workflows: chunk the external-download matrix across 4 parallel invocations

The `download` job in infrastructure-download-external.yml was hitting
GitHub Actions' 256-entry `strategy.matrix` cap (259 configurations
observed). Rather than trimming the matrix (which would drop legitimate
arch × release combos users need) or duplicating a 500-line job block,
lean on the fact that infrastructure-download-external.yml is *already*
a reusable workflow — call it N times from the parent
(infrastructure-repository-update.yml) with a `CHUNK_INDEX` /
`CHUNK_COUNT` pair, and have the child filter its own matrix to its
assigned slice.

Child (infrastructure-download-external.yml):
- Add CHUNK_INDEX (0..CHUNK_COUNT-1) and CHUNK_COUNT (default 1) inputs.
- In the `start` job, after building MATRIX_JSON, slice the include[]
  list so each invocation keeps only entries where
  `index % CHUNK_COUNT == CHUNK_INDEX`. Modular slicing (not contiguous
  ranges) avoids clustering slow package types into one chunk.
- Suffix the `assets-for-download` artifact name with CHUNK_INDEX so
  parallel uploads don't race against each other.

Parent (infrastructure-repository-update.yml):
- Turn the single `external:` reusable-workflow call into a
  `strategy.matrix` over `chunk_index: [0, 1, 2, 3]`, passing
  CHUNK_COUNT: 4 to the child.

Effect: 4 parallel invocations, each with its own 256-matrix cap and
its own `max-parallel=180`. Headroom 1024 total matrix entries,
effective concurrency 720. Scale past that by bumping `chunk_index`
list and CHUNK_COUNT in lockstep — no block duplication, no file
extraction, no matrix trimming.

Legacy/un-chunked callers that omit the chunk inputs get CHUNK_COUNT=1
and receive the entire matrix as before.

Author: igorpecovnik

.github/workflows/infrastructure-download-external.yml

@@ -42,6 +42,18 @@ on:
         required: false
         type: boolean
         default: false
+      CHUNK_INDEX:
+        # Which slice of the matrix this invocation processes (0..CHUNK_COUNT-1).
+        # Used to keep strategy.matrix under GitHub Actions' 256-entry cap when
+        # the number of packages × arches × releases grows past that. Defaults
+        # to 0/1 so the workflow still works when called un-chunked.
+        required: false
+        type: number
+        default: 0
+      CHUNK_COUNT:
+        required: false
+        type: number
+        default: 1
     secrets:
       GPG_KEY1:
         required: true
@@ -209,7 +221,7 @@ jobs:
       - name: Upload Artifact
         uses: actions/upload-artifact@v7
         with:
-          name: assets-for-download
+          name: assets-for-download-${{ inputs.CHUNK_INDEX }}
           path: downloads
           overwrite: true
           retention-days: 5
@@ -360,11 +372,36 @@ jobs:
             echo "::warning::No matrix entries generated, adding placeholder" >&2
             MATRIX_JSON_COMPACTED='{"include":[{"name":"none","arch":"amd64","release":"bookworm"}]}'
           else
-            # Debug: Show raw matrix JSON
-            echo "::debug::Raw matrix JSON: ${MATRIX_JSON}" >&2
+            # Chunk the matrix so each invocation keeps strategy.matrix
+            # below GitHub Actions' 256-entry cap. Callers that don't
+            # know about chunking get CHUNK_COUNT=1 and pass the whole
+            # thing through (legacy behavior).
+            CHUNK_INDEX="${{ inputs.CHUNK_INDEX }}"
+            CHUNK_COUNT="${{ inputs.CHUNK_COUNT }}"
+            if [[ "${CHUNK_COUNT}" -lt 1 ]]; then CHUNK_COUNT=1; fi
+            if [[ "${CHUNK_INDEX}" -ge "${CHUNK_COUNT}" ]]; then
+              echo "::error::CHUNK_INDEX=${CHUNK_INDEX} must be < CHUNK_COUNT=${CHUNK_COUNT}" >&2
+              exit 1
+            fi
 
-            # Compact the JSON for GitHub Actions
-            MATRIX_JSON_COMPACTED=$(echo "${MATRIX_JSON}" | jq -c)
+            # Slice jq: split includes into CHUNK_COUNT roughly-equal
+            # groups by modular index (not contiguous ranges) so a
+            # slow package type doesn't cluster into one chunk.
+            SLICED=$(echo "${MATRIX_JSON}" | jq -c \
+              --argjson idx "${CHUNK_INDEX}" \
+              --argjson cnt "${CHUNK_COUNT}" \
+              '{include: [.include | to_entries[] | select(.key % $cnt == $idx) | .value]}')
+
+            SLICE_COUNT=$(echo "${SLICED}" | jq '.include | length')
+            echo "::notice::chunk ${CHUNK_INDEX}/${CHUNK_COUNT}: ${SLICE_COUNT} of ${MATRIX_COUNT} entries" >&2
+
+            # Empty slice needs a placeholder for the downstream job to
+            # run at all — it'll skip entries with name=none.
+            if [[ "${SLICE_COUNT}" -eq 0 ]]; then
+              MATRIX_JSON_COMPACTED='{"include":[{"name":"none","arch":"amd64","release":"bookworm"}]}'
+            else
+              MATRIX_JSON_COMPACTED="${SLICED}"
+            fi
             echo "::debug::Compacted matrix JSON: ${MATRIX_JSON_COMPACTED}" >&2
           fi
 
@@ -897,5 +934,5 @@ jobs:
       - name: Clean artifacts
         uses: geekyeggo/delete-artifact@v6
         with:
-          name: assets-for-download
+          name: assets-for-download-${{ inputs.CHUNK_INDEX }}
           failOnError: false

.github/workflows/infrastructure-repository-update.yml

@@ -41,8 +41,18 @@ jobs:
           TEAM: "Release manager"
 
   external:
-    name: "Download external"
+    name: "Download external (chunk ${{ matrix.chunk_index }}/4)"
     needs: Check
+    # Fan out across 4 chunks. The child workflow filters its matrix to
+    # only entries where `index % CHUNK_COUNT == CHUNK_INDEX`, so each
+    # invocation stays under GitHub Actions' 256-entry strategy.matrix
+    # cap. Effective concurrency is 4 × max-parallel (180) = 720.
+    # Bump `chunk_index` and `CHUNK_COUNT` together when total packages
+    # × arches × releases approaches 4 × 256 = 1024.
+    strategy:
+      fail-fast: false
+      matrix:
+        chunk_index: [0, 1, 2, 3]
     uses: armbian/armbian.github.io/.github/workflows/infrastructure-download-external.yml@main
     with:
       ENABLED: ${{ inputs.download_external != false || github.event.client_payload.download_external != false }}
@@ -51,6 +61,8 @@ jobs:
       BUILD_RUNNER: "docker"
       HOST_DEPLOY: "repo.armbian.com"
       PURGE: ${{ inputs.purge_external || false }}
+      CHUNK_INDEX: ${{ matrix.chunk_index }}
+      CHUNK_COUNT: 4
     secrets:
       GPG_KEY1: ${{ secrets.GPG_KEY3 }}
       GPG_KEY2: ${{ secrets.GPG_KEY4 }}