Introduce check to re-exports CI for error types

diff --git a/.github/workflows/rust.yml b/.github/workflows/rust.yml
index 8bbffa1c..2337d2f0 100644
--- a/.github/workflows/rust.yml
+++ b/.github/workflows/rust.yml
@@ -236,6 +236,8 @@ jobs:
         run: |
           contrib/generate-primitives-re-export-test.sh && (cd ./primitives && cargo test --all-features)
           contrib/generate-bitcoin-re-export-test.sh && (cd ./bitcoin && cargo test --all-features)
+      - name: "Check error type re-exports"
+        run: contrib/check-error-reexports.sh
 
   DiffMutants:
     name: Check cargo mutants in diff - stable toolchain
diff --git a/contrib/check-error-reexports.sh b/contrib/check-error-reexports.sh
new file mode 100755
index 00000000..9d0d21c1
--- /dev/null
+++ b/contrib/check-error-reexports.sh
@@ -0,0 +1,108 @@
+#!/usr/bin/env bash
+#
+# Check that every error type defined in an `error` submodule is re-exported
+# at the parent module level.
+#
+# The policy is: if a type is defined at `foo::error::BarError` then it must
+# also be accessible as `foo::BarError` (i.e. re-exported by the parent module).
+#
+# Uses the API text files to verify the policy. Types are identified by
+# `pub struct` or `pub enum` lines whose path contains `::error::` as a path
+# segment (not as part of a type name). A re-export is present when the same
+# type name appears at the parent path in any `pub struct`, `pub enum`, or
+# `pub type` line (without the `::error::` segment).
+#
+# Usage: ./contrib/check-error-reexports.sh
+
+set -euo pipefail
+
+main() {
+    check_required_commands
+
+    local has_violations=false
+
+    # Auto-discover all crates that have API files.
+    while IFS= read -r api_file; do
+        local crate
+        crate=$(basename "$(dirname "$(dirname "$api_file")")")
+
+        # Collect all types defined in ::error:: submodules.
+        # We match `pub struct` and `pub enum` lines where the path contains
+        # `::error::` as a segment, and the type name is the final segment
+        # (no further `::` after the type name).
+        local error_module_types
+        error_module_types=$(grep -oP '^(?:#\[non_exhaustive\] )?pub (?:struct|enum|use) \K[A-Za-z0-9_]+(?:::[A-Za-z0-9_]+)*::error::[A-Za-z0-9_]+Error(?=\(|;|\s|<|$)' "$api_file" \
+            | sort -u || true)
+
+        if [[ -z "$error_module_types" ]]; then
+            say "$crate: OK (no ::error:: submodule types found)"
+            continue
+        fi
+
+        local violations=""
+
+        while IFS= read -r type_path; do
+            # Derive the expected re-export path by removing the `::error` segment.
+            # e.g. foo::bar::error::BazError -> foo::bar::BazError
+            local parent_path
+            parent_path="${type_path/::error::/::}"
+
+            # Escape the path for use as a fixed string in grep.
+            local escaped
+            escaped=$(printf '%s' "$parent_path" | sed 's/[.[\*^$]/\\&/g')
+
+            # A re-export is present when pub struct, enum, or type appears at
+            # exactly this path (followed by end-of-input, whitespace, or `(`).
+            # The line may be prefixed with an attribute such as `#[non_exhaustive]`.
+            if ! grep -qP "^(?:#\[[^\]]+\] )?pub (?:struct|enum|type|use) ${escaped}(?:\(|;|\s|<|$)" "$api_file"; then
+                violations="${violations}  - ${type_path} -> missing ${parent_path}"$'\n'
+            fi
+        done <<< "$error_module_types"
+
+        if [[ -n "$violations" ]]; then
+            has_violations=true
+            say_err "Crate '$crate': error types without a parent-level re-export:"
+            say_err "$violations"
+        else
+            say "$crate: OK"
+        fi
+    done < <(find . -path "*/api/all-features.txt" | sort)
+
+    if $has_violations; then
+        err "Some error types are missing a re-export in the parent module."
+    fi
+
+    say "All checks passed."
+}
+
+check_required_commands() {
+    need_cmd find
+    need_cmd grep
+    need_cmd sed
+    need_cmd sort
+}
+
+say() {
+    echo "$1"
+}
+
+say_err() {
+    echo "$1" >&2
+}
+
+err() {
+    echo "$1" >&2
+    exit 1
+}
+
+need_cmd() {
+    if ! command -v "$1" > /dev/null 2>&1; then
+        err "need '$1' (command not found)"
+    fi
+}
+
+#
+# Main script
+#
+main "$@"
+exit 0