test(okf): capture block-form fixture and collection baseline before any decoder

Co-Authored-By: Claude <claude-opus-5>

tests/golden/block-form-provenance/expected-read-context.md

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+A repo-owned fixture bundle whose concepts carry OKF provenance in **block** form:
+`verified` as a YAML sequence of mappings (SPEC §5.2) rather than the single-line flow
+shorthand. Navigation must stay tolerant of it — the bytes rendered here are the "before"
+referent that later decoder work compares against.
+
+- [Attested computation](attested.md)
+- [Multi-verified concept](multi-verified.md)
+
+## concept: Attested computation
+
+One verification event, written as a single-entry block sequence — the SPEC-canonical
+long form of `verified: { by: ..., at: ... }`. The actor is a `process:` one, so the
+trust tier a consumer derives from it is machine-confirmed, never human-reviewed.
+
+`sources` is written in block form too, so a reader that only understands the flow
+shorthand loses the provenance of this concept entirely rather than reporting that it
+could not read it.
+
+## concept: Multi-verified concept
+
+Two independent verification events: a human sign-off FIRST, a nightly process SECOND.
+The order is the whole point of this file. A reader that keeps the last entry it sees
+reports machine-confirmed for a concept a human actually signed off, so the tier flips
+downward without anything failing — the defect has no error channel of its own.