Phase 1a: content schema validator (freeze the schema)

Implements AGENTS.md section 7 front-matter schema as a single-file,
standard-library-only Python validator; no third-party YAML dependency
and no framework. Adds the `make validate` gate, a 20-case fixture set
and docs/content-schema.md.

DoD satisfied:
- make validate runs and exits 0 on an empty/clean content/ tree
  (missing dir and empty dir both exit 0; fixture ok-empty covers it).
- Every violation class has a fixture under test/fixtures/fail-*; each
  exits non-zero with one line per violation (file:line: field: rule).
  `make test` runs all 20 cases: 20/20 pass.
- Dangling artefact reference is fatal (fail-dangling-artefact;
  artefacts[].url must resolve to an existing in-repo L3 stub or asset).
- Unknown front-matter field is fatal (fail-unknown-field), including
  unknown keys nested inside artefacts[]/metrics[].
- docs/content-schema.md committed; states the frozen schema, links to
  AGENTS.md section 7, and records that any later schema change is a
  breaking change requiring Sam's approval.
- Scope respected: no content authored, no rendering, no site code.

Files: Makefile, tools/validate_content.py, test/fixtures/**,
docs/content-schema.md, .gitignore (__pycache__).

test/fixtures/fail-area-enum/content/assets/audio-rack.svg

@@ -0,0 +1 @@
+<svg xmlns="http://www.w3.org/2000/svg" width="10" height="10"/>

test/fixtures/fail-area-enum/content/edge/audio.md

@@ -0,0 +1,21 @@
+---
+id: audio
+area: security
+level: 2
+title: "Distributed Audio"
+claim: "Eight synchronised endpoints with music ducking for voice."
+confidence: running
+period: "2023-"
+tech: [Snapcast, Mopidy, Spotify]
+metrics: [{label: "endpoints", value: 8}]
+artefacts:
+  - type: doc
+    label: "Architecture note"
+    url: "content/edge/l3/audio-architecture.md"
+  - {type: image, label: "Rack diagram", url: "content/assets/audio-rack.svg"}
+public: true
+last_verified: 2026-10-20
+tags: [audio, snapcast]
+---
+
+# Distributed Audio

test/fixtures/fail-area-enum/content/edge/l3/audio-architecture.md

@@ -0,0 +1,17 @@
+---
+id: audio-architecture
+area: edge
+level: 3
+title: "Audio architecture note"
+claim: "How the eight endpoints stay in sync."
+confidence: running
+period: "2023-"
+tech: []
+metrics: []
+artefacts: []
+public: true
+last_verified: 2026-10-20
+tags: [audio]
+---
+
+# Audio architecture note

test/fixtures/fail-area-enum/expect.txt

@@ -0,0 +1 @@
+area: must be one of ai, platform, edge, products, history, about

test/fixtures/fail-artefact-external-url/content/assets/audio-rack.svg

@@ -0,0 +1 @@
+<svg xmlns="http://www.w3.org/2000/svg" width="10" height="10"/>

test/fixtures/fail-artefact-external-url/content/edge/audio.md

@@ -0,0 +1,21 @@
+---
+id: audio
+area: edge
+level: 2
+title: "Distributed Audio"
+claim: "Eight synchronised endpoints with music ducking for voice."
+confidence: running
+period: "2023-"
+tech: [Snapcast, Mopidy, Spotify]
+metrics: [{label: "endpoints", value: 8}]
+artefacts:
+  - type: doc
+    label: "Architecture note"
+    url: "content/edge/l3/audio-architecture.md"
+  - {type: image, label: "Rack diagram", url: "https://example.invalid/rack.svg"}
+public: true
+last_verified: 2026-10-20
+tags: [audio, snapcast]
+---
+
+# Distributed Audio

test/fixtures/fail-artefact-external-url/content/edge/l3/audio-architecture.md

@@ -0,0 +1,17 @@
+---
+id: audio-architecture
+area: edge
+level: 3
+title: "Audio architecture note"
+claim: "How the eight endpoints stay in sync."
+confidence: running
+period: "2023-"
+tech: []
+metrics: []
+artefacts: []
+public: true
+last_verified: 2026-10-20
+tags: [audio]
+---
+
+# Audio architecture note

