feat: write leafs incrementally without rebuilding the graph.

Ladybug 0.19 stays FTS/HNSW queryable on MERGE of new ids; DROP INDEX
was the fatal path. bin/brain/add.go and POST /ingest land facts+info
in one transaction so watch/mail/git can become leafs now (Gitea #14).

internal/httpapi/mcp.go

@@ -144,7 +144,15 @@ func (s *Server) mcpCall(r *http.Request, params json.RawMessage) (any, error) {
 			return nil, fmt.Errorf("cancelled")
 		}
 		defer s.release()
-		body, err = s.api.Ingest(r.Context())
+		var payload []byte
+		text := strings.TrimSpace(fmt.Sprint(p.Arguments["text"]))
+		if text != "" && text != "<nil>" {
+			payload, err = json.Marshal(p.Arguments)
+			if err != nil {
+				return nil, err
+			}
+		}
+		body, err = s.api.Ingest(r.Context(), payload)
 	default:
 		return nil, fmt.Errorf("unknown tool %s", p.Name)
 	}

internal/httpapi/server.go

@@ -11,6 +11,7 @@ import (
 	"context"
 	"encoding/json"
 	"errors"
+	"io"
 	"log"
 	"net/http"
 	"os"
@@ -27,7 +28,7 @@ type API interface {
 	Get(ctx context.Context, id string, body bool) ([]byte, error)
 	Stats(ctx context.Context) ([]byte, error)
 	Audit(ctx context.Context) ([]byte, error)
-	Ingest(ctx context.Context) ([]byte, error)
+	Ingest(ctx context.Context, body []byte) ([]byte, error)
 }
 
 type Server struct {
@@ -59,7 +60,7 @@ func (s *Server) ServeHTTP(w http.ResponseWriter, r *http.Request) {
 	case PathAudit:
 		s.handleJSON(w, r, s.api.Audit)
 	case PathIngest:
-		s.handleJSON(w, r, s.api.Ingest)
+		s.handleIngest(w, r)
 	case PathOpenAPI:
 		s.handleOpenAPI(w, r)
 	case PathMCP:
@@ -116,6 +117,24 @@ func (s *Server) handleJSON(w http.ResponseWriter, r *http.Request, fn func(cont
 	writeAPI(w, body, err)
 }
 
+func (s *Server) handleIngest(w http.ResponseWriter, r *http.Request) {
+	var raw []byte
+	if r.Method == http.MethodPost {
+		b, err := io.ReadAll(io.LimitReader(r.Body, 1<<20))
+		if err != nil {
+			writeJSON(w, http.StatusBadRequest, map[string]any{"error": "read body"})
+			return
+		}
+		raw = b
+	}
+	if !s.acquire(w, r) {
+		return
+	}
+	defer s.release()
+	body, err := s.api.Ingest(r.Context(), raw)
+	writeAPI(w, body, err)
+}
+
 func (s *Server) tryAcquire(r *http.Request) bool {
 	return s.acquire(nopWriter{}, r)
 }
@@ -191,11 +210,30 @@ func (ExecSearcher) Get(context.Context, string, bool) ([]byte, error) {
 }
 func (ExecSearcher) Stats(context.Context) ([]byte, error) { return nil, errUnimplemented }
 func (ExecSearcher) Audit(context.Context) ([]byte, error) { return nil, errUnimplemented }
-func (ExecSearcher) Ingest(context.Context) ([]byte, error) {
-	return json.Marshal(map[string]any{
-		"mode":    "rebuild",
-		"command": "bin/brain/index.go --rebuild",
-	})
+func (b ExecSearcher) Ingest(ctx context.Context, body []byte) ([]byte, error) {
+	if len(strings.TrimSpace(string(body))) == 0 {
+		return json.Marshal(map[string]any{
+			"mode":    "add",
+			"command": "bin/brain/add.go",
+			"rebuild": "bin/brain/index.go --rebuild",
+		})
+	}
+	root := os.Getenv("KB_ROOT")
+	if root == "" {
+		root = "."
+	}
+	cmd := exec.CommandContext(ctx, filepath.Join(root, "bin/kb/add"), "--json")
+	cmd.Stdin = strings.NewReader(string(body))
+	cmd.Dir = root
+	out, err := cmd.Output()
+	if err != nil {
+		var exitErr *exec.ExitError
+		if errors.As(err, &exitErr) {
+			return nil, errors.New("add failed: " + strings.TrimSpace(string(exitErr.Stderr)))
+		}
+		return nil, err
+	}
+	return out, nil
 }
 
 func defaultSearchCmd(root string) string {

internal/httpapi/server_test.go

@@ -1,6 +1,7 @@
 package httpapi
 
 import (
+	"bytes"
 	"context"
 	"encoding/json"
 	"net/http"
@@ -64,8 +65,11 @@ func (f *fakeSearcher) Audit(context.Context) ([]byte, error) {
 	return []byte(`{"status":"ok"}`), nil
 }
 
