feat(brain): structured wing/hall taxonomy + obsidian-compatible layout

Adds a two-dimensional address (wing, hall) to brain notes. A wing is a
topic domain (e.g. jepa-fx, hyperguild); a hall is one of a closed
vocabulary of memory types (facts, decisions, failures, hypotheses,
sources). Notes route to brain/wiki/<wing>/<hall>/<slug>.md with
wing/hall/created_at YAML frontmatter, making the directory a valid
Obsidian vault.

Changes:
- new package ingestion/internal/brain (NotePath, ValidHalls, Sanitise,
  BuildWingIndex, BuildAllWingIndexes)
- api.WriteNote refactored to WriteNoteOptions; wing+hall routes to
  brain/wiki/, otherwise falls back to brain/knowledge/ (legacy)
- search.Query → QueryOptions with optional Wing/Hall filtering; Result
  carries wing/hall extracted from frontmatter or path segments
- MCP tools brain_write and brain_query gain optional wing/hall params
  (hall enum-validated); new brain_index tool regenerates _index.md MOC
- POST /index REST endpoint mirrors brain_index
- brain_write auto-rebuilds the wing's _index.md after a wing+hall write
- scripts/migrate-brain-halls.sh migrates flat brain/wiki/{concepts,entities}/
  into the new layout (dry-run by default, --commit applies)

All existing tests pass; new tests cover wing/hall write routing, scope
filtering, invalid hall rejection, _index.md generation, and migration
script paths.

Closes hyperguild#1.

ingestion/cmd/server/main.go

@@ -94,6 +94,7 @@ func main() {
 	mux := http.NewServeMux()
 	mux.HandleFunc("POST /query", h.Query)
 	mux.HandleFunc("POST /write", h.Write)
+	mux.HandleFunc("POST /index", h.Index)
 	mux.HandleFunc("POST /ingest", h.Ingest)
 	mux.HandleFunc("POST /ingest-path", h.IngestPath)
 	mux.HandleFunc("POST /ingest-raw", h.IngestRaw)

ingestion/internal/api/handler.go

@@ -11,6 +11,7 @@ import (
 	"strings"
 	"time"
 
+	"github.com/mathiasbq/hyperguild/ingestion/internal/brain"
 	"github.com/mathiasbq/hyperguild/ingestion/internal/extract"
 	"github.com/mathiasbq/hyperguild/ingestion/internal/pipeline"
 	"github.com/mathiasbq/hyperguild/ingestion/internal/search"
@@ -34,6 +35,8 @@ func NewHandler(brainDir string, logger *slog.Logger, pipelineCfg pipeline.Confi
 type queryRequest struct {
 	Query string `json:"query"`
 	Limit int    `json:"limit,omitempty"`
+	Wing  string `json:"wing,omitempty"`
+	Hall  string `json:"hall,omitempty"`
 }
 
 type writeRequest struct {
@@ -41,6 +44,8 @@ type writeRequest struct {
 	Filename string `json:"filename,omitempty"`
 	Type     string `json:"type,omitempty"`
 	Domain   string `json:"domain,omitempty"`
+	Wing     string `json:"wing,omitempty"`
+	Hall     string `json:"hall,omitempty"`
 }
 
 type ingestRequest struct {
@@ -75,7 +80,12 @@ func (h *Handler) Query(w http.ResponseWriter, r *http.Request) {
 		req.Limit = 5
 	}
 
-	results, err := search.Query(h.brainDir, req.Query, req.Limit)
+	results, err := search.Query(h.brainDir, search.QueryOptions{
+		Query: req.Query,
+		Limit: req.Limit,
+		Wing:  req.Wing,
+		Hall:  req.Hall,
+	})
 	if err != nil {
 		h.logger.Error("query failed", "err", err)
 		writeError(w, http.StatusInternalServerError, "search error")
@@ -85,13 +95,78 @@ func (h *Handler) Query(w http.ResponseWriter, r *http.Request) {
 	writeJSON(w, map[string]any{"results": results})
 }
 
-// WriteNote writes a markdown file to brainDir/knowledge/<filename>, optionally
-// prefixed with YAML frontmatter built from typ and domain. Returns the path
+// WriteNoteOptions configures how a brain note is written.
+//
+// When both Wing and Hall are non-empty, the note routes into the
+// structured wiki at brain/wiki/<wing>/<hall>/<slug>.md and gets
+// wing/hall/created_at injected into its YAML frontmatter.
+//
+// When either is empty, the note falls back to brain/knowledge/<filename>
+// with optional type/domain frontmatter (legacy behaviour).
+type WriteNoteOptions struct {
+	Content  string
+	Filename string
+	Type     string
+	Domain   string
+	Wing     string
+	Hall     string
+}
+
+// WriteNote writes a markdown note into the brain. Returns the path
 // relative to brainDir (forward-slashed). Filename traversal is rejected.
-func WriteNote(brainDir, content, filename, typ, domain string) (string, error) {
-	if content == "" {
+func WriteNote(brainDir string, opts WriteNoteOptions) (string, error) {
+	if opts.Content == "" {
 		return "", fmt.Errorf("content is required")
 	}
+
+	if opts.Wing != "" && opts.Hall != "" {
+		return writeHallNote(brainDir, opts)
+	}
+	if opts.Wing != "" || opts.Hall != "" {
+		return "", fmt.Errorf("wing and hall must be set together")
+	}
+	return writeLegacyNote(brainDir, opts)
+}
+
+// writeHallNote routes a note into brain/wiki/<wing>/<hall>/ and injects
+// wing/hall/created_at frontmatter.
+func writeHallNote(brainDir string, opts WriteNoteOptions) (string, error) {
+	slug := opts.Filename
+	if slug == "" {
+		slug = time.Now().UTC().Format("2006-01-02-150405") + "-auto"
+	}
+	dest, err := brain.NotePath(brainDir, opts.Wing, opts.Hall, slug)
+	if err != nil {
+		return "", err
+	}
+	if err := os.MkdirAll(filepath.Dir(dest), 0o755); err != nil {
+		return "", fmt.Errorf("create hall dir: %w", err)
+	}
+
+	var fm strings.Builder
+	fm.WriteString("---\n")
+	fmt.Fprintf(&fm, "wing: %s\n", brain.Sanitise(opts.Wing))
+	fmt.Fprintf(&fm, "hall: %s\n", opts.Hall)
+	fmt.Fprintf(&fm, "created_at: %s\n", time.Now().UTC().Format(time.RFC3339))
+	if opts.Type != "" {
+		fmt.Fprintf(&fm, "type: %s\n", opts.Type)
+	}
+	if opts.Domain != "" {
+		fmt.Fprintf(&fm, "domain: %s\n", opts.Domain)
+	}
+	fm.WriteString("---\n")
+
+	if err := os.WriteFile(dest, []byte(fm.String()+opts.Content), 0o644); err != nil {
+		return "", fmt.Errorf("write: %w", err)
+	}
+	rel, _ := filepath.Rel(brainDir, dest)
+	return filepath.ToSlash(rel), nil
+}
+
+// writeLegacyNote preserves the original brain/knowledge/ behaviour for
+// callers that have not adopted the wing/hall taxonomy.
+func writeLegacyNote(brainDir string, opts WriteNoteOptions) (string, error) {
+	filename := opts.Filename
 	if filename == "" {
 		filename = fmt.Sprintf("%s-auto.md", time.Now().UTC().Format("2006-01-02-150405"))
 	}
@@ -101,26 +176,24 @@ func WriteNote(brainDir, content, filename, typ, domain string) (string, error)
 		return "", fmt.Errorf("create raw dir: %w", err)
 	}
 
