diff --git a/scripts/check-examples.sh b/scripts/check-examples.sh
index 9e7d1ce17..f866248e8 100755
--- a/scripts/check-examples.sh
+++ b/scripts/check-examples.sh
@@ -20,6 +20,8 @@
 #                                        # uses checkouts of your own (example-app/ and
 #                                        # example-plugin/ in that directory), as they are on
 #                                        # disk, copied so they are left untouched
+#   EXAMPLES_BUILDS="" scripts/check-examples.sh
+#                                        # builds none of their apps: the build API fixture alone
 #
 # CI: the examples job of .github/workflows/ci.yml.
 set -euo pipefail
@@ -48,29 +50,32 @@ pack "$root" | gzip > "$work/fizzy.tar.gz"
 bash scripts/pack-sdk.sh "$work/sdk" >/dev/null
 sdk_tarball="$(ls "$work"/sdk/fizzy-sdk-v*.tar.gz)"
 
-for repo in example-app example-plugin; do
-  if [[ -n "${EXAMPLES_DIR:-}" ]]; then
-    mkdir -p "$work/$repo"
-    pack "$EXAMPLES_DIR/$repo" | tar -x -C "$work/$repo"
-  else
-    git clone --quiet --depth 1 "https://github.com/fizzyedit/$repo" "$work/$repo"
-  fi
-done
-
-(cd "$work/example-plugin" && zig fetch --save=fizzy "$sdk_tarball" >/dev/null)
-# example-app bundles example-plugin (`hello`), pinned by URL: the copy here, on this tree's SDK.
-pack "$work/example-plugin" | gzip > "$work/example-plugin.tar.gz"
-(
-  cd "$work/example-app"
-  zig fetch --save=hello "$work/example-plugin.tar.gz" >/dev/null
-  zig fetch --save=fizzy "$work/fizzy.tar.gz" >/dev/null
-  # Its replay app depends on the plugin SDK alone: this tree's, packed as a release would be.
-  zig fetch --save=fizzy_sdk "$sdk_tarball" >/dev/null
-  # So do the plugins it carries, each pinning a released SDK of its own.
-  for plugin in plugins/*/; do
-    (cd "$plugin" && zig fetch --save=fizzy "$sdk_tarball" >/dev/null)
+builds="${EXAMPLES_BUILDS-plugin minimal studio endless studio-zon replay dvui dvui-sdl3}"
+if [[ -n $builds ]]; then
+  for repo in example-app example-plugin; do
+    if [[ -n "${EXAMPLES_DIR:-}" ]]; then
+      mkdir -p "$work/$repo"
+      pack "$EXAMPLES_DIR/$repo" | tar -x -C "$work/$repo"
+    else
+      git clone --quiet --depth 1 "https://github.com/fizzyedit/$repo" "$work/$repo"
+    fi
   done
-)
+
+  (cd "$work/example-plugin" && zig fetch --save=fizzy "$sdk_tarball" >/dev/null)
+  # example-app bundles example-plugin (`hello`), pinned by URL: the copy here, on this tree's SDK.
+  pack "$work/example-plugin" | gzip > "$work/example-plugin.tar.gz"
+  (
+    cd "$work/example-app"
+    zig fetch --save=hello "$work/example-plugin.tar.gz" >/dev/null
+    zig fetch --save=fizzy "$work/fizzy.tar.gz" >/dev/null
+    # Its replay app depends on the plugin SDK alone: this tree's, packed as a release would be.
+    zig fetch --save=fizzy_sdk "$sdk_tarball" >/dev/null
+    # So do the plugins it carries, each pinning a released SDK of its own.
