fix(iOS): opt spm_dependency pod targets out of Swift explicit modules

A pod target consuming an SPM binary target via spm_dependency sees the
binary target's module.modulemap twice: Xcode processes the xcframework
into both the platform-wide products dir and the pod's TARGET_BUILD_DIR,
and the existing SWIFT_INCLUDE_PATHS workaround makes the former visible.

Implicit modules tolerate the duplicate definition; the explicit-modules
dependency scanner (the default starting with Xcode 26) fails with
"redefinition of module". Before the VFS-overlay removal these targets
carried -ivfsoverlay, which disqualified them from explicit modules and
masked the problem; the overlay's removal made them eligible and the
nightly-tests react-native-enriched-markdown (RaTeX) job went red.

Set SWIFT_ENABLE_EXPLICIT_MODULES=NO on exactly the targets
spm_dependency touches, restoring the previous compile mode for the
CocoaPods+SPM interop path only.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

Author: chrfalch

packages/react-native/scripts/cocoapods/__tests__/spm-test.rb

@@ -97,4 +97,37 @@ def test_injected_uuids_are_unique_across_all_objects
     uuids = reopened.objects.map(&:uuid)
     assert_equal(uuids.length, uuids.uniq.length, "all object UUIDs must be unique")
   end
+
+  # A pod target consuming an SPM binary xcframework sees the product's
+  # module.modulemap twice (once in the global products dir — reachable via the
+  # SWIFT_INCLUDE_PATHS workaround — and once in its own TARGET_BUILD_DIR).
+  # Implicit modules tolerate the duplicate; the explicit-modules dependency
+  # scanner (Xcode 26 default) hard-errors with "redefinition of module".
+  # spm_dependency targets must therefore opt out of explicit modules.
+  def test_spm_targets_opt_out_of_swift_explicit_modules
+    project = build_project(3)
+    inject_spm(project)
+    target = project.targets.find { |t| t.name == POD_NAME }
+    target.build_configurations.each do |config|
+      assert_equal(
+        "NO",
+        target.build_settings(config.name)["SWIFT_ENABLE_EXPLICIT_MODULES"],
+        "SPM-consuming pod targets must disable Swift explicit modules " \
+        "(#{config.name}) — the duplicate binary-target modulemap trips the " \
+        "explicit-modules dependency scanner"
+      )
+    end
+  end
+
+  def test_non_spm_targets_keep_explicit_modules_untouched
+    project = build_project(3)
+    inject_spm(project)
+    other = project.targets.find { |t| t.name == "Pod0" }
+    other.build_configurations.each do |config|
+      assert_nil(
+        other.build_settings(config.name)["SWIFT_ENABLE_EXPLICIT_MODULES"],
+        "targets without SPM dependencies must not be touched (#{config.name})"
+      )
+    end
+  end
 end

packages/react-native/scripts/cocoapods/spm.rb

@@ -37,6 +37,14 @@ def apply_on_post_install(installer)
           unless target.build_settings(config.name)['SWIFT_INCLUDE_PATHS'].include?(search_path)
             target.build_settings(config.name)['SWIFT_INCLUDE_PATHS'].push(search_path)
           end
+          # The search path above makes the platform-wide products dir visible
+          # to this target, so an SPM binary target's module.modulemap is seen
+          # twice: once there and once in the target's own build dir (Xcode
+          # processes the xcframework into both). Implicit modules tolerate the
+          # duplicate, but the explicit-modules dependency scanner (the default
+          # starting with Xcode 26) fails with "redefinition of module". Opt
+          # SPM-consuming pod targets out of explicit modules.
+          target.build_settings(config.name)['SWIFT_ENABLE_EXPLICIT_MODULES'] = 'NO'
         end
       end
     end