diff --git a/harness/.pi/extensions/gate/__tests__/builders.test.js b/harness/.pi/extensions/gate/__tests__/builders.test.js
new file mode 100644
index 00000000..612fb3ea
--- /dev/null
+++ b/harness/.pi/extensions/gate/__tests__/builders.test.js
@@ -0,0 +1,161 @@
+// L1 tests for the pure widget-descriptor builders (spec D2/D4, §4.1).
+// Each builder turns plain params into a ui_request descriptor object -- no Pi
+// context, no I/O. Golden files pin the exact shape; fuzzy tests check that bad
+// params throw clearly rather than silently produce a broken widget.
+// Run: npm test  (node --test)
+
+const test = require("node:test");
+const assert = require("node:assert");
+const fs = require("node:fs");
+const path = require("node:path");
+
+const {
+  buildSelectRequest,
+  buildMultiselectRequest,
+  buildArtifactGate,
+  buildInfoRequest,
+  buildFreetextRequest,
+  withChildLinkage,
+} = require("../builders.js");
+
+const GOLDEN = path.join(__dirname, "golden");
+const golden = (name) => JSON.parse(fs.readFileSync(path.join(GOLDEN, name)));
+
+// --- golden shape tests -------------------------------------------------------
+
+test("select F1 matches golden shape", () => {
+  const result = buildSelectRequest({
+    id: "u1", phase: "F1", title: "Disambigua 'ablazione'",
+    options: [{ id: "o1", label: "procedura" }, { id: "o2", label: "patologia" }],
+  });
+  const g = golden("select_F1.json");
+  assert.equal(result.widget, "select");
+  assert.equal(result.type, "ui_request");
+  assert.equal(result.schema_version, 1);
+  assert.deepEqual(result.reserved, g.reserved); // back/exit/other framework hatches
+  assert.deepEqual(
+    result.options.filter((o) => o.id !== "other"),
+    g.options.filter((o) => o.id !== "other"),
+  );
+});
+
+test("select always carries the Altro escape hatch with freetext linkage", () => {
+  const result = buildSelectRequest({
+    id: "u", phase: "F1", title: "x",
+    options: [{ id: "a", label: "A" }],
+  });
+  const other = result.options.find((o) => o.id === "other");
+  assert.ok(other, "Altro option must always be present");
+  assert.equal(other.opens.widget, "freetext");
+});
+
+test("select surfaces a recommended marker when given", () => {
+  const result = buildSelectRequest({
+    id: "u", phase: "F1", title: "x",
+    options: [{ id: "a", label: "A" }, { id: "b", label: "B" }],
+    recommended: "b",
+  });
+  assert.equal(result.recommended, "b");
+});
+
+test("multiselect F4 matches golden + carries content + allowEmpty", () => {
+  // a multiselect with allow_empty:false MUST have options (zero options is a
+  // broken widget); the golden uses allow_empty:true for the empty-options case
+  // and allow_empty:false when options are present.
