diff --git a/.github/workflows/ci.yml b/.github/workflows/ci.yml
index 148e118..7a38b0e 100644
--- a/.github/workflows/ci.yml
+++ b/.github/workflows/ci.yml
@@ -8,10 +8,11 @@
 # would pressure people into editing code the repo deliberately keeps as
 # upstream's.
 #
-# Native code is not compiled here: these are watchOS FFI plugins, and every
-# test fakes the bindings through a `forTesting` constructor, so nothing needs
-# a Mac. Compiling the `.m` sources needs a watchOS SDK and belongs in the
-# per-package `example` build, run on a Mac by hand — see AUTHORING.md §3.
+# The package tests fake the native bindings through a `forTesting`
+# constructor, so they need no Mac. The `native` job compiles the native
+# sources on macOS with -fsyntax-only, the way the CLI builds them, on Xcode 26
+# and 27; running the code is still each package's `example` build on a Mac
+# (AUTHORING.md §3).
 name: CI
 
 on:
@@ -187,3 +188,53 @@ jobs:
         if: success() || failure()
         working-directory: tool
         run: dart run bin/check_test_names.dart
+
+  native:
+    # Spec 0022 D1 (#17): every plugin's .m, .mm, .c and SwiftUI view source,
+    # compiled the way the CLI compiles it, with -fsyntax-only, for a watch
+    # and for the Simulator. macos-26 runs the oldest Xcode 26 the CLI
+    # supports and its default; xcode-27 runs Xcode 27. A symbol one SDK lacks
+    # (CLActivityTypeMaritime in #12) fails here, not in an app's build.
+    name: native sources (${{ matrix.label }})
+    runs-on: ${{ matrix.runner }}
+    timeout-minutes: 20
+    strategy:
+      fail-fast: false
+      matrix:
+        include:
+          - label: Xcode 26
+            runner: macos-26
+            developer_dirs: >-
+              /Applications/Xcode_26.0.1.app/Contents/Developer
+              /Applications/Xcode_26.6.app/Contents/Developer
+          - label: Xcode 27
+            runner: xcode-27
+            developer_dirs: /Applications/Xcode_27.app/Contents/Developer
+    steps:
+      - uses: actions/checkout@v4
+
+      - name: Compile with each Xcode
+        env:
+          DEVELOPER_DIRS: ${{ matrix.developer_dirs }}
+        run: |
+          status=0
+          for developer_dir in $DEVELOPER_DIRS; do
+            if [ ! -d "$developer_dir" ]; then
+              echo "FAILED no Xcode at $developer_dir"
+              status=1
+              continue
+            fi
+            DEVELOPER_DIR="$developer_dir" tool/check_native_sources.sh || status=1
+          done
+          exit "$status"
+
+      # The check must be able to fail. Its fixtures hold an undeclared
+      # symbol and a warning, which fail, and a clean source with a
+      # deprecation, which passes.
+      - uses: dart-lang/setup-dart@v1
+
+      - name: Test the check
+        working-directory: tool
+        run: |
+          dart pub get
+          dart test test/check_native_sources_test.dart
diff --git a/tool/README.md b/tool/README.md
index 39802e7..e9a2c8a 100644
--- a/tool/README.md
+++ b/tool/README.md
@@ -18,6 +18,13 @@ tool/check_generated_ignored.sh
 (cd tool && dart run bin/publish_dry_run.dart)
 ```
 
+The `native` job of `ci.yml` runs one more on macOS, once per Xcode, as
+`DEVELOPER_DIR` picks it. It needs Xcode, so the Ubuntu jobs leave it out:
+
+```sh
+tool/check_native_sources.sh
+```
+
 The weekly workflow `.github/workflows/upstream.yml` runs two more, which
 read pub.dev and so are not part of the per-change checks:
 
@@ -108,6 +115,22 @@ runs it in the package job, after the tests. Its report goes into a public
 log, so a line of pub's output that holds a forbidden word is withheld and
 fails the package.
