Gate uploads on a built firmware, refuse unclaimed native builds, seed the CI toolchain cache from dev

The upload path now checks CORE.firmware_bin exists before invoking
esptool and names the fix (compile first) instead of failing inside
esptool. compile_program raises when a native toolchain resolved but no
platform backend claimed the build rather than falling through to a
mis-configured PlatformIO project. The addr2line failure warning now
includes the exception so the cause is visible without debug logging.

CI: the native toolchain cache is restore-only on PRs and seeded by a
new dev-push job, mirroring seed-apt-cache; the key resolves the pinned
core and toolchain versions from code instead of hashing framework.py.
determine-jobs main() output tests now pin the esp8266_native pair.

.github/workflows/ci.yml

@@ -177,6 +177,41 @@ jobs:
           path: .temp/components_graph.json
           key: components-graph-${{ hashFiles('esphome/components/**/*.py') }}
 
+  seed-esp8266-native-cache:
+    name: Seed the esp8266 native toolchain cache
+    runs-on: ubuntu-24.04
+    needs:
+      - common
+    # PR-branch cache saves are invisible to other PRs, so pushes seed the
+    # shared entry test-esp8266-native restores (same pattern as
+    # seed-apt-cache / cache-esp-idf).
+    if: github.event_name == 'push'
+    timeout-minutes: 15
+    steps:
+      - name: Check out code from GitHub
+        uses: actions/checkout@3d3c42e5aac5ba805825da76410c181273ba90b1 # v7.0.1
+      - name: Restore Python
+        uses: ./.github/actions/restore-python
+        with:
+          python-version: ${{ env.DEFAULT_PYTHON }}
+          cache-key: ${{ needs.common.outputs.cache-key }}
+      - name: Resolve the native toolchain cache key
+        id: esp8266-native-cache-key
+        run: |
+          . venv/bin/activate
+          echo "key=esp8266-native-$(python -c 'from esphome.components.esp8266 import RECOMMENDED_ARDUINO_FRAMEWORK_VERSION as f; from esphome.arduino8266.framework import TOOLCHAIN_VERSION as t; print(f"{f}-{t}")')" >> $GITHUB_OUTPUT
+      - name: Cache the native toolchain
+        id: esp8266-native-cache
+        uses: actions/cache@55cc8345863c7cc4c66a329aec7e433d2d1c52a9 # v6.1.0
+        with:
+          path: ~/.cache/esphome/arduino8266
+          key: ${{ steps.esp8266-native-cache-key.outputs.key }}
+      - name: Install the native toolchain
+        if: steps.esp8266-native-cache.outputs.cache-hit != 'true'
+        run: |
+          . venv/bin/activate
+          python -c "from esphome.arduino8266.framework import check_and_install; from esphome.components.esp8266 import RECOMMENDED_ARDUINO_FRAMEWORK_VERSION; check_and_install(RECOMMENDED_ARDUINO_FRAMEWORK_VERSION)"
+
   ci-custom:
     name: Run script/ci-custom
     runs-on: ubuntu-24.04
@@ -1152,13 +1187,22 @@ jobs:
           python-version: ${{ env.DEFAULT_PYTHON }}
           cache-key: ${{ needs.common.outputs.cache-key }}
 
-      # ~110 MB of framework + toolchain plus the ccache store; keyed on the
-      # pinned versions in arduino8266/framework.py so a bump re-downloads
-      - name: Cache the native toolchain and ccache
-        uses: actions/cache@55cc8345863c7cc4c66a329aec7e433d2d1c52a9 # v6.1.0
+      # ~110 MB of framework + toolchain plus the ccache store. The versions
+      # are pinned in code, not in a hashable file, so resolve them for the
+      # key (actions/cache never overwrites a key, so a bump must change it).
+      # PRs are restore-only; the shared entry is seeded on pushes to dev by
+      # seed-esp8266-native-cache, mirroring the seed-apt-cache scoping.
+      - name: Resolve the native toolchain cache key
+        id: esp8266-native-cache-key
+        run: |
+          . venv/bin/activate
+          echo "key=esp8266-native-$(python -c 'from esphome.components.esp8266 import RECOMMENDED_ARDUINO_FRAMEWORK_VERSION as f; from esphome.arduino8266.framework import TOOLCHAIN_VERSION as t; print(f"{f}-{t}")')" >> $GITHUB_OUTPUT
+
+      - name: Restore the native toolchain and ccache
+        uses: actions/cache/restore@55cc8345863c7cc4c66a329aec7e433d2d1c52a9 # v6.1.0
         with:
           path: ~/.cache/esphome/arduino8266
-          key: esp8266-native-${{ hashFiles('esphome/arduino8266/framework.py') }}
+          key: ${{ steps.esp8266-native-cache-key.outputs.key }}
 
       - name: Run native toolchain compile test
         run: |
@@ -1533,6 +1577,7 @@ jobs:
     needs:
       - common
       - seed-apt-cache
+      - seed-esp8266-native-cache
       - determine-jobs
       - ci-custom
       - pylint