+  const result = buildMultiselectRequest({
+    id: "u3", phase: "F4", title: "Tabelle",
+    options: [{ id: "dim_pazienti", label: "dim_pazienti" }],
+    content: { candidates: [] }, allowEmpty: false,
+  });
+  const g = golden("multiselect_F4.json");
+  assert.equal(result.widget, "multiselect");
+  assert.equal(result.allow_empty, false);
+  assert.ok("content" in result);
+  assert.deepEqual(result.reserved, g.reserved);
+});
+
+test("multiselect with allow_empty:true accepts zero options", () => {
+  const result = buildMultiselectRequest({
+    id: "u", phase: "F4", title: "x", options: [], allowEmpty: true,
+  });
+  assert.equal(result.allow_empty, true);
+  assert.deepEqual(result.options, []);
+});
+
+test("multiselect with allowEmpty:false and zero options throws", () => {
+  assert.throws(
+    () => buildMultiselectRequest({ id: "u", phase: "F4", title: "x", options: [], allowEmpty: false }),
+    /allow_empty|options/i,
+  );
+});
+
+test("artifact-gate F5 schema matches golden", () => {
+  const result = buildArtifactGate({
+    id: "u2", phase: "F5", title: "Schema-linking",
+    artifact: { kind: "schema_linking", data: { candidates: [] }, version: 1 },
+    action: { kind: "confirm", prompt: "Confermi?" },
+  });
+  const g = golden("artifact_gate_F5.json");
+  assert.equal(result.widget, "artifact-gate");
+  assert.equal(result.artifact.kind, "schema_linking");
+  assert.equal(result.action.kind, "confirm");
+  assert.deepEqual(result.reserved, g.reserved);
+});
+
+// --- the other widgets --------------------------------------------------------
+
+test("info request is fire-and-forget (no reserved, no options)", () => {
+  const result = buildInfoRequest({ phase: "F2", level: "info", text: "sto per proporti lo schema-linking" });
+  assert.equal(result.widget, "info");
+  assert.equal(result.level, "info");
+  assert.equal(result.type, "ui_request");
+  assert.equal(result.id, undefined, "info is not correlated like a blocking widget");
+  assert.ok(!("reserved" in result));
+});
+
+test("freetext request carries a title and no options", () => {
+  const result = buildFreetextRequest({ id: "u9", phase: "F1", title: "Specifica…" });
+  assert.equal(result.widget, "freetext");
+  assert.equal(result.title, "Specifica…");
+  assert.deepEqual(result.reserved, ["back", "exit", "other"]);
+});
+
+test("withChildLinkage sets option.opens and returns the option", () => {
+  const child = { widget: "freetext", title: "Motivazione del rifiuto" };
+  const option = withChildLinkage({ id: "reject", label: "Rifiuta" }, child);
+  assert.deepEqual(option.opens, child);
+});
+
+// --- fuzzy tests (bad params must throw clearly, never silently break) --------
+
+test("select with missing title throws clearly", () => {
+  assert.throws(
+    () => buildSelectRequest({ id: "u", phase: "F1", options: [] }),
+    /title/i,
+  );
+});
+
+test("select with non-array options throws clearly", () => {
+  assert.throws(
+    () => buildSelectRequest({ id: "u", phase: "F1", title: "x", options: "notalist" }),
+    /options/i,
+  );
+});
+
+test("artifact-gate with missing artifact throws clearly", () => {
+  assert.throws(
+    () => buildArtifactGate({ id: "u", phase: "F5", title: "x", action: { kind: "confirm" } }),
+    /artifact/i,
+  );
+});
+
+test("artifact-gate with unknown action kind throws clearly", () => {
+  assert.throws(
+    () => buildArtifactGate({
+      id: "u", phase: "F5", title: "x",
+      artifact: { kind: "cte", data: {}, version: 1 },
+      action: { kind: "bogus" },
+    }),
+    /action/i,
+  );
+});
diff --git a/harness/.pi/extensions/gate/__tests__/golden/artifact_gate_F5.json b/harness/.pi/extensions/gate/__tests__/golden/artifact_gate_F5.json
new file mode 100644
index 00000000..32268c5a
--- /dev/null
+++ b/harness/.pi/extensions/gate/__tests__/golden/artifact_gate_F5.json
@@ -0,0 +1,15 @@
+{
+  "type": "ui_request",
+  "id": "u2",
+  "phase": "F5",
+  "schema_version": 1,
+  "widget": "artifact-gate",
+  "title": "Schema-linking",
+  "artifact": {
+    "kind": "schema_linking",
+    "data": { "candidates": [] },
+    "version": 1
+  },
+  "action": { "kind": "confirm", "prompt": "Confermi?" },
