CI: also run the tests in a debug build

.claude/PROGRESS.md

@@ -152,4 +152,5 @@ reports, inbound C ports) is tracked in HPCBio/wfa2lib-rs#19.
   Null steps no longer end a corrected search while a candidate is pending
   (FIXED_BUGS 14c, with `BandedStatic`).
   Also HPCBio/wfa2lib-rs#41: empty pattern + text no longer panics in debug
-  (FIXED_BUGS 15).
+  (FIXED_BUGS 15). CI now also runs the tests in a debug build (Linux and
+  macOS), so overflows like it fail CI.

.github/workflows/ci.yml

@@ -57,6 +57,29 @@ jobs:
       - name: Stock C unit tests
         run: bash tests/wfa_utest.sh
 
+  # Debug build: overflow checks and debug_assert!s are on, catching what
+  # release builds silently wrap past (HPCBio/wfa2lib-rs#41). A separate job
+  # so it runs alongside the release tests; both architectures, since the
+  # x86 and ARM SIMD paths differ.
+  test-debug:
+    name: Test debug (${{ matrix.os }})
+    runs-on: ${{ matrix.os }}
+    timeout-minutes: 30
+    strategy:
+      fail-fast: false
+      matrix:
+        os: [ubuntu-latest, macos-latest]
+    steps:
+      - uses: actions/checkout@v4
+      - uses: dtolnay/rust-toolchain@stable
+      - uses: Swatinem/rust-cache@v2
+      - name: Fetch C WFA2-lib
+        run: |
+          git clone --quiet https://github.com/smarco/WFA2-lib WFA2-lib
+          git -C WFA2-lib checkout --quiet "$(cat tests/differential/C_COMMIT)"
+      - name: Tests (debug)
+        run: cargo test
+
   # Suites run as parallel jobs; span is the longest (~15 min on Linux).
   # Linux runs Rust's x86 AVX2 kernels, macOS (arm64) its NEON ones, so
   # together they check that Rust gives the same output on both. macOS

README.md

@@ -82,13 +82,15 @@ For broader parity checks, `tests/differential/run.sh` builds C's
 1300 configurations (metrics, spans, heuristics, memory modes); see
 [`tests/differential/README.md`](tests/differential/README.md).
 
-CI (`.github/workflows/ci.yml`) runs clippy, the tests, a library-only build,
+CI (`.github/workflows/ci.yml`) runs clippy, the tests (release, and debug
+with overflow checks and debug assertions), a library-only build,
 `wfa_utest.sh` and the differential harness on Linux (x86-64) and macOS
 (arm64) for every pull request and push to `main`. Running the harness on both
 checks that Rust's x86 and ARM SIMD paths give the same output. Linux also
-runs everything with `RUSTFLAGS="-C target-cpu=x86-64-v3"`, so the AVX2
-kernels are tested both when selected at run time and when enabled at compile
-time (as in `target-cpu=native` builds).
+runs the release tests and the harness with
+`RUSTFLAGS="-C target-cpu=x86-64-v3"`, so the AVX2 kernels are tested both
+when selected at run time and when enabled at compile time (as in
+`target-cpu=native` builds).
 
 ## Usage