Bugfix: type-scoped context activation resolves against the active context only

[skydudie]

Proposed changes

Problem — the two spec deviations left in Expansion::activateTypeScopedContexts() after #38:

1. documentBase fallback: a type-scoped context defined only at the document level could still activate inside a node whose context had been reset. In the VC 2.0 verifiableCredential @context: null isolation shape, a presentation-level type-scoped context (Individual) leaked into the isolated embedded credential and emitted a quad no conformant processor derives:

   + <did:example:subject-456> <https://vocab.example.org/credentials#fullName> "Jane Citizen" _:b0 .
   

   (the exact diff vs jsonld.js from the vc-context-null-isolation interop case, which was listed as a known deviation in Test: cross-implementation interop corpus (jsonld.js RDFC-1.0 goldens) #40). Notably the Individual type quad itself was not emitted — the scoped context activated for a type that couldn't even expand to an IRI there.
2. findTypeDefRecursive(): the recursive walk through nested @context entries in the document context. Dead weight since Bugfix: Type-scoped context lookup ignores the active context #38 — its stated use case (a type like DataIntegrityProof defined inside an imported security context) is handled by property-scoped context activation, which has already made the type visible in the active context by the time the typed node is entered.

Fix — per JSON-LD 1.1 exp. §5.5 step 11, the type resolves against the active context (the type-scoped snapshot) and nothing else. Both fallbacks removed; net −54/+? lines in Expansion.php.

Evidence the fallbacks were dead weight (beyond the fixed case)

• W3C suite unchanged: 1287 passed, 15 xfail-skipped — zero regressions across expand/compact/flatten/toRdf/fromRdf/frame.
• Full unit suite: the only test that changed behavior was the interop xfail guard, which flipped green the moment the fallback was removed — exactly as designed in Test: cross-implementation interop corpus (jsonld.js RDFC-1.0 goldens) #40 — and is delisted here (INTEROP_KNOWN_DEVIATIONS is now empty).

Tests

• New expansion unit test pinning the isolation behavior (document-level type-scoped context must NOT activate after a property-scoped @context: null reset; the unexpandable type stays "Thing", label drops). Expectations generated with jsonld.js 8.3.3; confirmed red against main's Expansion.php.
• vc-context-null-isolation interop case now passes for real: our canonical N-Quads for the VC 2.0 isolation shape are dataset-identical to jsonld.js.
• Unit: 343 passed, 0 skipped (was 341 + 1 skip). Pint + PHPStan (max) clean.

Jira ticket link

• N/A

Checklist

• New unit test red on main, green with the fix
• W3C conformance suite unchanged (verified in Linux container; CI covers it)
• Interop corpus fully green, known-deviations list emptied
• Pint + PHPStan pass

Further comments

• Behavior change is quad-removing for the isolation shape (quads that only this library emitted, never conformant verifiers). Standard VC/VP documents — where embedded credentials carry their own @context, as the VC 2.0 spec requires — are unaffected: the active-context lookup (Bugfix: Type-scoped context lookup ignores the active context #38) already resolves their types. Same caveat as Bugfix: Type-scoped context lookup ignores the active context #38 applies to any artifacts signed by pre-fix versions of this library over the (non-conformant) isolation shape.
• Completes the follow-up plan from Test: cross-implementation interop corpus (jsonld.js RDFC-1.0 goldens) #40, which was merged specifically to guard this change.