rpn: eliminate RPN.mode duplication with Operations.mode

Remove the mode field from the RPN struct, which was duplicated from
Operations.mode. All reads of r.mode in rpn_parse.go and rpn_ops.go
now go through r.ops.GetMode().

- Add GetMode() to the Operator interface so RPN can access mode
  through its Operator dependency
- Remove mode field from RPN struct in rpn_state.go
- Remove mode initialization from NewRPN
- Update SetMode to only set mode on Operations
- Update GetMode to delegate to Operations
- Replace r.mode with r.ops.GetMode() in rpn_parse.go (5 sites)
- Replace r.mode with r.ops.GetMode() in rpn_ops.go (1 site)

4 files changed, 9 insertions, 10 deletions

diff --git a/internal/rpn/operations_interfaces.go b/internal/rpn/operations_interfaces.go
index 6076ec0..002ec33 100644
--- a/internal/rpn/operations_interfaces.go
+++ b/internal/rpn/operations_interfaces.go
@@ -86,6 +86,8 @@ type Operator interface {
 	PowerIntOperator
 	// SetMode sets the calculation mode (e.g., FloatMode, RationalMode).
 	SetMode(CalculationMode)
+	// GetMode returns the current calculation mode.
+	GetMode() CalculationMode
 	// SetPrefixMode sets the prefix mode for data size calculations
 	SetPrefixMode(PrefixMode)
 	// GetPrefixMode returns the current prefix mode
diff --git a/internal/rpn/rpn_ops.go b/internal/rpn/rpn_ops.go
index 5f0863a..8620197 100644
--- a/internal/rpn/rpn_ops.go
+++ b/internal/rpn/rpn_ops.go
@@ -20,7 +20,7 @@ func Tokenize(input string) []string {
 // This is useful for commands that need to show the stack without consuming it.
 func (r *RPN) ResultStack(tokens []string) (string, error) {
 	r.mu.RLock()
-	mode := r.mode
+	mode := r.ops.GetMode()
 	r.mu.RUnlock()
 
 	stack := NewStack()
diff --git a/internal/rpn/rpn_parse.go b/internal/rpn/rpn_parse.go
index 2eaab04..615e804 100644
--- a/internal/rpn/rpn_parse.go
+++ b/internal/rpn/rpn_parse.go
@@ -388,12 +388,12 @@ func (r *RPN) handleOperator(stack *Stack, token string, tokenIndex int) (string
 
 	// Check if it's a variable reference first (before operators)
 	if val, exists := r.vars.GetVariable(token); exists {
-		stack.Push(NewNumber(val, r.mode))
+		stack.Push(NewNumber(val, r.ops.GetMode()))
 		return "", nil
 	}
 	// Check if it's a constant reference (before operators)
 	if val, exists := r.consts.GetConstant(token); exists {
-		stack.Push(NewNumber(val, r.mode))
+		stack.Push(NewNumber(val, r.ops.GetMode()))
 		return "", nil
 	}
 
@@ -486,7 +486,7 @@ func (r *RPN) pushLiteral(stack *Stack, token string) (bool, error) {
 		if stack.Len() >= r.maxStack {
 			return false, fmt.Errorf("stack overflow")
 		}
-		stack.Push(NewNumber(num, r.mode))
+		stack.Push(NewNumber(num, r.ops.GetMode()))
 		return true, nil
 	}
 
@@ -495,7 +495,7 @@ func (r *RPN) pushLiteral(stack *Stack, token string) (bool, error) {
 		if stack.Len() >= r.maxStack {
 			return false, fmt.Errorf("stack overflow")
 		}
-		stack.Push(NewNumberWithMetric(num, r.mode, metric))
+		stack.Push(NewNumberWithMetric(num, r.ops.GetMode(), metric))
 		return true, nil
 	}
 
@@ -507,7 +507,7 @@ func (r *RPN) pushLiteral(stack *Stack, token string) (bool, error) {
 			if stack.Len() >= r.maxStack {
 				return false, fmt.Errorf("stack overflow")
 			}
-			stack.Push(NewNumberWithMetric(1, r.mode, metric))
+			stack.Push(NewNumberWithMetric(1, r.ops.GetMode(), metric))
 			return true, nil
 		}
 		return false, fmt.Errorf("unknown metric %q in %q", metricName, token)
diff --git a/internal/rpn/rpn_state.go b/internal/rpn/rpn_state.go
index baf64de..647b5c3 100644
--- a/internal/rpn/rpn_state.go
+++ b/internal/rpn/rpn_state.go
@@ -19,7 +19,6 @@ type RPN struct {
 	assignHandler  *assignmentHandler
 	maxStack       int
 	currentStack   *Stack
-	mode           CalculationMode
 	metricRegistry *MetricRegistry
 }
 
@@ -42,7 +41,6 @@ func NewRPN(vars VariableStore, reg ...*MetricRegistry) *RPN {
 		assignHandler:  newAssignmentHandler(),
 		maxStack:       1000, // Reasonable limit for RPN expressions
 		currentStack:   NewStack(),
-		mode:           FloatMode, // Default mode
 		metricRegistry: r,
 	}
 }
@@ -58,7 +56,7 @@ func (r *RPN) GetConstants() ConstantsProvider {
 func (r *RPN) GetMode() CalculationMode {
 	r.mu.RLock()
 	defer r.mu.RUnlock()
-	return r.mode
+	return r.ops.GetMode()
 }
 
 // SetMode sets the calculation mode.
@@ -66,7 +64,6 @@ func (r *RPN) GetMode() CalculationMode {
 func (r *RPN) SetMode(mode CalculationMode) {
 	r.mu.Lock()
 	defer r.mu.Unlock()
-	r.mode = mode
 	r.ops.SetMode(mode)
 }