+    for plugin in plugins/*/; do
+      (cd "$plugin" && zig fetch --save=fizzy "$sdk_tarball" >/dev/null)
+    done
+  )
+fi
 
 # The plugin build installs the plugin: into a profile of its own, not this machine's fizzy.
 export FIZZY_PROFILE="$work/profile"
@@ -107,8 +112,6 @@ build_one() {
 }
 export -f build_args build_one
 
-builds="plugin minimal studio endless studio-zon replay dvui dvui-sdl3"
-
 # Each build is one compile of an app that mostly keeps one core busy, so they run side by side,
 # EXAMPLES_JOBS at once (3: CI's runner has 4 cores and 16 GB). First each configuration is
 # configured alone (`-l` lists its steps), which fetches the lazy dependencies it asks for, so
@@ -119,8 +122,10 @@ for b in $builds; do
   for a in "${args[@]:1}"; do [[ $a == -* ]] && opts+=("$a"); done
   (cd "$work/${args[0]}" && zig build -l ${opts[@]+"${opts[@]}"} > /dev/null)
 done
-echo "== example-plugin and example-app, against this tree"
-printf '%s\n' $builds | xargs -P "${EXAMPLES_JOBS:-3}" -n 1 bash -c 'build_one "$1"' _
+if [[ -n $builds ]]; then
+  echo "== example-plugin and example-app, against this tree"
+  printf '%s\n' $builds | xargs -P "${EXAMPLES_JOBS:-3}" -n 1 bash -c 'build_one "$1"' _
+fi
 
 # An app's list is exact: one naming none of fizzy's, workbench included, fails while build.zig
 # configures, which compiles nothing. The build must fail and say which plugin is missing.
@@ -138,3 +143,63 @@ if ! grep -q 'fizzy\.plugins\.workbench' "$work/log-app-only.txt"; then
   exit 1
 fi
 echo "ok    app-only (failed as expected)"
+
+# The build API an app and a plugin package call (`fizzy.framework`, `staticModule`, `addApp`,
+# `addWebSteps`, `addPackageSteps`; design/build-api.md), on a fixture app of its own: two plugin
+# packages, one for both kinds of executable and one `.native` only, which fails to compile if it
+# reaches the wasm.
+fixtures="scripts/fixtures/build-api"
+for id in fixture_both fixture_native; do
+  mkdir -p "$work/$id"
+  cp "$fixtures"/plugin/{build.zig,build.zig.zon,plugin.zig,lib.zig,lib.c} "$work/$id/"
+  sed "s/@ID@/$id/g" "$fixtures/plugin/plugin.zig.zon.tmpl" > "$work/$id/plugin.zig.zon"
+  (cd "$work/$id" && zig fetch --save=fizzy "$sdk_tarball" >/dev/null)
+done
+mkdir -p "$work/fixture-app"
+cp "$fixtures"/app/{build.zig,build.zig.zon} "$work/fixture-app/"
+(cd "$work/fixture-app" && zig fetch --save=fizzy "$work/fizzy.tar.gz" >/dev/null \
+  && zig build -l > /dev/null)
+
+echo "== build API fixture app"
+fixture_fail=0
+# step <label> <ok|fail|any> <expected text in the output> <zig build arguments…>
+step() {
+  local label=$1 want=$2 text=$3 got=0
+  shift 3
+  (cd "$work/fixture-app" && zig build "$@") > "$work/log-fixture.txt" 2>&1 || got=$?
+  if { [[ $want == ok && $got -eq 0 ]] || [[ $want == fail && $got -ne 0 ]] || [[ $want == any ]]; } \
+    && { [[ -z $text ]] || grep -q -- "$text" "$work/log-fixture.txt"; }; then
+    echo "ok    $label"
+  else
+    echo "FAIL  $label (wanted $want, exit $got, output containing '$text')"
+    tail -n 30 "$work/log-fixture.txt" | cut -c1-300 | sed "s/^/      /"
+    fixture_fail=1
+  fi
+}
+step "native executable, both plugins linked" ok "" --prefix "$work/out/fixture"
+# The step list holds what the API adds: `web`, and `package`, `desktop` and `packageall`.