-	finalContent := content
-	if typ != "" || domain != "" {
+	finalContent := opts.Content
+	if opts.Type != "" || opts.Domain != "" {
 		var fm strings.Builder
 		fm.WriteString("---\n")
-		if typ != "" {
-			fmt.Fprintf(&fm, "type: %s\n", typ)
+		if opts.Type != "" {
+			fmt.Fprintf(&fm, "type: %s\n", opts.Type)
 		}
-		if domain != "" {
-			fmt.Fprintf(&fm, "domain: %s\n", domain)
+		if opts.Domain != "" {
+			fmt.Fprintf(&fm, "domain: %s\n", opts.Domain)
 		}
 		fm.WriteString("---\n")
-		finalContent = fm.String() + content
+		finalContent = fm.String() + opts.Content
 	}
 
-	// Reject path separators outright; any non-flat filename is misuse.
 	if strings.ContainsAny(filename, `/\`) {
 		return "", fmt.Errorf("invalid filename")
 	}
 	base := filepath.Base(filename)
-	// After Base, "." and ".." remain. Reject those before adding .md.
 	if base == "." || base == ".." || base == "" {
 		return "", fmt.Errorf("invalid filename")
 	}
@@ -143,15 +216,51 @@ func (h *Handler) Write(w http.ResponseWriter, r *http.Request) {
 		writeError(w, http.StatusBadRequest, "invalid JSON")
 		return
 	}
-	relPath, err := WriteNote(h.brainDir, req.Content, req.Filename, req.Type, req.Domain)
+	relPath, err := WriteNote(h.brainDir, WriteNoteOptions(req))
 	if err != nil {
 		h.logger.Error("write failed", "err", err)
 		writeError(w, http.StatusBadRequest, err.Error())
 		return
 	}
+	if req.Wing != "" && req.Hall != "" {
+		if err := brain.BuildWingIndex(h.brainDir, req.Wing); err != nil {
+			h.logger.Warn("auto-index failed", "wing", req.Wing, "err", err)
+		}
+	}
 	writeJSON(w, map[string]string{"path": relPath})
 }
 
+type indexRequest struct {
+	Wing string `json:"wing,omitempty"`
+}
+
+// Index handles POST /index — regenerate the _index.md MOC for one wing
+// (when "wing" is set) or for every wing (when omitted).
+func (h *Handler) Index(w http.ResponseWriter, r *http.Request) {
+	var req indexRequest
+	if r.ContentLength > 0 {
+		if err := json.NewDecoder(r.Body).Decode(&req); err != nil {
+			writeError(w, http.StatusBadRequest, "invalid JSON")
+			return
+		}
+	}
+	if req.Wing == "" {
+		if err := brain.BuildAllWingIndexes(h.brainDir); err != nil {
+			h.logger.Error("index all failed", "err", err)
+			writeError(w, http.StatusInternalServerError, "index error")
+			return
+		}
+		writeJSON(w, map[string]any{"status": "ok", "scope": "all"})
+		return
+	}
+	if err := brain.BuildWingIndex(h.brainDir, req.Wing); err != nil {
+		h.logger.Error("index failed", "wing", req.Wing, "err", err)
+		writeError(w, http.StatusBadRequest, err.Error())
+		return
+	}
+	writeJSON(w, map[string]any{"status": "ok", "scope": req.Wing})
+}
+
 // Ingest handles POST /ingest — run the pipeline on provided content.
 func (h *Handler) Ingest(w http.ResponseWriter, r *http.Request) {
 	var req ingestRequest

