diff --git a/.github/workflows/fuzz.yml b/.github/workflows/fuzz.yml
new file mode 100644
index 00000000..b4b832cc
--- /dev/null
+++ b/.github/workflows/fuzz.yml
@@ -0,0 +1,74 @@
+name: Fuzz
+
+# Coverage-guided fuzzing of the two parsers of zone bytes (docs/design/broker.md), weekly on a pinned nightly.
+
+on:
+  schedule:
+    - cron: '0 4 * * 0'
+  workflow_dispatch:
+
+permissions:
+  contents: read
+
+jobs:
+  fuzz:
+    name: Fuzz ${{ matrix.target }}
+    runs-on: ubuntu-24.04
+    timeout-minutes: 60
+    strategy:
+      fail-fast: false
+      matrix:
+        include:
+          - target: broker_request
+            dir: compartments/kryptikd
+            seeds: compartments/kryptikd/fuzz-corpus/broker-requests
+            max_len: 4096
+          - target: wire
+            dir: compositor/wlproxy
+            seeds: ''
+            max_len: 8192
+    env:
+      # A dated nightly, so a new finding is never a new compiler's.
+      RUSTUP_TOOLCHAIN: nightly-2026-09-28
+      FUZZ_TARGET: ${{ matrix.target }}
+      CRATE_DIR: ${{ matrix.dir }}
+      SEEDS: ${{ matrix.seeds }}
+      MAX_LEN: ${{ matrix.max_len }}
+    steps:
+      - uses: actions/checkout@fbc6f3992d24b796d5a048ff273f7fcc4a7b6c09 # v5.1.0
+
+      - name: Nightly Rust and cargo-fuzz
+        run: |
+          rustup toolchain install "$RUSTUP_TOOLCHAIN" --profile minimal
+          cargo +stable install cargo-fuzz --version 0.13.2 --locked
+
+      # libfuzzer-sys comes from the fuzz crate's own lockfile, never from what ships.
+      - name: The fuzz crate's lockfile holds
+        run: cargo fetch --locked --manifest-path "$CRATE_DIR/fuzz/Cargo.toml"
+
+      - name: Seeds from the corpus in the tree
+        run: |
+          mkdir -p "$RUNNER_TEMP/corpus"
+          # The tree keeps one request per line; libFuzzer takes one input per file.
+          if [ -n "$SEEDS" ]; then
+            n=0
+            while IFS= read -r line || [ -n "$line" ]; do
+              n=$((n + 1))
+              printf '%s\n' "$line" > "$RUNNER_TEMP/corpus/seed-$n"
+            done < "$SEEDS"
+          fi
+          echo "$(find "$RUNNER_TEMP/corpus" -type f | wc -l) seeds"
+
+      # Safe Rust throughout, so no sanitizer: panics, overflow checks and the harness's asserts are the oracle.
+      - name: Twenty minutes of fuzzing
+        working-directory: ${{ matrix.dir }}
+        run: cargo fuzz run --sanitizer none "$FUZZ_TARGET" "$RUNNER_TEMP/corpus" -- -max_total_time=1200 -max_len="$MAX_LEN" -timeout=10 -print_final_stats=1
+
+      - name: Inputs that broke the parser
+        if: always()
+        uses: actions/upload-artifact@b7c566a772e6b6bfb58ed0dc250532a479d7789f # v6.0.0
+        with:
+          name: fuzz-${{ matrix.target }}
+          path: ${{ matrix.dir }}/fuzz/artifacts/
+          retention-days: 30
+          if-no-files-found: ignore
diff --git a/.gitignore b/.gitignore
index f2be4355..6560196f 100644
--- a/.gitignore
+++ b/.gitignore
@@ -18,6 +18,10 @@
 # Rust and Python
 /compartments/kryptikd/target/
 compositor/target/
+**/fuzz/target/
+**/fuzz/corpus/
+**/fuzz/artifacts/
+**/fuzz/coverage/
 __pycache__/
 
 # Editor / OS noise
diff --git a/compartments/kryptikd/Cargo.toml b/compartments/kryptikd/Cargo.toml
index df31a6b5..c3220108 100644
--- a/compartments/kryptikd/Cargo.toml
+++ b/compartments/kryptikd/Cargo.toml
@@ -10,6 +10,10 @@ license = "GPL-2.0-or-later"
 [dependencies]
 libc = "0.2"
 
+# Set only by cargo fuzz, which builds main.rs from fuzz/Cargo.toml.
