feat: implement Step.Condition evaluation in bd cook (bd-7zka.1)

Add compile-time step filtering based on formula variables:
- New EvaluateStepCondition function for {{var}} truthy and equality checks
- FilterStepsByCondition to exclude steps based on conditions
- Integration into pour, wisp, and mol bond commands
- Supports: {{var}}, {{var}} == value, {{var}} != value

Steps with conditions that evaluate to false are excluded from the
cooked formula, along with their children.

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

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

internal/formula/stepcondition.go

@@ -0,0 +1,141 @@
+// Package formula provides Step.Condition evaluation for compile-time step filtering.
+//
+// Step.Condition is simpler than the runtime condition evaluation in condition.go.
+// It evaluates at cook/pour time to include or exclude steps based on formula variables.
+//
+// Supported formats:
+//   - "{{var}}" - truthy check (non-empty, non-"false", non-"0")
+//   - "{{var}} == value" - equality check
+//   - "{{var}} != value" - inequality check
+package formula
+
+import (
+	"fmt"
+	"regexp"
+	"strings"
+)
+
+// Step condition patterns
+var (
+	// {{var}} - simple variable reference for truthy check
+	stepCondVarPattern = regexp.MustCompile(`^\{\{(\w+)\}\}$`)
+
+	// {{var}} == value or {{var}} != value
+	stepCondComparePattern = regexp.MustCompile(`^\{\{(\w+)\}\}\s*(==|!=)\s*(.+)$`)
+)
+
+// EvaluateStepCondition evaluates a step's condition against variable values.
+// Returns true if the step should be included, false if it should be skipped.
+//
+// Condition formats:
+//   - "" (empty) - always include
+//   - "{{var}}" - include if var is truthy (non-empty, non-"false", non-"0")
+//   - "{{var}} == value" - include if var equals value
+//   - "{{var}} != value" - include if var does not equal value
+func EvaluateStepCondition(condition string, vars map[string]string) (bool, error) {
+	condition = strings.TrimSpace(condition)
+
+	// Empty condition means always include
+	if condition == "" {
+		return true, nil
+	}
+
+	// Try truthy pattern: {{var}}
+	if m := stepCondVarPattern.FindStringSubmatch(condition); m != nil {
+		varName := m[1]
+		value := vars[varName]
+		return isTruthy(value), nil
+	}
+
+	// Try comparison pattern: {{var}} == value or {{var}} != value
+	if m := stepCondComparePattern.FindStringSubmatch(condition); m != nil {
+		varName := m[1]
+		operator := m[2]
+		expected := strings.TrimSpace(m[3])
+
+		// Remove quotes from expected value if present
+		expected = unquoteValue(expected)
+
+		actual := vars[varName]
+
+		switch operator {
+		case "==":
+			return actual == expected, nil
+		case "!=":
+			return actual != expected, nil
+		}
+	}
+
+	return false, fmt.Errorf("invalid step condition format: %q (expected {{var}} or {{var}} == value)", condition)
+}
+
+// isTruthy returns true if a value is considered "truthy" for step conditions.
+// Falsy values: empty string, "false", "0", "no", "off"
+// All other values are truthy.
+func isTruthy(value string) bool {
+	if value == "" {
+		return false
+	}
+	lower := strings.ToLower(value)
+	switch lower {
+	case "false", "0", "no", "off":
+		return false
+	}
+	return true
+}
+
+// unquoteValue removes surrounding quotes from a value if present.
+func unquoteValue(s string) string {
+	if len(s) >= 2 {
+		if (s[0] == '"' && s[len(s)-1] == '"') || (s[0] == '\'' && s[len(s)-1] == '\'') {
+			return s[1 : len(s)-1]
+		}
+	}
+	return s
+}
+
+// FilterStepsByCondition filters a list of steps based on their Condition field.
+// Steps with conditions that evaluate to false are excluded from the result.
+// Children of excluded steps are also excluded.
+//
+// Parameters:
+//   - steps: the steps to filter
+//   - vars: variable values for condition evaluation
+//
+// Returns the filtered steps and any error encountered during evaluation.
+func FilterStepsByCondition(steps []*Step, vars map[string]string) ([]*Step, error) {
+	if vars == nil {
+		vars = make(map[string]string)
+	}
+
+	result := make([]*Step, 0, len(steps))
+
+	for _, step := range steps {
+		// Evaluate step condition
+		include, err := EvaluateStepCondition(step.Condition, vars)
+		if err != nil {
+			return nil, fmt.Errorf("step %q: %w", step.ID, err)
+		}
+
+		if !include {
+			// Skip this step and all its children
+			continue
+		}
+
+		// Clone the step to avoid mutating input
+		clone := cloneStep(step)
+
+		// Recursively filter children
+		if len(step.Children) > 0 {
+			filteredChildren, err := FilterStepsByCondition(step.Children, vars)
+			if err != nil {
+				return nil, err
+			}
+			clone.Children = filteredChildren
+		}
+
+		result = append(result, clone)
+	}
+
+	return result, nil
+}

