diff --git a/cmd/ninja/cmd/plugin.go b/cmd/ninja/cmd/plugin.go
index c39825f..dc666e9 100644
--- a/cmd/ninja/cmd/plugin.go
+++ b/cmd/ninja/cmd/plugin.go
@@ -1130,6 +1130,20 @@ func writeMod(path string, m *core.ModFile) error {
 	if m.Plugin.MaxResponseMB > 0 {
 		fmt.Fprintf(&b, "max_response_mb = %d\n", m.Plugin.MaxResponseMB)
 	}
+	if len(m.Plugin.PublicRoutes) > 0 {
+		entries := make([]string, len(m.Plugin.PublicRoutes))
+		for i, r := range m.Plugin.PublicRoutes {
+			if r.Prefix {
+				entries[i] = fmt.Sprintf("{ path = %q, prefix = true }", r.Path)
+			} else {
+				entries[i] = fmt.Sprintf("{ path = %q }", r.Path)
+			}
+		}
+		fmt.Fprintf(&b, "public_routes = [%s]\n", strings.Join(entries, ", "))
+	}
+	if m.Plugin.Sitemap {
+		b.WriteString("sitemap = true\n")
+	}
 	if m.Compatibility != nil {
 		b.WriteString("\n[compatibility]\n")
 		fmt.Fprintf(&b, "block_core = %q\n", m.Compatibility.BlockCore)
diff --git a/cmd/ninja/cmd/plugin_test.go b/cmd/ninja/cmd/plugin_test.go
index 8020c49..866ef3b 100644
--- a/cmd/ninja/cmd/plugin_test.go
+++ b/cmd/ninja/cmd/plugin_test.go
@@ -380,6 +380,11 @@ func TestWriteMod_RoundTripsFirstClassFields(t *testing.T) {
 		AllowedHosts:      []string{"api.cal.com", "*.example.com"},
 		MaxResponseMB:     25,
 		RequiredIconPacks: []string{"tabler"},
+		PublicRoutes: []core.ModPublicRoute{
+			{Path: "/area", Prefix: true},
+			{Path: "/api/semantic-search"},
+		},
+		Sitemap: true,
 	}}
 	if err := writeMod(path, m); err != nil {
 		t.Fatalf("writeMod: %v", err)
@@ -401,6 +406,14 @@ func TestWriteMod_RoundTripsFirstClassFields(t *testing.T) {
 	if got := back.Plugin.RequiredIconPacks; len(got) != 1 || got[0] != "tabler" {
 		t.Errorf("required_icon_packs not preserved: %v\n%s", got, data)
 	}
+	if got := back.Plugin.PublicRoutes; len(got) != 2 ||
+		got[0] != (core.ModPublicRoute{Path: "/area", Prefix: true}) ||
+		got[1] != (core.ModPublicRoute{Path: "/api/semantic-search"}) {
+		t.Errorf("public_routes not preserved: %v\n%s", got, data)
+	}
+	if !back.Plugin.Sitemap {
+		t.Errorf("sitemap not preserved\n%s", data)
+	}
 }
 
 func TestParsePrivateCoord(t *testing.T) {
diff --git a/go.mod b/go.mod
index d6b80ae..98a1bc4 100644
--- a/go.mod
+++ b/go.mod
@@ -5,7 +5,7 @@ go 1.26.4
 require (
 	connectrpc.com/connect v1.20.0
 	git.dev.alexdunmow.com/block/core v0.18.2
-	git.dev.alexdunmow.com/block/pluginsdk v0.2.5
+	git.dev.alexdunmow.com/block/pluginsdk v0.2.7
 	github.com/chromedp/cdproto v0.0.0-20260321001828-e3e3800016bc
 	github.com/chromedp/chromedp v0.15.1
 	github.com/klauspost/compress v1.18.6
diff --git a/go.sum b/go.sum
index 05a33e3..0a6ff53 100644
--- a/go.sum
+++ b/go.sum
@@ -2,8 +2,8 @@ connectrpc.com/connect v1.20.0 h1:6TNDAB+WeNd2uolWNlYczB5E0KNNaVMNUEx8JEUsPmQ=
 connectrpc.com/connect v1.20.0/go.mod h1:A2ygJrukXwWy32vkCAAHNVguZrqZ+jeZ9rGRnGR4dN4=
 git.dev.alexdunmow.com/block/core v0.18.2 h1:+3OfZ424yoc1k1CucXYARk8TBkh8Z693HRkhf5Ci2wU=
 git.dev.alexdunmow.com/block/core v0.18.2/go.mod h1:GGuUu826AoJepC/hKLGJ7BX3PQaDss9ueCT0se6Ao2w=
-git.dev.alexdunmow.com/block/pluginsdk v0.2.5 h1:01d+5stAywSENScafnNKyMc2ZM5GGFt+hCBKuKTFJW4=
