feat(db): add wiki-link extraction, resolution, and backlinks

[[wiki-links]] in entry bodies are extracted at save time, resolved
to entity IDs (title match first, body substring fallback), and
stored in entity_links junction table. Backlinks surface in TUI
detail view showing entries that link to the current entry.

Schema migration v5 adds entity_links with CASCADE/SET NULL
semantics. Links sync on Create, Update, and Absorb.

internal/db/db.go

@@ -56,7 +56,7 @@ func (s *Store) Backup(dst string) error {
 	return err
 }
 
-const currentSchema = 4
+const currentSchema = 5
 
 var migrations = []func(db *sql.DB) error{
 	// v1: initial schema
@@ -188,6 +188,20 @@ var migrations = []func(db *sql.DB) error{
 		}
 		return nil
 	},
+
+	// v5: add entity_links table for wiki-links
+	func(db *sql.DB) error {
+		_, err := db.Exec(`
+			CREATE TABLE entity_links (
+				from_id   TEXT NOT NULL REFERENCES entities(id) ON DELETE CASCADE,
+				to_id     TEXT REFERENCES entities(id) ON DELETE SET NULL,
+				link_text TEXT NOT NULL,
+				PRIMARY KEY (from_id, link_text)
+			);
+			CREATE INDEX idx_entity_links_to ON entity_links(to_id) WHERE to_id IS NOT NULL;
+		`)
+		return err
+	},
 }
 
 func (s *Store) migrate() error {

internal/db/entities.go

@@ -152,6 +152,10 @@ func (s *Store) Create(ctx context.Context, e *Entity) error {
 		return err
 	}
 
+	if err := syncLinks(ctx, tx, s, e.ID, e.Body); err != nil {
+		return err
+	}
+
 	return tx.Commit()
 }
 
@@ -383,6 +387,12 @@ func (s *Store) Update(ctx context.Context, id string, u *EntityUpdate) error {
 		}
 	}
 
+	if u.Body != nil {
+		if err := syncLinks(ctx, tx, s, existing.ID, *u.Body); err != nil {
+			return err
+		}
+	}
+
 	return tx.Commit()
 }
 
@@ -495,6 +505,10 @@ func (s *Store) Absorb(ctx context.Context, targetID, sourceID string) error {
 		}
 	}
 
+	if err := syncLinks(ctx, tx, s, targetID, merged); err != nil {
+		return err
+	}
+
 	if source.CardType != nil {
 		if _, err := tx.ExecContext(ctx, `UPDATE entities SET card_type = NULL, card_data = NULL,
 			use_count = 0, last_used_at = NULL, modified_at = ? WHERE id = ?`,

