diff --git a/ingestion/internal/pipeline/refs.go b/ingestion/internal/pipeline/refs.go
new file mode 100644
index 0000000..ae633a2
--- /dev/null
+++ b/ingestion/internal/pipeline/refs.go
@@ -0,0 +1,115 @@
+// ingestion/internal/pipeline/refs.go
+package pipeline
+
+import (
+	"os"
+	"path/filepath"
+	"regexp"
+	"strings"
+
+	"github.com/mathiasbq/hyperguild/ingestion/internal/wiki"
+)
+
+var wikilinkRE = regexp.MustCompile(`\[\[([^|\]]+)\|`)
+
+// injectSourceRefs finds the source page in the proposed batch, extracts its
+// wikilinks, and injects a back-reference into every linked concept or entity page.
+// Pages that exist on disk but are not in the current batch are loaded and
+// appended so they will be updated on write.
+func injectSourceRefs(pages []wiki.Page, inventory map[wiki.PageType][]wiki.Entry, brainDir string) []wiki.Page {
+	sourceSlug, sourceTitle, found := findSourcePage(pages)
+	if !found {
+		return pages
+	}
+
+	var sourceContent string
+	for _, p := range pages {
+		if strings.HasPrefix(p.Path, "wiki/sources/") &&
+			strings.TrimSuffix(filepath.Base(p.Path), ".md") == sourceSlug {
+			sourceContent = p.Content
+			break
+		}
+	}
+
+	linkedSlugs := extractWikilinks(sourceContent)
+	sourceRef := "- [[" + sourceSlug + "|" + sourceTitle + "]]"
+
+	bySlug := make(map[string]int, len(pages))
+	for i, p := range pages {
+		if !strings.HasPrefix(p.Path, "wiki/sources/") {
+			bySlug[strings.TrimSuffix(filepath.Base(p.Path), ".md")] = i
+		}
+	}
+
+	for slug := range linkedSlugs {
+		if slug == sourceSlug {
+			continue
+		}
+		if idx, ok := bySlug[slug]; ok {
+			pages[idx] = addSourceRef(pages[idx], sourceRef)
+			continue
+		}
+		pt, ok := findInInventory(slug, inventory)
+		if !ok {
+			continue
+		}
+		diskPath := filepath.Join(brainDir, "wiki", string(pt), slug+".md")
+		b, err := os.ReadFile(diskPath)
+		if err != nil {
+			continue
+		}
+		page := wiki.Page{
+			Path:    "wiki/" + string(pt) + "/" + slug + ".md",
+			Content: string(b),
+		}
+		pages = append(pages, addSourceRef(page, sourceRef))
+	}
+
+	return pages
+}
+
+// addSourceRef injects sourceRef into the ## Sources bullet section of page
+// using wiki.Merge, which deduplicates bullets automatically.
+func addSourceRef(page wiki.Page, sourceRef string) wiki.Page {
+	patch := wiki.Page{
+		Path:    page.Path,
+		Content: "\n## Sources\n\n" + sourceRef + "\n",
+	}
+	return wiki.Merge(page, patch)
+}
+
+// extractWikilinks returns the set of slugs referenced as [[slug|...]] in content.
+func extractWikilinks(content string) map[string]bool {
+	slugs := make(map[string]bool)
+	for _, m := range wikilinkRE.FindAllStringSubmatch(content, -1) {
+		slugs[m[1]] = true
+	}
+	return slugs
+}
+
+// findSourcePage returns the slug and title of the first wiki/sources/ page in pages.
+func findSourcePage(pages []wiki.Page) (slug, title string, found bool) {
+	for _, p := range pages {
+		if strings.HasPrefix(p.Path, "wiki/sources/") {
+			slug = strings.TrimSuffix(filepath.Base(p.Path), ".md")
+			title = extractTitle(p.Content)
+			if title == "" {
+				title = slug
+			}
+			return slug, title, true
+		}
+	}
+	return "", "", false
+}
+
+// findInInventory returns the PageType for a slug if it appears in the inventory.