 
+## Native sources
+
+`check_native_sources.sh` compiles every plugin's native watchOS sources the way
+the CLI does, with `-fsyntax-only`, for `arm64-apple-watchos26.0` and its
+Simulator triple:
+- `.m`, `.mm` and `.c` files go through clang, with the CLI's flags;
+- SwiftUI view sources go through `swiftc -typecheck`, with a copy of the
+  CLI's registration shim (`native/plugin_views_shim.swift`).
+
+An error or a warning fails, except a deprecation, which is counted.
+in_app_purchase_watchos uses StoreKit 1 on purpose. A package whose
+`watchos/Package.swift` names a SwiftPM package is listed and skipped, as only
+a SwiftPM build provides its modules. `--list` prints the plan without
+compiling, and the Ubuntu tool tests run it on fixtures. The compile fixtures
+run on macOS, in the `native` job.
+
 ## Weekly upstream compatibility
 
 `.github/workflows/upstream.yml` runs every Monday and by hand, and never
diff --git a/tool/check_native_sources.sh b/tool/check_native_sources.sh
new file mode 100755
index 0000000..88995ab
--- /dev/null
+++ b/tool/check_native_sources.sh
@@ -0,0 +1,159 @@
+#!/usr/bin/env bash
+# Copyright 2026 The FlutterWatch Authors. All rights reserved.
+# Use of this source code is governed by a BSD-style license that can be
+# found in the LICENSE file.
+#
+# Compiles every plugin's native watchOS sources the way flutter-watchos does,
+# with -fsyntax-only, for a watch and for the Simulator, with the Xcode that
+# DEVELOPER_DIR (or xcode-select) picks. CI runs it with the oldest Xcode 26
+# the CLI supports, the newest Xcode 26 and Xcode 27, so a symbol that one
+# SDK lacks fails here and not in an app's build (spec 0022 D1, #17).
+#
+# - Objective-C and C sources (.m, .mm, .c) go through clang with the CLI's
+#   flags (lib/build_targets/application.dart in flutter-watchos 0.1.1).
+# - SwiftUI view sources (.swift under watchos/, except Package.swift and
+#   anything under Flutter/ or a dot-directory) go through swiftc -typecheck,
+#   one module per plugin, with the CLI's registration shim
+#   (tool/native/plugin_views_shim.swift).
+# - A plugin whose watchos/Package.swift names a SwiftPM package is skipped
+#   and listed: its sources import that package's modules, which only a
+#   SwiftPM build provides, and the CLI builds such a plugin with xcodebuild.
+#
+# Only git-tracked files are read. A warning fails like an error, as in the
+# CLI's own host typecheck, except a deprecation: those are counted and left
+# to the package (in_app_purchase_watchos uses StoreKit 1 on purpose).
+#
+# Usage: tool/check_native_sources.sh [--root <repository>] [--list]
+#   --list  prints what would be compiled and runs nothing; no Xcode needed.
+set -euo pipefail
+
+# The deployment target `flutter-watchos create` writes.
+readonly deployment_target="26.0"
+readonly targets="watchos:arm64-apple-watchos${deployment_target} watchsimulator:arm64-apple-watchos${deployment_target}-simulator"
+
+root=""
+list=0
+while [ $# -gt 0 ]; do
+  case "$1" in
+    --root) [ $# -ge 2 ] || { echo "--root needs a value" >&2; exit 2; }; root="$2"; shift 2 ;;
+    --list) list=1; shift ;;
+    *) echo "usage: $0 [--root <repository>] [--list]" >&2; exit 2 ;;
+  esac
+done
+if [ -z "$root" ]; then
+  root="$(git rev-parse --show-toplevel)"
+fi
+shim="$(cd "$(dirname "$0")" && pwd)/native/plugin_views_shim.swift"
+cd "$root"
+
+# The tracked files under each package's own watchos/ directory. In a
+# pathspec `*` also crosses `/`, so the pattern alone would take in each
+# example's watchos/ app too; the grep keeps the package's.