-git.dev.alexdunmow.com/block/pluginsdk v0.2.5/go.mod h1:Z+eG+WZxAP0jfreLqlGcc0kkWKt8RWevzWyWn8d+dhM=
+git.dev.alexdunmow.com/block/pluginsdk v0.2.7 h1:iL6Qvg2xHqHtii/0ZF9TIjjDzMrYkmxvLwqU300nmac=
+git.dev.alexdunmow.com/block/pluginsdk v0.2.7/go.mod h1:Z+eG+WZxAP0jfreLqlGcc0kkWKt8RWevzWyWn8d+dhM=
 github.com/BurntSushi/toml v1.6.0 h1:dRaEfpa2VI55EwlIW72hMRHdWouJeRF7TPYhI+AUQjk=
 github.com/BurntSushi/toml v1.6.0/go.mod h1:ukJfTF/6rtPPRCnwkur4qwRxa8vTRFBF0uk2lLoLwho=
 github.com/chromedp/cdproto v0.0.0-20260321001828-e3e3800016bc h1:wkN/LMi5vc60pBRWx6qpbk/aEvq3/ZVNpnMvsw8PVVU=
diff --git a/internal/bnp/build.go b/internal/bnp/build.go
index 96911c3..ebf24c4 100644
--- a/internal/bnp/build.go
+++ b/internal/bnp/build.go
@@ -139,7 +139,16 @@ func Build(ctx context.Context, opts BuildOptions) (*BuildResult, error) {
 	manifest.AllowedHosts = mod.Plugin.AllowedHosts
 	manifest.MaxResponseMb = mod.Plugin.MaxResponseMB
 
-	// 4b. Mixed-form artifacts (WO-WZ-021): a reduced wasm plugin may keep a
+	// 4b. Stamp the public-route claims (ADR 0026, cms repo). Same
+	//     mod-is-the-source rule as data_dir/allowed_hosts; validate here so a
+	//     bad claim fails the build, not the install. Conflict resolution
+	//     (core wins, first-installed plugin wins) is host-side: it needs the
+	//     instance's install set, which the packer lacks.
+	if err := stampPublicRoutes(manifest, mod); err != nil {
+		return nil, err
+	}
+
+	// 4c. Mixed-form artifacts (WO-WZ-021): a reduced wasm plugin may keep a
 	//     minimal guest for genuine logic (a contact route, Stripe) while its
 	//     declarative surfaces (theme presets, bundled fonts, master pages,
 	//     system/page templates, template overrides, email wrappers, css,
@@ -243,6 +252,29 @@ func Build(ctx context.Context, opts BuildOptions) (*BuildResult, error) {
 	}, nil
 }
 
+// stampPublicRoutes validates the plugin.mod public-route declaration and
+// copies it into the manifest (ADR 0026, cms repo). Routes and the sitemap
+// flag are served by the guest HTTP handler, so declaring either without one
+// fails the build.
+func stampPublicRoutes(manifest *abiv1.PluginManifest, mod *core.ModFile) error {
+	if err := core.ValidatePublicRoutes(mod.Plugin.PublicRoutes); err != nil {
+		return fmt.Errorf("public_routes: %w", err)
+	}
+	if !manifest.GetHasHttpHandler() {
+		if len(mod.Plugin.PublicRoutes) > 0 {
+			return fmt.Errorf("public_routes declared but the plugin registers no HTTP handler to serve them")
+		}
+		if mod.Plugin.Sitemap {
+			return fmt.Errorf("sitemap = true but the plugin registers no HTTP handler to serve the sitemap endpoint")
+		}
+	}
+	for _, r := range mod.Plugin.PublicRoutes {
+		manifest.PublicRoutes = append(manifest.PublicRoutes, &abiv1.PublicRoute{Path: r.Path, Prefix: r.Prefix})
+	}
+	manifest.Sitemap = mod.Plugin.Sitemap
+	return nil
+}
+
 // buildWasm runs the reactor-mode wasip1 c-shared build in dir.
 func buildWasm(ctx context.Context, dir, outPath string) error {
 	cmd := exec.CommandContext(ctx, "go", "build", "-buildmode=c-shared", "-o", outPath, ".")
