diff --git a/.trinity/seals/t27mcp_T27mcpVisualOutput.json b/.trinity/seals/t27mcp_T27mcpVisualOutput.json
index 53bca11e6d..a6e39b09ed 100644
--- a/.trinity/seals/t27mcp_T27mcpVisualOutput.json
+++ b/.trinity/seals/t27mcp_T27mcpVisualOutput.json
@@ -2,23 +2,23 @@
   "built_by": "t27c-bootstrap@0.5.2+9448ab4be",
   "closure": [],
   "config": "gen=c,rust,verilog,zig;tests=zig",
-  "gen_hash_c": "sha256:076a0683dcc4e8487922bd6ff561422a1dfa707069e639fffaafea9d70ad8e2d",
-  "gen_hash_rust": "sha256:6267998500edaecfe3378c6ff7ed7482d1b0c239e1b8480fa697a8fd05b0d7b8",
-  "gen_hash_verilog": "sha256:241e62e3030919b4f540ff38480f8d726a4cc8301fbc30443369e7978adbbb1b",
-  "gen_hash_zig": "sha256:e7446390463513c4496f484f375ef59ae2f260172c8e46326f21008d84860411",
+  "gen_hash_c": "sha256:42e25ac4e6d33d72e11f45318478ef154bfc23b77daaa9a63e92d482718381c7",
+  "gen_hash_rust": "sha256:51c33ae8d38c5eebeaf38905c7577519df66fc057adee87a3d65c4eacf78818a",
+  "gen_hash_verilog": "sha256:a8af847801b01cfc44a3a88761714a6bf699fc91553ed72b5eaae7b40f60d5df",
+  "gen_hash_zig": "sha256:eb037cb00adb5f970d714f5c6a4d182289f326d3f8e890c124ebc5c3ef571b19",
   "module": "T27mcpVisualOutput",
   "ring": 12,
   "seal_schema": 2,
-  "sealed_at": "2026-10-18T15:31:37Z",
+  "sealed_at": "2026-10-18T17:13:49Z",
   "sealed_by": "t27c-bootstrap@0.5.2",
-  "spec_hash": "sha256:06c1c5e73142e2f79fa5d7be037eace63c1f20597a6e33274ebf8e1b428b7584",
+  "spec_hash": "sha256:2c44da44a1f662108a7b3558e763ff86e89db4bc9f49fe749dd7617051343960",
   "spec_path": "specs/t27mcp/visual_output.t27",
   "tests": {
     "failed": 0,
     "failing": [],
     "forced": false,
-    "passed": 9,
-    "total": 9,
+    "passed": 12,
+    "total": 12,
     "vacuous": 0
   },
   "toolchain": {
diff --git a/specs/t27mcp/visual_output.t27 b/specs/t27mcp/visual_output.t27
index 95a2fd98a1..22ad5fda9d 100644
--- a/specs/t27mcp/visual_output.t27
+++ b/specs/t27mcp/visual_output.t27
@@ -25,6 +25,15 @@
 ; readable when F * INLINE_W >= MIN_FONT_PX * W for its smallest text. A tool SVG is embedded as it is only
 ; when readable and at most INLINE_MAX_BYTES (the model re-emits it, so its bytes are output); otherwise it
 ; is redrawn at INLINE_W from t27f_outline rows.
+; UI resource (MCP Apps, the extension UI_EXTENSION): a client says it renders MCP Apps by naming
+; UI_EXTENSION in its initialize capabilities with UI_MIME among its mimeTypes. Only that client is
+; HOST_MCP_APPS (client_host); a client that says nothing is served the file path, the floor every host
+; reads, since the server cannot tell the desktop app from the CLI. On HOST_MCP_APPS t27f_view and
+; t27f_graph add a ui:// resource to their tools/call result: the SVG between UI_PAGE[0..2], a page with
+; no script and nothing fetched. Each tool names its URI (UI_URI_*) in its tools/list _meta.ui.resourceUri,
+; and resources/read of that URI returns the tool's latest drawing, UI_EMPTY before the first. Other hosts
+; get no resource: its bytes would reach the model as text. With no drawing there is nothing to carry, so
+; HOST_MCP_APPS falls back to the markdown table.
 ; phi^2 + 1/phi^2 = 3 | TRINITY
 
 module T27mcpVisualOutput;
@@ -68,6 +77,20 @@ pub const INLINE_W : u32 = 680;
 pub const MIN_FONT_PX : u32 = 11;
 pub const INLINE_MAX_BYTES : u32 = 16384;
 
