ci: auto-derive versionCode from commit count (never reuse a code)

Releases were silently no-op'ing on fdroid: versionCode was a hand-maintained
constant, so a commit that didn't bump it rebuilt the same debug_<vc>.apk, the
publish receiver's anti-downgrade guard refused the duplicate (exit 3 =
"nothing to do"), and the CI went green having shipped nothing. build.yml now
patches ProjectConfig's versionCode from `git rev-list --count HEAD` (minus an
offset keeping it continuous with the manual era, last=91) before assembling,
so every main commit auto-produces a new monotonic code. The ProjectConfig
literal is now just the local-dev default.

.forgejo/workflows/build.yml

@@ -62,6 +62,25 @@ jobs:
           KS_B64: ${{ secrets.STRAW_SIGNING_KEYSTORE_B64 }}
         run: echo "$KS_B64" | base64 -d > "$GITHUB_WORKSPACE/straw.keystore"
 
+      # Auto-derive versionCode from the main commit count so a release can
+      # NEVER silently reuse a code — the 2026-07-29 trap where a commit that
+      # didn't hand-bump ProjectConfig rebuilt the same debug_<vc>.apk, the
+      # publish receiver's anti-downgrade guard refused the duplicate (exit 3 =
+      # "nothing to do"), and the CI went green having shipped nothing. The
+      # OFFSET keeps the number continuous with the manual era (last hand-set
+      # code was 91). Full clone above ⇒ rev-list --count is the true count.
+      - name: Auto versionCode from commit count
+        working-directory: straw
+        run: |
+          set -euo pipefail
+          COUNT=$(git rev-list --count HEAD)
+          VC=$(( COUNT - 12208 ))
+          sed -i "s/^const val STRAW_VERSION_CODE = .*/const val STRAW_VERSION_CODE = $VC/" \
+            buildSrc/src/main/kotlin/ProjectConfig.kt
+          grep -q "STRAW_VERSION_CODE = $VC\$" buildSrc/src/main/kotlin/ProjectConfig.kt \
+            || { echo "::error::versionCode auto-patch failed (sed matched nothing)"; exit 1; }
+          echo "auto versionCode = $VC (commit count $COUNT)"
+
       - name: Assemble debug APK
         working-directory: straw
         env:

buildSrc/src/main/kotlin/ProjectConfig.kt

@@ -359,6 +359,10 @@ const val STRAW_SDK_TARGET = 35
 // vc=19 / 0.1.0-AE — rust pipeline cutover. Extraction via
 // strawcore-core (Sulkta-OSS/strawcore) via the UniFFI wrapper; no
 // NewPipeExtractor in the runtime path.
+// versionCode is AUTO-DERIVED in CI from the git commit count (see
+// .forgejo/workflows/build.yml "Auto versionCode from commit count") so a
+// release can never silently reuse a code. This literal is the local-dev
+// default only; CI overwrites it at build time.
 const val STRAW_VERSION_CODE = 92
 const val STRAW_VERSION_NAME = "0.1.0-CZ"
 const val STRAW_APPLICATION_ID = "com.sulkta.straw"