ingestion/internal/brain/index.go

@@ -0,0 +1,161 @@
+package brain
+
+import (
+	"bufio"
+	"fmt"
+	"os"
+	"path/filepath"
+	"sort"
+	"strings"
+	"time"
+)
+
+// noteEntry is one row in a Wing _index.md.
+type noteEntry struct {
+	Hall    string
+	Slug    string
+	Title   string
+	Created string
+}
+
+// BuildWingIndex regenerates brain/wiki/<wing>/_index.md as a Map of
+// Content listing every note in that wing with its Hall and creation
+// date. Returns nil if the wing directory does not exist.
+func BuildWingIndex(brainDir, wing string) error {
+	w := Sanitise(wing)
+	if w == "" {
+		return fmt.Errorf("invalid wing %q", wing)
+	}
+	wingDir := filepath.Join(brainDir, "wiki", w)
+	if _, err := os.Stat(wingDir); os.IsNotExist(err) {
+		return nil
+	} else if err != nil {
+		return fmt.Errorf("stat wing: %w", err)
+	}
+
+	entries, err := collectWingEntries(wingDir)
+	if err != nil {
+		return err
+	}
+	sort.Slice(entries, func(i, j int) bool {
+		if entries[i].Hall != entries[j].Hall {
+			return entries[i].Hall < entries[j].Hall
+		}
+		return entries[i].Slug < entries[j].Slug
+	})
+
+	var b strings.Builder
+	fmt.Fprintf(&b, "# %s\n\n", w)
+	b.WriteString("| Hall | Note | Created |\n")
+	b.WriteString("|------|------|---------|\n")
+	for _, e := range entries {
+		fmt.Fprintf(&b, "| %s | [%s](%s/%s.md) | %s |\n", e.Hall, e.Title, e.Hall, e.Slug, e.Created)
+	}
+
+	dest := filepath.Join(wingDir, "_index.md")
+	return os.WriteFile(dest, []byte(b.String()), 0o644)
+}
+
+// BuildAllWingIndexes regenerates _index.md for every wing under brain/wiki/.
+func BuildAllWingIndexes(brainDir string) error {
+	wikiDir := filepath.Join(brainDir, "wiki")
+	ents, err := os.ReadDir(wikiDir)
+	if os.IsNotExist(err) {
+		return nil
+	}
+	if err != nil {
+		return fmt.Errorf("read wiki: %w", err)
+	}
+	for _, e := range ents {
+		if !e.IsDir() {
+			continue
+		}
+		if err := BuildWingIndex(brainDir, e.Name()); err != nil {
+			return fmt.Errorf("index %s: %w", e.Name(), err)
+		}
+	}
+	return nil
+}
+
+func collectWingEntries(wingDir string) ([]noteEntry, error) {
+	var out []noteEntry
+	ents, err := os.ReadDir(wingDir)
+	if err != nil {
+		return nil, fmt.Errorf("read wing: %w", err)
+	}
+	for _, hallEnt := range ents {
+		if !hallEnt.IsDir() {
+			continue
+		}
+		hall := hallEnt.Name()
+		if !IsValidHall(hall) {
+			continue
+		}
+		hallDir := filepath.Join(wingDir, hall)
+		notes, err := os.ReadDir(hallDir)
+		if err != nil {
+			return nil, fmt.Errorf("read hall %s: %w", hall, err)
+		}
+		for _, n := range notes {
+			if n.IsDir() || !strings.HasSuffix(n.Name(), ".md") || n.Name() == "_index.md" {
+				continue
+			}
+			slug := strings.TrimSuffix(n.Name(), ".md")
+			full := filepath.Join(hallDir, n.Name())
+			title, created := readTitleAndCreated(full, slug)
+			out = append(out, noteEntry{Hall: hall, Slug: slug, Title: title, Created: created})
+		}
+	}
+	return out, nil
+}
+
+// readTitleAndCreated reads YAML frontmatter for title + created_at; falls
+// back to slug and file mtime when absent.
+func readTitleAndCreated(path, slug string) (string, string) {
+	f, err := os.Open(path)
+	if err != nil {
+		return slug, ""
+	}
+	defer func() { _ = f.Close() }()
+
+	title, created := "", ""
+	scanner := bufio.NewScanner(f)
+	inFrontmatter := false
+	for scanner.Scan() {
+		line := scanner.Text()
+		if strings.TrimSpace(line) == "---" {
+			if !inFrontmatter {
+				inFrontmatter = true
+				continue
+			}
+			break
+		}
+		if !inFrontmatter {
+			continue
+		}
+		key, val, ok := strings.Cut(line, ":")
+		if !ok {
+			continue
+		}
+		v := strings.Trim(strings.TrimSpace(val), `"'`)
+		switch strings.TrimSpace(key) {
+		case "title":
+			title = v
+		case "created_at":
+			if t, err := time.Parse(time.RFC3339, v); err == nil {
+				created = t.UTC().Format("2006-01-02")
+			} else {
+				created = v
+			}
+		}
+	}
+	if title == "" {
+		title = slug
+	}
+	if created == "" {
+		if info, err := os.Stat(path); err == nil {
+			created = info.ModTime().UTC().Format("2006-01-02")
+		}
+	}
+	return title, created
+}