test/fixtures/fail-artefact-external-url/expect.txt

@@ -0,0 +1 @@
+artefacts[1].url: must be an in-repo path to an L3 stub or asset, not an external URL

test/fixtures/fail-artefact-missing-url/content/assets/audio-rack.svg

@@ -0,0 +1 @@
+<svg xmlns="http://www.w3.org/2000/svg" width="10" height="10"/>

test/fixtures/fail-artefact-missing-url/content/edge/audio.md

@@ -0,0 +1,21 @@
+---
+id: audio
+area: edge
+level: 2
+title: "Distributed Audio"
+claim: "Eight synchronised endpoints with music ducking for voice."
+confidence: running
+period: "2023-"
+tech: [Snapcast, Mopidy, Spotify]
+metrics: [{label: "endpoints", value: 8}]
+artefacts:
+  - type: doc
+    label: "Architecture note"
+    url: "content/edge/l3/audio-architecture.md"
+  - {type: image, label: "Rack diagram"}
+public: true
+last_verified: 2026-10-20
+tags: [audio, snapcast]
+---
+
+# Distributed Audio

test/fixtures/fail-artefact-missing-url/content/edge/l3/audio-architecture.md

@@ -0,0 +1,17 @@
+---
+id: audio-architecture
+area: edge
+level: 3
+title: "Audio architecture note"
+claim: "How the eight endpoints stay in sync."
+confidence: running
+period: "2023-"
+tech: []
+metrics: []
+artefacts: []
+public: true
+last_verified: 2026-10-20
+tags: [audio]
+---
+
+# Audio architecture note

test/fixtures/fail-artefact-missing-url/expect.txt

@@ -0,0 +1 @@
+artefacts[1].url: missing required field

test/fixtures/fail-artefact-type-enum/content/assets/audio-rack.svg

@@ -0,0 +1 @@
+<svg xmlns="http://www.w3.org/2000/svg" width="10" height="10"/>

test/fixtures/fail-artefact-type-enum/content/edge/audio.md

@@ -0,0 +1,21 @@
+---
+id: audio
+area: edge
+level: 2
+title: "Distributed Audio"
+claim: "Eight synchronised endpoints with music ducking for voice."
+confidence: running
+period: "2023-"
+tech: [Snapcast, Mopidy, Spotify]
+metrics: [{label: "endpoints", value: 8}]
+artefacts:
+  - type: screenshot
+    label: "Architecture note"
+    url: "content/edge/l3/audio-architecture.md"
+  - {type: image, label: "Rack diagram", url: "content/assets/audio-rack.svg"}
+public: true
+last_verified: 2026-10-20
+tags: [audio, snapcast]
+---
+
+# Distributed Audio

test/fixtures/fail-artefact-type-enum/content/edge/l3/audio-architecture.md

@@ -0,0 +1,17 @@
+---
+id: audio-architecture
+area: edge
+level: 3
+title: "Audio architecture note"
+claim: "How the eight endpoints stay in sync."
+confidence: running
+period: "2023-"
+tech: []
+metrics: []
+artefacts: []
+public: true
+last_verified: 2026-10-20
+tags: [audio]
+---
+
+# Audio architecture note

test/fixtures/fail-artefact-type-enum/expect.txt

@@ -0,0 +1 @@
+artefacts[0].type: must be one of repo, image, video, doc

test/fixtures/fail-bad-yaml/content/assets/audio-rack.svg

@@ -0,0 +1 @@
+<svg xmlns="http://www.w3.org/2000/svg" width="10" height="10"/>

test/fixtures/fail-bad-yaml/content/edge/audio.md

@@ -0,0 +1,21 @@
+---
+id: audio
+area: edge
+level: 2
+title: "Distributed Audio
+claim: "Eight synchronised endpoints with music ducking for voice."
+confidence: running
+period: "2023-"
+tech: [Snapcast, Mopidy, Spotify]
+metrics: [{label: "endpoints", value: 8}]
+artefacts:
+  - type: doc
+    label: "Architecture note"
+    url: "content/edge/l3/audio-architecture.md"
+  - {type: image, label: "Rack diagram", url: "content/assets/audio-rack.svg"}
+public: true
+last_verified: 2026-10-20
+tags: [audio, snapcast]
+---
+
+# Distributed Audio

