Use selected branch for automated mapping updates

.github/workflows/update-mappings.yml

@@ -23,7 +23,7 @@ jobs:
     runs-on: ubuntu-latest
 
     env:
-      AUTOMATION_BRANCH: dev/automated-mapping-update
+      AUTOMATION_BRANCH: dev/automated-mapping-update-${{ github.ref_name }}
       NTE_ASSETS_REF: ${{ inputs.source_ref }}
       GH_TOKEN: ${{ secrets.GITHUB_TOKEN }}
 
@@ -32,7 +32,7 @@ jobs:
         uses: actions/checkout@v5
         with:
           fetch-depth: 0
-          ref: ${{ github.event.repository.default_branch }}
+          ref: ${{ github.ref_name }}
 
       - name: Get Python
         uses: actions/setup-python@v6
@@ -91,7 +91,7 @@ jobs:
         if: steps.changes.outputs.changed == 'true'
         shell: bash
         env:
-          BASE_BRANCH: ${{ github.event.repository.default_branch }}
+          BASE_BRANCH: ${{ github.ref_name }}
           RUN_URL: ${{ github.server_url }}/${{ github.repository }}/actions/runs/${{ github.run_id }}
         run: |
           python - <<'PY'

docs/mapping-updates.md

@@ -18,15 +18,17 @@ game whose asset tables evolve over time.
 
 ### GitHub Actions
 
-Run **Update reward mappings** from the repository's Actions tab. The optional
-`source_ref` input accepts an NTE_Assets branch, tag, or commit and defaults to
-`main`.
+Run **Update reward mappings** from the repository's Actions tab. **Use
+workflow from** selects the exporter branch whose updater is run and the target
+branch for the resulting pull request. The `source_ref` input separately
+selects an NTE_Assets branch, tag, or commit and defaults to `main`.
 
 The workflow rebuilds the mappings, runs the complete test suite, uploads the
 JSON review report, and opens a pull request from
-`dev/automated-mapping-update`. Running it again updates the same open pull
-request. If the authoritative snapshot has not changed, it reports zero changes
-and does not create a commit or pull request.
+`dev/automated-mapping-update-<selected-branch>`. Running it again for the same
+selected branch updates that branch's open pull request. If the authoritative
+snapshot has not changed, it reports zero changes and does not create a commit
+or pull request.
 
 The repository setting **Allow GitHub Actions to create and approve pull
 requests** must be enabled for automatic pull-request creation. The workflow