fix(capture): name what escalated the classification in an I1 refusal (#91 part 1) (#95)

The tickets array was never broken. Every ticket in the reported batch
targeted a client repo, and the I1 gate refuses a confidential capture
through a us-nexus origin at any length — reproduced live: length 1 and
20 both fine for an internal repo, length 1 refused for a client one.

What made it look like an array bug is that the refusal named neither the
offending target nor that a policy had said no, so with 20 tickets in
flight "the array is broken" was a reasonable conclusion. The refusal now
names the targets carrying the effective classification, and tells a
caller who declared confidential themselves exactly that.

Regression tests at length 1 and 20 pin the path that was already
correct; a third pins per-item partial success.

Closes #91 part 1.

Co-authored-by: Mathias <mthbqv@gmail.com>

ingestion/internal/capture/service.go

@@ -83,7 +83,7 @@ func (s *Service) Capture(ctx context.Context, in CaptureInput) (CaptureReceipt,
 		declared, _ = classification.ParseLevel(in.Context.Classification)
 	}
 
-	effective, securityEvents := s.resolveClassification(declared, in)
+	effective, securityEvents, escalators := s.resolveClassification(declared, in)
 
 	// Server-derived origin governs the I1 gate; a caller-asserted harness
 	// label that names a different zone is descriptive-only and logged as a
@@ -107,8 +107,8 @@ func (s *Service) Capture(ctx context.Context, in CaptureInput) (CaptureReceipt,
 			Items:                   nil, // refused before any write
 			SecurityEvents:          append(securityEvents, "I1 refusal: confidential capture via us-nexus origin"),
 		}, AuditCentral)
-		return CaptureReceipt{}, fmt.Errorf("%w: effective classification confidential through %s origin",
-			ErrSovereigntyRefused, in.Context.Origin)
+		return CaptureReceipt{}, fmt.Errorf("%w: effective classification confidential through %s origin (%s)",
+			ErrSovereigntyRefused, in.Context.Origin, escalationReason(escalators))
 	}
 
 	receipt := CaptureReceipt{
@@ -221,15 +221,28 @@ func (s *Service) validate(in CaptureInput) error {
 	return nil
 }
 
-// resolveClassification computes the effective level (stricter of
-// declared and every target's derived level) and collects a security
-// event whenever the caller under-declared relative to a target floor.
-func (s *Service) resolveClassification(declared classification.Level, in CaptureInput) (classification.Level, []string) {
+// resolveClassification computes the effective level (stricter of declared
+// and every target's derived level), collects a security event whenever the
+// caller under-declared relative to a target floor, and names the targets
+// that carry the strictest level.
+//
+// That third return is what makes an I1 refusal actionable. A caller sending
+// twenty tickets gets one refusal; without the offending target it cannot
+// tell which repo tripped the gate, and infra#265 shows what happens next —
+// the caller concluded the tickets ARRAY was broken, built a fallback of
+// twenty individual calls, and filed a bug against the wrong thing.
+func (s *Service) resolveClassification(declared classification.Level, in CaptureInput) (classification.Level, []string, []string) {
 	effective := declared
 	var events []string
+	derivedFor := map[string]classification.Level{}
+	var order []string
 	consider := func(kind classification.TargetKind, name string) {
 		derived := s.policy.Derive(classification.Target{Kind: kind, Name: name})
 		effective = classification.Stricter(effective, derived)
+		if _, seen := derivedFor[name]; !seen {
+			derivedFor[name] = derived
+			order = append(order, name)
+		}
 		if declared < derived {
 			events = append(events, fmt.Sprintf("classification under-declared: declared=%s target=%s(%s) derived=%s",
 				declared, name, kindString(kind), derived))
@@ -241,7 +254,28 @@ func (s *Service) resolveClassification(declared classification.Level, in Captur
 	for _, tk := range in.Tickets {
 		consider(classification.RepoTarget, tk.Repo)
 	}
-	return effective, events
+
+	// Only targets that actually reach the effective level are named: at
+	// twenty tickets, listing the innocent ones is noise that hides the one
+	// that matters.
+	var escalators []string
+	for _, name := range order {
+		if derivedFor[name] == effective && effective > declared {
+			escalators = append(escalators, name)
+		}
+	}
+	return effective, events, escalators
+}
+
+// escalationReason renders why the effective classification landed where it
+// did, for an operator reading a refusal. Naming the caller's own declaration
+// matters as much as naming a target: "you asked for this" and "a repo you
+// touched required it" call for different fixes.
+func escalationReason(escalators []string) string {
+	if len(escalators) == 0 {
+		return "declared by the caller; no target required it"
+	}
+	return "required by: " + strings.Join(escalators, ", ")
 }
 
 func (s *Service) persistInsight(ctx context.Context, ins Insight) (InsightResult, string, error) {