[kochizufan]

Serve an old map's image straight from a IIIF Image API service. A map setting can carry delivery: { type: "iiifImage", url }; Core reads the service's info.json and requests tiles in the IIIF URL form instead of tiles/{mapID}/{z}/{x}/{y}.jpg.

dist/ is not rebuilt in this PR yet; a build: rebuild dist commit is added right before merging.

What changes

• src/iiif/delivery.ts (new; not exported from src/index)
  • checkIiifDelivery(info, expected?) — pure check (no fetch) whether Core can serve the image: { ok, version, level, tiling: "arbitrary" | "level0-256" } or { ok: false, reason }.
  • resolveIiifDelivery(delivery, expected, opts?) — fetches info.json (credentials: "omit", 10 s timeout, 1 MiB limit) and returns a tileUrlFunction for HistMap (plus minZoom for level 0 tiles). Tiles outside the image return the transparent PNG.
  • IiifDeliveryError with reason (bad-url, fetch-failed, timeout, too-large, not-json, unsupported-version, unsupported-level0, size-mismatch).
  • Parsing info.json and building the request URL (region, size, quality, format) is left entirely to OpenLayers (ol/format IIIFInfo, ol/source IIIF). Only the tile grid is Maplat's own HistMap grid; Core does not build IIIF URLs itself.
• src/source_ex.ts: mapSourceFactory resolves delivery on both the map-setting path and the noload path. Because OpenLayers' UrlTile regenerates the URL function from url (which HistMap fills in from mapID), the IIIF function is re-applied on the created source with setTileUrlFunction. url/urls next to delivery are dropped with a warning. IIIF maps are never registered with the tile cache (getMapCacheEnable is false).
• src/index.ts: a map whose IIIF image cannot be used no longer fails the whole startup. It is logged with console.error, left out of the raw sourceLoaded list and reported as { mapID, usable: false } in the element's sourceLoaded detail; the other maps start normally. If the initial map (startFrom or the restored map) is not usable, startup falls back to the default map with a warning (this also covers maps dropped because the GL library is missing).
• vite.config.ts: ol/format is external (like ol/source), so OpenLayers' IIIF code is not bundled.
• Level 0 services with tiles other than 256 px, sizes-only level 0 and Image API 1 are reported as unusable for now.
• Demo: new region niigata — the 1920 Map of Niigata City from the National Diet Library (public domain), shown directly from the NDL IIIF image service (canvas 3; alignment is provisional, 6 control points). A copy with a broken delivery shows that startup continues; a panel section lists recent old-map tile requests and the cache status.
• README (en/ja): section "Serving a map image from a IIIF Image API service (delivery)". CHANGELOG: one line under Added.

Tests

• spec/iiif-delivery-grid.spec.ts: for every tile of every zoom of the grid built by HistMap_tin (including one ring outside the image), the requested region equals the tile's extent mapped back to image pixels and clipped to the image, the requested size equals ceil(clipped size / scale) and is at most 256, every tile touching the image is requested and none outside it. Run on four info.json fixtures: NDL (v2, level 1, 1024 tiles), iiif.io example (v3, level 1, 512 tiles), Stanford (v2, level 2) and a hand-written level 0 with 256 tiles. Fixed URL expectations are listed in the spec.
• spec/iiif-delivery.spec.ts: the check's cases and the resolver's failure modes (URL form, fetch failure, timeout, size limit by header and by streamed bytes, non-JSON, v1, size mismatch, @id mismatch warning, minZoom).
• spec/iiif-source-factory.spec.ts: both factory paths with the same fixtures (tile URL on the created source with a mapID, no tile cache, url + delivery, failures as IiifDeliveryError).
• spec/iiif-unusable-source.spec.ts: startup with an unusable IIIF map, including when it is the initial map.
• e2e/iiif-image.spec.ts: the demo region with NDL responses served from fixtures — map shown, every tile request in the IIIF form, not cached, no manifest request.
• e2e/iiif-live.spec.ts: 5 requests to NDL (info.json and 4 tiles); runs only with MAPLAT_IIIF_LIVE=1, skipped in CI.
• Also checked locally: the same grid measurement passes with OpenLayers 9.2.4 (the peer lower bound).

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