+step "web, package and packageall steps added" ok "packageall" -l
+for name in web package desktop; do
+  grep -q "^  $name " "$work/log-fixture.txt" || { echo "FAIL  step '$name' missing"; fixture_fail=1; }
+done
+step "web build leaves the native-only plugin out" ok "" web --prefix "$work/out/fixture-web"
+[[ -f "$work/out/fixture-web/web/index.html" ]] \
+  || { echo "FAIL  addWebSteps installed no web/index.html"; fixture_fail=1; }
+# `package` runs vpk, which needs dotnet; `--verbose` prints its command line, `vpk-args` on it.
+# Whether vpk then packs the fixture is not the question, so the status is not read; the files of
+# `package-dirs` are staged into the pack input before vpk runs, and that is read from disk.
+if command -v dotnet > /dev/null; then
+  step "vpk-args reach vpk pack" any "--fixture-vpk-arg" package --verbose --prefix "$work/out/fixture-pkg"
+  staged=$(ls "$work"/out/fixture-pkg/*/.pack-input/fixture-helper.txt 2>/dev/null || true)
+  if [[ -n $staged && $(cat "$staged") == "beside the executable" ]]; then
+    echo "ok    package-dirs staged into the pack input"
+  else
+    echo "FAIL  package-dirs file missing from the pack input"
+    fixture_fail=1
+  fi
+else
+  echo "skip  vpk-args reach vpk pack, package-dirs staged (no dotnet)"
+fi
+step "a plugin listed twice is an error" fail "listed twice" -Dfixture-fail=twice
+step "an app's own web step is an error" fail "already has a \`web\` step" -Dfixture-fail=web-taken
+[[ $fixture_fail -eq 0 ]]
diff --git a/scripts/fixtures/build-api/app/build.zig b/scripts/fixtures/build-api/app/build.zig
new file mode 100644
index 000000000..736fc2c34
--- /dev/null
+++ b/scripts/fixtures/build-api/app/build.zig
@@ -0,0 +1,50 @@
+//! An application over fizzy's build API, for `scripts/check-examples.sh`: two plugin packages
+//! built with `fizzy.framework` (one for both kinds of executable, one native-only), the web and
+//! package steps, and the failures the API promises.
+//!
+//! `-Dfixture-fail=<case>` builds a list the API refuses: `twice` lists a plugin twice,
+//! `web-taken` has a `web` step already.
+const std = @import("std");
+const fizzy = @import("fizzy");
+const both = @import("fixture_both");
+const native = @import("fixture_native");
+
+pub fn build(b: *std.Build) !void {
+    const target = b.standardTargetOptions(.{});
+    const optimize = b.standardOptimizeOption(.{});
+    const fail = b.option([]const u8, "fixture-fail", "A case the API must refuse") orelse "";
+
+    // Files that go beside the executable in the pack input, and an argument for `vpk pack`.
+    const helpers = b.addWriteFiles();
+    _ = helpers.add("fixture-helper.txt", "beside the executable\n");
+
+    const fizzy_dep = b.dependency("fizzy", .{
+        .target = target,
+        .optimize = optimize,
+        .@"defer-app" = true,
+        .@"app-name" = @as([]const u8, "fixtureapp"),
+        .@"package-dirs" = &[_]std.Build.LazyPath{helpers.getDirectory()},
+        .@"vpk-args" = &[_][]const u8{ "--fixture-vpk-arg", "1" },
+    });
+    const both_dep = b.dependency("fixture_both", .{});
+    const native_dep = b.dependency("fixture_native", .{});
+
+    const list = [_]fizzy.BundledPlugin{
+        fizzy.plugins.workbench,
+        fizzy.plugins.text,
+        .{ .name = "fixture_both", .targets = &.{
+            .{ .target = .native, .module = both.staticModule(both_dep.builder, fizzy.framework(fizzy_dep, .native)) },
+            .{ .target = .web, .module = both.staticModule(both_dep.builder, fizzy.framework(fizzy_dep, .web)) },
+        } },
+        .{ .name = "fixture_native", .targets = &.{
+            .{ .target = .native, .module = native.staticModule(native_dep.builder, fizzy.framework(fizzy_dep, .native)) },
+        } },
+    };
+    const twice = list ++ [_]fizzy.BundledPlugin{list[2]};
+    const app = try fizzy.addApp(fizzy_dep, if (std.mem.eql(u8, fail, "twice")) &twice else &list);
+    b.installArtifact(app.exe);
+
+    if (std.mem.eql(u8, fail, "web-taken")) _ = b.step("web", "taken before the API's");
+    try fizzy.addWebSteps(b, fizzy_dep);
+    try fizzy.addPackageSteps(b, fizzy_dep);
+}
diff --git a/scripts/fixtures/build-api/app/build.zig.zon b/scripts/fixtures/build-api/app/build.zig.zon
new file mode 100644
index 000000000..eb5bf2540
--- /dev/null
+++ b/scripts/fixtures/build-api/app/build.zig.zon
@@ -0,0 +1,16 @@
+.{
+    .name = .fixture_app,
+    .version = "0.0.1",
+    .fingerprint = 0x915c21d842947814,
+    .minimum_zig_version = "0.17.0",
+    .paths = .{ "build.zig", "build.zig.zon" },
+    .dependencies = .{
+        // Replaced by `zig fetch --save=fizzy` with this tree.
