diff --git a/.trinity/seals/t27mcp_T27mcpVisualOutput.json b/.trinity/seals/t27mcp_T27mcpVisualOutput.json
new file mode 100644
index 0000000000..53bca11e6d
--- /dev/null
+++ b/.trinity/seals/t27mcp_T27mcpVisualOutput.json
@@ -0,0 +1,28 @@
+{
+  "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",
+  "module": "T27mcpVisualOutput",
+  "ring": 12,
+  "seal_schema": 2,
+  "sealed_at": "2026-10-18T15:31:37Z",
+  "sealed_by": "t27c-bootstrap@0.5.2",
+  "spec_hash": "sha256:06c1c5e73142e2f79fa5d7be037eace63c1f20597a6e33274ebf8e1b428b7584",
+  "spec_path": "specs/t27mcp/visual_output.t27",
+  "tests": {
+    "failed": 0,
+    "failing": [],
+    "forced": false,
+    "passed": 9,
+    "total": 9,
+    "vacuous": 0
+  },
+  "toolchain": {
+    "test_runner": "sha256:1982ae948e24d00c5d221ccec12dfce1eb01204b53e37b0f857f93b16d64629d",
+    "zig": "0.16.0"
+  }
+}
\ No newline at end of file
diff --git a/specs/t27mcp/visual_output.t27 b/specs/t27mcp/visual_output.t27
new file mode 100644
index 0000000000..95a2fd98a1
--- /dev/null
+++ b/specs/t27mcp/visual_output.t27
@@ -0,0 +1,243 @@
+// SPDX-License-Identifier: Apache-2.0
+; specs/t27mcp/visual_output.t27 -- every answer about a spec, a flow, numbers or a piece of work carries
+; one visual, and the visual is the T27F way: drawn from tool rows, labelled, with the file it came from.
+; Where it is drawn depends on the host. The rule is said to Claude Code through the MCP server's
+; `instructions` (gHashTag/t27-mcp) and to TRI CLAW's chat agent through its prompt
+; (gHashTag/999-multibots-telegraf, apps/vibee-editor/render): both read RULE_* from this spec, so the rule
+; has one home. See the epic #10066 and T27F, gHashTag/trinity#1648.
+; --
+; What was measured (2026-10-18, t27-mcp db98153):
+; - t27f_graph of the reel fixture: an SVG 1860 wide, text at 13 px, 5923 bytes. Shown inline at 680 px it
+;   scales to 0.37, so its text is about 4.75 px: unreadable. t27f_view deck-evidence-wide: 1280 wide, body
+;   text 26 px (13.8 px inline, readable), a caption at 15 px (8 px inline, not readable).
+; - The Claude Code desktop app draws an inline SVG or HTML visual with its visual tool (show_widget), at a
+;   container 680 wide, text at least 11 px. The CLI draws no image; it renders markdown tables.
+; - An MCP server's `instructions` (the initialize result) reach the client model's system prompt; a tool
+;   result does not reach the user as an image on these hosts (reel.t27 header, 2026-10-17).
+; - TRI CLAW's chat shows an image for an https URL ending in .svg on its own line or for ![title](url)
+;   (player/src/components/Chat/ChatAssets.tsx IMAGE_RE). The t27f tools write their SVG to the server's
+;   temporary directory, so TRI CLAW serves that directory by URL.
+; --
+; Hosts 0..3 carry the numbers of reel.t27's HOST_*, and channels 0..3 its CHANNEL_*; this spec adds TRI
+; CLAW, the inline widget, the image URL and the markdown table. reel.t27 channel_for() stays the channel
+; of a reel still; answer_channel() here is the channel of an answer's visual.
+; Readability: a drawing of width W shown at INLINE_W shows a font of F px at F * INLINE_W / W px, so it is
+; 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.
+; phi^2 + 1/phi^2 = 3 | TRINITY
+
+module T27mcpVisualOutput;
+
+/// Hosts. 0..3 are reel.t27's numbers.