test/fixtures/fail-bad-yaml/content/edge/l3/audio-architecture.md

@@ -0,0 +1,17 @@
+---
+id: audio-architecture
+area: edge
+level: 3
+title: "Audio architecture note"
+claim: "How the eight endpoints stay in sync."
+confidence: running
+period: "2023-"
+tech: []
+metrics: []
+artefacts: []
+public: true
+last_verified: 2026-10-20
+tags: [audio]
+---
+
+# Audio architecture note

test/fixtures/fail-bad-yaml/expect.txt

@@ -0,0 +1 @@
+invalid YAML: unterminated quoted string

test/fixtures/fail-confidence-enum/content/assets/audio-rack.svg

@@ -0,0 +1 @@
+<svg xmlns="http://www.w3.org/2000/svg" width="10" height="10"/>

test/fixtures/fail-confidence-enum/content/edge/audio.md

@@ -0,0 +1,21 @@
+---
+id: audio
+area: edge
+level: 2
+title: "Distributed Audio"
+claim: "Eight synchronised endpoints with music ducking for voice."
+confidence: planned
+period: "2023-"
+tech: [Snapcast, Mopidy, Spotify]
+metrics: [{label: "endpoints", value: 8}]
+artefacts:
+  - type: doc
+    label: "Architecture note"
+    url: "content/edge/l3/audio-architecture.md"
+  - {type: image, label: "Rack diagram", url: "content/assets/audio-rack.svg"}
+public: true
+last_verified: 2026-10-20
+tags: [audio, snapcast]
+---
+
+# Distributed Audio

test/fixtures/fail-confidence-enum/content/edge/l3/audio-architecture.md

@@ -0,0 +1,17 @@
+---
+id: audio-architecture
+area: edge
+level: 3
+title: "Audio architecture note"
+claim: "How the eight endpoints stay in sync."
+confidence: running
+period: "2023-"
+tech: []
+metrics: []
+artefacts: []
+public: true
+last_verified: 2026-10-20
+tags: [audio]
+---
+
+# Audio architecture note

test/fixtures/fail-confidence-enum/expect.txt

@@ -0,0 +1 @@
+confidence: must be one of delivered, running, in-progress, abandoned, historic

test/fixtures/fail-dangling-artefact/content/assets/audio-rack.svg

@@ -0,0 +1 @@
+<svg xmlns="http://www.w3.org/2000/svg" width="10" height="10"/>

test/fixtures/fail-dangling-artefact/content/edge/audio.md

@@ -0,0 +1,21 @@
+---
+id: audio
+area: edge
+level: 2
+title: "Distributed Audio"
+claim: "Eight synchronised endpoints with music ducking for voice."
+confidence: running
+period: "2023-"
+tech: [Snapcast, Mopidy, Spotify]
+metrics: [{label: "endpoints", value: 8}]
+artefacts:
+  - type: doc
+    label: "Architecture note"
+    url: "content/edge/l3/not-written-yet.md"
+  - {type: image, label: "Rack diagram", url: "content/assets/audio-rack.svg"}
+public: true
+last_verified: 2026-10-20
+tags: [audio, snapcast]
+---
+
+# Distributed Audio

test/fixtures/fail-dangling-artefact/content/edge/l3/audio-architecture.md

@@ -0,0 +1,17 @@
+---
+id: audio-architecture
+area: edge
+level: 3
+title: "Audio architecture note"
+claim: "How the eight endpoints stay in sync."
+confidence: running
+period: "2023-"
+tech: []
+metrics: []
+artefacts: []
+public: true
+last_verified: 2026-10-20
+tags: [audio]
+---
+
+# Audio architecture note

test/fixtures/fail-dangling-artefact/expect.txt

@@ -0,0 +1 @@
+artefacts[0].url: dangling reference: 'content/edge/l3/not-written-yet.md' does not exist

