fix(ingest): thread source/author/published frontmatter through extraction (#85)

pipeline.Run parses source/author/published from the raw content's own
frontmatter and applies them deterministically to source-type RawPages
after LLM extraction — never relies on the LLM to copy them through.
buildFrontmatter now emits all three (source pages only) when present.

Backfill of the 46 already-affected wiki/sources/*.md notes is a
separate concern per the issue, not done here.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01Roq1ajWKR5f1hG5Df9wC6A

ingestion/internal/pipeline/build_test.go

@@ -154,6 +154,52 @@ func TestBuildPages_EntityNoSubtype(t *testing.T) {
 	assert.Contains(t, pages[0].Content, "title: 'Basecamp'")
 }
 
+func TestBuildPages_SourcePageCarriesSourceAuthorPublished(t *testing.T) {
+	raw := []RawPage{
+		{
+			Title:     "Ornith",
+			Type:      "source",
+			Subtype:   "article",
+			Content:   "## Summary\n\nAn agentic coding model.\n",
+			Source:    "https://example.com/ornith",
+			Author:    "Jane Doe",
+			Published: "2026-07-20",
+		},
+	}
+	pages, warnings := BuildPages(raw, "ornith", "2026-07-26")
+	require.Len(t, pages, 1)
+	assert.Empty(t, warnings)
+
+	p := pages[0]
+	assert.Contains(t, p.Content, "source: 'https://example.com/ornith'")
+	assert.Contains(t, p.Content, "author: 'Jane Doe'")
+	assert.Contains(t, p.Content, "published: '2026-07-20'")
+}
+
+func TestBuildPages_SourcePageOmitsSourceAuthorPublishedWhenEmpty(t *testing.T) {
+	raw := []RawPage{
+		{Title: "Shape Up", Type: "source", Subtype: "book", Content: "## Summary\n\nA book.\n"},
+	}
+	pages, _ := BuildPages(raw, "shape-up", "2026-04-23")
+	require.Len(t, pages, 1)
+	assert.NotContains(t, pages[0].Content, "source:")
+	assert.NotContains(t, pages[0].Content, "author:")
+	assert.NotContains(t, pages[0].Content, "published:")
+}
+
+func TestBuildPages_ConceptPageIgnoresSourceAuthorPublished(t *testing.T) {
+	// source/author/published are source-note-only metadata; a concept page
+	// shouldn't carry them even if somehow set on the RawPage.
+	raw := []RawPage{
+		{Title: "Betting", Type: "concept", Content: "## Definition\n\nFoo.\n", Source: "x", Author: "y", Published: "z"},
+	}
+	pages, _ := BuildPages(raw, "src", "2026-04-23")
+	require.Len(t, pages, 1)
+	assert.NotContains(t, pages[0].Content, "source:")
+	assert.NotContains(t, pages[0].Content, "author:")
+	assert.NotContains(t, pages[0].Content, "published:")
+}
+
 func TestBuildPages_EmptyTitleSkippedWithWarning(t *testing.T) {
 	raw := []RawPage{
 		{Title: "", Type: "concept", Content: "## Definition\n\nFoo.\n"},