docs(examples): nav-golden fixture class — bundle → read-context goldens

New fixture class for the D4 step-0 split (commons-owned; delivered into
catalog's corpus/runner). A nav-golden case is bundle in / expected-read-
context out — the shape that expresses "two conformant implementations MUST
produce an identical read-context" (method-spec §3 Step 1).

- nav-golden-hierarchy/ (positive): depth-first first-seen order, both link
  forms (/ = bundle root vs relative), one segment per level, resolved-path
  dedup, cycle termination, recursive verdict exclusion, missing-index binds
  root alone, flat render.
- nav-golden-escape/ (negative, gate must go red): .. escapes and a
  /etc/passwd root-relative trap; conformant returns only valid.md.

Both expected-read-context.md verified byte-for-byte against a conformant
navigator implementing §3 Step 1; the negative case verified to diverge
under a naive navigator.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01VUCuNNvnCkayuUDy2WFgeU

examples/nav-golden-hierarchy/README.md

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+# nav-golden-hierarchy — hierarchical navigation golden
+
+Fixture class **nav-golden** (commons-owned, per the D4 step-0 split): `bundle/` in,
+`expected-read-context.md` out. Unlike the ingest-golden class (ingest-spec §11,
+extraction-shaped: `manifest.json` → `expected-bundle/`), a nav-golden case is
+**bundle → read-context** — the only shape that can express the load-bearing property
+"two conformant implementations MUST produce an identical read-context from the same
+bundle" (method-spec §3 Step 1).
+
+This **positive** case exercises every decision the Q3 navigation contract pins:
+
+| Decision (method-spec §3 Step 1) | How this bundle exercises it |
+|---|---|
+| Hierarchy allowed; escape, not depth, forbidden | `a/`, `a/b/` are navigated; nothing escapes |
+| Link syntax: leading `/` = bundle root, else relative | `index.md`: relative `overview.md` + root-relative `/a/index.md`; `a/index.md`: relative `b/index.md` + root-relative `/overview.md` |
+| Depth-first, first-seen order | render order is `overview` → `doc-a` → `doc-b` |
+| Dedup on resolved path | `/overview.md` (from `a/`) resolves to the already-seen `overview.md` → one entry |
+| Cycle termination | `a/b/index.md` links back to `/a/index.md` (already seen) → stops |
+| One segment per level | each index links only its immediate children |
+| Missing `index.md` binds the root alone | `c/` has no `index.md` and nothing links `c/orphan.md`; it is simply unreachable, not an error |
+| Verdict exclusion = type check per reached file, recursive | `a/verdict-nested.md` is reached but excluded |
+| Flat render regardless of depth | nested concepts render as the same `## {type}: {title}` sections; no level heading; nested index bodies are navigation, not content, and are not rendered |
+
+**Traversal trace:** `index.md` (its body is the leading summary) → `overview.md` →
+`/a/index.md` → `a/doc-a.md` → `a/verdict-nested.md` (reached, excluded) → `a/b/index.md`
+→ `a/b/doc-b.md` → `/a/index.md` (seen, deduped) → `/overview.md` (seen, deduped).
+Unreachable: `c/orphan.md`.
+
+**Serialization** the gate compares against: the root index body verbatim, then each
+**non-index** concept as `## {type}: {title}` + blank line + the file body, sections
+separated by one blank line, file ending in exactly one trailing newline. The spec does
+not pin whitespace beyond this shape; a gate MAY compare byte-exact or after
+trailing-whitespace normalization. **Only the root index body is the summary** — nested
+index bodies (`a/index.md`, `a/b/index.md`) are navigation and do not appear.

examples/nav-golden-hierarchy/bundle/a/b/doc-b.md

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

examples/nav-golden-hierarchy/bundle/a/b/index.md

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

examples/nav-golden-hierarchy/bundle/a/doc-a.md

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

examples/nav-golden-hierarchy/bundle/a/index.md

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+---
+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)

examples/nav-golden-hierarchy/bundle/a/verdict-nested.md

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+---
+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.

examples/nav-golden-hierarchy/bundle/c/orphan.md

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+---
+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).

examples/nav-golden-hierarchy/bundle/index.md

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+---
+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)

examples/nav-golden-hierarchy/bundle/overview.md

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+---
+type: project
+title: "Overview"
+---
+
+Root-level concept reached by a relative link.

examples/nav-golden-hierarchy/expected-read-context.md

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+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)
+
+## project: Overview
+
+Root-level concept reached by a relative link.
+
+## methodology: Doc A
+
+Level-1 concept reached depth-first after Overview.
+
+## reference: Doc B
+
+Level-2 concept reached depth-first, deepest in the traversal.