ingestion/internal/brain/index_test.go

@@ -0,0 +1,85 @@
+package brain_test
+
+import (
+	"os"
+	"path/filepath"
+	"testing"
+
+	"github.com/mathiasbq/hyperguild/ingestion/internal/brain"
+	"github.com/stretchr/testify/assert"
+	"github.com/stretchr/testify/require"
+)
+
+func TestBuildWingIndex(t *testing.T) {
+	dir := t.TempDir()
+	for _, p := range []struct{ rel, body string }{
+		{"wiki/jepa-fx/decisions/val-vol.md", "---\ntitle: Val Vol R2\ncreated_at: 2026-05-06T10:00:00Z\n---\nbody\n"},
+		{"wiki/jepa-fx/facts/architecture.md", "---\ntitle: Architecture\ncreated_at: 2026-05-04T10:00:00Z\n---\nbody\n"},
+		{"wiki/jepa-fx/sources/paper.md", "---\n---\nbody\n"},
+	} {
+		full := filepath.Join(dir, p.rel)
+		require.NoError(t, os.MkdirAll(filepath.Dir(full), 0o755))
+		require.NoError(t, os.WriteFile(full, []byte(p.body), 0o644))
+	}
+
+	require.NoError(t, brain.BuildWingIndex(dir, "jepa-fx"))
+
+	got, err := os.ReadFile(filepath.Join(dir, "wiki", "jepa-fx", "_index.md"))
+	require.NoError(t, err)
+	s := string(got)
+	assert.Contains(t, s, "# jepa-fx")
+	assert.Contains(t, s, "| Hall | Note | Created |")
+	assert.Contains(t, s, "| decisions | [Val Vol R2](decisions/val-vol.md) | 2026-05-06 |")
+	assert.Contains(t, s, "| facts | [Architecture](facts/architecture.md) | 2026-05-04 |")
+	assert.Contains(t, s, "| sources | [paper](sources/paper.md) |")
+	// Halls sorted alphabetically.
+	assert.Less(t, indexOf(s, "decisions"), indexOf(s, "facts"))
+	assert.Less(t, indexOf(s, "facts"), indexOf(s, "sources"))
+}
+
+func TestBuildWingIndex_SkipsInvalidHalls(t *testing.T) {
+	dir := t.TempDir()
+	wingDir := filepath.Join(dir, "wiki", "jepa-fx")
+	require.NoError(t, os.MkdirAll(filepath.Join(wingDir, "garbage"), 0o755))
+	require.NoError(t, os.WriteFile(filepath.Join(wingDir, "garbage", "x.md"), []byte("x"), 0o644))
+	require.NoError(t, os.MkdirAll(filepath.Join(wingDir, "facts"), 0o755))
+	require.NoError(t, os.WriteFile(filepath.Join(wingDir, "facts", "y.md"), []byte("y"), 0o644))
+
+	require.NoError(t, brain.BuildWingIndex(dir, "jepa-fx"))
+	got, err := os.ReadFile(filepath.Join(wingDir, "_index.md"))
+	require.NoError(t, err)
+	s := string(got)
+	assert.Contains(t, s, "facts")
+	assert.NotContains(t, s, "garbage")
+}
+
+func TestBuildAllWingIndexes(t *testing.T) {
+	dir := t.TempDir()
+	for _, p := range []struct{ rel, body string }{
+		{"wiki/a/facts/x.md", "x"},
+		{"wiki/b/facts/y.md", "y"},
+	} {
+		full := filepath.Join(dir, p.rel)
+		require.NoError(t, os.MkdirAll(filepath.Dir(full), 0o755))
+		require.NoError(t, os.WriteFile(full, []byte(p.body), 0o644))
+	}
+	require.NoError(t, brain.BuildAllWingIndexes(dir))
+	_, err := os.Stat(filepath.Join(dir, "wiki", "a", "_index.md"))
+	require.NoError(t, err)
+	_, err = os.Stat(filepath.Join(dir, "wiki", "b", "_index.md"))
+	require.NoError(t, err)
+}
+
+func TestBuildWingIndex_NoWingDir(t *testing.T) {
+	dir := t.TempDir()
+	require.NoError(t, brain.BuildWingIndex(dir, "ghost"))
+}
+
+func indexOf(s, sub string) int {
+	for i := 0; i+len(sub) <= len(s); i++ {
+		if s[i:i+len(sub)] == sub {
+			return i
+		}
+	}
+	return -1
+}

ingestion/internal/brain/path.go

@@ -0,0 +1,70 @@
+// Package brain provides the wing/hall path taxonomy used by the brain
+// wiki layout. A note's canonical location is
+// brain/wiki/<wing>/<hall>/<slug>.md, where Wing is a free-form topic
+// domain and Hall is one of a closed vocabulary of memory types.
+package brain
+
+import (
+	"fmt"
+	"path/filepath"
+	"strings"
+)
+
+// ValidHalls is the closed vocabulary of hall names. A hall captures the
+// memory type of a note within any wing.
+var ValidHalls = map[string]bool{
+	"facts":      true,
+	"decisions":  true,
+	"failures":   true,
+	"hypotheses": true,
+	"sources":    true,
+}
+
+// IsValidHall reports whether h is in the closed Hall vocabulary.
+func IsValidHall(h string) bool {
+	return ValidHalls[h]
+}
+
+// NotePath resolves the canonical filesystem path for a note given a
+// wing, hall, and slug. Returns an error if hall is not in ValidHalls
+// or if wing/slug sanitise to empty strings.
+//
+// The returned path is brain/wiki/<wing>/<hall>/<slug>.md with all
+// segments sanitised: lowercased, alphanumerics and hyphens only.
+func NotePath(brainDir, wing, hall, slug string) (string, error) {
+	if !IsValidHall(hall) {
+		return "", fmt.Errorf("invalid hall %q: must be one of facts/decisions/failures/hypotheses/sources", hall)
+	}
+	w := Sanitise(wing)
+	if w == "" {
+		return "", fmt.Errorf("invalid wing %q: must contain at least one alphanumeric character", wing)
+	}
+	s := Sanitise(strings.TrimSuffix(slug, ".md"))
+	if s == "" {
+		return "", fmt.Errorf("invalid slug %q: must contain at least one alphanumeric character", slug)
+	}
+	return filepath.Join(brainDir, "wiki", w, hall, s+".md"), nil
+}
+
+// Sanitise lowercases s and keeps only [a-z0-9-], collapsing any other
+// character (including path separators) to a hyphen. Leading/trailing
+// hyphens and runs of hyphens are collapsed.
+func Sanitise(s string) string {
+	s = strings.ToLower(strings.TrimSpace(s))
+	var b strings.Builder
+	prevHyphen := true
+	for _, r := range s {
+		switch {
+		case r >= 'a' && r <= 'z', r >= '0' && r <= '9':
+			b.WriteRune(r)
+			prevHyphen = false
+		case r == '-' || r == '_' || r == ' ' || r == '/' || r == '\\' || r == '.':
+			if !prevHyphen {
+				b.WriteByte('-')
+				prevHyphen = true
+			}
+		}
+	}
+	out := b.String()
+	return strings.Trim(out, "-")
+}

