feat(pipeline): write into wiki/<wing>/{sources,facts}/ when Config.Wing is set (#205 S2)

Sources -> wiki/<wing>/sources, concepts/entities -> wiki/<wing>/facts with
kind: frontmatter; inventory, title resolution and back-references are
confined to the target wing. Empty Wing keeps the retired layout unchanged.
Mutation-checked: widening the inventory beyond the wing fails the
cross-wing back-reference test; a non-plain wing name is rejected.

Co-Authored-By: Claude Sonnet 5.5 <noreply@anthropic.com>

ingestion/internal/wiki/inventory.go

@@ -96,3 +96,79 @@ func readFrontmatter(bfs *brainfs.Brain, rel, fallbackSlug string) (title string
 	}
 	return
 }
+
+// LoadWingInventory returns the pages of ONE wing, grouped by type. Sources
+// come from wiki/<wing>/sources/; concepts and entities live together in
+// wiki/<wing>/facts/ and are told apart by their `kind:` frontmatter. A facts
+// page without a kind (a hand-written note) is left out, so extraction can
+// never merge into something it did not create. Other wings are never read.
+func LoadWingInventory(brainDir, wing string) (map[PageType][]Entry, error) {
+	result := map[PageType][]Entry{PageTypeConcept: {}, PageTypeEntity: {}, PageTypeSource: {}}
+	bfs, err := brainfs.Open(brainDir)
+	if err != nil {
+		return nil, fmt.Errorf("open brain: %w", err)
+	}
+	defer func() { _ = bfs.Close() }()
+	for _, hall := range []string{"sources", "facts"} {
+		dir := "wiki/" + wing + "/" + hall
+		names, err := bfs.ReadDirRegular(dir)
+		if errors.Is(err, fs.ErrNotExist) {
+			continue
+		}
+		if err != nil {
+			return nil, fmt.Errorf("read dir %s: %w", dir, err)
+		}
+		for _, name := range names {
+			if !strings.HasSuffix(name, ".md") {
+				continue
+			}
+			rel := dir + "/" + name
+			slug := strings.TrimSuffix(name, ".md")
+			pt := PageTypeSource
+			if hall == "facts" {
+				var ok bool
+				if pt, ok = kindOf(bfs, rel); !ok {
+					continue
+				}
+			}
+			title, aliases := readFrontmatter(bfs, rel, slug)
+			result[pt] = append(result[pt], Entry{Slug: slug, Title: title, Aliases: aliases, Type: pt, Path: rel})
+		}
+	}
+	return result, nil
+}
+
+// kindOf reads `kind:` from a facts page's frontmatter.
+func kindOf(bfs *brainfs.Brain, rel string) (PageType, bool) {
+	content, err := bfs.ReadRegular(rel)
+	if err != nil {
+		return "", false
+	}
+	return KindFromContent(string(content))
+}
+
+// KindFromContent maps frontmatter `kind: concept|entity` to a PageType.
+func KindFromContent(content string) (PageType, bool) {
+	inFM := false
+	for _, line := range strings.Split(content, "\n") {
+		if strings.TrimSpace(line) == "---" {
+			if inFM {
+				break
+			}
+			inFM = true
+			continue
+		}
+		if !inFM {
+			continue
+		}
+		if key, val, ok := strings.Cut(line, ":"); ok && strings.TrimSpace(key) == "kind" {
+			switch strings.Trim(strings.TrimSpace(val), `"'`) {
+			case "concept":
+				return PageTypeConcept, true
+			case "entity":
+				return PageTypeEntity, true
+			}
+		}
+	}
+	return "", false
+}

ingestion/internal/wiki/types.go

@@ -22,4 +22,5 @@ type Entry struct {
 	Title   string
 	Aliases []string
 	Type    PageType
+	Path    string // brain-relative path; set for wing-layout entries
 }