internal/db/links.go

@@ -0,0 +1,83 @@
+package db
+
+import (
+	"context"
+	"database/sql"
+	"strings"
+
+	"github.com/lerko/nib/internal/link"
+)
+
+type Backlink struct {
+	EntityID string
+	Title    *string
+	Body     string
+	LinkText string
+}
+
+func (s *Store) resolveLink(ctx context.Context, tx *sql.Tx, linkText string, excludeID string) *string {
+	lower := strings.ToLower(linkText)
+
+	var id string
+	err := tx.QueryRowContext(ctx, `
+		SELECT id FROM entities
+		WHERE LOWER(title) = ? AND id != ? AND deleted_at IS NULL
+		ORDER BY created_at DESC LIMIT 1`, lower, excludeID).Scan(&id)
+	if err == nil {
+		return &id
+	}
+
+	err = tx.QueryRowContext(ctx, `
+		SELECT id FROM entities
+		WHERE LOWER(body) LIKE ? AND id != ? AND deleted_at IS NULL
+		ORDER BY created_at DESC LIMIT 1`, "%"+lower+"%", excludeID).Scan(&id)
+	if err == nil {
+		return &id
+	}
+
+	return nil
+}
+
+func syncLinks(ctx context.Context, tx *sql.Tx, s *Store, entityID string, body string) error {
+	if _, err := tx.ExecContext(ctx, "DELETE FROM entity_links WHERE from_id = ?", entityID); err != nil {
+		return err
+	}
+
+	linkTexts := link.ExtractLinks(body)
+	for _, lt := range linkTexts {
+		toID := s.resolveLink(ctx, tx, lt, entityID)
+		if _, err := tx.ExecContext(ctx,
+			"INSERT OR IGNORE INTO entity_links (from_id, to_id, link_text) VALUES (?, ?, ?)",
+			entityID, toID, lt); err != nil {
+			return err
+		}
+	}
+	return nil
+}
+
+func (s *Store) LoadBacklinks(ctx context.Context, entityID string) ([]Backlink, error) {
+	rows, err := s.db.QueryContext(ctx, `
+		SELECT e.id, e.title, e.body, el.link_text
+		FROM entity_links el
+		JOIN entities e ON e.id = el.from_id
+		WHERE el.to_id = ? AND e.deleted_at IS NULL
+		ORDER BY e.created_at DESC`, entityID)
+	if err != nil {
+		return nil, err
+	}
+	defer rows.Close()
+
+	var backlinks []Backlink
+	for rows.Next() {
+		var bl Backlink
+		var title sql.NullString
+		if err := rows.Scan(&bl.EntityID, &title, &bl.Body, &bl.LinkText); err != nil {
+			return nil, err
+		}
+		if title.Valid {
+			bl.Title = &title.String
+		}
+		backlinks = append(backlinks, bl)
+	}
+	return backlinks, rows.Err()
+}