+        .fizzy = .{
+            .url = "git+https://github.com/fizzyedit/fizzy#d99a7509032aea580d2db7a2eae5100bdb9b6afd",
+            .hash = "fizzy-0.2.0-c46aVltCpgC5UG61y5Nm4TH_52KKUl5xQHTS7SayqK3W",
+        },
+        .fixture_both = .{ .path = "../fixture_both" },
+        .fixture_native = .{ .path = "../fixture_native" },
+    },
+}
diff --git a/scripts/fixtures/build-api/plugin/build.zig b/scripts/fixtures/build-api/plugin/build.zig
new file mode 100644
index 000000000..62b27d0b3
--- /dev/null
+++ b/scripts/fixtures/build-api/plugin/build.zig
@@ -0,0 +1,24 @@
+//! A plugin package the way `fizzy.plugin.staticModule` documents it: the module is built against
+//! the framework the application's executables link, with a dependency of its own added.
+const std = @import("std");
+const fizzy = @import("fizzy");
+
+// anytype: the Framework of fizzy's build, a build-time duck type (pinned SDKs have their own type)
+pub fn staticModule(b: *std.Build, framework: anytype) *std.Build.Module {
+    const m = fizzy.plugin.staticModule(b, framework, .{});
+    const lib = b.createModule(.{
+        .root_source_file = b.path("lib.zig"),
+        .target = framework.target,
+        .optimize = framework.optimize,
+    });
+    lib.addCSourceFile(.{ .file = b.path("lib.c") });
+    m.addImport("fixture_lib", lib);
+    return m;
+}
+
+pub fn build(b: *std.Build) void {
+    const target = b.standardTargetOptions(.{});
+    const optimize = b.standardOptimizeOption(.{});
+    const plugin = fizzy.plugin.create(b, .{ .target = target, .optimize = optimize });
+    fizzy.plugin.install(b, plugin.lib, .{});
+}
diff --git a/scripts/fixtures/build-api/plugin/build.zig.zon b/scripts/fixtures/build-api/plugin/build.zig.zon
new file mode 100644
index 000000000..2644c0d58
--- /dev/null
+++ b/scripts/fixtures/build-api/plugin/build.zig.zon
@@ -0,0 +1,14 @@
+.{
+    .name = .fixture_plugin,
+    .version = "0.0.1",
+    .minimum_zig_version = "0.17.0",
+    .fingerprint = 0x9b70afac3d2d8bc6,
+    .paths = .{ "build.zig", "build.zig.zon", "plugin.zig", "plugin.zig.zon", "lib.zig", "lib.c" },
+    .dependencies = .{
+        // Replaced by `zig fetch --save=fizzy` with this tree's packed SDK.
