feat(ota): implement build number suffix for firmware versioning

Enhanced the firmware versioning system by appending a build number
suffix when available, allowing for better tracking of published builds.
This change improves the OTA update process by providing clearer
versioning information in the embedded firmware string.

.github/workflows/build-observer-firmwares.yml

@@ -47,6 +47,7 @@ jobs:
     runs-on: ubuntu-latest
     outputs:
       matrix: ${{ steps.split.outputs.matrix }}
+      build_number: ${{ steps.buildnum.outputs.n }}
     steps:
       - name: Clone Repo
         uses: actions/checkout@v4
@@ -66,6 +67,27 @@ jobs:
               | jq -cs .)
           echo "matrix=$MATRIX" >> "$GITHUB_OUTPUT"
 
+      - name: Compute observer build number
+        id: buildnum
+        shell: bash
+        run: |
+          # Per-base published-build counter. N increments once per release and
+          # resets to 1 when FIRMWARE_VERSION (the MeshCore base version) changes.
+          # Read-only here (off the published counter); the release job is the sole
+          # writer and only writes on a successful build, so a failed build doesn't
+          # burn a number. First run / 404 -> empty -> N=1.
+          COUNTER_URL="https://observer.gessaman.com/observer-build-counter.json"
+          CUR=$(curl -fsSL "$COUNTER_URL" 2>/dev/null || echo '{}')
+          PREV_BASE=$(echo "$CUR" | jq -r '.baseVersion // ""')
+          PREV_BUILD=$(echo "$CUR" | jq -r '.build // 0')
+          if [ "$PREV_BASE" = "$FIRMWARE_VERSION" ]; then
+            N=$((PREV_BUILD + 1))
+          else
+            N=1
+          fi
+          echo "Base $FIRMWARE_VERSION; previous build $PREV_BUILD (base $PREV_BASE) -> N=$N"
+          echo "n=$N" >> "$GITHUB_OUTPUT"
+
   # Build one shard (several envs) per runner. build.sh emits both the app
   # .bin and the ESP32 -merged.bin into out/ for each env.
   build:
@@ -100,6 +122,9 @@ jobs:
         uses: ./.github/actions/setup-build-environment
 
       - name: Build Shard ${{ matrix.shard.idx }}
+        env:
+          # Stamp the per-base build number into the embedded version (v1.16.0.N).
+          FIRMWARE_BUILD_NUMBER: ${{ needs.enumerate.outputs.build_number }}
         run: /usr/bin/env bash build.sh build-firmware ${{ matrix.shard.envs }}
 
       - name: Upload Shard Artifact
@@ -112,7 +137,7 @@ jobs:
   # Collect all shard outputs, publish the rolling release, then point the
   # flasher at the new build by bumping the hash + notes in its config.json.
   release:
-    needs: build
+    needs: [enumerate, build]
     runs-on: ubuntu-latest
     steps:
       - name: Clone Repo
@@ -196,6 +221,23 @@ jobs:
             "${{ steps.sha.outputs.short }}" \
             "$GITHUB_WORKSPACE/firmware-notes.html"
 
+      - name: Generate Slim Per-Variant Manifests + Persist Build Counter
+        env:
+          BUILD_NUMBER: ${{ needs.enumerate.outputs.build_number }}
+        run: |
+          # Derive the slim per-variant manifests (flasher/v/<env>.json) that the
+          # firmware fetches for `ota check`/`ota update`, from the just-updated
+          # config.json (single source of truth), stamping this build's number.
+          # Then persist the counter so the next run increments from here.
+          python3 flasher/scripts/gen-slim-manifests.py \
+            --config flasher/config.json \
+            --out-dir flasher/v \
+            --base-version "$FIRMWARE_VERSION" \
+            --build "$BUILD_NUMBER"
+          printf '{\n  "baseVersion": "%s",\n  "build": %s\n}\n' \
+            "$FIRMWARE_VERSION" "$BUILD_NUMBER" > flasher/observer-build-counter.json
+          echo "Build $FIRMWARE_VERSION.$BUILD_NUMBER"
+
       - name: Unshallow for Changelog
         run: |
           # gen_changelog.py needs the full branch history; deepen only now, AFTER
@@ -233,11 +275,15 @@ jobs:
       - name: Commit & Push Flasher Config
         working-directory: flasher
         run: |
-          if git diff --quiet; then
+          # Stage everything: update-firmware.py edits config.json in place, but the
+          # slim manifests (v/*.json) and the build counter can be NEW files, which
+          # `commit -am` would miss — so add -A and check the staged diff.
+          git add -A
+          if git diff --cached --quiet; then
             echo "No flasher changes to commit."
             exit 0
           fi
           git config user.name "meshcore-bot"
           git config user.email "noreply@gessaman.com"
-          git commit -am "Update observer firmware to ${{ steps.sha.outputs.short }}"
+          git commit -m "Update observer firmware to ${{ steps.sha.outputs.short }} (build ${FIRMWARE_VERSION}.${{ needs.enumerate.outputs.build_number }})"
           git push