+pub const HOST_CLAUDE_CODE_CLI : u32 = 0;
+pub const HOST_CLAUDE_CODE_DESKTOP : u32 = 1;
+pub const HOST_MCP_APPS : u32 = 2;
+pub const HOST_SITE : u32 = 3;
+pub const HOST_TRI_CLAW : u32 = 4;
+pub const HOST_COUNT : u32 = 5;
+
+/// Channels. 0..3 are reel.t27's numbers.
+pub const CH_FILE_PATH : u32 = 0;
+pub const CH_FILE_AND_PANE : u32 = 1;
+pub const CH_UI_RESOURCE : u32 = 2;
+pub const CH_LIVE_PLAYER : u32 = 3;
+pub const CH_INLINE_WIDGET : u32 = 4;
+pub const CH_IMAGE_URL : u32 = 5;
+pub const CH_MARKDOWN_TABLE : u32 = 6;
+pub const CHANNEL_NAME : [7]str = [
+    "file path",
+    "file and pane",
+    "ui resource",
+    "live player",
+    "inline widget",
+    "image url",
+    "markdown table"
+];
+
+/// Answer kinds. The first four carry a visual.
+pub const K_SPEC : u32 = 0;
+pub const K_FLOW : u32 = 1;
+pub const K_NUMBERS : u32 = 2;
+pub const K_REPORT : u32 = 3;
+pub const K_ONE_SENTENCE : u32 = 4;
+pub const K_QUESTION : u32 = 5;
+
+/// The inline container and the smallest text it may show.
+pub const INLINE_W : u32 = 680;
+pub const MIN_FONT_PX : u32 = 11;
+pub const INLINE_MAX_BYTES : u32 = 16384;
+
+/// Where a tool SVG's drawing comes from.
+pub const SRC_EMBED : u32 = 0;
+pub const SRC_REDRAW : u32 = 1;
+
+/// The T27F labels, as t27f_outline gives them.
+pub const LABEL_NAMES : [4]str = ["exact", "derived", "suggested", "unknown"];
+
+/// answer_verdict() answers.
+pub const V_OK : u32 = 0;
+pub const V_NO_VISUAL : u32 = 1;
+pub const V_INVENTED : u32 = 2;
+pub const V_NO_LEGEND : u32 = 3;
+pub const V_NO_SOURCE : u32 = 4;
+pub const V_UNREADABLE : u32 = 5;
+pub const VERDICT_TEXT : [6]str = [
+    "ok",
+    "no visual: this answer needs one",
+    "invented: a node no tool row backs",
+    "no legend: labels drawn without their key",
+    "no source: the file or URL the drawing came from is not given",
+    "unreadable: its smallest text is under 11 px where it is shown"
+];
+
+/// The rule as Claude Code reads it, from the t27 MCP server's `instructions`. ASCII, one line each.
+pub const RULE_CLAUDE_CODE : [7]str = [
+    "Visual output (specs/t27mcp/visual_output.t27):",
+    "- Every answer that explains a spec, a flow, numbers or a piece of work carries one visual. Only a one-sentence reply or a question back goes without.",
+    "- In the Claude Code desktop app, draw it inline with your visual tool (show_widget) when you have one; else give the SVG path, which the app opens. In the CLI, give the path, or a markdown table when there is no SVG.",
+    "- Draw from tool rows, never from memory: t27f_outline, t27f_graph, t27f_view, t27_spec. Nothing is drawn that a row does not back.",
+    "- Label every node exact, derived, suggested or unknown as its row says, and show the legend.",
+    "- Embed a tool SVG as it is only when its smallest font_px * 680 >= 11 * its width and it is at most 16384 bytes; else redraw it 680 wide from t27f_outline rows.",
+    "- Always name the file the drawing came from: the file is the record, the drawing is a view of it."
+];
+
+/// The rule as TRI CLAW's chat agent reads it, from its prompt. ASCII, one line each.
+pub const RULE_TRI_CLAW : [6]str = [
+    "Visual output (specs/t27mcp/visual_output.t27):",
+    "- Every answer that explains a spec, a flow, numbers or a piece of work carries one visual. Only a one-sentence reply or a question back goes without.",
+    "- When a t27f tool answered, show its drawing as an image: its https URL ending in .svg on a line of its own, or ![title](url). Never paste SVG source into the chat.",
+    "- With no drawing, show the rows as a markdown table, not as prose.",
+    "- Draw from tool rows, never from memory. Label every item exact, derived, suggested or unknown as its row says, and give the legend.",
+    "- Name where the drawing came from: the tool and its file or URL."