test/fixtures/fail-duplicate-id/content/assets/audio-rack.svg

@@ -0,0 +1 @@
+<svg xmlns="http://www.w3.org/2000/svg" width="10" height="10"/>

test/fixtures/fail-duplicate-id/content/edge/audio.md

@@ -0,0 +1,21 @@
+---
+id: audio
+area: edge
+level: 2
+title: "Distributed Audio"
+claim: "Eight synchronised endpoints with music ducking for voice."
+confidence: running
+period: "2023-"
+tech: [Snapcast, Mopidy, Spotify]
+metrics: [{label: "endpoints", value: 8}]
+artefacts:
+  - type: doc
+    label: "Architecture note"
+    url: "content/edge/l3/audio-architecture.md"
+  - {type: image, label: "Rack diagram", url: "content/assets/audio-rack.svg"}
+public: true
+last_verified: 2026-10-20
+tags: [audio, snapcast]
+---
+
+# Distributed Audio

test/fixtures/fail-duplicate-id/content/edge/l3/audio-architecture.md

@@ -0,0 +1,17 @@
+---
+id: audio-architecture
+area: edge
+level: 3
+title: "Audio architecture note"
+claim: "How the eight endpoints stay in sync."
+confidence: running
+period: "2023-"
+tech: []
+metrics: []
+artefacts: []
+public: true
+last_verified: 2026-10-20
+tags: [audio]
+---
+
+# Audio architecture note

test/fixtures/fail-duplicate-id/content/platform/audio.md

@@ -0,0 +1,21 @@
+---
+id: audio
+area: platform
+level: 2
+title: "Distributed Audio"
+claim: "Eight synchronised endpoints with music ducking for voice."
+confidence: running
+period: "2023-"
+tech: [Snapcast, Mopidy, Spotify]
+metrics: [{label: "endpoints", value: 8}]
+artefacts:
+  - type: doc
+    label: "Architecture note"
+    url: "content/edge/l3/audio-architecture.md"
+  - {type: image, label: "Rack diagram", url: "content/assets/audio-rack.svg"}
+public: true
+last_verified: 2026-10-20
+tags: [audio, snapcast]
+---
+
+# Distributed Audio

test/fixtures/fail-duplicate-id/expect.txt

@@ -0,0 +1 @@
+duplicate id 'audio'

test/fixtures/fail-filename-mismatch/content/assets/audio-rack.svg

@@ -0,0 +1 @@
+<svg xmlns="http://www.w3.org/2000/svg" width="10" height="10"/>

test/fixtures/fail-filename-mismatch/content/edge/audio.md

@@ -0,0 +1,21 @@
+---
+id: edge-audio
+area: edge
+level: 2
+title: "Distributed Audio"
+claim: "Eight synchronised endpoints with music ducking for voice."
+confidence: running
+period: "2023-"
+tech: [Snapcast, Mopidy, Spotify]
+metrics: [{label: "endpoints", value: 8}]
+artefacts:
+  - type: doc
+    label: "Architecture note"
+    url: "content/edge/l3/audio-architecture.md"
+  - {type: image, label: "Rack diagram", url: "content/assets/audio-rack.svg"}
+public: true
+last_verified: 2026-10-20
+tags: [audio, snapcast]
+---
+
+# Distributed Audio

test/fixtures/fail-filename-mismatch/content/edge/l3/audio-architecture.md

@@ -0,0 +1,17 @@
+---
+id: audio-architecture
+area: edge
+level: 3
+title: "Audio architecture note"
+claim: "How the eight endpoints stay in sync."
+confidence: running
+period: "2023-"
+tech: []
+metrics: []
+artefacts: []
+public: true
+last_verified: 2026-10-20
+tags: [audio]
+---
+
+# Audio architecture note

test/fixtures/fail-filename-mismatch/expect.txt

@@ -0,0 +1 @@
+must match the file name (expected 'audio', got 'edge-audio')

test/fixtures/fail-last-verified-date/content/assets/audio-rack.svg

@@ -0,0 +1 @@
+<svg xmlns="http://www.w3.org/2000/svg" width="10" height="10"/>

test/fixtures/fail-last-verified-date/content/edge/audio.md

@@ -0,0 +1,21 @@
+---
+id: audio
+area: edge
+level: 2
+title: "Distributed Audio"
+claim: "Eight synchronised endpoints with music ducking for voice."
+confidence: running
+period: "2023-"
+tech: [Snapcast, Mopidy, Spotify]
+metrics: [{label: "endpoints", value: 8}]
+artefacts:
+  - type: doc
+    label: "Architecture note"
+    url: "content/edge/l3/audio-architecture.md"
+  - {type: image, label: "Rack diagram", url: "content/assets/audio-rack.svg"}
+public: true
+last_verified: 2026-13-45
+tags: [audio, snapcast]
+---
+
+# Distributed Audio

