test(okf): consume nav-golden fixtures + thin STEG 0 corpus gate

Consume commons' nav-golden fixture class byte-exact from
portfolio-optimiser-commons @ b641741 (nav-golden-hierarchy positive +
nav-golden-escape boundary) into test/nav-golden-corpus/ and wire a thin
gate scripts/check-nav-golden.mjs (+ .test.mjs, 10 tests).

Scope (operator decision, thin): the catalog is the convention owner and
holds no consumer (null konsument), and the shared retrieval skill is
deferred (spec.md §10 Stage 3). So the gate does NOT run a read-context
navigator and does NOT assert the goldens byte-exact. It asserts only what
the catalog owns: each fixture bundle/ is a conformant OKF bundle under the
existing §3 checkBundle (every concept typed + root okf_version), and the
committed expected-read-context.md golden is present and non-empty. Byte-exact
navigator conformance stays a consumer concern (okr STEG 4 / Stage 3 skill).

Fixtures pinned byte-exact (.gitattributes -text); manifest carries source
repo+SHA per the vendoring-provenance rule. Naming: the stale "§5 pts 1-5"
read-context label maps to the settled method-spec §3 Step 1 (commons 9801d35);
no open §5 dependency. commons confirmed b641741 complete + goldens derived
from §3 Step 1 (via coord).

Verified: check-nav-golden 10/10; gate CLI exit 0 (2 fixtures PASS); full
suite 73/73 across the six test files.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01NeK9hkxrU9wFPBYGYnSV1V

test/nav-golden-corpus/nav-golden-hierarchy/bundle/a/b/doc-b.md

@@ -0,0 +1,6 @@
+---
+type: reference
+title: "Doc B"
+---
+
+Level-2 concept reached depth-first, deepest in the traversal.

test/nav-golden-corpus/nav-golden-hierarchy/bundle/a/b/index.md

@@ -0,0 +1,8 @@
+---
+type: index
+okf_version: 0.1
+title: "Subsection B index"
+---
+
+- [Doc B](doc-b.md)
+- [Back to A](/a/index.md)

test/nav-golden-corpus/nav-golden-hierarchy/bundle/a/doc-a.md

@@ -0,0 +1,6 @@
+---
+type: methodology
+title: "Doc A"
+---
+
+Level-1 concept reached depth-first after Overview.

test/nav-golden-corpus/nav-golden-hierarchy/bundle/a/index.md

@@ -0,0 +1,10 @@
+---
+type: index
+okf_version: 0.1
+title: "Section A index"
+---
+
+- [Doc A](doc-a.md)
+- [Nested verdict](verdict-nested.md)
+- [Subsection B](b/index.md)
+- [Overview again](/overview.md)

test/nav-golden-corpus/nav-golden-hierarchy/bundle/a/verdict-nested.md

@@ -0,0 +1,8 @@
+---
+type: verdict
+title: "Nested verdict — must be excluded"
+decision: approved
+description: "A verdict file at a nested level. A conformant navigator reaches it (dedup marks it seen) but MUST exclude it from the read-context — recursively, not only at the root. This is the leakage surface a graph-based exclusion would miss."
+---
+
+This body MUST NOT appear in the read-context.

test/nav-golden-corpus/nav-golden-hierarchy/bundle/c/orphan.md

@@ -0,0 +1,6 @@
+---
+type: project
+title: "Orphan — unreachable"
+---
+
+Directory `c/` has no `index.md`, and nothing links to this file. A link-following navigator never reaches it; a directory-walking one wrongly would. It MUST be absent from the read-context, and its parent directory's missing `index.md` MUST NOT be an error (that rule binds the bundle root alone).

test/nav-golden-corpus/nav-golden-hierarchy/bundle/index.md

@@ -0,0 +1,10 @@
+---
+type: index
+okf_version: 0.1
+title: "Nav-golden — hierarchical navigation case"
+---
+
+Nav-golden hierarchical case. This bundle exercises depth-first traversal, both link forms (root-relative and relative), recursive verdict exclusion, resolved-path de-duplication, cycle termination, and the root-only binding of the missing-index rule.
+
+- [Overview](overview.md)
+- [Section A](/a/index.md)

test/nav-golden-corpus/nav-golden-hierarchy/bundle/overview.md

@@ -0,0 +1,6 @@
+---
+type: project
+title: "Overview"
+---
+
+Root-level concept reached by a relative link.