+[lints.rust]
+unexpected_cfgs = { level = "warn", check-cfg = ["cfg(fuzzing)"] }
+
 [profile.release]
 opt-level = 2
 lto = true
diff --git a/compartments/kryptikd/fuzz/Cargo.lock b/compartments/kryptikd/fuzz/Cargo.lock
new file mode 100644
index 00000000..9d691662
--- /dev/null
+++ b/compartments/kryptikd/fuzz/Cargo.lock
@@ -0,0 +1,90 @@
+# This file is automatically @generated by Cargo.
+# It is not intended for manual editing.
+version = 4
+
+[[package]]
+name = "arbitrary"
+version = "1.4.2"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "c3d036a3c4ab069c7b410a2ce876bd74808d2d0888a82667669f8e783a898bf1"
+
+[[package]]
+name = "cc"
+version = "1.5.1"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "f360145194ee8e21db5ee7f3fcd4fe52210864c75c985dae33218202c8bbe040"
+dependencies = [
+ "find-msvc-tools",
+ "jobserver",
+ "libc",
+ "shlex",
+]
+
+[[package]]
+name = "cfg-if"
+version = "1.0.5"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "4e7648175b45a9a48536d676f68d918270699102aa8dab5496df06904c914600"
+
+[[package]]
+name = "find-msvc-tools"
+version = "0.1.14"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "aedcfb3409746eddb02b9e19ebda1c3394f759a152e48ee875a0844d1b955484"
+
+[[package]]
+name = "getrandom"
+version = "0.4.3"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "300e883d756b2e4ec94e02791f39b04b522276138852cfc41d9fb7e904106099"
+dependencies = [
+ "cfg-if",
+ "libc",
+ "r-efi",
+]
+
+[[package]]
+name = "jobserver"
+version = "0.1.35"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "1c00acbd29eabad4a2392fa0e921c874934dbbf4194312ad20f04a0ed67a3cb3"
+dependencies = [
+ "getrandom",
+ "libc",
+]
+
+[[package]]
+name = "kryptikd-fuzz"
+version = "0.0.0"
+dependencies = [
+ "libc",
+ "libfuzzer-sys",
+]
+
+[[package]]
+name = "libc"
+version = "0.2.189"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "3eaf3ede3fee6db1a4c2ee091bf8a8b4dccdc6d17f656fb07896ee72867612f2"
+
+[[package]]
+name = "libfuzzer-sys"
+version = "0.4.13"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "a9fd2f41a1cba099f79a0b6b6c35656cf7c03351a7bae8ff0f28f25270f929d2"
+dependencies = [
+ "arbitrary",
+ "cc",
+]
+
+[[package]]
+name = "r-efi"
+version = "6.0.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "f8dcc9c7d52a811697d2151c701e0d08956f92b0e24136cf4cf27b57a6a0d9bf"
+
+[[package]]
+name = "shlex"
+version = "2.0.1"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "f8fadd59c855ef2080decdef8ff161eb6661b86933c9d82e5ba29dc602a55aba"
diff --git a/compartments/kryptikd/fuzz/Cargo.toml b/compartments/kryptikd/fuzz/Cargo.toml
new file mode 100644
index 00000000..a1fbf9fa
--- /dev/null
+++ b/compartments/kryptikd/fuzz/Cargo.toml
@@ -0,0 +1,33 @@
+# The broker's request parser under libFuzzer, run weekly by
+# .github/workflows/fuzz.yml. A package and lockfile of its own, so
+# libfuzzer-sys never reaches kryptikd's dependencies or Cargo.lock (ADR-010).