internal/formula/stepcondition_test.go

@@ -0,0 +1,331 @@
+package formula
+
+import (
+	"testing"
+)
+
+func TestEvaluateStepCondition(t *testing.T) {
+	tests := []struct {
+		name      string
+		condition string
+		vars      map[string]string
+		want      bool
+		wantErr   bool
+	}{
+		// Empty condition - always include
+		{
+			name:      "empty condition",
+			condition: "",
+			vars:      nil,
+			want:      true,
+			wantErr:   false,
+		},
+		// Truthy checks: {{var}}
+		{
+			name:      "truthy - non-empty value",
+			condition: "{{enabled}}",
+			vars:      map[string]string{"enabled": "yes"},
+			want:      true,
+			wantErr:   false,
+		},
+		{
+			name:      "truthy - empty value",
+			condition: "{{enabled}}",
+			vars:      map[string]string{"enabled": ""},
+			want:      false,
+			wantErr:   false,
+		},
+		{
+			name:      "truthy - missing variable",
+			condition: "{{enabled}}",
+			vars:      map[string]string{},
+			want:      false,
+			wantErr:   false,
+		},
+		{
+			name:      "truthy - false string",
+			condition: "{{enabled}}",
+			vars:      map[string]string{"enabled": "false"},
+			want:      false,
+			wantErr:   false,
+		},
+		{
+			name:      "truthy - FALSE string",
+			condition: "{{enabled}}",
+			vars:      map[string]string{"enabled": "FALSE"},
+			want:      false,
+			wantErr:   false,
+		},
+		{
+			name:      "truthy - 0 string",
+			condition: "{{enabled}}",
+			vars:      map[string]string{"enabled": "0"},
+			want:      false,
+			wantErr:   false,
+		},
+		{
+			name:      "truthy - no string",
+			condition: "{{enabled}}",
+			vars:      map[string]string{"enabled": "no"},
+			want:      false,
+			wantErr:   false,
+		},
+		{
+			name:      "truthy - off string",
+			condition: "{{enabled}}",
+			vars:      map[string]string{"enabled": "off"},
+			want:      false,
+			wantErr:   false,
+		},
+		{
+			name:      "truthy - true string",
+			condition: "{{enabled}}",
+			vars:      map[string]string{"enabled": "true"},
+			want:      true,
+			wantErr:   false,
+		},
+		// Equality checks: {{var}} == value
+		{
+			name:      "equality - match",
+			condition: "{{env}} == staging",
+			vars:      map[string]string{"env": "staging"},
+			want:      true,
+			wantErr:   false,
+		},
+		{
+			name:      "equality - no match",
+			condition: "{{env}} == production",
+			vars:      map[string]string{"env": "staging"},
+			want:      false,
+			wantErr:   false,
+		},
+		{
+			name:      "equality - quoted value match",
+			condition: "{{env}} == 'staging'",
+			vars:      map[string]string{"env": "staging"},
+			want:      true,
+			wantErr:   false,
+		},
+		{
+			name:      "equality - double quoted value match",
+			condition: `{{env}} == "staging"`,
+			vars:      map[string]string{"env": "staging"},
+			want:      true,
+			wantErr:   false,
+		},
+		// Inequality checks: {{var}} != value
+		{
+			name:      "inequality - different value",
+			condition: "{{env}} != production",
+			vars:      map[string]string{"env": "staging"},