test/fixtures/fail-last-verified-date/content/edge/l3/audio-architecture.md

@@ -0,0 +1,17 @@
+---
+id: audio-architecture
+area: edge
+level: 3
+title: "Audio architecture note"
+claim: "How the eight endpoints stay in sync."
+confidence: running
+period: "2023-"
+tech: []
+metrics: []
+artefacts: []
+public: true
+last_verified: 2026-10-20
+tags: [audio]
+---
+
+# Audio architecture note

test/fixtures/fail-last-verified-date/expect.txt

@@ -0,0 +1 @@
+last_verified: must be a real calendar date (YYYY-MM-DD)

test/fixtures/fail-last-verified-format/content/assets/audio-rack.svg

@@ -0,0 +1 @@
+<svg xmlns="http://www.w3.org/2000/svg" width="10" height="10"/>

test/fixtures/fail-last-verified-format/content/edge/audio.md

@@ -0,0 +1,21 @@
+---
+id: audio
+area: edge
+level: 2
+title: "Distributed Audio"
+claim: "Eight synchronised endpoints with music ducking for voice."
+confidence: running
+period: "2023-"
+tech: [Snapcast, Mopidy, Spotify]
+metrics: [{label: "endpoints", value: 8}]
+artefacts:
+  - type: doc
+    label: "Architecture note"
+    url: "content/edge/l3/audio-architecture.md"
+  - {type: image, label: "Rack diagram", url: "content/assets/audio-rack.svg"}
+public: true
+last_verified: "20 October 2026"
+tags: [audio, snapcast]
+---
+
+# Distributed Audio

test/fixtures/fail-last-verified-format/content/edge/l3/audio-architecture.md

@@ -0,0 +1,17 @@
+---
+id: audio-architecture
+area: edge
+level: 3
+title: "Audio architecture note"
+claim: "How the eight endpoints stay in sync."
+confidence: running
+period: "2023-"
+tech: []
+metrics: []
+artefacts: []
+public: true
+last_verified: 2026-10-20
+tags: [audio]
+---
+
+# Audio architecture note

test/fixtures/fail-last-verified-format/expect.txt

@@ -0,0 +1 @@
+last_verified: must be a date written as YYYY-MM-DD

test/fixtures/fail-level-enum/content/assets/audio-rack.svg

@@ -0,0 +1 @@
+<svg xmlns="http://www.w3.org/2000/svg" width="10" height="10"/>

test/fixtures/fail-level-enum/content/edge/audio.md

@@ -0,0 +1,21 @@
+---
+id: audio
+area: edge
+level: 4
+title: "Distributed Audio"
+claim: "Eight synchronised endpoints with music ducking for voice."
+confidence: running
+period: "2023-"
+tech: [Snapcast, Mopidy, Spotify]
+metrics: [{label: "endpoints", value: 8}]
+artefacts:
+  - type: doc
+    label: "Architecture note"
+    url: "content/edge/l3/audio-architecture.md"
+  - {type: image, label: "Rack diagram", url: "content/assets/audio-rack.svg"}
+public: true
+last_verified: 2026-10-20
+tags: [audio, snapcast]
+---
+
+# Distributed Audio

test/fixtures/fail-level-enum/content/edge/l3/audio-architecture.md

@@ -0,0 +1,17 @@
+---
+id: audio-architecture
+area: edge
+level: 3
+title: "Audio architecture note"
+claim: "How the eight endpoints stay in sync."
+confidence: running
+period: "2023-"
+tech: []
+metrics: []
+artefacts: []
+public: true
+last_verified: 2026-10-20
+tags: [audio]
+---
+
+# Audio architecture note

