Add comprehensive test coverage and edge case handling for terminate_processes

Improvements based on PR feedback:

1. Test Coverage:
   - Add 7 new test cases for terminate_processes method
   - Cover ESRCH, EPERM, ArgumentError, RangeError scenarios
   - Test mixed success/error cases

2. Edge Case Handling:
   - Handle ArgumentError (invalid signal)
   - Handle RangeError (invalid PID)
   - Consistent with file_manager.rb patterns

3. Return Value Consistency:
   - All rescue branches now explicitly return nil
   - Consistent behavior across all error types

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude <noreply@anthropic.com>

Author: justin808

lib/react_on_rails/dev/server_manager.rb

@@ -70,12 +70,13 @@ def find_process_pids(pattern)
         def terminate_processes(pids)
           pids.each do |pid|
             Process.kill("TERM", pid)
-          rescue Errno::ESRCH
-            # Process already stopped - this is fine
+          rescue Errno::ESRCH, ArgumentError, RangeError
+            # Process already stopped, or invalid signal/PID - silently skip
             nil
           rescue Errno::EPERM
             # Permission denied - warn the user
             puts "   ⚠️  Process #{pid} - permission denied (process owned by another user)"
+            nil
           end
         end
 

spec/react_on_rails/dev/server_manager_spec.rb

@@ -203,6 +203,66 @@ def mock_system_calls
     end
   end
 
+  describe ".terminate_processes" do
+    it "successfully kills processes" do
+      pids = [1234, 5678]
+      expect(Process).to receive(:kill).with("TERM", 1234)
+      expect(Process).to receive(:kill).with("TERM", 5678)
+
+      described_class.terminate_processes(pids)
+    end
+
+    it "handles ESRCH (process not found) silently" do
+      pids = [1234]
+      allow(Process).to receive(:kill).with("TERM", 1234).and_raise(Errno::ESRCH)
+
+      # Should not raise an error and should not output anything
+      expect { described_class.terminate_processes(pids) }.not_to raise_error
+    end
+
+    it "handles EPERM (permission denied) with warning" do
+      pids = [1234]
+      allow(Process).to receive(:kill).with("TERM", 1234).and_raise(Errno::EPERM)
+
+      # Should not raise an error but should output a warning
+      expect { described_class.terminate_processes(pids) }.to output(/permission denied/).to_stdout_from_any_process
+    end
+
+    it "handles mixed success and ESRCH" do
+      pids = [1234, 5678]
+      expect(Process).to receive(:kill).with("TERM", 1234)
+      allow(Process).to receive(:kill).with("TERM", 5678).and_raise(Errno::ESRCH)
+
+      expect { described_class.terminate_processes(pids) }.not_to raise_error
+    end
+
+    it "handles mixed success and EPERM" do
+      pids = [1234, 5678]
+      expect(Process).to receive(:kill).with("TERM", 1234)
+      allow(Process).to receive(:kill).with("TERM", 5678).and_raise(Errno::EPERM)
+
+      expect do
+        described_class.terminate_processes(pids)
+      end.to output(/5678.*permission denied/).to_stdout_from_any_process
+    end
+
+    it "handles ArgumentError (invalid signal)" do
+      pids = [1234]
+      allow(Process).to receive(:kill).with("TERM", 1234).and_raise(ArgumentError)
+
+      # Should not raise an error
+      expect { described_class.terminate_processes(pids) }.not_to raise_error
+    end
+
+    it "handles RangeError (invalid PID)" do
+      pids = [999_999_999_999]
+      allow(Process).to receive(:kill).with("TERM", 999_999_999_999).and_raise(RangeError)
+
+      # Should not raise an error
+      expect { described_class.terminate_processes(pids) }.not_to raise_error
+    end
+  end
+
   describe ".show_help" do
     it "displays help information" do
       expect { described_class.show_help }.to output(%r{Usage: bin/dev \[command\]}).to_stdout_from_any_process