+[package]
+name = "kryptikd-fuzz"
+version = "0.0.0"
+edition = "2021"
+publish = false
+
+[package.metadata]
+cargo-fuzz = true
+
+[dependencies]
+libc = "0.2"
+libfuzzer-sys = "0.4"
+
+# The daemon itself: under cfg(fuzzing) main.rs takes broker_request.rs in place of main.
+[[bin]]
+name = "broker_request"
+path = "../src/main.rs"
+test = false
+doc = false
+bench = false
+
+# The release build's overflow checks, and debug assertions as well.
+[profile.release]
+debug-assertions = true
+overflow-checks = true
+
+[lints.rust]
+unexpected_cfgs = { level = "warn", check-cfg = ["cfg(fuzzing)"] }
+
+[workspace]
diff --git a/compartments/kryptikd/fuzz/broker_request.rs b/compartments/kryptikd/fuzz/broker_request.rs
new file mode 100644
index 00000000..3012a511
--- /dev/null
+++ b/compartments/kryptikd/fuzz/broker_request.rs
@@ -0,0 +1,27 @@
+//! The broker's request parser under libFuzzer: any header line a zone can
+//! send, and whatever it accepts held to the bounds its refusals enforce.
+
+use libfuzzer_sys::fuzz_target;
+
+use crate::broker::{check_transfer_name, parse_request, Request, CLIPBOARD_MAX, MIME_TYPES};
+use crate::update::{POINTER_MAX, PUT_MAX};
+
+fuzz_target!(|data: &[u8]| {
+    // The header as serve_connection takes it: up to the first newline, decoded lossily.
+    let Some(nl) = data.iter().position(|b| *b == b'\n') else { return };
+    let header = String::from_utf8_lossy(&data[..nl]);
+    match parse_request(&header) {
+        Err(_) | Ok(Request::Version | Request::ClipboardGet | Request::UpdatePoll) => {}
+        Ok(Request::ClipboardSet { mime, len }) => assert!(MIME_TYPES.contains(&mime.as_str()) && len <= CLIPBOARD_MAX),
+        Ok(Request::Transfer { dest, name }) => {
+            assert!((1..=12).contains(&dest.len()));
+            assert!(dest.bytes().all(|b| b.is_ascii_lowercase() || b.is_ascii_digit() || b == b'-'));
+            assert!(check_transfer_name(&name).is_ok());
+        }
+        Ok(Request::TimeOffset(c)) => assert!(c.offset.is_finite() && c.offset.abs() <= 1e10 && (1..=16).contains(&c.sources)),
+        Ok(Request::UpdateLatest { plen, slen }) => assert!((1..=POINTER_MAX).contains(&plen) && (1..=POINTER_MAX).contains(&slen)),
+        Ok(Request::UpdatePut { name, len, .. }) => assert!(check_transfer_name(&name).is_ok() && (1..=PUT_MAX).contains(&len)),
+        Ok(Request::NotAZoneVerb(v)) => assert_eq!(v, "clipboard-move"),
+        Ok(Request::Unknown(v)) => assert!(!v.is_empty() && !v.contains(char::is_whitespace)),
+    }
+});
diff --git a/compartments/kryptikd/src/main.rs b/compartments/kryptikd/src/main.rs
index d2f54db7..ab7b5b9e 100644
--- a/compartments/kryptikd/src/main.rs
+++ b/compartments/kryptikd/src/main.rs
@@ -4,6 +4,9 @@
 //! process that creates zones or moves data between them. Anything not built
 //! is refused with an error, never a silent no-op.
 
+// cargo fuzz builds this file with cfg(fuzzing), and libFuzzer brings its own main.
+#![cfg_attr(fuzzing, no_main, allow(dead_code))]
+
 mod broker;
 mod caps;
 mod cgroup;
@@ -24,6 +27,10 @@ mod update;
 mod volume;
 mod wifi;
 mod zone;
+// The parser is private to the daemon, so its fuzz target compiles inside it (fuzz/Cargo.toml).