+func findInInventory(slug string, inventory map[wiki.PageType][]wiki.Entry) (wiki.PageType, bool) {
+	for pt, entries := range inventory {
+		for _, e := range entries {
+			if e.Slug == slug {
+				return pt, true
+			}
+		}
+	}
+	return "", false
+}
diff --git a/ingestion/internal/pipeline/refs_test.go b/ingestion/internal/pipeline/refs_test.go
new file mode 100644
index 0000000..a694d2c
--- /dev/null
+++ b/ingestion/internal/pipeline/refs_test.go
@@ -0,0 +1,172 @@
+// ingestion/internal/pipeline/refs_test.go
+package pipeline
+
+import (
+	"os"
+	"path/filepath"
+	"testing"
+
+	"github.com/stretchr/testify/assert"
+	"github.com/stretchr/testify/require"
+
+	"github.com/mathiasbq/hyperguild/ingestion/internal/wiki"
+)
+
+func makeInventory(concepts, entities []string) map[wiki.PageType][]wiki.Entry {
+	inv := map[wiki.PageType][]wiki.Entry{
+		wiki.PageTypeConcept: {},
+		wiki.PageTypeEntity:  {},
+		wiki.PageTypeSource:  {},
+	}
+	for _, slug := range concepts {
+		inv[wiki.PageTypeConcept] = append(inv[wiki.PageTypeConcept], wiki.Entry{Slug: slug, Title: slug})
+	}
+	for _, slug := range entities {
+		inv[wiki.PageTypeEntity] = append(inv[wiki.PageTypeEntity], wiki.Entry{Slug: slug, Title: slug})
+	}
+	return inv
+}
+
+func TestInjectSourceRefs_NoSourcePage(t *testing.T) {
+	pages := []wiki.Page{
+		{Path: "wiki/concepts/foo.md", Content: "---\ntitle: Foo\n---\n\n## Definition\n\nFoo.\n"},
+	}
+	got := injectSourceRefs(pages, makeInventory(nil, nil), t.TempDir())
+	assert.Equal(t, pages, got)
+}
+
+func TestInjectSourceRefs_InjectsIntoProposedConcept(t *testing.T) {
+	pages := []wiki.Page{
+		{
+			Path:    "wiki/sources/my-article.md",
+			Content: "---\ntitle: My Article\n---\n\n## Summary\n\nSee [[domain-driven-design|Domain Driven Design]].\n",
+		},
+		{
+			Path:    "wiki/concepts/domain-driven-design.md",
+			Content: "---\ntitle: Domain Driven Design\n---\n\n## Definition\n\nA methodology.\n",
+		},
+	}
+
+	got := injectSourceRefs(pages, makeInventory(nil, nil), t.TempDir())
+
+	require.Len(t, got, 2)
+	assert.Contains(t, got[1].Content, "## Sources")
+	assert.Contains(t, got[1].Content, "[[my-article|My Article]]")
+}
+
+func TestInjectSourceRefs_LoadsConceptFromDisk(t *testing.T) {
+	brainDir := t.TempDir()
+	conceptDir := filepath.Join(brainDir, "wiki", "concepts")
+	require.NoError(t, os.MkdirAll(conceptDir, 0o755))
+	require.NoError(t, os.WriteFile(
+		filepath.Join(conceptDir, "shape-up.md"),
+		[]byte("---\ntitle: Shape Up\n---\n\n## Definition\n\nA methodology.\n"),
+		0o644,
+	))
+
+	pages := []wiki.Page{
+		{
+			Path:    "wiki/sources/my-article.md",
+			Content: "---\ntitle: My Article\n---\n\n## Summary\n\nSee [[shape-up|Shape Up]].\n",
+		},
+	}
+	inv := makeInventory([]string{"shape-up"}, nil)
+
+	got := injectSourceRefs(pages, inv, brainDir)
+
+	require.Len(t, got, 2)
+	var conceptPage wiki.Page
+	for _, p := range got {
+		if p.Path == "wiki/concepts/shape-up.md" {
+			conceptPage = p
+		}
+	}
+	assert.Contains(t, conceptPage.Content, "## Sources")
+	assert.Contains(t, conceptPage.Content, "[[my-article|My Article]]")
+	assert.Contains(t, conceptPage.Content, "## Definition")
+}
+
+func TestInjectSourceRefs_NoSelfReference(t *testing.T) {
+	pages := []wiki.Page{
+		{
+			Path:    "wiki/sources/my-article.md",
+			Content: "---\ntitle: My Article\n---\n\n## Summary\n\nSelf-link [[my-article|My Article]].\n",
+		},
+	}
+
+	got := injectSourceRefs(pages, makeInventory(nil, nil), t.TempDir())
+	assert.Len(t, got, 1)
+}
+
+func TestInjectSourceRefs_DeduplicatesOnReingestion(t *testing.T) {
+	pages := []wiki.Page{
+		{
+			Path:    "wiki/sources/my-article.md",
+			Content: "---\ntitle: My Article\n---\n\n## Summary\n\nSee [[ddd|DDD]].\n",
+		},
+		{
+			Path:    "wiki/concepts/ddd.md",
+			Content: "---\ntitle: DDD\n---\n\n## Definition\n\nA thing.\n\n## Sources\n\n- [[my-article|My Article]]\n",
+		},
+	}
+
+	got := injectSourceRefs(pages, makeInventory(nil, nil), t.TempDir())
+
+	require.Len(t, got, 2)
+	count := 0
+	for _, line := range splitLines(got[1].Content) {
+		if line == "- [[my-article|My Article]]" {
+			count++
+		}
+	}
+	assert.Equal(t, 1, count, "source ref should appear exactly once")
+}
+
+func TestInjectSourceRefs_InjectsIntoEntity(t *testing.T) {
+	pages := []wiki.Page{
+		{
+			Path:    "wiki/sources/book.md",
+			Content: "---\ntitle: Book\n---\n\n## Summary\n\nBy [[ryan-singer|Ryan Singer]].\n",
+		},
+		{
+			Path:    "wiki/entities/ryan-singer.md",
+			Content: "---\ntitle: Ryan Singer\n---\n\n## Description\n\nA designer.\n",
+		},
+	}
+
+	got := injectSourceRefs(pages, makeInventory(nil, nil), t.TempDir())
+
+	require.Len(t, got, 2)
+	var entity wiki.Page
+	for _, p := range got {
+		if p.Path == "wiki/entities/ryan-singer.md" {
+			entity = p
+		}
+	}
+	assert.Contains(t, entity.Content, "[[book|Book]]")
+}
+
+func TestExtractWikilinks(t *testing.T) {
+	content := "See [[foo|Foo]] and [[bar|Bar]] and [[foo|Foo again]]."
+	got := extractWikilinks(content)
+	assert.True(t, got["foo"])
+	assert.True(t, got["bar"])
+	assert.Len(t, got, 2, "duplicate slugs should be deduplicated")
+}
+
+func splitLines(s string) []string {
+	var out []string
+	start := 0
+	for i := 0; i < len(s); i++ {
+		if s[i] == '\n' {
+			if line := s[start:i]; line != "" {
+				out = append(out, line)
+			}
+			start = i + 1
+		}
+	}
+	if last := s[start:]; last != "" {
+		out = append(out, last)
+	}
+	return out
+}