test(01-04): PIPE-01 enforcement — schema violations throw at content load

- 2 happy-path tests: empty globs, valid YAML round-trip
- 3 throw assertions covering the schema-violation matrix:
  * numeric id (violates stable-string-ID rule)
  * season out of [0,7] range
  * Markdown frontmatter missing required id
- All 5 tests pass; full Phase-1 suite remains green
- Proves the throws that fail npm run build at module-eval time

src/content/loader.test.ts

@@ -0,0 +1,75 @@
+import { describe, it, expect } from 'vitest';
+import { loadFragmentsFromGlob } from './loader.ts';
+
+/**
+ * PIPE-01 enforcement: a schema violation in any /content/seasons/**.yaml
+ * or /content/seasons/**\/fragments/*.md file MUST fail the build.
+ *
+ * The exported `loadFragmentsFromGlob(yamlGlob, mdGlob)` helper accepts
+ * mocked glob outputs so we can prove the schema rejects bad input the
+ * same way `import.meta.glob` would feed real files into the build-time
+ * loader (which throws and bubbles up through Vite, exiting non-zero).
+ *
+ * Per .planning/phases/01-foundations-and-doctrine/01-RESEARCH.md
+ * § Validation Architecture (PIPE-01 row): "Vitest run with mocked
+ * import.meta.glob" — that's this file.
+ */
+describe('PIPE-01: content schema validation', () => {
+  it('returns [] when both globs are empty', () => {
+    expect(loadFragmentsFromGlob({}, {})).toEqual([]);
+  });
+
+  it('parses valid YAML fragments', () => {
+    const yamlGlob = {
+      '/content/seasons/00-demo/fragments.yaml': `
+fragments:
+  - id: season0.demo.test
+    season: 0
+    body: "demo body"
+`,
+    };
+    const result = loadFragmentsFromGlob(yamlGlob);
+    expect(result).toHaveLength(1);
+    expect(result[0]).toMatchObject({
+      id: 'season0.demo.test',
+      season: 0,
+      body: 'demo body',
+    });
+  });
+
+  it('THROWS on a numeric-id violation (stable-string-ID rule)', () => {
+    const yamlGlob = {
+      '/content/seasons/01-soil/fragments.yaml': `
+fragments:
+  - id: 42
+    season: 1
+    body: "this should fail because id must be a string matching the season<N>.<slug> regex"
+`,
+    };
+    expect(() => loadFragmentsFromGlob(yamlGlob)).toThrow(/\[content\] schema violation/);
+  });
+
+  it('THROWS when season is out of [0,7] range', () => {
+    const yamlGlob = {
+      '/content/seasons/99-bogus/fragments.yaml': `
+fragments:
+  - id: season99.bogus.test
+    season: 99
+    body: "season 99 doesn't exist"
+`,
+    };
+    expect(() => loadFragmentsFromGlob(yamlGlob)).toThrow(/\[content\] schema violation/);
+  });
+
+  it('THROWS when Markdown frontmatter omits required id', () => {
+    const mdGlob = {
+      '/content/seasons/01-soil/fragments/no-id.md': `---
+season: 1
+---
+
+Body text without an id frontmatter key.
+`,
+    };
+    expect(() => loadFragmentsFromGlob({}, mdGlob)).toThrow(/\[content\] schema violation/);
+  });
+});