+#[cfg(fuzzing)]
+#[path = "../fuzz/broker_request.rs"]
+mod fuzz;
 
 use std::path::{Path, PathBuf};
 use std::process::ExitCode;
diff --git a/compositor/wlproxy/fuzz/Cargo.lock b/compositor/wlproxy/fuzz/Cargo.lock
new file mode 100644
index 00000000..30cd514d
--- /dev/null
+++ b/compositor/wlproxy/fuzz/Cargo.lock
@@ -0,0 +1,89 @@
+# This file is automatically @generated by Cargo.
+# It is not intended for manual editing.
+version = 4
+
+[[package]]
+name = "arbitrary"
+version = "1.4.2"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "c3d036a3c4ab069c7b410a2ce876bd74808d2d0888a82667669f8e783a898bf1"
+
+[[package]]
+name = "cc"
+version = "1.5.1"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "f360145194ee8e21db5ee7f3fcd4fe52210864c75c985dae33218202c8bbe040"
+dependencies = [
+ "find-msvc-tools",
+ "jobserver",
+ "libc",
+ "shlex",
+]
+
+[[package]]
+name = "cfg-if"
+version = "1.0.5"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "4e7648175b45a9a48536d676f68d918270699102aa8dab5496df06904c914600"
+
+[[package]]
+name = "find-msvc-tools"
+version = "0.1.14"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "aedcfb3409746eddb02b9e19ebda1c3394f759a152e48ee875a0844d1b955484"
+
+[[package]]
+name = "getrandom"
+version = "0.4.3"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "300e883d756b2e4ec94e02791f39b04b522276138852cfc41d9fb7e904106099"
+dependencies = [
+ "cfg-if",
+ "libc",
+ "r-efi",
+]
+
+[[package]]
+name = "jobserver"
+version = "0.1.35"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "1c00acbd29eabad4a2392fa0e921c874934dbbf4194312ad20f04a0ed67a3cb3"
+dependencies = [
+ "getrandom",
+ "libc",
+]
+
+[[package]]
+name = "libc"
+version = "0.2.189"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "3eaf3ede3fee6db1a4c2ee091bf8a8b4dccdc6d17f656fb07896ee72867612f2"
+
+[[package]]
+name = "libfuzzer-sys"
+version = "0.4.13"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "a9fd2f41a1cba099f79a0b6b6c35656cf7c03351a7bae8ff0f28f25270f929d2"
+dependencies = [
+ "arbitrary",
+ "cc",
+]
+
+[[package]]
+name = "r-efi"
+version = "6.0.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "f8dcc9c7d52a811697d2151c701e0d08956f92b0e24136cf4cf27b57a6a0d9bf"
+
+[[package]]
+name = "shlex"
+version = "2.0.1"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "f8fadd59c855ef2080decdef8ff161eb6661b86933c9d82e5ba29dc602a55aba"
+
+[[package]]
+name = "wlproxy-fuzz"
+version = "0.0.0"
+dependencies = [
+ "libfuzzer-sys",
+]
diff --git a/compositor/wlproxy/fuzz/Cargo.toml b/compositor/wlproxy/fuzz/Cargo.toml
new file mode 100644
index 00000000..44a0c655
--- /dev/null
+++ b/compositor/wlproxy/fuzz/Cargo.toml
@@ -0,0 +1,29 @@
+# kryptik-wlproxy's wire parser under libFuzzer, run weekly by
+# .github/workflows/fuzz.yml. A package, workspace and lockfile of its own, so
+# libfuzzer-sys never reaches the compositor's dependencies or Cargo.lock
+# (ADR-010).
+[package]
+name = "wlproxy-fuzz"
+version = "0.0.0"
+edition = "2021"
+publish = false
+
+[package.metadata]
+cargo-fuzz = true
+
+[dependencies]
+libfuzzer-sys = "0.4"
+
+[[bin]]
+name = "wire"
+path = "wire.rs"
+test = false
+doc = false
+bench = false
+
+# The release build's overflow checks, and debug assertions as well.
