fix(wing): the client filter survives cheap evasions; lookalike and reserved folder names are refused (review of #211)

- client pattern is matched against the text and against an NFKC-folded,
  format-character-free, dash-normalised, whitespace-free form
  (non-breaking hyphen, zero-width characters, soft hyphen, line splits,
  fullwidth letters). x/text/unicode/norm was already in the module graph as an
  indirect dependency; this makes it direct, no new download.
- folder/frontmatter wing names must be ASCII (strings.ToLower folds the Kelvin
  sign to 'k') and must not be sources/concepts/entities/wiki; such names are
  never proposed as a wing, and a reserved default is a startup error
Mutation-checked.

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

ingestion/go.mod

@@ -69,6 +69,6 @@ require (
 	golang.org/x/crypto v0.51.0 // indirect
 	golang.org/x/sync v0.21.0 // indirect
 	golang.org/x/sys v0.45.0
-	golang.org/x/text v0.39.0 // indirect
+	golang.org/x/text v0.39.0
 	gopkg.in/yaml.v3 v3.0.1
 )

ingestion/internal/wing/router.go

@@ -6,6 +6,9 @@ import (
 	"regexp"
 	"slices"
 	"strings"
+	"unicode"
+
+	xnorm "golang.org/x/text/unicode/norm"
 )
 
 // Router places a note with rules only, no model (hyperguild#208):
@@ -28,6 +31,13 @@ type Router struct {
 // Resolve implements Placer. It never returns an error: anything it cannot
 // decide safely is an Exception with the reason spelled out.
 func (r Router) Resolve(_ context.Context, n Note) Decision {
+	for _, raw := range []string{n.Dir, n.FrontmatterWing} {
+		if !isASCII(raw) {
+			// strings.ToLower folds some non-ASCII runes to ASCII (the Kelvin
+			// sign becomes "k"), which would let a lookalike name a real wing.
+			return exception("", 0, fmt.Sprintf("wing name %q contains non-ASCII characters", strings.TrimSpace(raw)))
+		}
+	}
 	dir, fm := norm(n.Dir), norm(n.FrontmatterWing)
 	switch {
 	case dir != "" && fm != "" && dir != fm:
@@ -37,20 +47,20 @@ func (r Router) Resolve(_ context.Context, n Note) Decision {
 	case fm != "":
 		return r.explicit(fm, "frontmatter")
 	}
-	if r.ClientBlock != nil && r.ClientBlock.MatchString(n.Text) {
+	if r.ClientBlock != nil && matchesClient(r.ClientBlock, n.Text) {
 		return exception("", 0, "text matches the client-content marker; not defaulted into a shared wing")
 	}
-	if r.Default == "" || !plainWingName(r.Default) {
+	if r.Default == "" || !usableWingName(r.Default) {
 		return exception("", 0, "no valid default wing configured")
 	}
 	return Decision{Wing: r.Default, Source: Default, Confidence: 1, Reason: "no wing named; default wing"}
 }
 
 func (r Router) explicit(w, via string) Decision {
-	if !plainWingName(w) {
-		return exception("", 0, fmt.Sprintf("%s names %q, which is not a plain wing name", via, w))
+	if !usableWingName(w) {
+		return exception("", 0, fmt.Sprintf("%s names %q, which is not a usable wing name", via, w))
 	}
-	if w == r.Default && plainWingName(w) {
+	if w == r.Default {
 		return Decision{Wing: w, Source: Explicit, Confidence: 1, Reason: "named by " + via}
 	}
 	known, err := KnownWings(r.BrainDir)
@@ -69,8 +79,8 @@ func (r Router) explicit(w, via string) Decision {
 // startup rather than later: a client filter that silently does nothing is
 // worse than none.
 func NewRouter(brainDir, defaultWing, clientPattern string) (Router, error) {
-	if defaultWing == "" || !plainWingName(defaultWing) {
-		return Router{}, fmt.Errorf("default wing %q is not a plain wing name", defaultWing)
+	if defaultWing == "" || !usableWingName(defaultWing) {
+		return Router{}, fmt.Errorf("default wing %q is not a usable wing name", defaultWing)
 	}
 	r := Router{BrainDir: brainDir, Default: defaultWing}
 	if clientPattern != "" {
@@ -82,3 +92,42 @@ func NewRouter(brainDir, defaultWing, clientPattern string) (Router, error) {
 	}
 	return r, nil
 }
+
+// reservedWingNames are directory names under wiki/ that are not wings: the
+// retired layout and the root. A note must never be proposed into one.
+var reservedWingNames = map[string]bool{"sources": true, "concepts": true, "entities": true, "wiki": true}
+
+// usableWingName: a plain name that is not reserved.
+func usableWingName(w string) bool { return plainWingName(w) && !reservedWingNames[w] }
+
+func isASCII(s string) bool {
+	for _, r := range s {
+		if r > unicode.MaxASCII {
+			return false
+		}
+	}
+	return true
+}
+
+// matchesClient applies the client-content pattern to the text and to two
+// folded forms of it, so the cheap evasions do not defeat it: NFKC (fullwidth
+// letters), format characters removed (zero-width joiners, soft hyphens), every
+// dash made "-", and whitespace removed ("acme-\nclient", "acme - client"). It catches what it names and nothing else; it is a filter,
+// not a classifier.
+func matchesClient(re *regexp.Regexp, text string) bool {
+	folded := xnorm.NFKC.String(text)
+	var b strings.Builder
+	for _, r := range folded {
+		switch {
+		case unicode.Is(unicode.Cf, r):
+			continue
+		case unicode.Is(unicode.Pd, r) || r == '\u2212':
+			b.WriteRune('-')
+		default:
+			b.WriteRune(r)
+		}
+	}
+	clean := b.String()
+	squeezed := strings.Join(strings.Fields(clean), "")
+	return re.MatchString(text) || re.MatchString(squeezed)
+}

