[Crane: crane-migration-python-to-go-full-apm-cli-rewrite] Iteration 9: Milestone 7 (core/ partial) -- errors, scope, target detection, apm_yml

Port core/errors.py (TargetResolutionError hierarchy + renderers),
core/scope.py (InstallScope enum + path helpers), core/target_detection.py
(DetectTarget, ShouldCompile*, NormalizeTargetList, GetTargetDescription),
and core/apm_yml.py (ParseTargetsField with CSV/list sugar and validation).
Added 26 TestParity* tests across 4 files; all 136 Go tests pass.
Score: 0.4470 (was 0.3609, delta +0.0861).

Run: https://github.com/githubnext/apm/actions/runs/26326750518

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

Author: github-actions[bot]

internal/core/apm_yml.go

@@ -0,0 +1,108 @@
+package core
+
+import "fmt"
+
+// CanonicalTargets is the set of target names accepted by APM.
+var CanonicalTargets = map[string]bool{
+	"claude":       true,
+	"copilot":      true,
+	"cursor":       true,
+	"opencode":     true,
+	"codex":        true,
+	"gemini":       true,
+	"windsurf":     true,
+	"agent-skills": true,
+}
+
+// ParseTargetsField parses the targets/target field from a raw apm.yml data
+// map. Returns a canonical list of target names. An empty list means neither
+// key was present (caller should fall through to auto-detect).
+func ParseTargetsField(yamlData map[string]interface{}) ([]string, error) {
+	_, hasTargets := yamlData["targets"]
+	_, hasTarget := yamlData["target"]
+
+	if hasTargets && hasTarget {
+		return nil, NewConflictingTargetsError()
+	}
+
+	if hasTargets {
+		raw := yamlData["targets"]
+		switch v := raw.(type) {
+		case nil:
+			return nil, NewEmptyTargetsListError()
+		case []interface{}:
+			if len(v) == 0 {
+				return nil, NewEmptyTargetsListError()
+			}
+			tokens := make([]string, 0, len(v))
+			for _, item := range v {
+				t := fmt.Sprintf("%v", item)
+				if t != "" {
+					tokens = append(tokens, t)
+				}
+			}
+			if err := validateCanonical(tokens); err != nil {
+				return nil, err
+			}
+			return tokens, nil
+		default:
+			// Single value under targets key
+			tokens := []string{fmt.Sprintf("%v", v)}
+			if err := validateCanonical(tokens); err != nil {
+				return nil, err
+			}
+			return tokens, nil
+		}
+	}
+
+	if hasTarget {
+		raw := yamlData["target"]
+		if raw == nil {
+			return []string{}, nil
+		}
+		switch v := raw.(type) {
+		case []interface{}:
+			tokens := make([]string, 0, len(v))
+			for _, item := range v {
+				t := fmt.Sprintf("%v", item)
+				if t != "" {
+					tokens = append(tokens, t)
+				}
+			}
+			if len(tokens) == 0 {
+				return []string{}, nil
+			}
+			if err := validateCanonical(tokens); err != nil {
+				return nil, err
+			}
+			return tokens, nil
+		default:
+			rawStr := fmt.Sprintf("%v", v)
+			if rawStr == "" {
+				return []string{}, nil
+			}
+			// CSV sugar: "claude,copilot" -> ["claude", "copilot"]
+			tokens := splitCSV(rawStr)
+			if len(tokens) == 0 {
+				return []string{}, nil
+			}
+			if err := validateCanonical(tokens); err != nil {
+				return nil, err
+			}
+			return tokens, nil
+		}
+	}
+
+	return []string{}, nil
+}
+
+// validateCanonical checks every token is in CanonicalTargets.
+func validateCanonical(tokens []string) error {
+	valid := sortedKeys(CanonicalTargets)
+	for _, t := range tokens {
+		if !CanonicalTargets[t] {
+			return NewUnknownTargetError(t, valid)
+		}
+	}
+	return nil
+}