internal/db/links_test.go

@@ -0,0 +1,225 @@
+package db
+
+import (
+	"context"
+	"testing"
+)
+
+func TestSyncLinks_OnCreate(t *testing.T) {
+	s := testStore(t)
+	ctx := context.Background()
+
+	target := &Entity{Body: "nginx proxy config", Glyph: "note", Tags: []string{}}
+	if err := s.Create(ctx, target); err != nil {
+		t.Fatal(err)
+	}
+
+	source := &Entity{Body: "see [[nginx proxy config]] for setup", Glyph: "note", Tags: []string{}}
+	if err := s.Create(ctx, source); err != nil {
+		t.Fatal(err)
+	}
+
+	backlinks, err := s.LoadBacklinks(ctx, target.ID)
+	if err != nil {
+		t.Fatal(err)
+	}
+	if len(backlinks) != 1 {
+		t.Fatalf("expected 1 backlink, got %d", len(backlinks))
+	}
+	if backlinks[0].EntityID != source.ID {
+		t.Errorf("backlink entity = %s, want %s", backlinks[0].EntityID, source.ID)
+	}
+	if backlinks[0].LinkText != "nginx proxy config" {
+		t.Errorf("link text = %q, want %q", backlinks[0].LinkText, "nginx proxy config")
+	}
+}
+
+func TestSyncLinks_TitleMatch(t *testing.T) {
+	s := testStore(t)
+	ctx := context.Background()
+
+	title := "deploy checklist"
+	target := &Entity{Body: "steps to deploy", Title: &title, Glyph: "note", Tags: []string{}}
+	if err := s.Create(ctx, target); err != nil {
+		t.Fatal(err)
+	}
+
+	source := &Entity{Body: "follow [[deploy checklist]]", Glyph: "note", Tags: []string{}}
+	if err := s.Create(ctx, source); err != nil {
+		t.Fatal(err)
+	}
+
+	backlinks, err := s.LoadBacklinks(ctx, target.ID)
+	if err != nil {
+		t.Fatal(err)
+	}
+	if len(backlinks) != 1 {
+		t.Fatalf("expected 1 backlink, got %d", len(backlinks))
+	}
+}
+
+func TestSyncLinks_TitlePriority(t *testing.T) {
+	s := testStore(t)
+	ctx := context.Background()
+
+	title := "nginx config"
+	titled := &Entity{Body: "some body", Title: &title, Glyph: "note", Tags: []string{}}
+	if err := s.Create(ctx, titled); err != nil {
+		t.Fatal(err)
+	}
+
+	bodyMatch := &Entity{Body: "nginx config details", Glyph: "note", Tags: []string{}}
+	if err := s.Create(ctx, bodyMatch); err != nil {
+		t.Fatal(err)
+	}
+
+	source := &Entity{Body: "see [[nginx config]]", Glyph: "note", Tags: []string{}}
+	if err := s.Create(ctx, source); err != nil {
+		t.Fatal(err)
+	}
+
+	backlinks, err := s.LoadBacklinks(ctx, titled.ID)
+	if err != nil {
+		t.Fatal(err)
+	}
+	if len(backlinks) != 1 {
+		t.Fatalf("title match should win, got %d backlinks on titled entity", len(backlinks))
+	}
+
+	bodyBacklinks, err := s.LoadBacklinks(ctx, bodyMatch.ID)
+	if err != nil {
+		t.Fatal(err)
+	}
+	if len(bodyBacklinks) != 0 {
+		t.Fatalf("body match entity should have 0 backlinks, got %d", len(bodyBacklinks))
+	}
+}
+
+func TestSyncLinks_Unresolved(t *testing.T) {
+	s := testStore(t)
+	ctx := context.Background()
+
+	source := &Entity{Body: "see [[nonexistent entry]]", Glyph: "note", Tags: []string{}}
+	if err := s.Create(ctx, source); err != nil {
+		t.Fatal(err)
+	}
+
+	var count int
+	err := s.db.QueryRow("SELECT COUNT(*) FROM entity_links WHERE from_id = ?", source.ID).Scan(&count)
+	if err != nil {
+		t.Fatal(err)
+	}
+	if count != 1 {
+		t.Fatalf("expected 1 link row (unresolved), got %d", count)
+	}
+
+	var toID *string
+	err = s.db.QueryRow("SELECT to_id FROM entity_links WHERE from_id = ?", source.ID).Scan(&toID)
+	if err != nil {
+		t.Fatal(err)
+	}
+	if toID != nil {
+		t.Errorf("expected NULL to_id for unresolved link, got %v", *toID)
+	}
+}
+
+func TestSyncLinks_OnUpdate(t *testing.T) {
+	s := testStore(t)
+	ctx := context.Background()
+
+	target := &Entity{Body: "original target", Glyph: "note", Tags: []string{}}
+	if err := s.Create(ctx, target); err != nil {
+		t.Fatal(err)
+	}
+
+	source := &Entity{Body: "no links yet", Glyph: "note", Tags: []string{}}
+	if err := s.Create(ctx, source); err != nil {
+		t.Fatal(err)
+	}
+
+	newBody := "now has [[original target]]"
+	if err := s.Update(ctx, source.ID, &EntityUpdate{Body: &newBody}); err != nil {
+		t.Fatal(err)
+	}
+
+	backlinks, err := s.LoadBacklinks(ctx, target.ID)
+	if err != nil {
+		t.Fatal(err)
+	}
+	if len(backlinks) != 1 {
+		t.Fatalf("expected 1 backlink after update, got %d", len(backlinks))
+	}
+}
+
+func TestSyncLinks_SelfLinkUnresolved(t *testing.T) {
+	s := testStore(t)
+	ctx := context.Background()
+
+	e := &Entity{Body: "I reference [[I reference]]", Glyph: "note", Tags: []string{}}
+	if err := s.Create(ctx, e); err != nil {
+		t.Fatal(err)
+	}
+
+	var toID *string
+	err := s.db.QueryRow("SELECT to_id FROM entity_links WHERE from_id = ?", e.ID).Scan(&toID)
+	if err != nil {
+		t.Fatal(err)
+	}
+	if toID != nil {
+		t.Fatalf("self-matching link should be unresolved (NULL to_id), got %v", *toID)
+	}
+}
+
+func TestSyncLinks_NoLinks(t *testing.T) {
+	s := testStore(t)
+	ctx := context.Background()
+
+	e := &Entity{Body: "plain text no links", Glyph: "note", Tags: []string{}}
+	if err := s.Create(ctx, e); err != nil {
+		t.Fatal(err)
+	}
+
+	var count int
+	err := s.db.QueryRow("SELECT COUNT(*) FROM entity_links WHERE from_id = ?", e.ID).Scan(&count)
+	if err != nil {
+		t.Fatal(err)
+	}
+	if count != 0 {
+		t.Fatalf("expected 0 links, got %d", count)
+	}
+}
+
+func TestSyncLinks_DeletedSourceHidden(t *testing.T) {
+	s := testStore(t)
+	ctx := context.Background()
+
+	target := &Entity{Body: "target entry", Glyph: "note", Tags: []string{}}
+	if err := s.Create(ctx, target); err != nil {
+		t.Fatal(err)
+	}
+
+	source := &Entity{Body: "see [[target entry]]", Glyph: "note", Tags: []string{}}
+	if err := s.Create(ctx, source); err != nil {
+		t.Fatal(err)
+	}
+
+	backlinks, err := s.LoadBacklinks(ctx, target.ID)
+	if err != nil {
+		t.Fatal(err)
+	}
+	if len(backlinks) != 1 {
+		t.Fatalf("expected 1 backlink before delete, got %d", len(backlinks))
+	}
+
+	if _, err := s.SoftDelete(ctx, source.ID); err != nil {
+		t.Fatal(err)
+	}
+
+	backlinks, err = s.LoadBacklinks(ctx, target.ID)
+	if err != nil {
+		t.Fatal(err)
+	}
+	if len(backlinks) != 0 {
+		t.Fatalf("soft-deleted source should not appear in backlinks, got %d", len(backlinks))
+	}
+}

