diff --git a/nix/packages/hive-forge-tools.nix b/nix/packages/hive-forge-tools.nix
index 188b279..33eb6e5 100644
--- a/nix/packages/hive-forge-tools.nix
+++ b/nix/packages/hive-forge-tools.nix
@@ -27,21 +27,28 @@ pkgs.writeShellApplication {
     _token=$(cat "$_token_file")
     FORGE_API="$HIVE_FORGE_URL/api/v1"
 
+    # `-sS --fail-with-body` makes curl quiet on success, print errors to
+    # stderr on transport failures, AND surface the response body for HTTP
+    # error codes (4xx/5xx) before exiting non-zero. Without this, a 500 /
+    # 404 from forge silently returned an empty stdout — combined with the
+    # script's `set -o pipefail` + the `| jq ...` consumer, the failure
+    # propagated as "no output" with no clue about what went wrong (closes
+    # #353).
     forge_get() {
-      ${pkgs.curl}/bin/curl -sf \
+      ${pkgs.curl}/bin/curl -sS --fail-with-body \
         -H "Authorization: token $_token" \
         -H "Accept: application/json" \
         "$1"
     }
     forge_post() {
-      ${pkgs.curl}/bin/curl -sf -X POST \
+      ${pkgs.curl}/bin/curl -sS --fail-with-body -X POST \
         -H "Authorization: token $_token" \
         -H "Content-Type: application/json" \
         -H "Accept: application/json" \
         -d "$2" "$1"
     }
     forge_patch() {
-      ${pkgs.curl}/bin/curl -sf -X PATCH \
+      ${pkgs.curl}/bin/curl -sS --fail-with-body -X PATCH \
         -H "Authorization: token $_token" \
         -H "Content-Type: application/json" \
         -H "Accept: application/json" \
@@ -51,13 +58,13 @@ pkgs.writeShellApplication {
       local _url="$1"
       local _body="''${2:-}"
       if [ -n "$_body" ]; then
-        ${pkgs.curl}/bin/curl -sf -X DELETE \
+        ${pkgs.curl}/bin/curl -sS --fail-with-body -X DELETE \
           -H "Authorization: token $_token" \
           -H "Content-Type: application/json" \
           -H "Accept: application/json" \
           -d "$_body" "$_url"
       else
-        ${pkgs.curl}/bin/curl -sf -X DELETE \
+        ${pkgs.curl}/bin/curl -sS --fail-with-body -X DELETE \
           -H "Authorization: token $_token" \
           -H "Accept: application/json" \
           "$_url"
@@ -189,17 +196,29 @@ pkgs.writeShellApplication {
     cmd_assign() {
       # assign <number> <user> [--remove]
       # Assign or unassign a user on an issue or PR.
+      #
+      # The Forgejo API has no dedicated `POST /issues/{n}/assignees`
+      # endpoint (closes #353) — assignees are an EditIssueOption field
+      # on the issue itself. We patch the full assignee list:
+      #   - add: GET current assignees, append `_user`, PATCH back
+      #   - remove: GET current assignees, drop `_user`, PATCH back
+      # The PATCH is idempotent: re-adding an existing assignee or
+      # removing one that's not on the list is a no-op (the resulting
+      # assignee list is unchanged).
       if [ $# -lt 2 ]; then echo "usage: hive-forge assign <number> <user> [--remove]" >&2; exit 1; fi
       local _n="$1" _user="$2" _remove="''${3:-}"
-      local _payload
-      _payload=$(jq -n --arg u "$_user" '{assignees:[$u]}')
+      local _current _payload
+      _current=$(forge_get "$FORGE_API/repos/$HIVE_FORGE_REPO/issues/$_n" \
+        | jq -c '[.assignees[]?.login]')
       if [ "$_remove" = "--remove" ]; then
-        forge_delete "$FORGE_API/repos/$HIVE_FORGE_REPO/issues/$_n/assignees" "$_payload" \
-          | jq '{number,assignees:[.assignees[]?.login]}'
+        _payload=$(jq -n --argjson cur "$_current" --arg u "$_user" \
+          '{assignees: ($cur - [$u])}')
       else
-        forge_post "$FORGE_API/repos/$HIVE_FORGE_REPO/issues/$_n/assignees" "$_payload" \
-          | jq '{number,assignees:[.assignees[]?.login]}'
+        _payload=$(jq -n --argjson cur "$_current" --arg u "$_user" \
+          '{assignees: (($cur + [$u]) | unique)}')
       fi
+      forge_patch "$FORGE_API/repos/$HIVE_FORGE_REPO/issues/$_n" "$_payload" \
+        | jq '{number,assignees:[.assignees[]?.login]}'
     }
 
     cmd_close() {