+/// The MCP Apps resource: the capability a client names, the page's mime type, one URI per t27f tool,
+/// the page around the SVG (the SVG goes between [1] and [2], the title between [0] and [1]), and the
+/// page served before a tool has drawn.
+pub const UI_EXTENSION : str = "io.modelcontextprotocol/ui";
+pub const UI_MIME : str = "text/html;profile=mcp-app";
+pub const UI_URI_VIEW : str = "ui://t27f/view";
+pub const UI_URI_GRAPH : str = "ui://t27f/graph";
+pub const UI_PAGE : [3]str = [
+    "<!doctype html><html><head><meta charset=utf-8><title>",
+    "</title><style>body{margin:0;background:#000}svg{display:block;width:100%;height:auto}</style></head><body>",
+    "</body></html>"
+];
+pub const UI_EMPTY : str = "<!doctype html><html><head><meta charset=utf-8><title>t27f</title></head><body>No drawing yet: call the tool first.</body></html>";
+
 /// Where a tool SVG's drawing comes from.
 pub const SRC_EMBED : u32 = 0;
 pub const SRC_REDRAW : u32 = 1;
@@ -127,7 +150,10 @@ pub fn answer_channel(host: u32, inline_tool: bool, svg: bool) -> u32 {
         if (svg) { return CH_FILE_AND_PANE; }
         return CH_MARKDOWN_TABLE;
     }
-    if (host == HOST_MCP_APPS) { return CH_UI_RESOURCE; }
+    if (host == HOST_MCP_APPS) {
+        if (svg) { return CH_UI_RESOURCE; }
+        return CH_MARKDOWN_TABLE;
+    }
     if (host == HOST_SITE) { return CH_LIVE_PLAYER; }
     if (host == HOST_TRI_CLAW) {
         if (svg) { return CH_IMAGE_URL; }
@@ -137,6 +163,20 @@ pub fn answer_channel(host: u32, inline_tool: bool, svg: bool) -> u32 {
     return CH_MARKDOWN_TABLE;
 }
 
+/// The host an MCP client is, from its initialize capabilities: `ui_extension`, it names UI_EXTENSION;
+/// `ui_mime`, UI_MIME is among that extension's mimeTypes. Anything less is served the file path.
+pub fn client_host(ui_extension: bool, ui_mime: bool) -> u32 {
+    if (ui_extension) {
+        if (ui_mime) { return HOST_MCP_APPS; }
+    }
+    return HOST_CLAUDE_CODE_CLI;
+}
+
+/// Whether a t27f tool's tools/call result carries its drawing as a ui:// resource on `host`.
+pub fn carries_ui_resource(host: u32, svg: bool) -> bool {
+    return answer_channel(host, false, svg) == CH_UI_RESOURCE;
+}
+
 /// Whether text of `font_px` in a drawing `view_w` wide is at least MIN_FONT_PX when shown INLINE_W wide.
 pub fn inline_readable(view_w: u32, font_px: u32) -> bool {
     if (view_w == 0) { return false; }
@@ -204,6 +244,36 @@ test "answer_channel: with no inline tool or no drawing, a path or a markdown ta
     assert answer_channel(HOST_MCP_APPS, false, true) == CH_UI_RESOURCE;
     assert answer_channel(HOST_SITE, false, true) == CH_LIVE_PLAYER;
     assert answer_channel(HOST_COUNT, false, true) == CH_FILE_PATH;
+    assert answer_channel(HOST_MCP_APPS, false, false) == CH_MARKDOWN_TABLE;
+    assert answer_channel(HOST_MCP_APPS, true, false) == CH_MARKDOWN_TABLE;
+}
+
+test "client_host: only a client naming the extension and its mime is an MCP Apps host" {
+    assert client_host(true, true) == HOST_MCP_APPS;
+    assert client_host(true, false) == HOST_CLAUDE_CODE_CLI;
+    assert client_host(false, true) == HOST_CLAUDE_CODE_CLI;
+    assert client_host(false, false) == HOST_CLAUDE_CODE_CLI;
+}
+
+test "carries_ui_resource: an MCP Apps host gets the drawing as a ui:// resource" {
+    assert carries_ui_resource(HOST_MCP_APPS, true);
+    assert carries_ui_resource(client_host(true, true), true);
+    assert answer_channel(HOST_MCP_APPS, true, true) == CH_UI_RESOURCE;
+    assert UI_EXTENSION == "io.modelcontextprotocol/ui";
+    assert UI_MIME == "text/html;profile=mcp-app";
+    assert UI_URI_VIEW == "ui://t27f/view";
+    assert UI_URI_GRAPH == "ui://t27f/graph";
+    assert UI_PAGE[2] == "</body></html>";
+}
+
+test "negative control: no resource without a drawing, or on a host that did not ask for one" {
+    assert carries_ui_resource(HOST_MCP_APPS, false) == false;
+    assert carries_ui_resource(client_host(true, false), true) == false;
+    assert carries_ui_resource(client_host(false, false), true) == false;
+    assert carries_ui_resource(HOST_CLAUDE_CODE_DESKTOP, true) == false;
+    assert carries_ui_resource(HOST_TRI_CLAW, true) == false;
+    assert carries_ui_resource(HOST_SITE, true) == false;
+    assert carries_ui_resource(HOST_COUNT, true) == false;
 }
 
 test "inline_readable: the measured drawings" {