From 5dcfc2e953ff69f1d9df5898502fae97eb7a4eea Mon Sep 17 00:00:00 2001
From: Eric Rakestraw <eric@rakestraw.us>
Date: Thu, 5 Nov 2026 14:03:45 +0000
Subject: [PATCH] Merge condition evidence without repeated copies

---
 docs/roadmap/implementation.md       |  6 ++++++
 internal/prompt/requirements.go      | 31 +++++++++++++++-------------
 internal/prompt/requirements_test.go | 29 ++++++++++++++++++++++++++
 3 files changed, 52 insertions(+), 14 deletions(-)

diff --git a/docs/roadmap/implementation.md b/docs/roadmap/implementation.md
index 96750c2..c97f71f 100644
--- a/docs/roadmap/implementation.md
+++ b/docs/roadmap/implementation.md
@@ -444,6 +444,12 @@ rendering comparisons. Source work counts or focused measurements demonstrate
 removal of the identified growing-copy pattern; no grammar or expression limit
 changes, universal complexity promise, or allocation-count assertion is added.
 
+Completion: owned condition sets merge smaller into larger without retaining
+operand snapshots. For the documented distinct left-heavy cases, source work is
+3, 15, and 127 insertions at N=4, 16, and 128, respectively, excluding leaf
+creation (previously 9, 135, and 8,255). Prompt requirements tests pass on Go
+1.27.3; these counts are not a general complexity guarantee.
+
 ## Stage 17: Share Requirement Branch Orchestration
 
 **Catalog:** 23. **Files:** internal prompt requirement traversal/evaluation.
diff --git a/internal/prompt/requirements.go b/internal/prompt/requirements.go
index 1167c85..a6373a0 100644
--- a/internal/prompt/requirements.go
+++ b/internal/prompt/requirements.go
@@ -319,24 +319,27 @@ func mergeConditionEvaluations(left, right conditionEvaluation) conditionEvaluat
 	result := conditionEvaluation{
 		unsupported:      left.unsupported || right.unsupported,
 		inputNameUnknown: left.inputNameUnknown || right.inputNameUnknown,
-		missingVariables: make(map[string]struct{}, len(left.missingVariables)+len(right.missingVariables)),
-		contentInputs:    make(map[string]struct{}, len(left.contentInputs)+len(right.contentInputs)),
-	}
-	for name := range left.missingVariables {
-		result.missingVariables[name] = struct{}{}
-	}
-	for name := range right.missingVariables {
-		result.missingVariables[name] = struct{}{}
-	}
-	for name := range left.contentInputs {
-		result.contentInputs[name] = struct{}{}
-	}
-	for name := range right.contentInputs {
-		result.contentInputs[name] = struct{}{}
+		missingVariables: mergeOwnedNames(left.missingVariables, right.missingVariables),
+		contentInputs:    mergeOwnedNames(left.contentInputs, right.contentInputs),
 	}
 	return result
 }
 
+// Condition results own their sets; callers retain operand values and flags,
+// not independent snapshots of these maps after a merge.
+func mergeOwnedNames(left, right map[string]struct{}) map[string]struct{} {
+	if len(left) < len(right) {
+		left, right = right, left
+	}
+	if left == nil {
+		return right
+	}
+	for name := range right {
+		left[name] = struct{}{}
+	}
+	return left
+}
+
 func branchReach(parent requirementReachability, known, truth, selected bool) requirementReachability {
 	if parent == requirementInactive {
 		return requirementInactive
diff --git a/internal/prompt/requirements_test.go b/internal/prompt/requirements_test.go
index d26100c..737a1da 100644
--- a/internal/prompt/requirements_test.go
+++ b/internal/prompt/requirements_test.go
@@ -406,6 +406,35 @@ func TestAnalyzeRequirementsReportsUnresolvedDecisionAndContentConditions(t *tes
 	}
 }
 
+func TestConditionEvaluationMergesOwnedEvidence(t *testing.T) {
+	left := conditionEvaluation{missingVariables: map[string]struct{}{"a": {}, "b": {}}, contentInputs: map[string]struct{}{"document": {}}, unsupported: true}
+	right := conditionEvaluation{missingVariables: map[string]struct{}{"b": {}, "c": {}}, inputNameUnknown: true}
+	merged := mergeConditionEvaluations(left, right)
+	if !merged.unsupported || !merged.inputNameUnknown || len(merged.missingVariables) != 3 || len(merged.contentInputs) != 1 {
+		t.Fatalf("merged evidence = %+v", merged)
+	}
+	transferred := mergeConditionEvaluations(conditionEvaluation{}, conditionEvaluation{missingVariables: map[string]struct{}{"only": {}}})
+	if len(transferred.missingVariables) != 1 || transferred.contentInputs != nil {
+		t.Fatalf("transferred evidence = %+v", transferred)
+	}
+}
+
+func TestAnalyzeRequirementsRetainsLeftHeavyMissingConditions(t *testing.T) {
+	compiled := compileRequirementTemplate(t, "nested", `{{if eq (eq (eq .a .b) .c) .d}}{{input "yes"}}{{else}}{{input "no"}}{{end}}`)
+	result, err := AnalyzeRequirements(context.Background(), &domain.PromptDefinition{}, RequirementSnapshot{Templates: CompiledTemplates{Messages: []*template.Template{compiled}}}, nil, false)
+	if err != nil {
+		t.Fatal(err)
+	}
+	if result.Complete || len(result.Variables) != 4 || len(result.Inputs) != 2 {
+		t.Fatalf("requirements = %+v", result)
+	}
+	for i, name := range []string{"a", "b", "c", "d"} {
+		if result.Variables[i].Name != name {
+			t.Fatalf("variables = %+v", result.Variables)
+		}
+	}
+}
+
 func TestAnalyzeRequirementsRetainsInactiveEntriesAndPromotesActiveUses(t *testing.T) {
 	description := "declared for a reason"
 	definition := &domain.PromptDefinition{Templates: []domain.PromptMessageTemplate{{