feat: agent run loop, Generate[T], reflect-derived schemas

Phase 5:
- agent/: model + system prompt + toolboxes composition; bounded
  tool-dispatch loop (default 10 steps); panic-proof tool execution;
  unknown-tool and duplicate-name handling; history continuation; step
  observers; partial results on ErrMaxSteps/errors (ADR-0012)
- llm.SchemaFor[T]: strict-compatible JSON schemas from Go types
  (nullable pointers, description/enum tags, recursion rejected)
- majordomo.Generate[T]: typed structured output with fence-stripping
  decode and model-naming errors
- README agents/structured-output sections + matrix synced

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

generate_test.go

@@ -0,0 +1,89 @@
+package majordomo
+
+import (
+	"context"
+	"encoding/json"
+	"strings"
+	"testing"
+
+	"gitea.stevedudenhoeffer.com/steve/majordomo/llm"
+	"gitea.stevedudenhoeffer.com/steve/majordomo/provider/fake"
+)
+
+type verdict struct {
+	Guilty bool   `json:"guilty"`
+	Why    string `json:"why"`
+}
+
+func TestGenerateTyped(t *testing.T) {
+	r := newTestRegistry(t)
+	fp := fake.New("fp")
+	r.RegisterProvider(fp)
+	fp.Enqueue("judge", fake.Reply(`{"guilty":true,"why":"caught red-handed"}`))
+
+	m, _ := r.Parse("fp/judge")
+	v, err := Generate[verdict](context.Background(), m, Request{Messages: []Message{UserText("verdict?")}})
+	if err != nil {
+		t.Fatalf("Generate: %v", err)
+	}
+	if !v.Guilty || v.Why != "caught red-handed" {
+		t.Errorf("verdict = %+v", v)
+	}
+
+	// The schema derived from the struct reached the provider, named after
+	// the type.
+	req := fp.Calls()[0].Request
+	if req.SchemaName != "verdict" {
+		t.Errorf("schema name = %q", req.SchemaName)
+	}
+	var schema map[string]any
+	if err := json.Unmarshal(req.Schema, &schema); err != nil {
+		t.Fatalf("schema: %v", err)
+	}
+	props := schema["properties"].(map[string]any)
+	if _, ok := props["guilty"]; !ok {
+		t.Errorf("schema = %v", schema)
+	}
+}
+
+func TestGenerateStripsMarkdownFence(t *testing.T) {
+	r := newTestRegistry(t)
+	fp := fake.New("fp")
+	r.RegisterProvider(fp)
+	fp.Enqueue("judge", fake.Reply("```json\n{\"guilty\":false,\"why\":\"alibi\"}\n```"))
+
+	m, _ := r.Parse("fp/judge")
+	v, err := Generate[verdict](context.Background(), m, Request{Messages: []Message{UserText("verdict?")}})
+	if err != nil {
+		t.Fatalf("Generate: %v", err)
+	}
+	if v.Guilty || v.Why != "alibi" {
+		t.Errorf("verdict = %+v", v)
+	}
+}
+
+func TestGenerateDecodeErrorNamesModel(t *testing.T) {
+	r := newTestRegistry(t)
+	fp := fake.New("fp")
+	r.RegisterProvider(fp)
+	fp.Enqueue("judge", fake.Reply("not json at all"))
+
+	m, _ := r.Parse("fp/judge")
+	_, err := Generate[verdict](context.Background(), m, Request{Messages: []Message{UserText("verdict?")}})
+	if err == nil || !strings.Contains(err.Error(), "fp/judge") {
+		t.Errorf("err = %v, want decode error naming the model", err)
+	}
+}
+
+func TestGenerateEmptyResponse(t *testing.T) {
+	r := newTestRegistry(t)
+	fp := fake.New("fp")
+	r.RegisterProvider(fp)
+	fp.Enqueue("judge", fake.ReplyWith(llm.Response{FinishReason: llm.FinishLength}))
+
+	m, _ := r.Parse("fp/judge")
+	_, err := Generate[verdict](context.Background(), m, Request{Messages: []Message{UserText("verdict?")}})
+	if err == nil || !strings.Contains(err.Error(), "empty") {
+		t.Errorf("err = %v, want empty-response error", err)
+	}
+}