fix: Prevent aspect self-matching infinite recursion (gt-8tmz.16)

ApplyAdvice now collects original step IDs before applying rules and
only matches steps in that set. This prevents advice patterns (like "*")
from matching their own inserted before/after steps.

Added test case demonstrating that a "*" pattern only adds advice to
original steps, not to inserted steps.

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

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

internal/formula/advice.go

@@ -55,14 +55,33 @@ func MatchGlob(pattern, stepID string) bool {
 // ApplyAdvice transforms a formula's steps by applying advice rules.
 // Returns a new steps slice with advice steps inserted.
 // The original steps slice is not modified.
+//
+// Self-matching prevention (gt-8tmz.16): Advice only matches steps that
+// existed BEFORE this call. Steps inserted by advice (before/after/around)
+// are not matched, preventing infinite recursion.
 func ApplyAdvice(steps []*Step, advice []*AdviceRule) []*Step {
 	if len(advice) == 0 {
 		return steps
 	}
 
+	// Collect original step IDs to prevent self-matching (gt-8tmz.16)
+	originalIDs := collectStepIDs(steps)
+
+	return applyAdviceWithGuard(steps, advice, originalIDs)
+}
+
+// ApplyAdviceToOriginalOnly applies advice rules but only matches steps
+// whose IDs are in the originalIDs set. This prevents aspects from matching
+// steps they themselves inserted.
+func applyAdviceWithGuard(steps []*Step, advice []*AdviceRule, originalIDs map[string]bool) []*Step {
 	result := make([]*Step, 0, len(steps)*2) // Pre-allocate for insertions
 
 	for _, step := range steps {
+		// Skip steps not in original set (gt-8tmz.16)
+		if !originalIDs[step.ID] {
+			result = append(result, step)
+			continue
+		}
 		// Find matching advice rules for this step
 		var beforeSteps []*Step
 		var afterSteps []*Step
@@ -191,6 +210,23 @@ func appendUnique(slice []string, item string) []string {
 	return append(slice, item)
 }
 
+// collectStepIDs returns a set of all step IDs (including nested children).
+// Used by ApplyAdvice to prevent self-matching (gt-8tmz.16).
+func collectStepIDs(steps []*Step) map[string]bool {
+	ids := make(map[string]bool)
+	var collect func([]*Step)
+	collect = func(steps []*Step) {
+		for _, step := range steps {
+			ids[step.ID] = true
+			if len(step.Children) > 0 {
+				collect(step.Children)
+			}
+		}
+	}
+	collect(steps)
+	return ids
+}
+
 // MatchPointcut checks if a step matches a pointcut.
 func MatchPointcut(pc *Pointcut, step *Step) bool {
 	// Glob match on step ID

internal/formula/advice_test.go

@@ -321,3 +321,55 @@ func contains(slice []string, item string) bool {
 	}
 	return false
 }
+
+// TestApplyAdvice_SelfMatchingPrevention verifies that advice doesn't match
+// steps it inserted (gt-8tmz.16).
+func TestApplyAdvice_SelfMatchingPrevention(t *testing.T) {
+	// An advice rule with a broad pattern that would match its own insertions
+	// if self-matching weren't prevented.
+	advice := []*AdviceRule{
+		{
+			Target: "*", // Matches everything
+			Around: &AroundAdvice{
+				Before: []*AdviceStep{
+					{ID: "{step.id}-before", Title: "Before {step.id}"},
+				},
+				After: []*AdviceStep{
+					{ID: "{step.id}-after", Title: "After {step.id}"},
+				},
+			},
+		},
+	}
+
+	steps := []*Step{
+		{ID: "implement", Title: "Implement"},
+	}
+
+	result := ApplyAdvice(steps, advice)
+
+	// Without self-matching prevention, pattern "*" would match the inserted
+	// "implement-before" and "implement-after" steps, causing them to also
+	// get before/after steps, leading to potential infinite expansion.
+	// With prevention, we should only get the original step + its advice.
+
+	// Expected: implement-before, implement, implement-after (3 steps)
+	if len(result) != 3 {
+		t.Errorf("ApplyAdvice() produced %d steps, want 3. Got IDs: %v",
+			len(result), getStepIDs(result))
+	}
+
+	expectedIDs := []string{"implement-before", "implement", "implement-after"}
+	for i, want := range expectedIDs {
+		if result[i].ID != want {
+			t.Errorf("result[%d].ID = %q, want %q", i, result[i].ID, want)
+		}
+	}
+}
+
+func getStepIDs(steps []*Step) []string {
+	ids := make([]string, len(steps))
+	for i, s := range steps {
+		ids[i] = s.ID
+	}
+	return ids
+}