+			want:      true,
+			wantErr:   false,
+		},
+		{
+			name:      "inequality - same value",
+			condition: "{{env}} != staging",
+			vars:      map[string]string{"env": "staging"},
+			want:      false,
+			wantErr:   false,
+		},
+		// Invalid conditions
+		{
+			name:      "invalid - no variable braces",
+			condition: "env == staging",
+			vars:      map[string]string{"env": "staging"},
+			want:      false,
+			wantErr:   true,
+		},
+		{
+			name:      "invalid - random text",
+			condition: "something random",
+			vars:      map[string]string{},
+			want:      false,
+			wantErr:   true,
+		},
+		// Edge cases
+		{
+			name:      "whitespace in condition",
+			condition: "  {{env}}  ==  staging  ",
+			vars:      map[string]string{"env": "staging"},
+			want:      true,
+			wantErr:   false,
+		},
+		{
+			name:      "value with spaces",
+			condition: "{{msg}} == 'hello world'",
+			vars:      map[string]string{"msg": "hello world"},
+			want:      true,
+			wantErr:   false,
+		},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			got, err := EvaluateStepCondition(tt.condition, tt.vars)
+			if (err != nil) != tt.wantErr {
+				t.Errorf("EvaluateStepCondition() error = %v, wantErr %v", err, tt.wantErr)
+				return
+			}
+			if got != tt.want {
+				t.Errorf("EvaluateStepCondition() = %v, want %v", got, tt.want)
+			}
+		})
+	}
+}
+
+func TestIsTruthy(t *testing.T) {
+	tests := []struct {
+		value string
+		want  bool
+	}{
+		{"", false},
+		{"false", false},
+		{"False", false},
+		{"FALSE", false},
+		{"0", false},
+		{"no", false},
+		{"No", false},
+		{"NO", false},
+		{"off", false},
+		{"Off", false},
+		{"OFF", false},
+		{"true", true},
+		{"True", true},
+		{"TRUE", true},
+		{"1", true},
+		{"yes", true},
+		{"on", true},
+		{"anything", true},
+		{"enabled", true},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.value, func(t *testing.T) {
+			if got := isTruthy(tt.value); got != tt.want {
+				t.Errorf("isTruthy(%q) = %v, want %v", tt.value, got, tt.want)
+			}
+		})
+	}
+}
+
+func TestFilterStepsByCondition(t *testing.T) {
+	tests := []struct {
+		name     string
+		steps    []*Step
+		vars     map[string]string
+		wantIDs  []string // Expected step IDs in result
+		wantErr  bool
+	}{
+		{
+			name: "no conditions - all included",
+			steps: []*Step{
+				{ID: "step1", Title: "Step 1"},
+				{ID: "step2", Title: "Step 2"},
+			},
+			vars:    nil,
+			wantIDs: []string{"step1", "step2"},
+		},
+		{
+			name: "truthy condition - included",
+			steps: []*Step{
+				{ID: "step1", Title: "Step 1", Condition: "{{enabled}}"},
+			},
+			vars:    map[string]string{"enabled": "true"},
+			wantIDs: []string{"step1"},
+		},
+		{
+			name: "truthy condition - excluded",
+			steps: []*Step{
+				{ID: "step1", Title: "Step 1", Condition: "{{enabled}}"},
+			},
+			vars:    map[string]string{"enabled": "false"},
+			wantIDs: []string{},
+		},
+		{
+			name: "mixed conditions",
+			steps: []*Step{
+				{ID: "step1", Title: "Step 1"},
