Extend CI action to enforce encodable fuzzing

diff --git a/contrib/check-encodable-coverage.sh b/contrib/check-encodable-coverage.sh
index fa35260f..ee46963f 100755
--- a/contrib/check-encodable-coverage.sh
+++ b/contrib/check-encodable-coverage.sh
@@ -1,15 +1,18 @@
 #!/usr/bin/env bash
 #
 # Check that all types implementing encoding::Encodable are covered in the fuzz
-# test that compares encoding between old and new bitcoin crates.
+# tests:
+#   1. compare_consensus_encoding.rs - compares encoding between old and new bitcoin crates.
+#   2. fuzz/generate-encoding-roundtrip.sh - generates per-type roundtrip fuzz targets.
 
 set -euo pipefail
 
 REPO_DIR=$(git rev-parse --show-toplevel)
-FUZZ_FILE="$REPO_DIR/fuzz/fuzz_targets/bitcoin/compare_consensus_encoding.rs"
+COMPARE_FUZZ_FILE="$REPO_DIR/fuzz/fuzz_targets/bitcoin/compare_consensus_encoding.rs"
+ROUNDTRIP_FUZZ_SCRIPT="$REPO_DIR/fuzz/generate-encoding-roundtrip.sh"
 TRAIT_IMPL_JS="$REPO_DIR/target/doc/trait.impl/bitcoin_consensus_encoding/encode/trait.Encode.js"
 
-# Known exclusions (types that don't exist in old_bitcoin 0.32 or are generic).
+# Known exclusions for compare_consensus_encoding (types that don't exist in old_bitcoin 0.32 or are generic).
 # Add types here that have new Encodable but no old_bitcoin equivalent.
 # - CommandString has very different decoding functionality in new bitcoin.
 # - HeadersMessage has no type in 0.32 bitcoin. Vec<(Header, u8)> is not Decodable.
@@ -23,20 +26,45 @@ main() {
     generate_docs
     check_trait_impl_file
 
-    local new_types fuzz_types missing
+    local new_types
     new_types=$(extract_new_types)
-    fuzz_types=$(extract_fuzz_types)
-    missing=$(find_missing_types "$new_types" "$fuzz_types")
 
-    if [ -n "$missing" ]; then
-        echo "The following types implement encoding::Encode but are not in the fuzz test:" >&2
-        for type in $missing; do
+    local failed=0
+
+    # Check compare_consensus_encoding.rs (with exclusions)
+    local compare_types compare_missing
+    compare_types=$(extract_compare_fuzz_types)
+    compare_missing=$(find_missing_types "$new_types" "$compare_types" "$EXCLUSIONS")
+
+    if [ -n "$compare_missing" ]; then
+        echo "The following types implement encoding::Encode but are not in compare_consensus_encoding.rs:" >&2
+        for type in $compare_missing; do
+            echo "  - $type" >&2
+        done
+        echo "Either add them to compare_consensus_encoding.rs or add to EXCLUSIONS in this script" >&2
+        failed=1
+    fi
+
+    # Check generate-encoding-roundtrip.sh
+    local roundtrip_types roundtrip_missing exclusions
+    exclusions="Script Validation NetworkMessage V2NetworkMessage"
+    roundtrip_types=$(extract_roundtrip_fuzz_types)
+    roundtrip_missing=$(find_missing_types "$new_types" "$roundtrip_types" "$exclusions")
+
+    if [ -n "$roundtrip_missing" ]; then
+        echo "The following types implement encoding::Encode but are not in fuzz/generate-encoding-roundtrip.sh:" >&2
+        for type in $roundtrip_missing; do
             echo "  - $type" >&2
         done
-        err "Either add them to compare_consensus_encoding.rs or add to EXCLUSIONS in this script"
+        echo "Add them to ROUNDTRIP_TYPES or SCRIPT_ROUNDTRIP_TYPES in fuzz/generate-encoding-roundtrip.sh" >&2
+        failed=1
     fi
 
-    echo "All encoding::Encode types are covered (or excluded)"
+    if [ "$failed" -ne 0 ]; then
+        exit 1
+    fi
+
+    echo "All encoding::Encode types are covered"
 }
 
 generate_docs() {
@@ -60,9 +88,9 @@ extract_new_types() {
         | sort -u
 }
 
-# Extract types from the fuzz test file.
-extract_fuzz_types() {
-    grep -E 'compare_encoding!' "$FUZZ_FILE" \
+# Extract types from compare_consensus_encoding.rs.
+extract_compare_fuzz_types() {
+    grep -E 'compare_encoding!' "$COMPARE_FUZZ_FILE" \
         | grep -v '//' \
         | sed -E 's/.*compare_encoding!\s*\(\s*data\s*,\s*//' \
         | sed -E 's/\s*\);.*//' \
@@ -72,15 +100,27 @@ extract_fuzz_types() {
         | sort -u
 }
 
+# Extract types from generate-encoding-roundtrip.sh.
+# Types are listed as quoted Rust paths in the ROUNDTRIP_TYPES and SCRIPT_ROUNDTRIP_TYPES arrays,
+# e.g. "bitcoin::block::Header" or "p2p::Magic". Extract the last path component (the type name).
+extract_roundtrip_fuzz_types() {
+    grep -E '^\s+"[a-z]' "$ROUNDTRIP_FUZZ_SCRIPT" \
+        | sed -E 's/.*"([^"]+)".*/\1/' \
+        | sed -E 's/.*:://' \
+        | grep -E '^[A-Z]' \
+        | sort -u
+}
+
 # Find types that are in new_types but not in fuzz_types or exclusions.
 find_missing_types() {
     local new_types=$1
     local fuzz_types=$2
+    local exclusions=$3
     local missing=""
 
     for type in $new_types; do
         if ! echo "$fuzz_types" | grep -qw "$type"; then
-            if ! echo "$EXCLUSIONS" | grep -qw "$type"; then
+            if [ -z "$exclusions" ] || ! echo "$exclusions" | grep -qw "$type"; then
                 missing="$missing $type"
             fi
         fi