+  "reserved": ["back", "exit", "other"]
+}
diff --git a/harness/.pi/extensions/gate/__tests__/golden/multiselect_F4.json b/harness/.pi/extensions/gate/__tests__/golden/multiselect_F4.json
new file mode 100644
index 00000000..2d3fe773
--- /dev/null
+++ b/harness/.pi/extensions/gate/__tests__/golden/multiselect_F4.json
@@ -0,0 +1,14 @@
+{
+  "type": "ui_request",
+  "id": "u3",
+  "phase": "F4",
+  "schema_version": 1,
+  "widget": "multiselect",
+  "title": "Tabelle",
+  "allow_empty": false,
+  "allow_other": true,
+  "options": [],
+  "selected": [],
+  "content": { "candidates": [] },
+  "reserved": ["back", "exit", "other"]
+}
diff --git a/harness/.pi/extensions/gate/__tests__/golden/select_F1.json b/harness/.pi/extensions/gate/__tests__/golden/select_F1.json
new file mode 100644
index 00000000..bf5a40c3
--- /dev/null
+++ b/harness/.pi/extensions/gate/__tests__/golden/select_F1.json
@@ -0,0 +1,17 @@
+{
+  "type": "ui_request",
+  "id": "u1",
+  "phase": "F1",
+  "schema_version": 1,
+  "widget": "select",
+  "title": "Disambigua 'ablazione'",
+  "intro": null,
+  "allow_other": true,
+  "recommended": null,
+  "options": [
+    { "id": "o1", "label": "procedura" },
+    { "id": "o2", "label": "patologia" },
+    { "id": "other", "label": "Altro — specifica…", "opens": { "widget": "freetext", "title": "Specifica…" } }
+  ],
+  "reserved": ["back", "exit", "other"]
+}
diff --git a/harness/.pi/extensions/gate/builders.js b/harness/.pi/extensions/gate/builders.js
new file mode 100644
index 00000000..7d13eb63
--- /dev/null
+++ b/harness/.pi/extensions/gate/builders.js
@@ -0,0 +1,177 @@
+// Pure widget-descriptor builders (spec D2/D4, §4.1).
+//
+// Each function turns plain params into a ui_request descriptor object. No Pi
+// context, no I/O -- this is the part of the gate that is fully testable in L1
+// (in JS, in-language, no Python mirror). The glue (emission via ctx.sendRaw,
+// anti-bypass, the no-limbo loop) is in nsp-gate.js and is verified at L2.
+//
+// The 6 widget kinds: info, select, multiselect, freetext, artifact-gate, artifact.
+// `widget` is an open field (a new kind needs a renderer, not infra changes);
+// these are the initial 6. reserved = framework escape hatches always present on
+// blocking widgets: back / exit / other.
+
+"use strict";
+
+const SCHEMA_VERSION = 1;
+const RESERVED = ["back", "exit", "other"];
+
+const ALTRO_LABEL = "Altro — specifica…";
+const VALID_ACTION_KINDS = new Set(["confirm", "approve_reject", "view_only"]);
+const VALID_INFO_LEVELS = new Set(["info", "warning", "error"]);
+
+function requireString(value, name, ctx) {
+  if (typeof value !== "string" || value.length === 0) {
+    throw new Error(`builders: ${ctx} requires a non-empty ${name}`);
+  }
+  return value;
+}
+
+function requireArray(value, name, ctx) {
+  if (!Array.isArray(value)) {
+    throw new Error(`builders: ${ctx} requires ${name} to be an array`);
+  }
+  return value;
+}
+
+// An "other" option that opens a freetext child widget. Always present on
+// blocking pick widgets so the reviewer is never trapped in the listed options.
+function altroOption() {
+  return {
+    id: "other",
+    label: ALTRO_LABEL,
+    opens: { widget: "freetext", title: "Specifica…" },
+  };
+}
+
+// Build a `select` ui_request (single-pick). Reserved hatches (Altro/Back/Exit)
+// are injected; Altro carries the freetext linkage (§4.2). `recommended` is the
+// id of the option to highlight as "(consigliato)".
+function buildSelectRequest({
+  id, phase, title, options, intro = null, allowOther = true, recommended = null,
+}) {
+  requireString(title, "title", "select");
+  const opts = requireArray(options, "options", "select");
+  const out = {
+    type: "ui_request",
+    id,
+    phase,
+    schema_version: SCHEMA_VERSION,
+    widget: "select",
+    title,
+    intro,
+    allow_other: allowOther,
+    recommended,
+    options: allowOther ? [...opts, altroOption()] : [...opts],
+    reserved: RESERVED,
+  };
+  return out;
+}
+
+// Build a `multiselect` ui_request (multi-pick). `content` is the scrollable
+// context (e.g. schema candidates); `selected` the pre-checked option ids;
+// `allowEmpty:false` with zero options is a broken widget and throws.
