CI: build only the slices a caller needs in the prebuild-ios workflows

Add an optional `slices` input to prebuild-ios-dependencies.yml and
prebuild-ios-core.yml, driving their build matrix from it. It defaults
to the full platform set, so existing callers (test-all.yml, releases)
are unchanged.

The three SwiftPM iOS e2e workflows only ever compile for the iOS
simulator, so they now request `["ios-simulator"]` from both prebuild
workflows — cutting the dependencies matrix from 8 slices to 1 and the
core matrix from 3 to 1 (per flavor), which is the dominant cost of
those e2e runs.

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

Author: chrfalch

.github/workflows/prebuild-ios-core.yml

@@ -13,6 +13,11 @@ on:
         type: boolean
         required: false
         default: false
+      slices:
+        description: 'JSON array of Apple platform slices to build. Defaults to the full set; callers that only consume a subset (e.g. a simulator-only e2e build) can pass fewer to save time.'
+        type: string
+        required: false
+        default: '["ios", "ios-simulator", "mac-catalyst"]'
 
 jobs:
   build-rn-slice:
@@ -21,7 +26,7 @@ jobs:
       fail-fast: false
       matrix:
         flavor: ['Debug', 'Release']
-        slice: ['ios', 'ios-simulator', 'mac-catalyst']
+        slice: ${{ fromJSON(inputs.slices) }}
     steps:
       - name: Checkout
         uses: actions/checkout@v6

.github/workflows/prebuild-ios-dependencies.yml

@@ -2,6 +2,12 @@ name: Prebuild iOS Dependencies
 
 on:
   workflow_call: # this directive allow us to call this workflow from other workflows
+    inputs:
+      slices:
+        description: 'JSON array of Apple platform slices to build. Defaults to the full set; callers that only consume a subset (e.g. a simulator-only e2e build) can pass fewer to save time.'
+        type: string
+        required: false
+        default: '["ios", "ios-simulator", "macos", "mac-catalyst", "tvos", "tvos-simulator", "xros", "xros-simulator"]'
 
 jobs:
   prepare_workspace:
@@ -51,17 +57,7 @@ jobs:
       fail-fast: false
       matrix:
         flavor: ['Debug', 'Release']
-        slice:
-          [
-            'ios',
-            'ios-simulator',
-            'macos',
-            'mac-catalyst',
-            'tvos',
-            'tvos-simulator',
-            'xros',
-            'xros-simulator',
-          ]
+        slice: ${{ fromJSON(inputs.slices) }}
     steps:
       - name: Checkout
         uses: actions/checkout@v6

.github/workflows/test-ios-spm-helloworld.yml

@@ -21,6 +21,9 @@ on:
 jobs:
   prebuild_apple_dependencies:
     uses: ./.github/workflows/prebuild-ios-dependencies.yml
+    with:
+      # e2e only compiles for the iOS simulator — no need for device/catalyst/tv/xr slices.
+      slices: '["ios-simulator"]'
     secrets: inherit
 
   prebuild_react_native_core:
@@ -29,6 +32,7 @@ jobs:
     uses: ./.github/workflows/prebuild-ios-core.yml
     with:
       use-hermes-prebuilt: ${{ !endsWith(github.ref_name, '-stable') }}
+      slices: '["ios-simulator"]'
     secrets: inherit
 
   set_flavors:

.github/workflows/test-ios-spm-newapp.yml

@@ -21,6 +21,9 @@ on:
 jobs:
   prebuild_apple_dependencies:
     uses: ./.github/workflows/prebuild-ios-dependencies.yml
+    with:
+      # e2e only compiles for the iOS simulator — no need for device/catalyst/tv/xr slices.
+      slices: '["ios-simulator"]'
     secrets: inherit
 
   prebuild_react_native_core:
@@ -29,6 +32,7 @@ jobs:
     uses: ./.github/workflows/prebuild-ios-core.yml
     with:
       use-hermes-prebuilt: ${{ !endsWith(github.ref_name, '-stable') }}
+      slices: '["ios-simulator"]'
     secrets: inherit
 
   # Produces the `react-native-package` artifact (a local react-native .tgz) the

.github/workflows/test-ios-spm-rntester.yml

@@ -21,6 +21,9 @@ on:
 jobs:
   prebuild_apple_dependencies:
     uses: ./.github/workflows/prebuild-ios-dependencies.yml
+    with:
+      # e2e only compiles for the iOS simulator — no need for device/catalyst/tv/xr slices.
+      slices: '["ios-simulator"]'
     secrets: inherit
 
   prebuild_react_native_core:
@@ -29,6 +32,7 @@ jobs:
     uses: ./.github/workflows/prebuild-ios-core.yml
     with:
       use-hermes-prebuilt: ${{ !endsWith(github.ref_name, '-stable') }}
+      slices: '["ios-simulator"]'
     secrets: inherit
 
   set_flavors: