diff --git a/Makefile b/Makefile
index 5304745..e931a95 100644
--- a/Makefile
+++ b/Makefile
@@ -11,7 +11,15 @@ help:
 	@echo "  install     Sync venv, symlink bin, install shell completions"
 	@echo "  uninstall   Remove bin, completions and user symlinks"
 
+# Working tree: xiaohe-agent/packages/myagents (submodule of apaam/myagents).
+# Refuse ephemeral GHA runner checkouts (_work) so ~/.local/bin cannot point there.
 install:
+	@case "$(ROOT_DIR)" in \
+	  */_work/*|*/.xiaohe/actions-runner/*) \
+	    echo "ERROR: refuse install from GHA runner worktree: $(ROOT_DIR)" >&2; \
+	    echo "Use: cd <xiaohe-agent>/packages/myagents && make install" >&2; \
+	    exit 1 ;; \
+	esac
 	@cd "$(ROOT_DIR)" && \
 	if command -v uv >/dev/null 2>&1; then \
 		uv sync; \
@@ -22,6 +30,10 @@ install:
 	@$(MAKE) _symlink-commands
 	@echo "Installing shell completions…"
 	@myagents completion install || echo "Warning: completion install failed"
+	@case "$(ROOT_DIR)" in \
+	  */_work/*|*/.xiaohe/actions-runner/*) \
+	    echo "ERROR: install root still a runner tree: $(ROOT_DIR)" >&2; exit 1 ;; \
+	esac
 
 _symlink-commands:
 	@mkdir -p "$(USER_BIN_DIR)"