+function buildMultiselectRequest({
+  id, phase, title, options, content = null, selected = [], allowEmpty = false, allowOther = true,
+}) {
+  requireString(title, "title", "multiselect");
+  const opts = requireArray(options, "options", "multiselect");
+  if (!allowEmpty && opts.length === 0) {
+    throw new Error(
+      "builders: multiselect with allow_empty:false requires at least one option",
+    );
+  }
+  return {
+    type: "ui_request",
+    id,
+    phase,
+    schema_version: SCHEMA_VERSION,
+    widget: "multiselect",
+    title,
+    allow_empty: allowEmpty,
+    allow_other: allowOther,
+    options: [...opts],
+    selected: [...selected],
+    content,
+    reserved: RESERVED,
+  };
+}
+
+// Build an `artifact-gate` ui_request: a rendered artifact + a disposition list
+// (confirm / approve_reject / view_only). The decision is load-bearing on the
+// document, so the artifact is never shown alone (spec §4.1).
+function buildArtifactGate({ id, phase, title, artifact, action }) {
+  requireString(title, "title", "artifact-gate");
+  if (!artifact || typeof artifact !== "object") {
+    throw new Error("builders: artifact-gate requires an artifact object");
+  }
+  if (!artifact.kind) {
+    throw new Error("builders: artifact-gate artifact requires a kind");
+  }
+  if (!action || !action.kind || !VALID_ACTION_KINDS.has(action.kind)) {
+    throw new Error(
+      `builders: artifact-gate action.kind must be one of ${[...VALID_ACTION_KINDS].join(", ")}`,
+    );
+  }
+  return {
+    type: "ui_request",
+    id,
+    phase,
+    schema_version: SCHEMA_VERSION,
+    widget: "artifact-gate",
+    title,
+    artifact,
+    action,
+    reserved: RESERVED,
+  };
+}
+
+// Build an `info` ui_request: fire-and-forget notification (no response expected,
+// no reserved hatches, no correlated id).
+function buildInfoRequest({ phase, level, text }) {
+  if (!level || !VALID_INFO_LEVELS.has(level)) {
+    throw new Error(
+      `builders: info level must be one of ${[...VALID_INFO_LEVELS].join(", ")}`,
+    );
+  }
+  requireString(text, "text", "info");
+  return {
+    type: "ui_request",
+    phase,
+    schema_version: SCHEMA_VERSION,
+    widget: "info",
+    level,
+    text,
+  };
+}
+
+// Build a `freetext` ui_request: free-text input, always a child of
+// select/artifact-gate (via Altro/Rifiuta) or via the ambient steering channel.
+function buildFreetextRequest({ id, phase, title }) {
+  requireString(title, "title", "freetext");
+  return {
+    type: "ui_request",
+    id,
+    phase,
+    schema_version: SCHEMA_VERSION,
+    widget: "freetext",
+    title,
+    reserved: RESERVED,
+  };
+}
+
+// Attach a child-widget spec to an option (linkage, §4.2). Returns the option.
+function withChildLinkage(option, widgetSpec) {
+  option.opens = widgetSpec;
+  return option;
+}
+
+module.exports = {
+  buildSelectRequest,
+  buildMultiselectRequest,
+  buildArtifactGate,
+  buildInfoRequest,
+  buildFreetextRequest,
+  withChildLinkage,
+  SCHEMA_VERSION,
+  RESERVED,
+};
diff --git a/harness/package.json b/harness/package.json
new file mode 100644
index 00000000..2d3df32c
--- /dev/null
+++ b/harness/package.json
@@ -0,0 +1,9 @@
+{
+  "name": "thothii-harness-gate",
+  "version": "0.1.0",
+  "private": true,
+  "description": "Pi gate extension for the ThothII NL->SQL harness (widget-descriptor builders + glue)",
+  "scripts": {
+    "test": "node --test .pi/extensions/gate/__tests__/*.test.js"
+  }
+}