internal/link/extract.go

@@ -0,0 +1,27 @@
+package link
+
+import (
+	"regexp"
+	"strings"
+)
+
+var linkRe = regexp.MustCompile(`\[\[(.+?)\]\]`)
+
+func ExtractLinks(body string) []string {
+	matches := linkRe.FindAllStringSubmatch(body, -1)
+	if len(matches) == 0 {
+		return nil
+	}
+
+	seen := map[string]bool{}
+	var result []string
+	for _, m := range matches {
+		text := strings.TrimSpace(m[1])
+		if text == "" || seen[text] {
+			continue
+		}
+		seen[text] = true
+		result = append(result, text)
+	}
+	return result
+}

internal/link/extract_test.go

@@ -0,0 +1,38 @@
+package link
+
+import "testing"
+
+func TestExtractLinks(t *testing.T) {
+	tests := []struct {
+		name string
+		body string
+		want []string
+	}{
+		{"no links", "plain text with no links", nil},
+		{"single link", "see [[nginx config]] for details", []string{"nginx config"}},
+		{"multiple links", "see [[nginx config]] and [[deploy steps]]", []string{"nginx config", "deploy steps"}},
+		{"duplicate deduped", "[[foo]] then [[foo]] again", []string{"foo"}},
+		{"empty brackets", "empty [[ ]] ignored", nil},
+		{"just brackets no content", "[[]] empty", nil},
+		{"link with special chars", "see [[deploy: staging (v2)]]", []string{"deploy: staging (v2)"}},
+		{"link in markdown", "# heading\n\nsee [[my note]] for info", []string{"my note"}},
+		{"adjacent links", "[[one]][[two]]", []string{"one", "two"}},
+		{"partial brackets ignored", "not a [link] or [[incomplete", nil},
+		{"link with hash", "see [[#ops channel]]", []string{"#ops channel"}},
+		{"multiline body", "line one [[link one]]\nline two [[link two]]", []string{"link one", "link two"}},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			got := ExtractLinks(tt.body)
+			if len(got) != len(tt.want) {
+				t.Fatalf("got %v, want %v", got, tt.want)
+			}
+			for i := range got {
+				if got[i] != tt.want[i] {
+					t.Fatalf("got %v, want %v", got, tt.want)
+				}
+			}
+		})
+	}
+}

internal/tui/commands.go

@@ -55,6 +55,10 @@ type stepsPersistedMsg struct{}
 
 type templateCopiedMsg struct{}
 
+type backlinksLoadedMsg struct {
+	backlinks []db.Backlink
+}
+
 type tagsLoadedMsg struct {
 	tags []db.TagCount
 }
@@ -194,6 +198,16 @@ func loadTags(store *db.Store) tea.Cmd {
 	}
 }
 