+				{ID: "step2", Title: "Step 2", Condition: "{{run_tests}}"},
+				{ID: "step3", Title: "Step 3", Condition: "{{env}} == production"},
+			},
+			vars:    map[string]string{"run_tests": "yes", "env": "staging"},
+			wantIDs: []string{"step1", "step2"},
+		},
+		{
+			name: "children inherit parent filter",
+			steps: []*Step{
+				{
+					ID:        "parent",
+					Title:     "Parent",
+					Condition: "{{include_parent}}",
+					Children: []*Step{
+						{ID: "child1", Title: "Child 1"},
+						{ID: "child2", Title: "Child 2"},
+					},
+				},
+			},
+			vars:    map[string]string{"include_parent": "false"},
+			wantIDs: []string{}, // Parent excluded, children go with it
+		},
+		{
+			name: "child with own condition",
+			steps: []*Step{
+				{
+					ID:    "parent",
+					Title: "Parent",
+					Children: []*Step{
+						{ID: "child1", Title: "Child 1"},
+						{ID: "child2", Title: "Child 2", Condition: "{{include_child2}}"},
+					},
+				},
+			},
+			vars:    map[string]string{"include_child2": "no"},
+			wantIDs: []string{"parent", "child1"},
+		},
+		{
+			name: "equality condition",
+			steps: []*Step{
+				{ID: "deploy-staging", Title: "Deploy Staging", Condition: "{{env}} == staging"},
+				{ID: "deploy-prod", Title: "Deploy Prod", Condition: "{{env}} == production"},
+			},
+			vars:    map[string]string{"env": "staging"},
+			wantIDs: []string{"deploy-staging"},
+		},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			result, err := FilterStepsByCondition(tt.steps, tt.vars)
+			if (err != nil) != tt.wantErr {
+				t.Errorf("FilterStepsByCondition() error = %v, wantErr %v", err, tt.wantErr)
+				return
+			}
+
+			// Collect all IDs (including children) from result
+			gotIDs := collectStepIDsForTest(result)
+			if len(gotIDs) != len(tt.wantIDs) {
+				t.Errorf("FilterStepsByCondition() got %d steps %v, want %d steps %v",
+					len(gotIDs), gotIDs, len(tt.wantIDs), tt.wantIDs)
+				return
+			}
+
+			for i, wantID := range tt.wantIDs {
+				if i >= len(gotIDs) || gotIDs[i] != wantID {
+					t.Errorf("FilterStepsByCondition() step[%d] = %v, want %v", i, gotIDs, tt.wantIDs)
+					return
+				}
+			}
+		})
+	}
+}
+
+// collectStepIDsForTest collects all step IDs (including children) in order.
+func collectStepIDsForTest(steps []*Step) []string {
+	var ids []string
+	for _, s := range steps {
+		ids = append(ids, s.ID)
+		ids = append(ids, collectStepIDsForTest(s.Children)...)
+	}
+	return ids
+}

internal/formula/types.go

@@ -175,8 +175,8 @@ type Step struct {
 	ExpandVars map[string]string `json:"expand_vars,omitempty"`
 
 	// Condition makes this step optional based on a variable.
-	// Format: "{{var}}" (truthy) or "{{var}} == value".
-	// TODO(bd-7zka): Not yet implemented in bd cook. Filed as future work.
+	// Format: "{{var}}" (truthy) or "{{var}} == value" or "{{var}} != value".
+	// Evaluated at cook/pour time via FilterStepsByCondition.
 	Condition string `json:"condition,omitempty"`
 
 	// Children are nested steps (for creating epic hierarchies).