Tell the agent the artifact shape, and tell it when the shape is wrong

Two halves of the same failure, live on run 5.

F38: the phase brief named .orchestra/research.json and described its contents
in prose, never its schema. The agent guessed dead_ends as strings where the
decoder wants {tried, why_failed} objects. The brief now carries the shape, and
a test decodes each documented shape with the same function the worker uses, so
a struct change that is not mirrored fails the build.

F39: the local artifact check refused the request through recordError alone.
answerRefusedPhase only ran on a coordinator 409, so a decode failure told the
agent nothing. The session sat at a boundary rewriting nothing, which is the
silent-loop shape the comment above that block warns about, reached by the one
path with no delivery. Both local refusals now reach the agent.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_011xsXyr5J1RACo71YeKG3Pu

internal/agentctx/agentctx_test.go

@@ -7,6 +7,7 @@ import (
 
 	"orchestra/internal/continuity"
 	"orchestra/internal/domain"
+	"orchestra/internal/workphase"
 )
 
 func input() Input {
@@ -351,3 +352,36 @@ func TestPhaseBriefNamesTheArtifactToSeal(t *testing.T) {
 		}
 	}
 }
+
+// TestPhaseSealSchemasDecode guards F38. The brief tells the agent to seal an
+// artifact; until this existed it did not say what shape. Run 5 guessed
+// dead_ends as strings where the decoder wants objects, and every phase
+// request was refused for a field nobody had described.
+//
+// Each documented shape is decoded by the same function the worker uses, so a
+// struct change that is not mirrored in the brief fails here instead of in a
+// live run.
+func TestPhaseSealSchemasDecode(t *testing.T) {
+	for phase, schema := range phaseSealSchema {
+		if schema == "" {
+			t.Fatalf("%s has a seal file but no documented shape", phase)
+		}
+		var decErr error
+		switch phase {
+		case domain.WorkPhaseResearch:
+			_, decErr = workphase.DecodeResearch([]byte(schema))
+		case domain.WorkPhasePlan:
+			_, decErr = workphase.DecodePlan([]byte(schema))
+		default:
+			t.Fatalf("%s has a documented shape with nothing to decode it", phase)
+		}
+		if decErr != nil && !strings.Contains(decErr.Error(), "empty") && !strings.Contains(decErr.Error(), "required") && !strings.Contains(decErr.Error(), "must") {
+			t.Fatalf("%s brief shape does not match the decoder: %v", phase, decErr)
+		}
+	}
+	for phase := range phaseSealFile {
+		if phaseSealSchema[phase] == "" {
+			t.Fatalf("%s names a seal file but the brief never states its shape", phase)
+		}
+	}
+}