+tracked="$(git ls-files -- 'packages/*/watchos/*' | grep -E '^packages/[^/]+/watchos/' || true)"
+
+# Every directory that holds a tracked header: the CLI passes each one to
+# every plugin's compile.
+includes=()
+for dir in $(printf '%s\n' "$tracked" | grep '\.h$' | xargs -n1 dirname | sort -u); do
+  includes+=("-I$dir")
+done
+
+# True for a view source: not the manifest, and nothing under Flutter/ or a
+# dot-directory (CLI build output and SwiftPM state).
+is_view_source() {
+  local relative="${1#*/watchos/}"
+  case "$relative" in
+    Package.swift | Flutter/* | */Flutter/* | .* | */.*) return 1 ;;
+    *.swift) return 0 ;;
+    *) return 1 ;;
+  esac
+}
+
+# Prints the warnings in [1] that are not deprecations.
+other_warnings() {
+  grep 'warning:' <<< "$1" | grep -v -e 'is deprecated' -e 'was deprecated' || true
+}
+
+# Reports one compile: [1] its name, [2] its exit code, [3] its output.
+report() {
+  local deprecations
+  deprecations="$(grep -c 'warning:.*deprecated' <<< "$3" || true)"
+  if [ "$2" -eq 0 ] && [ -z "$(other_warnings "$3")" ]; then
+    if [ "$deprecations" -gt 0 ]; then
+      echo "ok     $xcode  $triple  $1  ($deprecations deprecation warning$([ "$deprecations" -eq 1 ] || echo s))"
+    else
+      echo "ok     $xcode  $triple  $1"
+    fi
+  else
+    echo "FAILED $xcode  $triple  $1"
+    echo "$3"
+    status=1
+  fi
+}
+
+xcode=""
+if [ "$list" -eq 0 ]; then
+  # sed, not head: head would close the pipe early, and pipefail would end
+  # the script on xcodebuild's SIGPIPE.
+  xcode="$(xcodebuild -version | sed -n 1p)"
+fi
+
+status=0
+checked=0
+for package_dir in $(printf '%s\n' "$tracked" | cut -d/ -f1-2 | sort -u); do
+  package="${package_dir#packages/}"
+  manifest="$package_dir/watchos/Package.swift"
+  if [ -f "$manifest" ] && grep -q '\.package(' "$manifest"; then
+    echo "skip   $package: its watchos/Package.swift names a SwiftPM package, which only a SwiftPM build provides"
+    continue
+  fi
+  c_sources=()
+  view_sources=()
+  for file in $(printf '%s\n' "$tracked" | grep "^$package_dir/"); do
+    case "$file" in
+      *.m | *.mm | *.c) c_sources+=("$file") ;;
+      *) if is_view_source "$file"; then view_sources+=("$file"); fi ;;
+    esac
+  done
+  for target in $targets; do
+    sdk="${target%%:*}"
+    triple="${target#*:}"
+    for source in ${c_sources[@]+"${c_sources[@]}"}; do
+      checked=$((checked + 1))
+      if [ "$list" -eq 1 ]; then
+        echo "plan   clang   $sdk $triple $source"
+        continue
+      fi
+      code=0
+      output="$(xcrun -sdk "$sdk" clang -fsyntax-only -target "$triple" \
+          -fobjc-arc -fmodules ${includes[@]+"${includes[@]}"} "$source" 2>&1)" || code=$?
+      report "$source" "$code" "$output"
+    done
+    if [ ${#view_sources[@]} -gt 0 ]; then
+      checked=$((checked + 1))
+      if [ "$list" -eq 1 ]; then
+        echo "plan   swiftc  $sdk $triple ${package}_views: ${view_sources[*]}"
+        continue
+      fi
+      code=0
+      output="$(xcrun -sdk "$sdk" swiftc -typecheck -target "$triple" \
+          -parse-as-library -module-name "${package}_views" \
+          "$shim" "${view_sources[@]}" 2>&1)" || code=$?
+      report "${package}_views" "$code" "$output"
+    fi
+  done
+done
+
+if [ "$checked" -eq 0 ]; then
+  echo "No native source found under packages/*/watchos/."
