Stop 500ing on a v3 manifest that has no canvases

[ShanaLMoore]

Story

Refs notch8/hykuup_knapsack#748

Expected Behavior Before Changes

sanitize_v3 did hash['items'].each with no guard, so a manifest with no items key raised NoMethodError (undefined method 'each' for nil) and the work's viewer showed "Unable to load manifest". sanitize_v2 has always guarded the equivalent loop.

Two ways to reach it: a work whose presenter yields no displayable file sets, and a v2-shaped hash sanitized as v3, which is what Hyrax's CachingIiifManifestBuilder produced until samvera/hyrax#7590 (it defaulted to the v2 factory while IiifPrint.config.default_iiif_manifest_version stayed 3). That combination took out roughly half the works on two production tenants.

Expected Behavior After Changes

A manifest with no canvases is returned as-is instead of 500ing.

Notes

• The label scrub on the line above used Hash#key, which takes a value, not a key, so it returned nil and the scrub never ran. Fixed to a lookup, which means canvas labels get scrubbed now too. Both call sites share one method that tolerates a missing label.
• Hyrax's fix is the real one for the caching mismatch; this is the guard so a factory/version mismatch degrades instead of 500ing.

Testing

spec/services/iiif_print/manifest_builder_service_decorator_spec.rb covers the canvas-less manifest, the label unescape, and a manifest with no label. Not run locally (needs the full engine cart stack); CI runs the suite.

🤖 Assisted-by: Opus 5