+];
+pub const RULE_CLAUDE_CODE_LINES : u32 = 7;
+pub const RULE_TRI_CLAW_LINES : u32 = 6;
+
+/// Whether an answer of kind `kind` carries a visual.
+pub fn needs_visual(kind: u32) -> bool {
+    return kind <= K_REPORT;
+}
+
+/// How an answer's visual reaches the user on `host`. `inline_tool`: the client has a visual tool
+/// (show_widget). `svg`: a t27f tool produced a drawing for this answer.
+pub fn answer_channel(host: u32, inline_tool: bool, svg: bool) -> u32 {
+    if (host == HOST_CLAUDE_CODE_DESKTOP) {
+        if (inline_tool) { return CH_INLINE_WIDGET; }
+        if (svg) { return CH_FILE_AND_PANE; }
+        return CH_MARKDOWN_TABLE;
+    }
+    if (host == HOST_MCP_APPS) { return CH_UI_RESOURCE; }
+    if (host == HOST_SITE) { return CH_LIVE_PLAYER; }
+    if (host == HOST_TRI_CLAW) {
+        if (svg) { return CH_IMAGE_URL; }
+        return CH_MARKDOWN_TABLE;
+    }
+    if (svg) { return CH_FILE_PATH; }
+    return CH_MARKDOWN_TABLE;
+}
+
+/// 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; }
+    return font_px * INLINE_W >= MIN_FONT_PX * view_w;
+}
+
+/// Whether a tool SVG goes inline as it is or is redrawn from t27f_outline rows. `min_font_px` is its
+/// smallest text.
+pub fn inline_source(view_w: u32, min_font_px: u32, bytes: u32) -> u32 {
+    if (inline_readable(view_w, min_font_px) == false) { return SRC_REDRAW; }
+    if (bytes > INLINE_MAX_BYTES) { return SRC_REDRAW; }
+    return SRC_EMBED;
+}
+
+/// The verdict on an answer. `drawn`: nodes in its visual; `backed`: those a tool row backs.
+/// `label_kinds`: how many of the four labels it draws. `view_w` / `min_font_px`: the drawing's width
+/// and its smallest text, in its own units (0 width when it is not shown inline).
+pub fn answer_verdict(kind: u32, has_visual: bool, drawn: u32, backed: u32, label_kinds: u32, legend: bool, source: bool, view_w: u32, min_font_px: u32) -> u32 {
+    if (needs_visual(kind) == false) { return V_OK; }
+    if (has_visual == false) { return V_NO_VISUAL; }
+    if (drawn > backed) { return V_INVENTED; }
+    if (label_kinds > 0) {
+        if (legend == false) { return V_NO_LEGEND; }
+    }
+    if (source == false) { return V_NO_SOURCE; }
+    if (view_w > 0) {
+        if (inline_readable(view_w, min_font_px) == false) { return V_UNREADABLE; }
+    }
+    return V_OK;
+}
+
+test "the tables are the size they say" {
+    assert CHANNEL_NAME[CH_INLINE_WIDGET] == "inline widget";
+    assert CHANNEL_NAME[CH_MARKDOWN_TABLE] == "markdown table";
+    assert LABEL_NAMES[3] == "unknown";
+    assert VERDICT_TEXT[V_OK] == "ok";
+    assert RULE_CLAUDE_CODE[0] == "Visual output (specs/t27mcp/visual_output.t27):";
+    assert RULE_TRI_CLAW[0] == "Visual output (specs/t27mcp/visual_output.t27):";
+    assert RULE_CLAUDE_CODE[1] == "- Every answer that explains a spec, a flow, numbers or a piece of work carries one visual. Only a one-sentence reply or a question back goes without.";
+    assert RULE_TRI_CLAW[1] == "- Every answer that explains a spec, a flow, numbers or a piece of work carries one visual. Only a one-sentence reply or a question back goes without.";
+}
+