ingestion/internal/wing/router_test.go

@@ -81,7 +81,7 @@ func TestRouter_ANameThatIsNotPlainIsRefusedAsSuch(t *testing.T) {
 			d := r.Resolve(context.Background(), wing.Note{Dir: bad, Text: "x"})
 			assert.Equal(t, wing.Exception, d.Source)
 			assert.Empty(t, d.Wing, "a malformed name is never echoed as a proposal")
-			assert.Contains(t, d.Reason, "not a plain wing name")
+			assert.Contains(t, d.Reason, "not a usable wing name")
 		})
 	}
 }
@@ -112,3 +112,63 @@ func TestNewRouter(t *testing.T) {
 		assert.Error(t, err, "a client filter that silently does nothing is worse than none")
 	})
 }
+
+// From the review of #211: the content filter is the only guard on the default
+// lane, so it must survive the cheap evasions.
+func TestRouter_ClientMarkerSurvivesCheapEvasions(t *testing.T) {
+	r := wing.Router{BrainDir: routerBrain(t), Default: "web-clip", ClientBlock: regexp.MustCompile(`(?i)acme-client`)}
+	tests := []struct{ name, text string }{
+		{"non-breaking hyphen", "notes on acme‑client"},
+		{"zero-width joiner inside", "notes on acme\u200d-client"},
+		{"zero-width space inside", "notes on ac\u200bme-client"},
+		{"split across lines", "notes on acme-\nclient"},
+		{"spaced hyphen", "notes on acme - client"},
+		{"fullwidth letters", "notes on ａｃｍｅ-client"},
+		{"soft hyphen", "notes on acme\u00ad-client"},
+		{"en dash", "notes on acme–client"},
+	}
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			d := r.Resolve(context.Background(), wing.Note{Text: tt.text})
+			assert.Equal(t, wing.Exception, d.Source, tt.text)
+		})
+	}
+	t.Run("an unrelated text still files", func(t *testing.T) {
+		d := r.Resolve(context.Background(), wing.Note{Text: "a talk about agents and a client-server model"})
+		assert.Equal(t, wing.Default, d.Source)
+	})
+}
+
+func TestRouter_FolderNamesAreAsciiAndNotReserved(t *testing.T) {
+	dir := routerBrain(t)
+	writePage(t, dir, "wiki/kubernetes/facts/a.md", "x")
+	r := wing.Router{BrainDir: dir, Default: "web-clip"}
+	tests := []struct {
+		name string
+		dir  string
+	}{
+		{"Kelvin sign lowercases to an ASCII k", "Kubernetes"},
+		{"cyrillic lookalike", "hоmelab"},
+		{"retired layout name: sources", "sources"},
+		{"retired layout name: concepts", "concepts"},
+		{"retired layout name: entities", "entities"},
+		{"wiki", "wiki"},
+	}
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			d := r.Resolve(context.Background(), wing.Note{Dir: tt.dir, Text: "x"})
+			assert.Equal(t, wing.Exception, d.Source)
+			assert.Empty(t, d.Wing, "never proposed as a wing")
+		})
+	}
+	t.Run("plain ASCII case folding still works", func(t *testing.T) {
+		d := r.Resolve(context.Background(), wing.Note{Dir: "KubernetEs", Text: "x"})
+		assert.Equal(t, wing.Explicit, d.Source)
+		assert.Equal(t, "kubernetes", d.Wing)
+	})
+}
+
+func TestNewRouter_AReservedDefaultIsRefused(t *testing.T) {
+	_, err := wing.NewRouter(routerBrain(t), "sources", "")
+	assert.Error(t, err)
+}