+  exit 1
+fi
+if [ "$list" -eq 1 ]; then
+  echo "include ${includes[*]+"${includes[*]}"}"
+  exit 0
+fi
+if [ "$status" -ne 0 ]; then
+  echo "Native sources: some do not compile cleanly with $xcode."
+  exit 1
+fi
+echo "Native sources: all compile cleanly with $xcode."
diff --git a/tool/native/plugin_views_shim.swift b/tool/native/plugin_views_shim.swift
new file mode 100644
index 0000000..14df696
--- /dev/null
+++ b/tool/native/plugin_views_shim.swift
@@ -0,0 +1,79 @@
+// A copy of the registration shim flutter-watchos compiles into every plugin
+// module with SwiftUI view sources (kPluginViewSupportSwift in the CLI's
+// lib/build_targets/watchos_plugin_views.dart, CLI 0.1.1). It is here only so
+// tool/check_native_sources.sh can type-check plugin view sources the way the
+// CLI compiles them. Update it with the CLI. Not part of any plugin.
+//
+// Compiled by flutter-watchos into every plugin module that ships SwiftUI
+// view sources. Not part of the plugin — do not copy it into one.
+//
+// Gives plugin code `FlutterWatchOSPluginViews.register(_:factory:)`, the
+// Swift face of the app runner's C registration entry point.
+
+import Darwin
+import Foundation
+import SwiftUI
+
+private let _factoriesLock = NSLock()
+private var _factories: [String: (String) -> AnyView] = [:]
+
+/// The @convention(c) trampoline handed to the runner, once per registered
+/// type. Receives (viewType, creationParams); returns the built AnyView
+/// RETAINED, boxed by the Swift runtime (`as AnyObject` — SwiftUI hard-rejects
+/// class-conforming Views, so the view itself must stay a struct and the
+/// runtime box is the only class in the crossing). The runner unwraps it with
+/// a plain dynamic cast, since AnyView is SwiftUI's own type on both sides.
+/// nil means no factory — render nothing.
+private let _factoryTrampoline: @convention(c) (
+    UnsafePointer<CChar>?, UnsafePointer<CChar>?
+) -> UnsafeMutableRawPointer? = { type, params in
+    guard let type else { return nil }
+    let viewType = String(cString: type)
+    let creationParams = params.map { String(cString: $0) } ?? ""
+    _factoriesLock.lock()
+    let factory = _factories[viewType]
+    _factoriesLock.unlock()
+    guard let factory else { return nil }
+    return Unmanaged.passRetained(factory(creationParams) as AnyObject).toOpaque()
+}
+
+/// Registration surface for a plugin's native SwiftUI views.
+public enum FlutterWatchOSPluginViews {
+    private typealias _Register = @convention(c) (
+        UnsafePointer<CChar>?,
+        (@convention(c) (
+            UnsafePointer<CChar>?, UnsafePointer<CChar>?
+        ) -> UnsafeMutableRawPointer?)?
+    ) -> Void
+
+    /// The runner's registration entry point, resolved via dlsym
+    /// (RTLD_DEFAULT is the special -2 handle) so nothing links against the
+    /// app at compile time. nil when the app was created by a CLI that
+    /// predates plugin platform views.
+    private static let _register: _Register? = {
+        guard let sym = dlsym(
+            UnsafeMutableRawPointer(bitPattern: -2),
+            "FlutterWatchOSPlatformViewRegisterNativeFactory")
+        else { return nil }
+        return unsafeBitCast(sym, to: _Register.self)
+    }()
+
+    /// Registers (or replaces) the native factory for `viewType`. The factory
+    /// receives the Dart widget's `creationParams` string and always runs on
+    /// the main thread; `register` itself may be called from any thread
+    /// (plugin registration typically arrives over FFI from Dart).