ingestion/internal/brain/path_test.go

@@ -0,0 +1,73 @@
+package brain_test
+
+import (
+	"path/filepath"
+	"testing"
+
+	"github.com/mathiasbq/hyperguild/ingestion/internal/brain"
+	"github.com/stretchr/testify/assert"
+	"github.com/stretchr/testify/require"
+)
+
+func TestNotePath_Valid(t *testing.T) {
+	got, err := brain.NotePath("/b", "jepa-fx", "decisions", "val-vol-r2")
+	require.NoError(t, err)
+	assert.Equal(t, filepath.Join("/b", "wiki", "jepa-fx", "decisions", "val-vol-r2.md"), got)
+}
+
+func TestNotePath_StripsMdSuffix(t *testing.T) {
+	got, err := brain.NotePath("/b", "x", "facts", "note.md")
+	require.NoError(t, err)
+	assert.Equal(t, filepath.Join("/b", "wiki", "x", "facts", "note.md"), got)
+}
+
+func TestNotePath_SanitisesWingAndSlug(t *testing.T) {
+	got, err := brain.NotePath("/b", "Jepa FX!", "facts", "Val Vol R2")
+	require.NoError(t, err)
+	assert.Equal(t, filepath.Join("/b", "wiki", "jepa-fx", "facts", "val-vol-r2.md"), got)
+}
+
+func TestNotePath_RejectsInvalidHall(t *testing.T) {
+	_, err := brain.NotePath("/b", "x", "garbage", "y")
+	require.Error(t, err)
+	assert.Contains(t, err.Error(), "invalid hall")
+}
+
+func TestNotePath_RejectsEmptyWing(t *testing.T) {
+	_, err := brain.NotePath("/b", "!!!", "facts", "y")
+	require.Error(t, err)
+	assert.Contains(t, err.Error(), "invalid wing")
+}
+
+func TestNotePath_RejectsEmptySlug(t *testing.T) {
+	_, err := brain.NotePath("/b", "x", "facts", "!!!")
+	require.Error(t, err)
+	assert.Contains(t, err.Error(), "invalid slug")
+}
+
+func TestSanitise(t *testing.T) {
+	cases := map[string]string{
+		"Jepa-FX":         "jepa-fx",
+		"  foo  bar  ":    "foo-bar",
+		"Val/Vol\\R2.md":  "val-vol-r2-md",
+		"!!!":             "",
+		"___leading":      "leading",
+		"trailing___":     "trailing",
+		"multi---hyphen":  "multi-hyphen",
+		"UPPER 123 mixed": "upper-123-mixed",
+	}
+	for in, want := range cases {
+		t.Run(in, func(t *testing.T) {
+			assert.Equal(t, want, brain.Sanitise(in))
+		})
+	}
+}
+
+func TestIsValidHall(t *testing.T) {
+	for _, h := range []string{"facts", "decisions", "failures", "hypotheses", "sources"} {
+		assert.True(t, brain.IsValidHall(h), h)
+	}
+	for _, h := range []string{"", "Facts", "facts ", "rooms", "concepts", "entities"} {
+		assert.False(t, brain.IsValidHall(h), h)
+	}
+}

ingestion/internal/mcp/handlers.go

@@ -4,11 +4,13 @@ import (
 	"context"
 	"encoding/json"
 	"fmt"
+	"log/slog"
 	"path/filepath"
 	"strings"
 	"time"
 
 	"github.com/mathiasbq/hyperguild/ingestion/internal/api"
+	"github.com/mathiasbq/hyperguild/ingestion/internal/brain"
 	"github.com/mathiasbq/hyperguild/ingestion/internal/extract"
 	"github.com/mathiasbq/hyperguild/ingestion/internal/pipeline"
 	"github.com/mathiasbq/hyperguild/ingestion/internal/search"
@@ -24,6 +26,10 @@ func (s *Server) tools() []map[string]any {
 	int_ := func(desc string) map[string]any {
 		return map[string]any{"type": "integer", "description": desc}
 	}
+	enum := func(desc string, vals ...string) map[string]any {
+		return map[string]any{"type": "string", "description": desc, "enum": vals}
+	}
+	halls := []string{"facts", "decisions", "failures", "hypotheses", "sources"}
 	schema := func(required []string, props map[string]any) json.RawMessage {
 		b, _ := json.Marshal(map[string]any{
 			"type": "object", "required": required, "properties": props,
@@ -34,20 +40,31 @@ func (s *Server) tools() []map[string]any {
 	return []map[string]any{
 		{
 			"name":        "brain_query",
-			"description": "BM25 full-text search across brain/knowledge/ and brain/wiki/ markdown files.",
+			"description": "BM25 full-text search across brain/knowledge/ and brain/wiki/ markdown files. Optionally scope by wing (topic domain) and hall (memory type).",
 			"inputSchema": schema([]string{"query"}, map[string]any{
 				"query": str("search terms"),
 				"limit": int_("max results, default 5"),
+				"wing":  str("optional wing to scope to, e.g. jepa-fx"),
+				"hall":  enum("optional hall to scope to (requires wing)", halls...),
 			}),
 		},
 		{
 			"name":        "brain_write",
-			"description": "Write a raw knowledge note to brain/knowledge/.",
+			"description": "Write a markdown note to the brain. With wing+hall set, routes to brain/wiki/<wing>/<hall>/ with wing/hall/created_at frontmatter; otherwise writes to brain/knowledge/ (legacy).",
 			"inputSchema": schema([]string{"content"}, map[string]any{
 				"content":  str("markdown content"),
-				"filename": str("optional filename"),
-				"type":     str("optional frontmatter type"),
-				"domain":   str("optional frontmatter domain"),
+				"filename": str("optional filename or slug"),
+				"type":     str("optional frontmatter type (legacy)"),
+				"domain":   str("optional frontmatter domain (legacy)"),
+				"wing":     str("optional topic domain, e.g. jepa-fx"),
+				"hall":     enum("optional memory type (requires wing)", halls...),
+			}),
+		},
+		{
+			"name":        "brain_index",
+			"description": "Regenerate _index.md (Map of Content) for one or all wings under brain/wiki/. Auto-called after brain_write with wing+hall.",
+			"inputSchema": schema([]string{}, map[string]any{
+				"wing": str("optional wing to index; if absent, rebuilds every wing"),
 			}),
 		},
 		{
@@ -104,6 +121,8 @@ func (s *Server) tools() []map[string]any {
 type brainQueryArgs struct {
 	Query string `json:"query"`
 	Limit int    `json:"limit,omitempty"`
+	Wing  string `json:"wing,omitempty"`
+	Hall  string `json:"hall,omitempty"`
 }
 
