feat(canvas): support unframed image snapshot nodes

Reviewed-on: #9

README.md

@@ -105,6 +105,11 @@ serialize autosaves and handle 412 explicitly. Restore node style dimensions
 from width/height and render edges as Bézier curves. These frontend changes are
 outside this Core delivery; local drafts alone are not database persistence.
 
+Canvas schema 1 supports unframed images: `type: "plainImage"` with
+`data.kind: "plain-image"`. They require the same validated `data.src` as image
+cards, support geometry/rotation/frame membership, and cannot connect to edges.
+This is a snapshot-format extension with no additional migration.
+
 Canvas schema 1 also supports frames: `type: "frame"` with `data.kind: "frame"`.
 Frame names use `data.title`; optional `data.labelMode` is `hidden`, `fixed`, or
 `scaled` (frontend default: `fixed`). Frames cannot rotate, connect to edges,

internal/platform/canvas.go

@@ -135,6 +135,8 @@ func normalizeCanvas(raw json.RawMessage) (json.RawMessage, bool) {
 		typ := "material"
 		if kind == "plain-text" {
 			typ = "plainText"
+		} else if kind == "plain-image" {
+			typ = "plainImage"
 		} else if kind == "icon" {
 			typ = "icon"
 		} else if kind == "frame" {
@@ -172,7 +174,7 @@ func normalizeCanvas(raw json.RawMessage) (json.RawMessage, bool) {
 				return nil, false
 			}
 		}
-		if src, exists := d["src"]; (exists || kind == "image") && !canvasImage(src) {
+		if src, exists := d["src"]; (exists || kind == "image" || kind == "plain-image") && !canvasImage(src) {
 			return nil, false
 		}
 		if value, exists := d["textStyle"]; exists {

internal/platform/canvas_test.go

@@ -88,3 +88,20 @@ func TestCanvasFrames(t *testing.T) {
 		t.Fatal("optional labelMode rejected")
 	}
 }
+
+func TestCanvasPlainImages(t *testing.T) {
+	fixture := `{"schema_version":1,"nodes":[{"id":"photo","type":"plainImage","position":{"x":20,"y":30},"width":320,"height":240,"data":{"kind":"plain-image","title":"Photo","text":"","src":"https://example.com/photo.png","rotation":30,"frameId":"frame"}},{"id":"frame","type":"frame","position":{"x":0,"y":0},"width":640,"height":400,"data":{"kind":"frame","title":"Frame","text":"","labelMode":"fixed"}}],"edges":[],"viewport":{"x":0,"y":0,"zoom":1}}`
+	if _, ok := normalizeCanvas(json.RawMessage(fixture)); !ok {
+		t.Fatal("plain image rejected")
+	}
+	for _, change := range [][2]string{
+		{`"type":"plainImage"`, `"type":"material"`},
+		{`,"src":"https://example.com/photo.png"`, ``},
+		{`"src":"https://example.com/photo.png"`, `"src":"javascript:bad"`},
+		{`"edges":[]`, `"edges":[{"id":"e","source":"photo","target":"photo"}]`},
+	} {
+		if _, ok := normalizeCanvas(json.RawMessage(strings.Replace(fixture, change[0], change[1], 1))); ok {
+			t.Fatal("invalid pure image accepted")
+		}
+	}
+}