test/fixtures/fail-level-enum/expect.txt

@@ -0,0 +1 @@
+level: must be the integer 1, 2 or 3

test/fixtures/fail-metrics-empty/content/assets/audio-rack.svg

@@ -0,0 +1 @@
+<svg xmlns="http://www.w3.org/2000/svg" width="10" height="10"/>

test/fixtures/fail-metrics-empty/content/edge/audio.md

@@ -0,0 +1,21 @@
+---
+id: audio
+area: edge
+level: 2
+title: "Distributed Audio"
+claim: "Eight synchronised endpoints with music ducking for voice."
+confidence: running
+period: "2023-"
+tech: [Snapcast, Mopidy, Spotify]
+metrics: [{label: "", value: 8}]
+artefacts:
+  - type: doc
+    label: "Architecture note"
+    url: "content/edge/l3/audio-architecture.md"
+  - {type: image, label: "Rack diagram", url: "content/assets/audio-rack.svg"}
+public: true
+last_verified: 2026-10-20
+tags: [audio, snapcast]
+---
+
+# Distributed Audio

test/fixtures/fail-metrics-empty/content/edge/l3/audio-architecture.md

@@ -0,0 +1,17 @@
+---
+id: audio-architecture
+area: edge
+level: 3
+title: "Audio architecture note"
+claim: "How the eight endpoints stay in sync."
+confidence: running
+period: "2023-"
+tech: []
+metrics: []
+artefacts: []
+public: true
+last_verified: 2026-10-20
+tags: [audio]
+---
+
+# Audio architecture note

test/fixtures/fail-metrics-empty/expect.txt

@@ -0,0 +1 @@
+metrics[0].label: must be non-empty

test/fixtures/fail-missing-field/content/assets/audio-rack.svg

@@ -0,0 +1 @@
+<svg xmlns="http://www.w3.org/2000/svg" width="10" height="10"/>

test/fixtures/fail-missing-field/content/edge/audio.md

@@ -0,0 +1,20 @@
+---
+id: audio
+area: edge
+level: 2
+title: "Distributed Audio"
+confidence: running
+period: "2023-"
+tech: [Snapcast, Mopidy, Spotify]
+metrics: [{label: "endpoints", value: 8}]
+artefacts:
+  - type: doc
+    label: "Architecture note"
+    url: "content/edge/l3/audio-architecture.md"
+  - {type: image, label: "Rack diagram", url: "content/assets/audio-rack.svg"}
+public: true
+last_verified: 2026-10-20
+tags: [audio, snapcast]
+---
+
+# Distributed Audio

test/fixtures/fail-missing-field/content/edge/l3/audio-architecture.md

@@ -0,0 +1,17 @@
+---
+id: audio-architecture
+area: edge
+level: 3
+title: "Audio architecture note"
+claim: "How the eight endpoints stay in sync."
+confidence: running
+period: "2023-"
+tech: []
+metrics: []
+artefacts: []
+public: true
+last_verified: 2026-10-20
+tags: [audio]
+---
+
+# Audio architecture note

test/fixtures/fail-missing-field/expect.txt

@@ -0,0 +1 @@
+claim: missing required field

test/fixtures/fail-no-front-matter/content/edge/audio.md

@@ -0,0 +1,3 @@
+# Distributed Audio
+
+No front-matter block at all.

test/fixtures/fail-no-front-matter/expect.txt

@@ -0,0 +1 @@
+missing front-matter block

test/fixtures/fail-unknown-field/content/assets/audio-rack.svg

@@ -0,0 +1 @@
+<svg xmlns="http://www.w3.org/2000/svg" width="10" height="10"/>

test/fixtures/fail-unknown-field/content/edge/audio.md

@@ -0,0 +1,22 @@
+---
+id: audio
+area: edge
+level: 2
+title: "Distributed Audio"
+claim: "Eight synchronised endpoints with music ducking for voice."
+confidence: running
+period: "2023-"
+tech: [Snapcast, Mopidy, Spotify]
+metrics: [{label: "endpoints", value: 8}]
+artefacts:
+  - type: doc
+    label: "Architecture note"
+    url: "content/edge/l3/audio-architecture.md"
+  - {type: image, label: "Rack diagram", url: "content/assets/audio-rack.svg"}
+public: true
+last_verified: 2026-10-20
+tags: [audio, snapcast]
+author: "Sam"
+---
+
+# Distributed Audio

