fix(letters): encode the mailto address; fuzz the register check and the letters weekly

.github/dependabot.yml

@@ -15,7 +15,7 @@ updates:
       # Policy pins move by hand to a reviewed release-policy commit.
       - dependency-name: "ryanduguid/release-policy/.github/workflows/*"
   - package-ecosystem: cargo
-    directory: /
+    directories: [/, /fuzz]
     schedule:
       interval: weekly
     cooldown:

.github/workflows/fuzz.yml

@@ -0,0 +1,39 @@
+name: Fuzz
+
+on:
+  schedule:
+    - cron: '41 3 * * 1'
+  workflow_dispatch:
+
+permissions:
+  contents: read
+
+jobs:
+  fuzz:
+    strategy:
+      fail-fast: false
+      matrix:
+        target: [register_letters, letter_text]
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@3d3c42e5aac5ba805825da76410c181273ba90b1 # v7.0.1
+        with:
+          persist-credentials: false
+      - name: Install nightly and the pinned cargo-fuzz
+        run: |
+          rustup toolchain install nightly --profile minimal
+          cargo +nightly install cargo-fuzz --locked --version 0.13.2
+      # The shipped register seeds the entry target and the letter templates the text target.
+      - name: Fuzz for 5 minutes
+        env:
+          TARGET: ${{ matrix.target }}
+        run: |
+          if [ "$TARGET" = register_letters ]; then seeds=registry/au; else seeds=letters/au; fi
+          mkdir -p "fuzz/corpus/$TARGET"
+          cargo +nightly fuzz run "$TARGET" "fuzz/corpus/$TARGET" "$seeds" -- -max_total_time=300 -rss_limit_mb=4096
+      - name: Keep the crashing input
+        if: failure()
+        uses: actions/upload-artifact@cf430e030ddbb5b0abf93d22962f4752f3646cd9 # v7.0.2
+        with:
+          name: fuzz-${{ matrix.target }}
+          path: fuzz/artifacts/${{ matrix.target }}

CONTRIBUTING.md

@@ -23,3 +23,5 @@ cargo run -- registry check --path registry/au
 ```
 
 New functionality and bug fixes come with automated tests, in `tests/` or a `#[cfg(test)]` module beside the code, and CI runs them on Linux and Windows.
+
+Changes to the register check or the letters should also survive the fuzz targets in `fuzz/`, which CI runs for 5 minutes each every Monday. They need a nightly toolchain and `cargo install cargo-fuzz`; run one with `cargo +nightly fuzz run register_letters` (or `letter_text`); CI seeds them from `registry/au` and `letters/au`. A crash leaves its input in `fuzz/artifacts/`; turn it into a test before fixing it.

fuzz/.gitignore

@@ -0,0 +1,4 @@
+target
+corpus
+artifacts
+coverage