diff --git a/internal/bnp/build_test.go b/internal/bnp/build_test.go
new file mode 100644
index 0000000..70f3753
--- /dev/null
+++ b/internal/bnp/build_test.go
@@ -0,0 +1,73 @@
+package bnp
+
+import (
+	"strings"
+	"testing"
+
+	abiv1 "git.dev.alexdunmow.com/block/pluginsdk/abi/v1"
+	core "git.dev.alexdunmow.com/block/pluginsdk/plugin"
+)
+
+func TestStampPublicRoutes(t *testing.T) {
+	manifest := &abiv1.PluginManifest{HasHttpHandler: true}
+	mod := &core.ModFile{Plugin: core.ModPlugin{
+		PublicRoutes: []core.ModPublicRoute{
+			{Path: "/area", Prefix: true},
+			{Path: "/api/semantic-search"},
+		},
+		Sitemap: true,
+	}}
+	if err := stampPublicRoutes(manifest, mod); err != nil {
+		t.Fatalf("stampPublicRoutes: %v", err)
+	}
+	routes := manifest.GetPublicRoutes()
+	if len(routes) != 2 {
+		t.Fatalf("manifest routes len = %d, want 2", len(routes))
+	}
+	if routes[0].GetPath() != "/area" || !routes[0].GetPrefix() {
+		t.Errorf("routes[0] = %+v, want /area prefix", routes[0])
+	}
+	if routes[1].GetPath() != "/api/semantic-search" || routes[1].GetPrefix() {
+		t.Errorf("routes[1] = %+v, want exact /api/semantic-search", routes[1])
+	}
+	if !manifest.GetSitemap() {
+		t.Errorf("manifest sitemap not stamped")
+	}
+}
+
+func TestStampPublicRoutes_RejectsReservedPrefix(t *testing.T) {
+	manifest := &abiv1.PluginManifest{HasHttpHandler: true}
+	mod := &core.ModFile{Plugin: core.ModPlugin{
+		PublicRoutes: []core.ModPublicRoute{{Path: "/api/plugins/mine", Prefix: true}},
+	}}
+	err := stampPublicRoutes(manifest, mod)
+	if err == nil {
+		t.Fatal("reserved prefix accepted; want error")
+	}
+	if !strings.Contains(err.Error(), "public_routes") || !strings.Contains(err.Error(), "reserved prefix") {
+		t.Errorf("error %q should name public_routes and the reserved prefix", err.Error())
+	}
+}
+
+func TestStampPublicRoutes_RequiresHTTPHandler(t *testing.T) {
+	mod := &core.ModFile{Plugin: core.ModPlugin{
+		PublicRoutes: []core.ModPublicRoute{{Path: "/area"}},
+	}}
+	if err := stampPublicRoutes(&abiv1.PluginManifest{}, mod); err == nil {
+		t.Error("public_routes without HTTP handler accepted; want error")
+	}
+	sitemapOnly := &core.ModFile{Plugin: core.ModPlugin{Sitemap: true}}
+	if err := stampPublicRoutes(&abiv1.PluginManifest{}, sitemapOnly); err == nil {
+		t.Error("sitemap without HTTP handler accepted; want error")
+	}
+}
+
+func TestStampPublicRoutes_NoDeclarationIsNoop(t *testing.T) {
+	manifest := &abiv1.PluginManifest{}
+	if err := stampPublicRoutes(manifest, &core.ModFile{}); err != nil {
+		t.Fatalf("empty declaration: %v", err)
+	}
+	if len(manifest.GetPublicRoutes()) != 0 || manifest.GetSitemap() {
+		t.Errorf("manifest gained routes from an empty mod: %+v", manifest)
+	}
+}
diff --git a/internal/bnp/codeless.go b/internal/bnp/codeless.go
index 9c1131d..3d4ca82 100644
--- a/internal/bnp/codeless.go
+++ b/internal/bnp/codeless.go
@@ -193,6 +193,9 @@ func BuildCodeless(_ context.Context, opts BuildOptions) (*BuildResult, error) {
 	if mod.Plugin.DataDir {
 		return nil, fmt.Errorf("codeless plugin cannot request data_dir — there is no code to use it")
 	}
+	if len(mod.Plugin.PublicRoutes) > 0 || mod.Plugin.Sitemap {
+		return nil, fmt.Errorf("codeless plugin cannot declare public_routes or sitemap: there is no HTTP handler to serve them")
+	}
 
 	manifest := &abiv1.PluginManifest{
 		AbiVersion: hostAbiVersion,
diff --git a/internal/bnp/codeless_test.go b/internal/bnp/codeless_test.go
index 9c111a4..2755835 100644
--- a/internal/bnp/codeless_test.go
+++ b/internal/bnp/codeless_test.go
@@ -135,6 +135,13 @@ func TestCodelessBuildRejectsBadDeclarations(t *testing.T) {
 		{"data_dir grant", map[string]string{
 			"plugin.mod": "[plugin]\nname = \"x\"\nversion = \"0.1.0\"\ndata_dir = true\n",
 		}},
+		{"public_routes claim", map[string]string{
+			"plugin.mod": "[plugin]\nname = \"x\"\nversion = \"0.1.0\"\n" +
+				"public_routes = [{ path = \"/area\", prefix = true }]\n",
+		}},
+		{"sitemap flag", map[string]string{
+			"plugin.mod": "[plugin]\nname = \"x\"\nversion = \"0.1.0\"\nsitemap = true\n",
+		}},
 		{"override missing template file", map[string]string{
 			"plugin.mod":    "[plugin]\nname = \"x\"\nversion = \"0.1.0\"\n",
 			"manifest.yaml": "template_overrides:\n  - template: x\n    block: heading\n",