diff --git a/.claude-plugin/marketplace.json b/.claude-plugin/marketplace.json
index ab081b9..11b534f 100644
--- a/.claude-plugin/marketplace.json
+++ b/.claude-plugin/marketplace.json
@@ -10,7 +10,7 @@
       "name": "warp",
       "description": "Native Warp notifications when Claude completes tasks or needs input",
       "source": "./plugins/warp",
-      "version": "2.2.0",
+      "version": "2.2.1",
       "category": "productivity",
       "tags": ["notifications", "terminal", "warp"]
     },
diff --git a/plugins/warp/.claude-plugin/plugin.json b/plugins/warp/.claude-plugin/plugin.json
index 1e29217..15e2ce4 100644
--- a/plugins/warp/.claude-plugin/plugin.json
+++ b/plugins/warp/.claude-plugin/plugin.json
@@ -1,7 +1,7 @@
 {
   "name": "warp",
   "description": "Warp terminal integration for Claude Code - native notifications, and more to come",
-  "version": "2.2.0",
+  "version": "2.2.1",
   "author": {
     "name": "Warp",
     "url": "https://warp.dev"
diff --git a/plugins/warp/scripts/emit-terminal-sequence.sh b/plugins/warp/scripts/emit-terminal-sequence.sh
index b6a83b9..9a46bc8 100644
--- a/plugins/warp/scripts/emit-terminal-sequence.sh
+++ b/plugins/warp/scripts/emit-terminal-sequence.sh
@@ -45,6 +45,17 @@ _parse_cc_version() {
     echo "$1" | grep -oE '[0-9]+\.[0-9]+\.[0-9]+' | head -1
 }
 
+# Returns 0 if we are running inside Claude Code.
+#
+# The `terminalSequence` output field is Claude Code-specific. Other harnesses
+# run Claude Code-format hooks (Codex, for one, maps hooks/hooks.json onto its
+# own event names) but reject unknown keys in hook stdout, so emitting it there
+# turns every hook into a user-visible error -- e.g. Codex prints
+# "hook returned invalid post-tool-use JSON output" on every tool call.
+_is_claude_code() {
+    [ -n "${CLAUDECODE:-}" ] || [ -n "${CLAUDE_CODE_VERSION:-}" ]
+}
+
 # Returns 0 if the running Claude Code version supports terminalSequence.
 _supports_terminal_sequence() {
     local raw="${CLAUDE_CODE_VERSION:-}"
@@ -82,5 +93,9 @@ emit_terminal_sequence() {
     if printf '%s' "$seq" > /dev/tty 2>/dev/null; then
         return 0
     fi
+
+    # No tty and no version. Only gamble on terminalSequence when we can still
+    # tell we are inside Claude Code; every other harness rejects the field.
+    _is_claude_code || return 0
     jq -nc --arg seq "$seq" '{terminalSequence: $seq}'
 }