+test "needs_visual: spec, flow, numbers and a report carry one; one sentence and a question do not" {
+    assert needs_visual(K_SPEC);
+    assert needs_visual(K_FLOW);
+    assert needs_visual(K_NUMBERS);
+    assert needs_visual(K_REPORT);
+    assert needs_visual(K_ONE_SENTENCE) == false;
+    assert needs_visual(K_QUESTION) == false;
+}
+
+test "answer_channel: the desktop app draws inline, TRI CLAW shows an image URL" {
+    assert answer_channel(HOST_CLAUDE_CODE_DESKTOP, true, true) == CH_INLINE_WIDGET;
+    assert answer_channel(HOST_CLAUDE_CODE_DESKTOP, true, false) == CH_INLINE_WIDGET;
+    assert answer_channel(HOST_TRI_CLAW, false, true) == CH_IMAGE_URL;
+    assert answer_channel(HOST_TRI_CLAW, true, true) == CH_IMAGE_URL;
+}
+
+test "answer_channel: with no inline tool or no drawing, a path or a markdown table" {
+    assert answer_channel(HOST_CLAUDE_CODE_DESKTOP, false, true) == CH_FILE_AND_PANE;
+    assert answer_channel(HOST_CLAUDE_CODE_DESKTOP, false, false) == CH_MARKDOWN_TABLE;
+    assert answer_channel(HOST_CLAUDE_CODE_CLI, false, true) == CH_FILE_PATH;
+    assert answer_channel(HOST_CLAUDE_CODE_CLI, false, false) == CH_MARKDOWN_TABLE;
+    assert answer_channel(HOST_TRI_CLAW, false, false) == CH_MARKDOWN_TABLE;
+    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;
+}
+
+test "inline_readable: the measured drawings" {
+    assert inline_readable(1860, 13) == false;
+    assert inline_readable(1280, 26);
+    assert inline_readable(1280, 15) == false;
+    assert inline_readable(680, 11);
+    assert inline_readable(680, 10) == false;
+    assert inline_readable(340, 6);
+}
+
+test "inline_source: embed a small readable SVG, redraw the rest" {
+    assert inline_source(680, 12, 5923) == SRC_EMBED;
+    assert inline_source(1860, 13, 5923) == SRC_REDRAW;
+    assert inline_source(680, 12, INLINE_MAX_BYTES) == SRC_EMBED;
+    assert inline_source(680, 12, INLINE_MAX_BYTES + 1) == SRC_REDRAW;
+}
+
+test "answer_verdict: a backed, labelled, sourced, readable drawing is ok" {
+    assert answer_verdict(K_SPEC, true, 12, 12, 3, true, true, 680, 12) == V_OK;
+    assert answer_verdict(K_REPORT, true, 4, 4, 0, false, true, 680, 11) == V_OK;
+    assert answer_verdict(K_ONE_SENTENCE, false, 0, 0, 0, false, false, 0, 0) == V_OK;
+    assert answer_verdict(K_NUMBERS, true, 5, 5, 1, true, true, 0, 0) == V_OK;
+}
+
+test "negative control: a spec answer with no visual, or with a node no row backs" {
+    assert answer_verdict(K_SPEC, false, 0, 0, 0, false, false, 0, 0) == V_NO_VISUAL;
+    assert answer_verdict(K_FLOW, false, 0, 0, 0, false, true, 0, 0) == V_NO_VISUAL;
+    assert answer_verdict(K_SPEC, true, 13, 12, 3, true, true, 680, 12) == V_INVENTED;
+}
+
+test "negative control: labels without a legend, a drawing without its source, unreadable text" {
+    assert answer_verdict(K_SPEC, true, 12, 12, 2, false, true, 680, 12) == V_NO_LEGEND;
+    assert answer_verdict(K_SPEC, true, 12, 12, 2, true, false, 680, 12) == V_NO_SOURCE;
+    assert answer_verdict(K_SPEC, true, 12, 12, 2, true, true, 1860, 13) == V_UNREADABLE;
+    assert inline_readable(0, 13) == false;
+}