+[profile.release]
+debug-assertions = true
+overflow-checks = true
+
+[workspace]
diff --git a/compositor/wlproxy/fuzz/wire.rs b/compositor/wlproxy/fuzz/wire.rs
new file mode 100644
index 00000000..5938f201
--- /dev/null
+++ b/compositor/wlproxy/fuzz/wire.rs
@@ -0,0 +1,49 @@
+//! kryptik-wlproxy's wire parser under libFuzzer: message framing, every
+//! signature in the generated tables, and the writer the rewrites use. These
+//! three files name nothing else in the proxy, so they compile here as they are.
+
+#![no_main]
+#![allow(dead_code)]
+
+#[path = "../src/protocol.rs"]
+mod protocol;
+#[path = "../src/protocol_tables.rs"]
+mod protocol_tables;
+#[path = "../src/wire.rs"]
+mod wire;
+
+use libfuzzer_sys::fuzz_target;
+use protocol::{decode, Arg, Message};
+use wire::{ArgReader, Header, MessageWriter, HEADER_LEN};
+
+/// Every request and event in the tables.
+fn messages() -> &'static [&'static Message] {
+    static ALL: std::sync::OnceLock<Vec<&'static Message>> = std::sync::OnceLock::new();
+    ALL.get_or_init(|| protocol_tables::INTERFACES.iter().flat_map(|i| i.requests.iter().chain(i.events)).collect())
+}
+
+fuzz_target!(|data: &[u8]| {
+    let all = messages();
+    let mut rest = data;
+    // A stream of messages, each read against the signature its object id picks.
+    while let Ok(h) = Header::parse(rest) {
+        assert_eq!(Header::parse(&h.encode()), Ok(h));
+        let size = h.size as usize;
+        let Some(body) = rest.get(HEADER_LEN..size) else { break };
+        let m = all[h.object as usize % all.len()];
+        if let Ok(d) = decode(m, body) {
+            assert_eq!(d.new_object.is_some(), m.args.iter().any(|a| matches!(a, Arg::NewId { .. })));
+            assert_eq!(d.bind_version.is_some(), m.args.contains(&Arg::NewId { iface: None }));
+            for (at, s) in &d.strings {
+                // The offset a rewrite trusts, and what the proxy would write in its place.
+                assert_eq!(&body[at + 4..at + 4 + s.len()], s.as_bytes());
+                assert_eq!(body[at + 4 + s.len()], 0);
+                if let Some(out) = MessageWriter::new(h.object, h.opcode).string(s).finish() {
+                    assert_eq!(Header::parse(&out).map(|w| w.size as usize), Ok(out.len()));
+                    assert_eq!(ArgReader::new(&out[HEADER_LEN..]).string(), Ok(Some(*s)));
+                }
+            }
+        }
+        rest = &rest[size..];
+    }
+});
diff --git a/docs/design/broker.md b/docs/design/broker.md
index 50ff3345..b8ef5d72 100755
--- a/docs/design/broker.md
+++ b/docs/design/broker.md
@@ -195,7 +195,14 @@ title to `[zone] ...`, from which the compositor draws the zone's border.
   the body, only exact parses accepted) and feeds a damaged opening through a
   live session in arbitrary fragments (only whole messages reach the
   compositor). Inputs that ever break a parser join the corpus.
-  Coverage-guided fuzzing needs nightly Rust and belongs in a scheduled job.
+- `.github/workflows/fuzz.yml` fuzzes both parsers under libFuzzer weekly,
+  twenty minutes each, on a nightly pinned by date. `compartments/kryptikd/fuzz`
+  takes the request parser, seeded from that corpus, and holds every request
+  it accepts to the bounds its refusals enforce; `compositor/wlproxy/fuzz`
+  takes the framing, every signature in the tables and the writer the
+  rewrites use. An input that breaks one is kept as the run's artifact. Each
+  is a package with a lockfile of its own, so libfuzzer-sys is in nothing that
+  ships.
 
 ## Not built