+    public static func register(
+        _ viewType: String, factory: @escaping (String) -> AnyView
+    ) {
+        _factoriesLock.lock()
+        _factories[viewType] = factory
+        _factoriesLock.unlock()
+        guard let register = _register else {
+            NSLog("FlutterWatchOSPluginViews: this app's runner predates "
+                + "plugin platform views; '\(viewType)' will not render. "
+                + "Re-create the app with a current flutter-watchos.")
+            return
+        }
+        viewType.withCString { register($0, _factoryTrampoline) }
+    }
+}
diff --git a/tool/test/check_native_sources_test.dart b/tool/test/check_native_sources_test.dart
new file mode 100644
index 0000000..36a7f10
--- /dev/null
+++ b/tool/test/check_native_sources_test.dart
@@ -0,0 +1,94 @@
+// Copyright 2026 The FlutterWatch Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+// tool/check_native_sources.sh on its fixtures, in
+// tool/test/fixtures/check_native_sources/. `--list` runs anywhere, so the
+// plan fixtures run on every machine. The compile fixtures need Xcode, so
+// they run on macOS only: the CI job that compiles the native sources runs
+// this file there.
+
+import 'dart:io';
+
+import 'package:path/path.dart' as p;
+import 'package:test/test.dart';
+
+import 'src/fixture_repo.dart';
+
+void main() {
+  final String script = p.absolute('check_native_sources.sh');
+  final List<Fixture> fixtures = fixturesIn(
+    p.join('test', 'fixtures', 'check_native_sources'),
+  );
+
+  /// Runs the script on [fixture]'s repository, with [arguments].
+  ProcessResult run(Fixture fixture, List<String> arguments) {
+    final String root = fixture.createRepository();
+    addTearDown(() => Directory(root).deleteSync(recursive: true));
+    return Process.runSync('bash', <String>[
+      script,
+      '--root',
+      root,
+      ...arguments,
+    ]);
+  }
+
+  /// Checks [result] against [fixture]'s `expect` file.
+  void expectFixture(Fixture fixture, ProcessResult result) {
+    final String output = '${result.stdout}${result.stderr}';
+    expect(result.exitCode, fixture.expectedExitCode, reason: output);
+    for (final String line in fixture.expectedOutput) {
+      expect(output, contains(line));
+    }
+  }
+
+  Fixture named(String name) =>
+      fixtures.singleWhere((Fixture f) => f.name == name);
+
+  group('--list', () {
+    test('plans what the CLI compiles, and nothing else', () {
+      final Fixture fixture = named('plan');
+      final ProcessResult result = run(fixture, <String>['--list']);
+      expectFixture(fixture, result);
+      final String output = '${result.stdout}';
+      expect(output, isNot(contains('scratch.m')), reason: 'untracked');
+      expect(
+        output,
+        isNot(contains('Flutter/Generated.swift')),
+        reason: 'CLI build output',
+      );
+      expect(
+        output,
+        isNot(contains('example/watchos')),
+        reason: "the example's app",
+      );
+      expect(
+        output,
+        isNot(contains('b_watchos_ffi.m')),
+        reason: 'a SwiftPM-dependency package is skipped',
+      );
+    });
+
+    test('a repository with no native source fails', () {
+      final Fixture fixture = named('no_sources');
+      expectFixture(fixture, run(fixture, <String>['--list']));
+    });
+  });
+
+  group('compiles', () {
+    test('a clean source passes, and a deprecation is counted', () {
+      final Fixture fixture = named('compile_clean');
+      expectFixture(fixture, run(fixture, <String>[]));
+    });
+
+    test('an undeclared symbol fails', () {
+      final Fixture fixture = named('compile_undeclared');
+      expectFixture(fixture, run(fixture, <String>[]));
+    });
+
+    test('a warning that is not a deprecation fails', () {
+      final Fixture fixture = named('compile_warning');
+      expectFixture(fixture, run(fixture, <String>[]));
