test(core): fuzz harness and proptest twin

.github/workflows/fuzz.yml

@@ -0,0 +1,52 @@
+# Fuzzing lives on `cargo fuzz`, which needs a nightly toolchain and must never
+# be part of the stable `cargo clippy --workspace` gate in ci.yml. This workflow
+# is therefore SCHEDULED (not a PR push/PR gate) and runs against the corpus
+# that is checked into this repo under `fuzz/corpus/node/`.
+#
+# The 24 CPU-hour budget mentioned in Task 12 is release-time; this scheduled run
+# uses a modest per-run budget so it stays cheap while still re-executing every
+# known input and continuing to grow the corpus.
+
+name: Fuzz
+
+on:
+  schedule:
+    # Daily at 00:05 UTC. Deliberately not push/PR — the nightly + cargo-fuzz
+    # toolchain is slow to install/build and has no place in a review gate.
+    - cron: "5 0 * * *"
+  workflow_dispatch: {}
+
+permissions:
+  contents: read
+
+jobs:
+  fuzz-node:
+    runs-on: ubuntu-latest
+    timeout-minutes: 120
+    steps:
+      - uses: actions/checkout@v4
+        with:
+          # The corpus is committed, so the run continues where it left off and
+          # re-runs every known crashing/non-crashing input on each schedule.
+          fetch-depth: 0
+
+      - name: Install nightly toolchain + cargo-fuzz
+        run: |
+          rustup toolchain install nightly --profile minimal --component rust-src
+          rustup default nightly
+          cargo install cargo-fuzz
+
+      - name: Run the Node harness against the checked-in corpus
+        # Re-runs every corpus entry (fast path) and then continues fuzzing for
+        # the run budget. The corpus directory is part of the repo, so it grows
+        # in place across schedules; a fresh checkout still has prior inputs.
+        run: cargo fuzz run node -- -max_total_time=1800
+
+      - name: Upload corpus artifacts (optional retention)
+        if: always()
+        uses: actions/upload-artifact@v4
+        with:
+          name: fuzz-corpus-node
+          path: fuzz/corpus/node/
+          if-no-files-found: ignore
+          retention-days: 7

Cargo.lock

@@ -1491,6 +1491,7 @@ dependencies = [
  "blake2",
  "heapless 0.8.0",
  "postcard",
+ "proptest",
  "serde",
 ]
 

fuzz/Cargo.lock

@@ -0,0 +1,304 @@
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+# It is not intended for manual editing.
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+
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fuzz/Cargo.toml

@@ -0,0 +1,28 @@
+[package]
+name = "fuzz"
+version = "0.0.0"
+publish = false
+edition = "2021"
+
+# cargo-fuzz needs this marker to treat the crate as a fuzzer root (rather than
+# erroring that it does not look like a cargo-fuzz manifest).
+[package.metadata]
+cargo-fuzz = true
+
+[dependencies]
+tines-core = { path = "../tines-core", version = "0.3.0", features = ["conformance"] }
+libfuzzer-sys = "0.4"
+heapless = "0.8"
+
+# The fuzz target is exposed as an explicit nightly release bin so cargo-fuzz can
+# find it (`cargo fuzz run node`). Without a [[bin]] entry cargo reports "no bin
+# target named node"; each file in fuzz_targets/ maps to one such [[bin]].
+[[bin]]
+name = "node"
+path = "fuzz_targets/node.rs"
+
+[features]
+default = ["conformance"]
+conformance = ["tines-core/conformance"]
+
+[workspace]

fuzz/corpus/node/0089e713336fe2bf533ada5f710dae8ad9152f19

@@ -0,0 +1 @@
+

fuzz/corpus/node/01ba0487e7eef79b487e75248a7048858ac87c07

@@ -0,0 +1 @@
+

fuzz/corpus/node/0203958c1ac7ea20c6e35b14733d86f4cf3c1749

@@ -0,0 +1 @@
+

fuzz/corpus/node/03ea95c944df7cb4d9a6ffde33914c1e40420798

@@ -0,0 +1 @@
+'

fuzz/corpus/node/05a1379faf15d1b86f90e0dc14941d121a7f03b8

@@ -0,0 +1 @@
+

fuzz/corpus/node/085da2e606786a7d221010f7148cb0626205ebcf

@@ -0,0 +1 @@
+
""""

fuzz/corpus/node/09aad90d648c72c9a6905fffe9ee8cc606e14a29

@@ -0,0 +1 @@
+

fuzz/corpus/node/127f5cfc91aa873fa353fc0c88eb5347f5cb253b

@@ -0,0 +1 @@
+†¿ Æ­…{{{{{{{¹Š7*i09ÒÃ