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/parse.go

@@ -15,6 +15,14 @@ type RawPage struct {
 	Subtype string `json:"subtype"` // entity: person|company|tool|model|framework|technology; source: article|pdf|book|video|note|project
 	Domain  string `json:"domain"`
 	Content string `json:"content"` // Markdown body only — no frontmatter
+
+	// Source, Author, Published are deterministic passthrough from the raw
+	// ingested content's own frontmatter (see parseContentFrontmatter) — never
+	// set by the LLM. json:"-" keeps them immune to same-named keys the LLM
+	// might emit. Only meaningful for Type == "source".
+	Source    string `json:"-"`
+	Author    string `json:"-"`
+	Published string `json:"-"`
 }
 
 // ParseRawPages parses LLM output as a JSON array of RawPage objects.
@@ -98,6 +106,60 @@ func repairJSON(s string) string {
 	return b.String()
 }
 
+// sourceMeta is source/author/published pulled from the raw ingested
+// content's own frontmatter — deterministic passthrough, never LLM output.
+type sourceMeta struct {
+	Source    string
+	Author    string
+	Published string
+}
+
+// parseContentFrontmatter extracts source/author/published from a leading
+// "---\n...\n---" YAML block in raw ingested content. Only these three flat
+// scalar keys are recognised; anything else in the block is ignored. Returns
+// a zero-value sourceMeta if content has no frontmatter block.
+func parseContentFrontmatter(content string) sourceMeta {
+	var meta sourceMeta
+	if !strings.HasPrefix(content, "---\n") && !strings.HasPrefix(content, "---\r\n") {
+		return meta
+	}
+
+	lines := strings.Split(content, "\n")
+	for _, line := range lines[1:] {
+		if strings.TrimSpace(line) == "---" {
+			break
+		}
+		key, val, ok := strings.Cut(line, ":")
+		if !ok {
+			continue
+		}
+		key = strings.TrimSpace(key)
+		val = strings.Trim(strings.TrimSpace(val), `"'`)
+		switch key {
+		case "source":
+			meta.Source = val
+		case "author":
+			meta.Author = val
+		case "published":
+			meta.Published = val
+		}
+	}
+	return meta
+}
+
+// applySourceMeta deterministically overwrites Source/Author/Published on
+// every "source"-type page with meta — the LLM never controls these fields.
+func applySourceMeta(pages []RawPage, meta sourceMeta) {
+	for i := range pages {
+		if pages[i].Type != "source" {
+			continue
+		}
+		pages[i].Source = meta.Source
+		pages[i].Author = meta.Author
+		pages[i].Published = meta.Published
+	}
+}
+
 func stripFences(s string) string {
 	for _, prefix := range []string{"```json\n", "```json\r\n", "```\n", "```\r\n"} {
 		if strings.HasPrefix(s, prefix) {