+    });
+  }, skip: Platform.isMacOS ? false : 'needs Xcode');
+}
diff --git a/tool/test/fixtures/check_native_sources/compile_clean/expect b/tool/test/fixtures/check_native_sources/compile_clean/expect
new file mode 100644
index 0000000..a3648fe
--- /dev/null
+++ b/tool/test/fixtures/check_native_sources/compile_clean/expect
@@ -0,0 +1,4 @@
+0
+packages/ok_watchos/watchos/Classes/ok_watchos_ffi.m  (1 deprecation warning)
+ok_watchos_views
+Native sources: all compile cleanly with
diff --git a/tool/test/fixtures/check_native_sources/compile_clean/repo/packages/ok_watchos/watchos/Classes/ok_watchos_ffi.m b/tool/test/fixtures/check_native_sources/compile_clean/repo/packages/ok_watchos/watchos/Classes/ok_watchos_ffi.m
new file mode 100644
index 0000000..c9e7139
--- /dev/null
+++ b/tool/test/fixtures/check_native_sources/compile_clean/repo/packages/ok_watchos/watchos/Classes/ok_watchos_ffi.m
@@ -0,0 +1,7 @@
+#import <Foundation/Foundation.h>
+
+__attribute__((deprecated("a newer call replaces it"))) static int ok_watchos_old_value(void) {
+  return 1;
+}
+
+int ok_watchos_value(void) { return ok_watchos_old_value(); }
diff --git a/tool/test/fixtures/check_native_sources/compile_clean/repo/packages/ok_watchos/watchos/Views/ok_watchos_views.swift b/tool/test/fixtures/check_native_sources/compile_clean/repo/packages/ok_watchos/watchos/Views/ok_watchos_views.swift
new file mode 100644
index 0000000..6ce3077
--- /dev/null
+++ b/tool/test/fixtures/check_native_sources/compile_clean/repo/packages/ok_watchos/watchos/Views/ok_watchos_views.swift
@@ -0,0 +1,8 @@
+import SwiftUI
+
+@_cdecl("ok_watchos_register_views")
+public func okWatchosRegisterViews() {
+    FlutterWatchOSPluginViews.register("ok_watchos") { params in
+        AnyView(Text(params))
+    }
+}
diff --git a/tool/test/fixtures/check_native_sources/compile_undeclared/expect b/tool/test/fixtures/check_native_sources/compile_undeclared/expect
new file mode 100644
index 0000000..03b7c03
--- /dev/null
+++ b/tool/test/fixtures/check_native_sources/compile_undeclared/expect
@@ -0,0 +1,4 @@
+1
+FAILED
+use of undeclared identifier 'bad_watchos_undeclared'
+Native sources: some do not compile cleanly with
diff --git a/tool/test/fixtures/check_native_sources/compile_undeclared/repo/packages/bad_watchos/watchos/Classes/bad_watchos_ffi.m b/tool/test/fixtures/check_native_sources/compile_undeclared/repo/packages/bad_watchos/watchos/Classes/bad_watchos_ffi.m
new file mode 100644
index 0000000..7910342
--- /dev/null
+++ b/tool/test/fixtures/check_native_sources/compile_undeclared/repo/packages/bad_watchos/watchos/Classes/bad_watchos_ffi.m
@@ -0,0 +1 @@
+int bad_watchos_value(void) { return bad_watchos_undeclared; }
diff --git a/tool/test/fixtures/check_native_sources/compile_warning/expect b/tool/test/fixtures/check_native_sources/compile_warning/expect
new file mode 100644
index 0000000..dc802f6
--- /dev/null
+++ b/tool/test/fixtures/check_native_sources/compile_warning/expect
@@ -0,0 +1,3 @@
+1
+FAILED
+implicit conversion from
diff --git a/tool/test/fixtures/check_native_sources/compile_warning/repo/packages/warn_watchos/watchos/Classes/warn_watchos_ffi.m b/tool/test/fixtures/check_native_sources/compile_warning/repo/packages/warn_watchos/watchos/Classes/warn_watchos_ffi.m
new file mode 100644
index 0000000..30bf883
--- /dev/null
+++ b/tool/test/fixtures/check_native_sources/compile_warning/repo/packages/warn_watchos/watchos/Classes/warn_watchos_ffi.m
@@ -0,0 +1,4 @@
+int warn_watchos_value(void) {
+  int truncated = 1.5;
+  return truncated;
+}
diff --git a/tool/test/fixtures/check_native_sources/no_sources/expect b/tool/test/fixtures/check_native_sources/no_sources/expect
new file mode 100644
index 0000000..7a6ef1d
--- /dev/null
+++ b/tool/test/fixtures/check_native_sources/no_sources/expect
@@ -0,0 +1,2 @@
+1
+No native source found under packages/*/watchos/.