 func (s *Server) brainQuery(ctx context.Context, args json.RawMessage) (json.RawMessage, error) {
@@ -117,7 +136,12 @@ func (s *Server) brainQuery(ctx context.Context, args json.RawMessage) (json.Raw
 	if a.Limit == 0 {
 		a.Limit = 5
 	}
-	results, err := search.Query(s.brainDir, a.Query, a.Limit)
+	results, err := search.Query(s.brainDir, search.QueryOptions{
+		Query: a.Query,
+		Limit: a.Limit,
+		Wing:  a.Wing,
+		Hall:  a.Hall,
+	})
 	if err != nil {
 		return nil, fmt.Errorf("search: %w", err)
 	}
@@ -129,6 +153,8 @@ type brainWriteArgs struct {
 	Filename string `json:"filename,omitempty"`
 	Type     string `json:"type,omitempty"`
 	Domain   string `json:"domain,omitempty"`
+	Wing     string `json:"wing,omitempty"`
+	Hall     string `json:"hall,omitempty"`
 }
 
 func (s *Server) brainWrite(ctx context.Context, args json.RawMessage) (json.RawMessage, error) {
@@ -136,13 +162,51 @@ func (s *Server) brainWrite(ctx context.Context, args json.RawMessage) (json.Raw
 	if err := json.Unmarshal(args, &a); err != nil {
 		return nil, fmt.Errorf("parse args: %w", err)
 	}
-	relPath, err := api.WriteNote(s.brainDir, a.Content, a.Filename, a.Type, a.Domain)
+	relPath, err := api.WriteNote(s.brainDir, api.WriteNoteOptions{
+		Content:  a.Content,
+		Filename: a.Filename,
+		Type:     a.Type,
+		Domain:   a.Domain,
+		Wing:     a.Wing,
+		Hall:     a.Hall,
+	})
 	if err != nil {
 		return nil, err
 	}
+	// Auto-regenerate the wing _index.md when the write landed in the
+	// structured wiki. A failure here is best-effort — log and move on,
+	// since the note itself is already written.
+	if a.Wing != "" && a.Hall != "" {
+		if err := brain.BuildWingIndex(s.brainDir, a.Wing); err != nil {
+			slog.Warn("brain_write: auto-index failed", "wing", a.Wing, "err", err)
+		}
+	}
 	return json.Marshal(map[string]string{"path": relPath})
 }
 
+type brainIndexArgs struct {
+	Wing string `json:"wing,omitempty"`
+}
+
+func (s *Server) brainIndex(ctx context.Context, args json.RawMessage) (json.RawMessage, error) {
+	var a brainIndexArgs
+	if len(args) > 0 {
+		if err := json.Unmarshal(args, &a); err != nil {
+			return nil, fmt.Errorf("parse args: %w", err)
+		}
+	}
+	if a.Wing == "" {
+		if err := brain.BuildAllWingIndexes(s.brainDir); err != nil {
+			return nil, fmt.Errorf("index: %w", err)
+		}
+		return json.Marshal(map[string]any{"status": "ok", "scope": "all"})
+	}
+	if err := brain.BuildWingIndex(s.brainDir, a.Wing); err != nil {
+		return nil, fmt.Errorf("index: %w", err)
+	}
+	return json.Marshal(map[string]any{"status": "ok", "scope": a.Wing})
+}
+
 type brainIngestRawArgs struct {
 	Source string             `json:"source"`
 	Pages  []pipeline.RawPage `json:"pages"`

ingestion/internal/mcp/handlers_test.go

@@ -70,6 +70,58 @@ func TestBrainWriteCreatesFile(t *testing.T) {
 	assert.Contains(t, string(got), "# Test")
 }
 
+func TestBrainWriteWingHallRoutesToWiki(t *testing.T) {
+	brainDir := t.TempDir()
+	srv := mcp.NewServer(brainDir, nil, nil, nil)
+
+	resp := toolCall(t, srv, "brain_write", map[string]any{
+		"content":  "# Val Vol\n\nbody",
+		"filename": "val-vol-r2",
+		"wing":     "jepa-fx",
+		"hall":     "decisions",
+	})
+	require.Nil(t, resp["error"])
+
+	got, err := os.ReadFile(filepath.Join(brainDir, "wiki", "jepa-fx", "decisions", "val-vol-r2.md"))
+	require.NoError(t, err)
+	assert.Contains(t, string(got), "wing: jepa-fx")
+	assert.Contains(t, string(got), "hall: decisions")
+	assert.Contains(t, string(got), "created_at:")
+	assert.Contains(t, string(got), "# Val Vol")
+}
+
+func TestBrainWriteRejectsInvalidHall(t *testing.T) {
+	brainDir := t.TempDir()
+	srv := mcp.NewServer(brainDir, nil, nil, nil)
+	resp := toolCall(t, srv, "brain_write", map[string]any{
+		"content": "x",
+		"wing":    "jepa-fx",
+		"hall":    "garbage",
+	})
+	require.NotNil(t, resp["error"])
+}
+
+func TestBrainQueryWingScope(t *testing.T) {
+	brainDir := t.TempDir()
+	for _, p := range []struct{ rel, body string }{
+		{"wiki/jepa-fx/facts/x.md", "---\nwing: jepa-fx\nhall: facts\n---\nfoo keyword.\n"},
+		{"wiki/other/facts/y.md", "---\nwing: other\nhall: facts\n---\nfoo keyword.\n"},
+	} {
+		full := filepath.Join(brainDir, p.rel)
+		require.NoError(t, os.MkdirAll(filepath.Dir(full), 0o755))
+		require.NoError(t, os.WriteFile(full, []byte(p.body), 0o644))
+	}
+	srv := mcp.NewServer(brainDir, nil, nil, nil)
+	resp := toolCall(t, srv, "brain_query", map[string]any{
+		"query": "foo",
+		"wing":  "jepa-fx",
+	})
+	require.Nil(t, resp["error"])
+	text := resp["result"].(map[string]any)["content"].([]any)[0].(map[string]any)["text"].(string)
+	assert.Contains(t, text, "wiki/jepa-fx/facts/x.md")
+	assert.NotContains(t, text, "wiki/other/facts/y.md")
+}
+
 func TestBrainWriteRejectsTraversal(t *testing.T) {
 	brainDir := t.TempDir()
 	srv := mcp.NewServer(brainDir, nil, nil, nil)