+        .fizzy = .{
+            .url = "https://github.com/fizzyedit/fizzy/releases/download/sdk-v0.2.30/fizzy-sdk-v0.2.30.tar.gz",
+            .hash = "fizzy-0.2.30-SGBwY1QnJwDznUMVnSLATxXgH2e8_Vz7eMwLj9UQ0sVU",
+        },
+    },
+}
diff --git a/scripts/fixtures/build-api/plugin/lib.c b/scripts/fixtures/build-api/plugin/lib.c
new file mode 100644
index 000000000..87c510882
--- /dev/null
+++ b/scripts/fixtures/build-api/plugin/lib.c
@@ -0,0 +1,4 @@
+// Weak: both fixture packages link this file into one executable.
+__attribute__((weak)) int fixture_answer(void) {
+    return 42;
+}
diff --git a/scripts/fixtures/build-api/plugin/lib.zig b/scripts/fixtures/build-api/plugin/lib.zig
new file mode 100644
index 000000000..0b9956a00
--- /dev/null
+++ b/scripts/fixtures/build-api/plugin/lib.zig
@@ -0,0 +1,3 @@
+//! The fixture plugin's dependency of its own: Zig declaring a function that `lib.c` defines, so
+//! a lost import or a lost C source fails the plugin's compile or link.
+pub extern fn fixture_answer() c_int;
diff --git a/scripts/fixtures/build-api/plugin/plugin.zig b/scripts/fixtures/build-api/plugin/plugin.zig
new file mode 100644
index 000000000..3e578d97f
--- /dev/null
+++ b/scripts/fixtures/build-api/plugin/plugin.zig
@@ -0,0 +1,49 @@
+//! The build-API fixture plugin: one surface, built by `staticModule` for each kind of
+//! executable. `scripts/check-examples.sh` links it into `app/`.
+const std = @import("std");
+const builtin = @import("builtin");
+const sdk = @import("fizzy_sdk");
+const dvui = @import("dvui");
+const fixture_lib = @import("fixture_lib");
+
+pub const plugin_options = @import("fizzy_plugin_options");
+pub const plugin_id = plugin_options.id;
+
+// The native-only fixture is the same file under another id: a web build that links it
+// fails here, which is how the check sees a `.native` entry kept out of the wasm.
+comptime {
+    if (std.mem.eql(u8, plugin_options.id, "fixture_native") and
+        builtin.cpu.arch == .wasm32)
+    {
+        @compileError("a native-only plugin was linked into the web build");
+    }
+}
+
+// The host writes plugin lifecycle state on the main UI thread.
+var plugin: sdk.Plugin = .{
+    .state = undefined,
+    .vtable = &vtable,
+    .id = plugin_id,
+    .display_name = plugin_options.name,
+};
+
+const vtable: sdk.Plugin.VTable = .{};
+
+pub fn register(host: *sdk.Host) !void {
+    // Calls into the C source of the package's own dependency: it must have reached the link.
+    if (fixture_lib.fixture_answer() != 42) return error.FixtureDependency;
+    try host.registerPlugin(&plugin);
+    try host.registerSurface(.{
+        .id = plugin_id ++ ".surface",
+        .owner = &plugin,
+        .icon = .{ .tvg = dvui.entypo.emoji_happy },
+        .title = plugin_options.name,
+        .keywords = sdk.keywords.ide.sidebar,
+        .draw = draw,
+    });
+}
+
+fn draw(_: ?*anyopaque) !dvui.App.Result {
+    dvui.label(@src(), "{s}", .{plugin_id}, .{});
+    return .ok;
+}
diff --git a/scripts/fixtures/build-api/plugin/plugin.zig.zon.tmpl b/scripts/fixtures/build-api/plugin/plugin.zig.zon.tmpl
new file mode 100644
index 000000000..95c87698d
--- /dev/null
+++ b/scripts/fixtures/build-api/plugin/plugin.zig.zon.tmpl
@@ -0,0 +1,7 @@
+.{
+    .id = "@ID@",
+    .name = "@ID@",
+    .version = "0.0.1",
+    .min_sdk_version = "0.2.30",
+    .description = "A build-API fixture.",
+}