diff --git a/tool/test/fixtures/check_native_sources/no_sources/repo/packages/d_watchos/lib/d_watchos.dart b/tool/test/fixtures/check_native_sources/no_sources/repo/packages/d_watchos/lib/d_watchos.dart
new file mode 100644
index 0000000..316a905
--- /dev/null
+++ b/tool/test/fixtures/check_native_sources/no_sources/repo/packages/d_watchos/lib/d_watchos.dart
@@ -0,0 +1 @@
+library;
diff --git a/tool/test/fixtures/check_native_sources/plan/expect b/tool/test/fixtures/check_native_sources/plan/expect
new file mode 100644
index 0000000..f8ac29c
--- /dev/null
+++ b/tool/test/fixtures/check_native_sources/plan/expect
@@ -0,0 +1,8 @@
+0
+plan   clang   watchos arm64-apple-watchos26.0 packages/a_watchos/watchos/Classes/a_watchos_ffi.m
+plan   clang   watchsimulator arm64-apple-watchos26.0-simulator packages/a_watchos/watchos/Classes/a_watchos_ffi.m
+skip   b_watchos: its watchos/Package.swift names a SwiftPM package, which only a SwiftPM build provides
+plan   clang   watchos arm64-apple-watchos26.0 packages/c_watchos/watchos/Classes/c_watchos.c
+plan   swiftc  watchos arm64-apple-watchos26.0 c_watchos_views: packages/c_watchos/watchos/Views/c_watchos_views.swift
+plan   swiftc  watchsimulator arm64-apple-watchos26.0-simulator c_watchos_views: packages/c_watchos/watchos/Views/c_watchos_views.swift
+include -Ipackages/a_watchos/watchos/Classes
diff --git a/tool/test/fixtures/check_native_sources/plan/repo/packages/a_watchos/watchos/Classes/a_watchos_ffi.h b/tool/test/fixtures/check_native_sources/plan/repo/packages/a_watchos/watchos/Classes/a_watchos_ffi.h
new file mode 100644
index 0000000..7a2b192
--- /dev/null
+++ b/tool/test/fixtures/check_native_sources/plan/repo/packages/a_watchos/watchos/Classes/a_watchos_ffi.h
@@ -0,0 +1 @@
+void a_watchos_value(void);
diff --git a/tool/test/fixtures/check_native_sources/plan/repo/packages/a_watchos/watchos/Classes/a_watchos_ffi.m b/tool/test/fixtures/check_native_sources/plan/repo/packages/a_watchos/watchos/Classes/a_watchos_ffi.m
new file mode 100644
index 0000000..a944f6b
--- /dev/null
+++ b/tool/test/fixtures/check_native_sources/plan/repo/packages/a_watchos/watchos/Classes/a_watchos_ffi.m
@@ -0,0 +1,3 @@
+#import "a_watchos_ffi.h"
+
+void a_watchos_value(void) {}
diff --git a/tool/test/fixtures/check_native_sources/plan/repo/packages/a_watchos/watchos/Package.swift b/tool/test/fixtures/check_native_sources/plan/repo/packages/a_watchos/watchos/Package.swift
new file mode 100644
index 0000000..72a57a0
--- /dev/null
+++ b/tool/test/fixtures/check_native_sources/plan/repo/packages/a_watchos/watchos/Package.swift
@@ -0,0 +1,7 @@
+// swift-tools-version: 5.9
+import PackageDescription
+
+let package = Package(
+    name: "a_watchos",
+    targets: [.target(name: "a_watchos", path: "Classes")]
+)
diff --git a/tool/test/fixtures/check_native_sources/plan/repo/packages/b_watchos/watchos/Classes/b_watchos_ffi.m b/tool/test/fixtures/check_native_sources/plan/repo/packages/b_watchos/watchos/Classes/b_watchos_ffi.m
