SwiftPM: stop baking an absolute HERMES_CLI_PATH into the app pbxproj

`spm add` wrote the machine-specific absolute path of hermesc from the
hermes-compiler npm package into every build configuration, and apps
commit that pbxproj. react-native-xcode.sh already resolves hermesc at
build time through react-native's dependency graph, so drop the write.

Widen the shell fallback correctly: it was gated on PODS_ROOT being
absent, so a SwiftPM app keeping side-by-side non-RN pods never reached
it. Key it on the hermes-engine pod directory instead, so any app that
has the pod keeps its previous behavior exactly.

Existing injected projects clean up on the next `spm add`/`update`,
which strips every recorded scalar before re-injecting.

Co-Authored-By: Claude Fable 5.1 <noreply@anthropic.com>

Author: chrfalch

packages/react-native/scripts/react-native-xcode.sh

@@ -80,18 +80,18 @@ source "$REACT_NATIVE_DIR/scripts/node-binary.sh"
 HERMES_ENGINE_PATH="$PODS_ROOT/hermes-engine"
 [ -z "$HERMES_CLI_PATH" ] && HERMES_CLI_PATH="$HERMES_ENGINE_PATH/destroot/bin/hermesc"
 
-# SwiftPM consumers have no Pods directory to provide hermesc. When there is
-# no Pods installation at all and the current HERMES_CLI_PATH does not exist
-# (unset, or an injector-baked path gone stale after a package-store move),
-# resolve the hermes-compiler npm package THROUGH react-native's own dependency
-# graph — react-native pins the hermes-compiler version, so the compiler's
-# bytecode version always matches the prebuilt hermes VM artifacts (a
-# mismatched pair crashes at launch with "Wrong bytecode version").
-# STRICTLY SwiftPM-scoped: in a CocoaPods build the hermes-engine pod owns both
-# the VM and hermesc, and its hermes train may legitimately differ from the npm
-# hermes-compiler — falling back there would compile bundles the podded VM
-# rejects.
-if [[ ( -z "$PODS_ROOT" || ! -d "$PODS_ROOT" ) && ! -f "$HERMES_CLI_PATH" ]]; then
+# SwiftPM consumers have no hermes-engine pod to provide hermesc, so resolve the
+# hermes-compiler npm package THROUGH react-native's own dependency graph —
+# react-native pins the hermes-compiler version, so the compiler's bytecode
+# version always matches the prebuilt hermes VM artifacts (a mismatched pair
+# crashes at launch with "Wrong bytecode version").
+# Fires only when Hermes is on, no hermes-engine pod is installed, and the
+# resolved path is not a file. Keyed on the pod DIRECTORY, not on PODS_ROOT: a
+# SwiftPM app may keep side-by-side non-RN pods, giving it a real PODS_ROOT.
+# Any app that does have the pod keeps its previous behavior exactly — including
+# a partial prebuild, where the missing hermesc must stay a build failure rather
+# than compile a bundle the podded VM rejects.
+if [[ "$USE_HERMES" != false && ! -d "$HERMES_ENGINE_PATH" && ! -f "$HERMES_CLI_PATH" ]]; then
   NODE_HERMESC=$(RN_DIR="$REACT_NATIVE_DIR" "$NODE_BINARY" --print \
     "require('path').join(require('path').dirname(require.resolve('hermes-compiler/package.json', {paths: [process.env.RN_DIR]})), 'hermesc', 'osx-bin', 'hermesc')" \
     2>/dev/null || true)