test/fixtures/fail-unknown-field/content/edge/l3/audio-architecture.md

@@ -0,0 +1,17 @@
+---
+id: audio-architecture
+area: edge
+level: 3
+title: "Audio architecture note"
+claim: "How the eight endpoints stay in sync."
+confidence: running
+period: "2023-"
+tech: []
+metrics: []
+artefacts: []
+public: true
+last_verified: 2026-10-20
+tags: [audio]
+---
+
+# Audio architecture note

test/fixtures/fail-unknown-field/expect.txt

@@ -0,0 +1 @@
+author: unknown field (the schema is frozen; see docs/content-schema.md)

test/fixtures/fail-unknown-nested-field/content/assets/audio-rack.svg

@@ -0,0 +1 @@
+<svg xmlns="http://www.w3.org/2000/svg" width="10" height="10"/>

test/fixtures/fail-unknown-nested-field/content/edge/audio.md

@@ -0,0 +1,19 @@
+---
+id: audio
+area: edge
+level: 2
+title: "Distributed Audio"
+claim: "Eight synchronised endpoints with music ducking for voice."
+confidence: running
+period: "2023-"
+tech: [Snapcast, Mopidy, Spotify]
+metrics: [{label: "endpoints", value: 8}]
+artefacts:
+  - type: doc
+    label: "Architecture note"
+    url: "content/edge/l3/audio-architecture.md"
+  - {type: image, label: "Rack diagram", url: "content/assets/audio-rack.svg", caption: "the rack"}
+public: true
+last_verified: 2026-10-20
+tags: [audio, snapcast]
+---

test/fixtures/fail-unknown-nested-field/content/edge/l3/audio-architecture.md

@@ -0,0 +1,15 @@
+---
+id: audio-architecture
+area: edge
+level: 3
+title: "Audio architecture note"
+claim: "How the eight endpoints stay in sync."
+confidence: running
+period: "2023-"
+tech: []
+metrics: []
+artefacts: []
+public: true
+last_verified: 2026-10-20
+tags: [audio]
+---

test/fixtures/fail-unknown-nested-field/expect.txt

@@ -0,0 +1 @@
+artefacts[1].caption: unknown field (artefacts allow only 'type', 'label' and 'url')

test/fixtures/ok-block-scalars/content/about/background.md

@@ -0,0 +1,25 @@
+---
+# a leading comment is allowed
+id: background
+area: about
+level: 1
+title: >-
+  Twenty-five years of delivery
+claim: |
+  Shipped software since 2000.
+  Now agent systems and the platform under them.
+confidence: delivered
+period: "2000-"
+tech:
+  - "NixOS"
+  - 'Golang'
+metrics:
+  - label: years
+    value: 25
+artefacts: []
+public: true
+last_verified: 2026-10-20
+tags: [narrative, career]
+---
+
+# Twenty-five years of delivery

test/fixtures/ok-clean/content/assets/audio-rack.svg

@@ -0,0 +1 @@
+<svg xmlns="http://www.w3.org/2000/svg" width="10" height="10"/>

test/fixtures/ok-clean/content/edge/audio.md

@@ -0,0 +1,21 @@
+---
+id: audio
+area: edge
+level: 2
+title: "Distributed Audio"
+claim: "Eight synchronised endpoints with music ducking for voice."
+confidence: running
+period: "2023-"
+tech: [Snapcast, Mopidy, Spotify]
+metrics: [{label: "endpoints", value: 8}]
+artefacts:
+  - type: doc
+    label: "Architecture note"
+    url: "content/edge/l3/audio-architecture.md"
+  - {type: image, label: "Rack diagram", url: "content/assets/audio-rack.svg"}
+public: true
+last_verified: 2026-10-20
+tags: [audio, snapcast]
+---
+
+# Distributed Audio

test/fixtures/ok-clean/content/edge/l3/audio-architecture.md

@@ -0,0 +1,17 @@
+---
+id: audio-architecture
+area: edge
+level: 3
+title: "Audio architecture note"
+claim: "How the eight endpoints stay in sync."
+confidence: running
+period: "2023-"
+tech: []
+metrics: []
+artefacts: []
+public: true
+last_verified: 2026-10-20
+tags: [audio]
+---
+
+# Audio architecture note