Error("Could not load features");
        return response.json() as Promise<Capabilities>;
      })
      .then(setCapability)
      .catch(err => {
        if (err.name !== "AbortError") setError(err.message);
      });
    return () => controller.abort();
  }, []);
  useEffect(() => {
    if (!capability?.savedFilters || !open) return;
    const controller = new AbortController();
    fetch("/v1/saved-filters", { signal: controller.signal, credentials: "include" })
      .then(response => {
        if (!response.ok) throw new Error("Could not load saved filters");
        return response.json() as Promise<Filter[]>;
      })
      .then(setFilters)
      .catch(err => {
        if (err.name !== "AbortError") setError(err.message);
      });
    return () => controller.abort();
  }, [capability?.savedFilters, open]);
  if (!capability?.savedFilters) {
    return error ? <p role="alert">{error}</p> : null;
  }
  return <section aria-label="Saved filters">
    <label>
      <input type="checkbox" checked={open} onChange={event => {
        const next = event.target.checked;
        setOpen(next);
        localStorage.setItem("saved-filters-open", String(next));
      }} />
      Show saved filters
    </label>
    {error && <p role="alert">{error}</p>}
    {open && <ul>{filters.map(filter =>
      <li key={filter.id}><button type="button" onClick={() => {
        // The order list owns applying filter.query, after validating its DSL.
        window.dispatchEvent(new CustomEvent("apply-saved-filter", {
          detail: { id: filter.id },
        }));
      }}>{filter.name}</button></li>,
    )}</ul>}
  </section>;
}

import SwiftUI
struct Capabilities: Decodable {
    let savedFilters: Bool
    let revision: String
}
struct SavedFilter: Decodable, Identifiable {
    let id: String
    let name: String
    let query: String
}
@MainActor
final class SavedFiltersModel: ObservableObject {
    @Published private(set) var capability: Capabilities?
    @Published private(set) var filters: [SavedFilter] = []
    @Published private(set) var errorMessage: String?
    // apiBase and URLSession are injected so previews/tests can use fixtures.
    private let apiBase: URL
    private let session: URLSession
    init(apiBase: URL, session: URLSession = .shared) {
        self.apiBase = apiBase
        self.session = session
    }
    func loadCapability() async {
        do {
            let (data, response) = try await session.data(
                from: apiBase.appending(path: "v1/me/features"))
            guard (response as? HTTPURLResponse)?.statusCode == 200 else {
                throw URLError(.badServerResponse)
            }
            capability = try JSONDecoder().decode(Capabilities.self, from: data)
            if capability?.savedFilters != true { filters = [] }
            errorMessage = nil
        } catch {
            capability = nil // unknown is off
            filters = []
            errorMessage = "Features could not be loaded."
        }
    }
    func loadFilters() async {
        guard capability?.savedFilters == true else { return }
        do {
            let (data, response) = try await session.data(
                from: apiBase.appending(path: "v1/saved-filters"))
            guard (response as? HTTPURLResponse)?.statusCode == 200 else {
                throw URLError(.badServerResponse)
            }
            filters = try JSONDecoder().decode([SavedFilter].self, from: data)
            errorMessage = nil
        } catch {
            filters = []
            errorMessage = "Saved filters could not be loaded."
        }
    }
}
struct SavedFiltersView: View {
    @StateObject private var model: SavedFiltersModel
    @AppStorage("savedFiltersOpen") private var isOpen = false
    let applyFilter: (String) -> Void
    init(apiBase: URL, applyFilter: @escaping (String) -> Void) {
        _model = StateObject(wrappedValue: SavedFiltersModel(apiBase: apiBase))
        self.applyFilter = applyFilter
    }
    var body: some View {
        Group {
            if model.capability?.savedFilters == true {
                Section("Saved filters") {
                    Toggle("Show saved filters", isOn: $isOpen)
                    if isOpen {
                        ForEach(model.filters) { filter in
                            Button(filter.name) { applyFilter(filter.id) }
                        }
                    }
                }
            }
            if let error = model.errorMessage {
                Text(error).foregroundStyle(.red)
            }
        }
        .task { await model.loadCapability() }
        .task(id: isOpen && model.capability?.savedFilters == true) {
            if isOpen { await model.loadFilters() }
        }
    }
}