feat: source back-references on concept and entity pages

After each ingestion, every concept and entity page linked from the
source page gains a ## Sources entry pointing back to that source.
Pages already on disk (from prior ingestions) are loaded and updated,
so re-ingesting a new source accumulates references over time.
Deduplication is handled by wiki.Merge's existing bullet-section logic.

docs/superpowers/plans/2026-04-23-source-backrefs.md

@@ -0,0 +1,433 @@
+# Source Back-References Implementation Plan
+
+> **For agentic workers:** REQUIRED SUB-SKILL: Use superpowers:subagent-driven-development (recommended) or superpowers:executing-plans to implement this plan task-by-task. Steps use checkbox (`- [ ]`) syntax for tracking.
+
+**Goal:** After the LLM produces wiki pages for an ingestion, automatically inject a `## Sources` back-reference on every concept and entity page that the source page links to.
+
+**Architecture:** A new `injectSourceRefs` post-processing step is inserted between `Resolve` and `mergeAll` in `pipeline.Run`. It finds the source page in the proposed batch, extracts all `[[slug|...]]` wikilinks, then calls `wiki.Merge` with a minimal patch page to add the back-reference. `wiki.Merge` already treats `## Sources` as a bullet section with deduplication — no custom section parsing is needed. For concepts/entities that exist on disk but weren't proposed in the current batch (the common case on re-ingestion), the function loads them from disk and adds them to the pages list so they are updated.
+
+**Tech Stack:** Go stdlib (`regexp`, `os`, `path/filepath`, `strings`), existing `wiki.Merge` and `wiki.Page` types.
+
+---
+
+## File Structure
+
+**New files:**
+- `ingestion/internal/pipeline/refs.go` — `injectSourceRefs`, `addSourceRef`, `extractWikilinks`, `findSourcePage`, `findInInventory`
+- `ingestion/internal/pipeline/refs_test.go` — table-driven tests
+
+**Modified files:**
+- `ingestion/internal/pipeline/pipeline.go` — insert `injectSourceRefs` call between `Resolve` and `mergeAll`
+
+---
+
+### Task 1: `refs.go` — source back-reference injection
+
+**Files:**
+- Create: `ingestion/internal/pipeline/refs_test.go`
+- Create: `ingestion/internal/pipeline/refs.go`
+
+- [ ] **Step 1: Write the failing tests**
+
+```go
+// 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"
+)
+
+// makeInventory builds a minimal inventory for test use.
+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)
+
+	// Should have loaded shape-up.md from disk and added it with source ref.
+	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]]")
+	// Original content preserved.
+	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())
+
+	// Only one page — source should not reference itself.
+	assert.Len(t, got, 1)
+}
+
+func TestInjectSourceRefs_DeduplicatesOnReingestion(t *testing.T) {
+	// Concept already has source ref from a prior ingestion.
+	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)
+	// The source ref must appear exactly once.
+	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")
+}
+
+// splitLines is a test helper.
+func splitLines(s string) []string {
+	var out []string
+	for _, l := range splitNewlines(s) {
+		if l != "" {
+			out = append(out, l)
+		}
+	}
+	return out
+}
+
+func splitNewlines(s string) []string {
+	var lines []string
+	start := 0
+	for i, c := range s {
+		if c == '\n' {
+			lines = append(lines, s[start:i])
+			start = i + 1
+		}
+	}
+	lines = append(lines, s[start:])
+	return lines
+}
+```
+
+- [ ] **Step 2: Run to verify they fail**
+
+```bash
+cd /Users/mathias/Documents/local-dev/AI/hyperguild/.worktrees/feat-source-backrefs/ingestion && go test ./internal/pipeline/... -run "TestInjectSourceRefs|TestExtractWikilinks" -v
+```
+Expected: compile error — `injectSourceRefs` and `extractWikilinks` not defined.
+
+- [ ] **Step 3: Implement refs.go**
+
+```go
+// 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
+	}
+
+	// Locate source page content for wikilink extraction.
+	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 + "]]"
+
+	// Build slug → index map for proposed pages (excluding wiki/sources/).
