fuzz: fold cycle.sh script into fuzz.sh

diff --git a/fuzz/README.md b/fuzz/README.md
index 448bfc99..cd5cc679 100644
--- a/fuzz/README.md
+++ b/fuzz/README.md
@@ -52,20 +52,24 @@ To see the full list of targets, the most straightforward way is to run
 cargo fuzz list
 ```
 
-To run each of them for an hour, run
+To run continuous fuzzing, use the `-cycle` flag:
 
 ```bash
-./cycle.sh
+./fuzz.sh -cycle
+```
+
+This will loop through each target indefinitely, running each for 1 hour
+by default. The fuzzer will run at low process priority (using `chrt`) to
+avoid blocking other work. Pass `-max_total_time` to customize the duration:
+
+```bash
+./fuzz.sh -cycle -max_total_time=7200
 ```
-This script uses the `chrt` utility to try to reduce the priority of the
-jobs. If you would like to run for longer, the most straightforward way
-is to edit `cycle.sh` before starting. To run the fuzz-tests in parallel,
-you will need to implement a custom harness.
 
 To run a single fuzztest indefinitely, run
 
 ```bash
-cargo +nightly fuzz run "<target>"
+./fuzz.sh -cycle <target>
 ```
 
 ## Adding fuzz tests
diff --git a/fuzz/cycle.sh b/fuzz/cycle.sh
deleted file mode 100755
index 84c1cb6a..00000000
--- a/fuzz/cycle.sh
+++ /dev/null
@@ -1,26 +0,0 @@
-#!/usr/bin/env bash
-
-# Continuously cycle over fuzz targets running each for 1 hour.
-# It uses chrt SCHED_IDLE so that other process takes priority.
-#
-# For cargo-fuzz usage see https://github.com/rust-fuzz/cargo-fuzz?tab=readme-ov-file#usage
-
-set -euo pipefail
-
-REPO_DIR=$(git rev-parse --show-toplevel)
-# can't find the file because of the ENV var
-# shellcheck source=/dev/null
-source "$REPO_DIR/fuzz/fuzz-util.sh"
-
-while :
-do
-  for targetFile in $(listTargetFiles); do
-    targetName=$(targetFileToName "$targetFile")
-    echo "Fuzzing target $targetName ($targetFile)"
-
-    # fuzz for one hour
-    chrt -i 0 cargo +nightly fuzz run "$targetName" -- -max_total_time=3600
-    cargo +nightly fuzz cmin "$targetName" 
-  done
-done
-
diff --git a/fuzz/fuzz.sh b/fuzz/fuzz.sh
index e4052637..eb43f8d0 100755
--- a/fuzz/fuzz.sh
+++ b/fuzz/fuzz.sh
@@ -1,8 +1,14 @@
 #!/usr/bin/env bash
 
-# Briefly fuzz the provided target, or all targets if none provided.
+# Fuzz the provided target(s), or all targets if none provided.
 #
-# Usage: fuzz.sh [TARGET] [-max_total_time=SECONDS]
+# Usage: fuzz.sh [TARGET] [-max_total_time=SECONDS] [-cycle]
+#
+# Options:
+#   TARGET                  Specific fuzz target to run (e.g., bitcoin_deserialize_block)
+#   -max_total_time=SECONDS Fuzzing duration in seconds (default: 100 in normal mode, 3600 in cycle mode)
+#   -cycle                  Continuous fuzzing: loop through all targets indefinitely,
+#                           running corpus minimization after each target, with low process priority
 
 set -euox pipefail
 
@@ -13,13 +19,17 @@ REPO_DIR=$(git rev-parse --show-toplevel)
 source "$REPO_DIR/fuzz/fuzz-util.sh"
 
 target=
-max_total_time=100
+max_total_time=
+cycle_mode=false
 
 for arg in "$@"; do
   case "$arg" in
     -max_total_time=*)
       max_total_time="${arg#-max_total_time=}"
       ;;
+    -cycle)
+      cycle_mode=true
+      ;;
     -*)
       echo "Unknown option: $arg"
       exit 2
@@ -34,6 +44,15 @@ for arg in "$@"; do
   esac
 done
 
+# Set default max_total_time based on mode, 1 hour for cycle, 100 seconds for default.
+if [ -z "$max_total_time" ]; then
+  if [ "$cycle_mode" = true ]; then
+    max_total_time=3600
+  else
+    max_total_time=100
+  fi
+fi
+
 case "$max_total_time" in
   ''|*[!0-9]*)
     echo "-max_total_time must be a non-negative integer number of seconds"
@@ -53,19 +72,37 @@ fi
 cargo --version
 rustc --version
 
-# Testing
 cargo install --force --locked --version 0.12.0 cargo-fuzz
-for targetFile in $targetFiles; do
-  targetName=$(targetFileToName "$targetFile")
-
-  echo "Fuzzing target $targetName ($targetFile) for $max_total_time seconds"
-  # Enable fuzz stubs in the hashes and cryptography libraries by default,
-  # unless we are fuzzing the hashes targets themselves.
-  fuzz_rustflags=''
-  if [[ ! "$targetName" =~ ^hashes_ ]]; then
-    fuzz_rustflags='--cfg=hashes_fuzz --cfg=secp256k1_fuzz'
+while :; do
+  for targetFile in $targetFiles; do
+    targetName=$(targetFileToName "$targetFile")
+
+    echo "Fuzzing target $targetName ($targetFile) for $max_total_time seconds"
+    # Enable fuzz stubs in the hashes and cryptography libraries by default,
+    # unless we are fuzzing the hashes targets themselves.
+    fuzz_rustflags=''
+    if [[ ! "$targetName" =~ ^hashes_ ]]; then
+      fuzz_rustflags='--cfg=hashes_fuzz --cfg=secp256k1_fuzz'
+    fi
+    # cargo-fuzz will check for the corpus at fuzz/corpus/<target>
+    # Use chrt to run at SCHED_IDLE priority (lowest) to avoid blocking other work.
+    chrt_cmd=''
+    if [ "$cycle_mode" = true ]; then
+      chrt_cmd='chrt -i 0'
+    fi
+    RUSTFLAGS="$RUSTFLAGS $fuzz_rustflags" $chrt_cmd cargo +nightly fuzz run "$targetName" -- -max_total_time="$max_total_time"
+
+    echo "Minimizing corpus for target $targetName"
+    cargo +nightly fuzz cmin "$targetName"
+
+    # Check for artifacts/crashes in normal mode.
+    if [ "$cycle_mode" = false ]; then
+      checkReport "$targetName"
+    fi
+  done
+
+  # Exit after one cycle if not in cycle mode.
+  if [ "$cycle_mode" = false ]; then
+    break
   fi
-  # cargo-fuzz will check for the corpus at fuzz/corpus/<target>
-  RUSTFLAGS="$RUSTFLAGS $fuzz_rustflags" cargo +nightly fuzz run "$targetName" -- -max_total_time="$max_total_time"
-  checkReport "$targetName"
 done