+func loadBacklinks(store *db.Store, entityID string) tea.Cmd {
+	return func() tea.Msg {
+		backlinks, err := store.LoadBacklinks(context.Background(), entityID)
+		if err != nil {
+			return errMsg{err}
+		}
+		return backlinksLoadedMsg{backlinks}
+	}
+}
+
 func loadRailTags(store *db.Store) tea.Cmd {
 	return func() tea.Msg {
 		tags, err := store.ListTags(context.Background(), false)

internal/tui/detail.go

@@ -22,6 +22,7 @@ const (
 
 type detailModel struct {
 	entity    *db.Entity
+	backlinks []db.Backlink
 	scroll    int
 	height    int
 	width     int
@@ -36,6 +37,7 @@ func newDetailModel() detailModel {
 
 func (d *detailModel) setEntity(e *db.Entity) {
 	d.entity = e
+	d.backlinks = nil
 	d.scroll = 0
 	d.mode = detailPreview
 }
@@ -144,6 +146,25 @@ func (d detailModel) previewView(width int) string {
 		b.WriteString("\n")
 	}
 
+	if len(d.backlinks) > 0 {
+		b.WriteString("\n")
+		b.WriteString(detailLabelStyle.Render("  ← backlinks"))
+		b.WriteString("\n")
+		for _, bl := range d.backlinks {
+			label := bl.Body
+			if bl.Title != nil {
+				label = *bl.Title
+			} else if len(label) > 40 {
+				label = label[:40] + "…"
+			}
+			line := "    " + backlinkStyle.Render(label)
+			if bl.LinkText != "" {
+				line += " " + hintDescStyle.Render("(as \""+bl.LinkText+"\")")
+			}
+			b.WriteString(line + "\n")
+		}
+	}
+
 	b.WriteString("\n")
 	meta := fmt.Sprintf("created  %s", e.CreatedAt.Format(time.DateTime))
 	if e.ModifiedAt != e.CreatedAt {

internal/tui/model.go

@@ -287,6 +287,12 @@ func (m model) Update(msg tea.Msg) (tea.Model, tea.Cmd) {
 		m.detail.mode = detailPreview
 		return m, tea.Batch(loadEntities(m.store, m.listParams()), m.setStatus("copied resolved"))
 
+	case backlinksLoadedMsg:
+		if m.detail.entity != nil {
+			m.detail.backlinks = msg.backlinks
+		}
+		return m, nil
+
 	case tagsLoadedMsg:
 		m.filter.setTags(msg.tags)
 		m.tagRail.setTags(msg.tags)
@@ -865,6 +871,7 @@ func (m model) updateBrowse(msg tea.KeyMsg) (tea.Model, tea.Cmd) {
 				} else {
 					m.state = stateDetail
 				}
+				return m, loadBacklinks(m.store, e.ID)
 			}
 		}
 		return m, nil
@@ -1212,6 +1219,7 @@ func (m model) selectedEntity() *db.Entity {
 func (m model) reloadDetail(id string) tea.Cmd {
 	return tea.Batch(
 		loadEntities(m.store, m.listParams()),
+		loadBacklinks(m.store, id),
 		func() tea.Msg {
 			e, err := m.store.Get(context.Background(), id)
 			if err != nil {

internal/tui/styles.go

@@ -43,6 +43,7 @@ var (
 	stumbleAgeStyle     lipgloss.Style
 	acSelectedStyle     lipgloss.Style
 	acItemStyle         lipgloss.Style
+	backlinkStyle       lipgloss.Style
 )
 
 func init() {
@@ -100,4 +101,5 @@ func applyTheme() {
 	stumbleAgeStyle = lipgloss.NewStyle().Foreground(remind)
 	acSelectedStyle = lipgloss.NewStyle().Foreground(accent).Bold(true)
 	acItemStyle = lipgloss.NewStyle().Foreground(muted)
+	backlinkStyle = lipgloss.NewStyle().Foreground(muted)
 }