+	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 // no self-reference
+		}
+
+		if idx, ok := bySlug[slug]; ok {
+			// Concept/entity is in the proposed batch — inject inline.
+			pages[idx] = addSourceRef(pages[idx], sourceRef)
+			continue
+		}
+
+		// Not in proposed batch — look for it in the inventory (exists on disk).
+		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 not found on disk; skip
+		}
+		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.
+// Uses wiki.Merge so that existing Sources entries are deduplicated and all
+// other sections are preserved unchanged.
+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
+}
+```
+
+- [ ] **Step 4: Run all pipeline tests**
+
+```bash
+cd /Users/mathias/Documents/local-dev/AI/hyperguild/.worktrees/feat-source-backrefs/ingestion && go test ./internal/pipeline/... -v
+```
+Expected: all existing tests PASS + 7 new refs tests PASS.
+
+- [ ] **Step 5: Commit**
+
+```bash
+cd /Users/mathias/Documents/local-dev/AI/hyperguild/.worktrees/feat-source-backrefs && git add ingestion/internal/pipeline/refs.go ingestion/internal/pipeline/refs_test.go && git commit -m "feat(pipeline): inject source back-references into concept and entity pages"
+```
+
+---
+
+### Task 2: Wire injectSourceRefs into pipeline.Run
+
+**Files:**
+- Modify: `ingestion/internal/pipeline/pipeline.go`
+
+- [ ] **Step 1: Insert the call**
+
+In `pipeline.go`, locate:
+
+```go
+	resolved := Resolve(allPages, inventory)
+	merged := mergeAll(resolved)
+```
+
+Replace with:
+
+```go
+	resolved := Resolve(allPages, inventory)
+	withRefs := injectSourceRefs(resolved, inventory, brainDir)
+	merged := mergeAll(withRefs)
+```
+
+No import changes needed — same package.
+
+- [ ] **Step 2: Run all pipeline tests**
+
+```bash
+cd /Users/mathias/Documents/local-dev/AI/hyperguild/.worktrees/feat-source-backrefs/ingestion && go test ./internal/pipeline/... -v
+```
+Expected: all tests PASS. The existing `TestRun_WritesPages` and `TestRun_DryRunDoesNotWrite` use LLM mocks that return source pages with no wikilinks to concepts — `injectSourceRefs` is a no-op for them.
+
+- [ ] **Step 3: Run full test suite + lint**
+
+```bash
+cd /Users/mathias/Documents/local-dev/AI/hyperguild/.worktrees/feat-source-backrefs/ingestion && go test ./... && golangci-lint run ./...
+```
+Expected: all packages PASS, 0 lint issues.
+
+- [ ] **Step 4: Commit**
+
+```bash
+cd /Users/mathias/Documents/local-dev/AI/hyperguild/.worktrees/feat-source-backrefs && git add ingestion/internal/pipeline/pipeline.go && git commit -m "feat(pipeline): wire source back-reference injection into Run"
+```
+
+---
+
+## Self-Review
+
+**Spec coverage:**
+
+| Requirement | Task |
+|---|---|
+| Concepts get `## Sources` back-link to ingested source | Task 1 |
+| Entities get `## Sources` back-link | Task 1 (TestInjectSourceRefs_InjectsIntoEntity) |
+| Existing pages on disk get updated with new source | Task 1 (TestInjectSourceRefs_LoadsConceptFromDisk) |
+| Re-ingestion of same source does not duplicate the ref | Task 1 (TestInjectSourceRefs_DeduplicatesOnReingestion) |
+| Source page does not reference itself | Task 1 (TestInjectSourceRefs_NoSelfReference) |
+| No-op when batch has no source page | Task 1 (TestInjectSourceRefs_NoSourcePage) |
+| Wired into Run between Resolve and mergeAll | Task 2 |
+| Full test suite and lint pass | Task 2 Step 3 |
+
+**Placeholder scan:** None.
+
+**Type consistency:** `injectSourceRefs([]wiki.Page, map[wiki.PageType][]wiki.Entry, string) []wiki.Page` — used identically in refs.go (definition) and pipeline.go (call site).

ingestion/internal/pipeline/pipeline.go

@@ -58,7 +58,8 @@ func Run(ctx context.Context, cfg Config, brainDir, content, source string, dryR
 	}
 
 	resolved := Resolve(allPages, inventory)
-	merged := mergeAll(resolved)
+	withRefs := injectSourceRefs(resolved, inventory, brainDir)
+	merged := mergeAll(withRefs)
 
 	date := time.Now().UTC().Format("2006-01-02")
 	var written []string

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
+}

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
+}