Only the viewport.

import { createOmeZarrReader } from 'purejsimage/scientific/readers/ome-zarr'
import { createOmeZarrHttpContext } from 'purejsimage/scientific/browser'

// Public context: only allowed object names, a bounded source cache, cancellation,
// range validation, request coalescing, and measured network statistics.
const context = await createOmeZarrHttpContext(storeUrl, {
  maxOpenSources: 8,
  maxCacheBytesPerSource: 8_388_608,
})

const reader = createOmeZarrReader({
  limits: { rowsPerBlock: 1_024 },
  metadataValidation: 'compatible',
})
const document = await reader.open(context)

// Choose any displayable image or plate field. The UI persists these indices.
const summary = document.datasets.find(({ descriptor }) =>
  descriptor.axes.some(({ id }) => id === 'x') &&
  descriptor.axes.some(({ id }) => id === 'y'),
)
if (!summary) throw new Error('No x/y image dataset found')

const dataset = await document.openDataset(summary.id)
const fixedIndices = dataset.descriptor.axes
  .filter(({ id }) => id !== 'x' && id !== 'y')
  .map(({ id, length }) => ({ axisId: id, index: viewerAxisIndex(id, length) }))

// level and region come from the current canvas zoom and viewport.
for await (const block of dataset.readPlane({
  displayAxes: ['x', 'y'],
  fixedIndices,
  resolutionLevel: level,
  x,
  y,
  width,
  height,
  signal: request.signal,
})) {
  try {
    compositeIntoRgba(block)
  } finally {
    block.release?.()
  }
}

console.log(context.store.stats())
context.store.close()

import {
  createOmeZarrHttpContext,
  type OmeZarrHttpContext,
} from 'purejsimage/scientific/browser'

export const openRemoteOmeZarr = async (
  storeUrl: string,
  signal: AbortSignal,
): Promise<OmeZarrHttpContext> =>
  createOmeZarrHttpContext(storeUrl, {
    signal,
    maxOpenSources: 16,
    blockBytes: 262_144,
    maxCacheBytesPerSource: 2_097_152,
  })

// Pass the returned context directly to createOmeZarrReader().open().
// Keep context.store to inspect stats, reset counters, or close the session.