-func (f *fakeSearcher) Ingest(context.Context) ([]byte, error) {
-	return []byte(`{"mode":"rebuild","command":"bin/brain/index.go --rebuild"}`), nil
+func (f *fakeSearcher) Ingest(_ context.Context, body []byte) ([]byte, error) {
+	if len(bytes.TrimSpace(body)) == 0 {
+		return []byte(`{"mode":"add","command":"bin/brain/add.go"}`), nil
+	}
+	return []byte(`{"mode":"add","ids":["fake-leaf"]}`), nil
 }
 
 func (f *fakeSearcher) count() int {
@@ -193,6 +197,27 @@ func TestStatsAuditIngest(t *testing.T) {
 	}
 }
 
+func TestIngestIsAddNotRebuildHint(t *testing.T) {
+	h := NewServer(&fakeSearcher{}, 1)
+	code, body := get(t, h, "/ingest")
+	if code != http.StatusOK {
+		t.Fatalf("GET /ingest code = %d body=%s", code, body)
+	}
+	if strings.Contains(string(body), `"add":"v2"`) || strings.Contains(string(body), "write is v2") {
+		t.Fatalf("GET /ingest still a v2 hint: %s", body)
+	}
+	if !strings.Contains(string(body), "bin/brain/add.go") {
+		t.Fatalf("GET /ingest should name add.go: %s", body)
+	}
+	code, body = postJSON(t, h, "/ingest", `{"text":"hello","root":"info","source":"t"}`)
+	if code != http.StatusOK {
+		t.Fatalf("POST /ingest code = %d body=%s", code, body)
+	}
+	if !strings.Contains(string(body), "fake-leaf") {
+		t.Fatalf("POST /ingest should add: %s", body)
+	}
+}
+
 func TestHTTPPackageDoesNotExecPython(t *testing.T) {
 	raw, err := os.ReadFile("server.go")
 	if err != nil {

internal/httpapi/spec.go

@@ -47,7 +47,15 @@ var Ops = []Op{
 	},
 	{Path: PathStats, Method: "get", ID: "stats", Summary: "index health", MCP: true},
 	{Path: PathAudit, Method: "get", ID: "audit", Summary: "facts confidence histogram", MCP: true},
-	{Path: PathIngest, Method: "get", ID: "ingest", Summary: "rebuild hint (write is v2)", MCP: true},
+	{
+		Path: PathIngest, Method: "post", ID: "ingest", Summary: "add a leaf without rebuild",
+		MCP: true,
+		Params: []Param{
+			{Name: "text", In: "query", Type: "string", Description: "leaf text (omit for CLI hint)"},
+			{Name: "root", In: "query", Type: "string", Description: "facts or info (default info)"},
+			{Name: "source", In: "query", Type: "string", Description: "evidence pointer; facts need two sources"},
+		},
+	},
 	{Path: PathOpenAPI, Method: "get", ID: "openapi", Summary: "OpenAPI 3 document for this server"},
 }
 

internal/httpapi/spec_test.go

@@ -38,11 +38,24 @@ func TestMCPToolsMatchOpenAPIPaths(t *testing.T) {
 			t.Fatalf("MCP tool %s has no OpenAPI path %s", tool.Name, path)
 		}
 	}
-	for _, need := range []string{"search", "get", "stats", "audit"} {
+	for _, need := range []string{"search", "get", "stats", "audit", "ingest"} {
 		if !names[need] {
 			t.Fatalf("MCP tools missing %s: %v", need, names)
 		}
 	}
+	var ingest MCPTool
+	for _, tool := range tools {
+		if tool.Name == "ingest" {
+			ingest = tool
+			break
+		}
+	}
+	if strings.Contains(ingest.Description, "v2") {
+		t.Fatalf("ingest still a v2 hint: %s", ingest.Description)
+	}
+	if !strings.Contains(ingest.Description, "add") {
+		t.Fatalf("ingest should describe add: %s", ingest.Description)
+	}
 }
 
 func TestOpenAPIHTTP(t *testing.T) {