ingestion/internal/mcp/server.go

@@ -1,5 +1,6 @@
 // Package mcp implements an MCP HTTP handler for the ingestion service.
-// Exposed tools: brain_query, brain_write, brain_ingest, brain_ingest_raw, session_log.
+// Exposed tools: brain_query, brain_write, brain_index, brain_ingest,
+// brain_ingest_raw, brain_answer, brain_classify, session_log.
 package mcp
 
 import (
@@ -136,6 +137,8 @@ func (s *Server) handleCall(ctx context.Context, name string, args json.RawMessa
 		return s.brainQuery(ctx, args)
 	case "brain_write":
 		return s.brainWrite(ctx, args)
+	case "brain_index":
+		return s.brainIndex(ctx, args)
 	case "brain_ingest_raw":
 		return s.brainIngestRaw(ctx, args)
 	case "brain_ingest":

ingestion/internal/mcp/server_test.go

@@ -55,7 +55,7 @@ func TestServerToolsList(t *testing.T) {
 		names = append(names, t.(map[string]any)["name"].(string))
 	}
 	assert.ElementsMatch(t, []string{
-		"brain_query", "brain_write", "brain_ingest_raw", "brain_ingest",
+		"brain_query", "brain_write", "brain_index", "brain_ingest_raw", "brain_ingest",
 		"brain_answer", "brain_classify", "session_log",
 	}, names)
 }

ingestion/internal/mcp/tools_answer.go

@@ -35,7 +35,7 @@ func (s *Server) brainAnswer(ctx context.Context, args json.RawMessage) (json.Ra
 		return nil, fmt.Errorf("query is required")
 	}
 
-	results, err := search.Query(s.brainDir, a.Query, 10)
+	results, err := search.Query(s.brainDir, search.QueryOptions{Query: a.Query, Limit: 10})
 	if err != nil {
 		return nil, fmt.Errorf("search: %w", err)
 	}

ingestion/internal/search/search.go

@@ -9,6 +9,8 @@ import (
 	"path/filepath"
 	"sort"
 	"strings"
+
+	"github.com/mathiasbq/hyperguild/ingestion/internal/brain"
 )
 
 // Result is a single search hit from the brain wiki.
@@ -17,24 +19,41 @@ type Result struct {
 	Title   string `json:"title"`
 	Excerpt string `json:"excerpt"`
 	Score   int    `json:"score"`
+	Wing    string `json:"wing,omitempty"`
+	Hall    string `json:"hall,omitempty"`
 }
 
-// Query searches all .md files under brainDir/wiki/ for pages containing
-// any of the whitespace-separated terms in query. Returns up to limit results
-// sorted by score descending.
-func Query(brainDir, query string, limit int) ([]Result, error) {
-	if limit <= 0 {
-		limit = 5
+// QueryOptions configures a search.
+//
+// When Wing is set, the walk is restricted to brain/wiki/<wing>/.
+// When Hall is additionally set, the walk is restricted to
+// brain/wiki/<wing>/<hall>/. Without either, the legacy walk over
+// brain/knowledge/ and brain/wiki/ is used.
+type QueryOptions struct {
+	Query string
+	Limit int
+	Wing  string
+	Hall  string
+}
+
+// Query searches the brain. Returns up to opts.Limit results sorted by
+// score descending. Empty query returns nil.
+func Query(brainDir string, opts QueryOptions) ([]Result, error) {
+	if opts.Limit <= 0 {
+		opts.Limit = 5
 	}
-	terms := strings.Fields(strings.ToLower(query))
+	terms := strings.Fields(strings.ToLower(opts.Query))
 	if len(terms) == 0 {
 		return nil, nil
 	}
 
-	var results []Result
+	roots, err := resolveRoots(brainDir, opts.Wing, opts.Hall)
+	if err != nil {
+		return nil, err
+	}
 
-	for _, subdir := range []string{"knowledge", "wiki"} {
-		dir := filepath.Join(brainDir, subdir)
+	var results []Result
+	for _, dir := range roots {
 		if _, statErr := os.Stat(dir); os.IsNotExist(statErr) {
 			continue
 		}
@@ -46,13 +65,11 @@ func Query(brainDir, query string, limit int) ([]Result, error) {
 			if d.IsDir() || !strings.HasSuffix(path, ".md") {
 				return nil
 			}
-
 			content, err := os.ReadFile(path)
 			if err != nil {
 				slog.Warn("search: skipping unreadable file", "path", path, "err", err)
 				return nil
 			}
-
 			lower := strings.ToLower(string(content))
 			score := 0
 			for _, term := range terms {
@@ -61,18 +78,19 @@ func Query(brainDir, query string, limit int) ([]Result, error) {
 			if score == 0 {
 				return nil
 			}
-
 			rel, err := filepath.Rel(brainDir, path)
 			if err != nil {
 				return fmt.Errorf("rel path: %w", err)
 			}
 			rel = filepath.ToSlash(rel)
-
+			wing, hall := extractWingHall(string(content), rel)
 			results = append(results, Result{
 				Path:    rel,
 				Title:   extractTitle(string(content), d.Name()),
 				Excerpt: excerpt(string(content), 300),
 				Score:   score,
+				Wing:    wing,
+				Hall:    hall,
 			})
 			return nil
 		})
@@ -84,12 +102,81 @@ func Query(brainDir, query string, limit int) ([]Result, error) {
 	sort.Slice(results, func(i, j int) bool {
 		return results[i].Score > results[j].Score
 	})
-	if len(results) > limit {
-		results = results[:limit]
+	if len(results) > opts.Limit {
+		results = results[:opts.Limit]
 	}
 	return results, nil
 }
 