new file mode 100644
index 0000000..eeff7e8
--- /dev/null
+++ b/tool/test/fixtures/check_native_sources/plan/repo/packages/b_watchos/watchos/Classes/b_watchos_ffi.m
@@ -0,0 +1 @@
+void b_watchos_value(void) {}
diff --git a/tool/test/fixtures/check_native_sources/plan/repo/packages/b_watchos/watchos/Package.swift b/tool/test/fixtures/check_native_sources/plan/repo/packages/b_watchos/watchos/Package.swift
new file mode 100644
index 0000000..3dc4b9d
--- /dev/null
+++ b/tool/test/fixtures/check_native_sources/plan/repo/packages/b_watchos/watchos/Package.swift
@@ -0,0 +1,8 @@
+// swift-tools-version: 5.9
+import PackageDescription
+
+let package = Package(
+    name: "b_watchos",
+    dependencies: [.package(url: "https://example.com/sdk.git", from: "1.0.0")],
+    targets: [.target(name: "b_watchos", path: "Classes")]
+)
diff --git a/tool/test/fixtures/check_native_sources/plan/repo/packages/c_watchos/example/watchos/Runner/App.swift b/tool/test/fixtures/check_native_sources/plan/repo/packages/c_watchos/example/watchos/Runner/App.swift
new file mode 100644
index 0000000..e6c6d46
--- /dev/null
+++ b/tool/test/fixtures/check_native_sources/plan/repo/packages/c_watchos/example/watchos/Runner/App.swift
@@ -0,0 +1 @@
+import SwiftUI
diff --git a/tool/test/fixtures/check_native_sources/plan/repo/packages/c_watchos/watchos/Classes/c_watchos.c b/tool/test/fixtures/check_native_sources/plan/repo/packages/c_watchos/watchos/Classes/c_watchos.c
new file mode 100644
index 0000000..9320441
--- /dev/null
+++ b/tool/test/fixtures/check_native_sources/plan/repo/packages/c_watchos/watchos/Classes/c_watchos.c
@@ -0,0 +1 @@
+int c_watchos_value(void) { return 1; }
diff --git a/tool/test/fixtures/check_native_sources/plan/repo/packages/c_watchos/watchos/Flutter/Generated.swift b/tool/test/fixtures/check_native_sources/plan/repo/packages/c_watchos/watchos/Flutter/Generated.swift
new file mode 100644
index 0000000..e6a31cc
--- /dev/null
+++ b/tool/test/fixtures/check_native_sources/plan/repo/packages/c_watchos/watchos/Flutter/Generated.swift
@@ -0,0 +1 @@
+// Build output the CLI writes; not a view source.
diff --git a/tool/test/fixtures/check_native_sources/plan/repo/packages/c_watchos/watchos/Views/c_watchos_views.swift b/tool/test/fixtures/check_native_sources/plan/repo/packages/c_watchos/watchos/Views/c_watchos_views.swift
new file mode 100644
index 0000000..e6c6d46
--- /dev/null
+++ b/tool/test/fixtures/check_native_sources/plan/repo/packages/c_watchos/watchos/Views/c_watchos_views.swift
@@ -0,0 +1 @@
+import SwiftUI
diff --git a/tool/test/fixtures/check_native_sources/plan/untracked/packages/a_watchos/watchos/Classes/scratch.m b/tool/test/fixtures/check_native_sources/plan/untracked/packages/a_watchos/watchos/Classes/scratch.m
new file mode 100644
index 0000000..3f6bfcc
--- /dev/null
+++ b/tool/test/fixtures/check_native_sources/plan/untracked/packages/a_watchos/watchos/Classes/scratch.m
@@ -0,0 +1 @@
+void scratch(void) {}