+// resolveRoots returns the directories to walk for the given wing/hall
+// filters. Validates hall against the closed vocabulary when set.
+func resolveRoots(brainDir, wing, hall string) ([]string, error) {
+	if hall != "" && !brain.IsValidHall(hall) {
+		return nil, fmt.Errorf("invalid hall %q", hall)
+	}
+	if wing != "" {
+		w := brain.Sanitise(wing)
+		if w == "" {
+			return nil, fmt.Errorf("invalid wing %q", wing)
+		}
+		if hall != "" {
+			return []string{filepath.Join(brainDir, "wiki", w, hall)}, nil
+		}
+		return []string{filepath.Join(brainDir, "wiki", w)}, nil
+	}
+	if hall != "" {
+		return nil, fmt.Errorf("hall filter requires wing")
+	}
+	return []string{
+		filepath.Join(brainDir, "knowledge"),
+		filepath.Join(brainDir, "wiki"),
+	}, nil
+}
+
+// extractWingHall reads wing/hall from frontmatter first, falling back to
+// path segments brain/wiki/<wing>/<hall>/.
+func extractWingHall(content, relPath string) (wing, hall string) {
+	scanner := bufio.NewScanner(strings.NewReader(content))
+	inFrontmatter := false
+	for scanner.Scan() {
+		line := scanner.Text()
+		if strings.TrimSpace(line) == "---" {
+			if !inFrontmatter {
+				inFrontmatter = true
+				continue
+			}
+			break
+		}
+		if !inFrontmatter {
+			continue
+		}
+		key, val, ok := strings.Cut(line, ":")
+		if !ok {
+			continue
+		}
+		v := strings.Trim(strings.TrimSpace(val), `"'`)
+		switch strings.TrimSpace(key) {
+		case "wing":
+			wing = v
+		case "hall":
+			hall = v
+		}
+	}
+	if wing != "" && hall != "" {
+		return wing, hall
+	}
+	parts := strings.Split(relPath, "/")
+	if len(parts) >= 4 && parts[0] == "wiki" {
+		if wing == "" {
+			wing = parts[1]
+		}
+		if hall == "" && brain.IsValidHall(parts[2]) {
+			hall = parts[2]
+		}
+	}
+	return wing, hall
+}
+
 func extractTitle(content, filename string) string {
 	scanner := bufio.NewScanner(strings.NewReader(content))
 	inFrontmatter := false
@@ -113,7 +200,6 @@ func extractTitle(content, filename string) string {
 }
 
 func excerpt(content string, maxLen int) string {
-	// Skip frontmatter, return first maxLen chars of body.
 	parts := strings.SplitN(content, "---", 3)
 	body := content
 	if len(parts) == 3 {

ingestion/internal/search/search_test.go

@@ -27,7 +27,7 @@ func TestSearch_ReturnsMatchingPages(t *testing.T) {
 		0o644,
 	))
 
-	results, err := search.Query(dir, "retry transient", 5)
+	results, err := search.Query(dir, search.QueryOptions{Query: "retry transient", Limit: 5})
 	require.NoError(t, err)
 	require.Len(t, results, 1)
 	assert.Equal(t, "knowledge/retry-logic.md", results[0].Path)
@@ -36,6 +36,49 @@ func TestSearch_ReturnsMatchingPages(t *testing.T) {
 	assert.Contains(t, results[0].Excerpt, "Retry")
 }
 
+func TestSearch_WingHallScoping(t *testing.T) {
+	dir := t.TempDir()
+	for _, p := range []struct{ rel, body string }{
+		{"wiki/jepa-fx/decisions/val-vol.md", "---\nwing: jepa-fx\nhall: decisions\n---\nval-vol-r2 keyword.\n"},
+		{"wiki/jepa-fx/facts/architecture.md", "---\nwing: jepa-fx\nhall: facts\n---\nval-vol-r2 keyword in facts.\n"},
+		{"wiki/hyperguild/decisions/routing.md", "---\nwing: hyperguild\nhall: decisions\n---\nval-vol-r2 reference.\n"},
+		{"knowledge/loose.md", "---\n---\nval-vol-r2 in knowledge.\n"},
+	} {
+		full := filepath.Join(dir, p.rel)
+		require.NoError(t, os.MkdirAll(filepath.Dir(full), 0o755))
+		require.NoError(t, os.WriteFile(full, []byte(p.body), 0o644))
+	}
+
+	// No filter: walk both knowledge/ and wiki/ — all 4 match.
+	got, err := search.Query(dir, search.QueryOptions{Query: "val-vol-r2", Limit: 10})
+	require.NoError(t, err)
+	assert.Len(t, got, 4)
+
+	// Wing scope: 2 jepa-fx hits, no hyperguild, no knowledge.
+	got, err = search.Query(dir, search.QueryOptions{Query: "val-vol-r2", Limit: 10, Wing: "jepa-fx"})
+	require.NoError(t, err)
+	require.Len(t, got, 2)
+	for _, r := range got {
+		assert.Equal(t, "jepa-fx", r.Wing)
+	}
+
+	// Wing+Hall scope: 1 hit.
+	got, err = search.Query(dir, search.QueryOptions{Query: "val-vol-r2", Limit: 10, Wing: "jepa-fx", Hall: "decisions"})
+	require.NoError(t, err)
+	require.Len(t, got, 1)
+	assert.Equal(t, "jepa-fx", got[0].Wing)
+	assert.Equal(t, "decisions", got[0].Hall)
+	assert.Equal(t, "wiki/jepa-fx/decisions/val-vol.md", got[0].Path)
+
+	// Invalid hall rejected.
+	_, err = search.Query(dir, search.QueryOptions{Query: "x", Wing: "jepa-fx", Hall: "garbage"})
+	require.Error(t, err)
+
+	// Hall without wing rejected.
+	_, err = search.Query(dir, search.QueryOptions{Query: "x", Hall: "facts"})
+	require.Error(t, err)
+}
+
 func TestSearch_RespectsLimit(t *testing.T) {
 	dir := t.TempDir()
 	require.NoError(t, os.MkdirAll(filepath.Join(dir, "knowledge"), 0o755))
@@ -46,7 +89,7 @@ func TestSearch_RespectsLimit(t *testing.T) {
 			0o644,
 		))
 	}
-	results, err := search.Query(dir, "retry", 3)
+	results, err := search.Query(dir, search.QueryOptions{Query: "retry", Limit: 3})
 	require.NoError(t, err)
 	assert.LessOrEqual(t, len(results), 3)
 }