diff --git a/app/ui/features/sampler/hub.test.js b/app/ui/features/sampler/hub.test.js
new file mode 100644
index 00000000..966333ad
--- /dev/null
+++ b/app/ui/features/sampler/hub.test.js
@@ -0,0 +1,32 @@
+import test from "node:test";
+import assert from "node:assert/strict";
+import { setupDom, teardownDom } from "../../composer/tests/_dom.js";
+
+let hub;
+test.before(async () => { setupDom(); hub = (await import("./index.js")).default; });
+test.after(() => teardownDom());
+
+test("the Sampler window shows the pipeline's steps and sampler, and a change saves into that slot", async () => {
+  const saved = [];
+  const slot = { id: "sampler", node: "S", inputs: { steps: 20, sampler_name: "euler", seed: 0 },
+    roles: [{ at: "generation.sampling", input: "steps", label: "Steps" }, { at: "generation.sampling", input: "sampler_name", label: "Sampler" }, { at: "generation.seed", input: "seed" }] };
+  const ps = { slots: () => [slot], activeModules: () => [], useful: () => true, currentValues: () => ({}), loading: () => false, loadError: () => null,
+    subscribe: () => () => {}, ensureLoaded: async () => {}, save: async (b) => { saved.push(b); } };
+  const api = { describeNodes: async () => ({ nodes: { S: { widgets: [{ name: "steps", type: "INT", min: 1, max: 100 }, { name: "sampler_name", type: "COMBO", choices: ["euler", "dpmpp_2m"] }, { name: "seed", type: "INT" }] } } }) };
+  const host = document.createElement("div");
+  document.body.append(host);
+  hub.setup({ host, app: { pipeline: ps, api, on: () => () => {}, actions: null } });
+  await new Promise((r) => setTimeout(r, 0));
+  const button = host.querySelector("button");
+  assert.equal(button.hidden, false, "shown with no sampling module, because the pipeline marks sampling inputs");
+  button.click();
+  await new Promise((r) => setTimeout(r, 0));
+  const text = document.body.textContent;
+  assert.match(text, /Steps/);
+  assert.match(text, /Sampler/);
+  const select = [...document.querySelectorAll("select")].find((s) => [...s.options].some((o) => o.value === "dpmpp_2m"));
+  select.value = "dpmpp_2m";
+  select.dispatchEvent(new Event("change", { bubbles: true }));
+  await new Promise((r) => setTimeout(r, 0));
+  assert.deepStrictEqual(saved, [{ inputs: { sampler: { sampler_name: "dpmpp_2m" } } }]);
+});
diff --git a/app/ui/features/sampler/index.js b/app/ui/features/sampler/index.js
index 78a3cbec..a981922b 100644
--- a/app/ui/features/sampler/index.js
+++ b/app/ui/features/sampler/index.js
@@ -1,8 +1,10 @@
-// "⏱ Sampler": steps, scheduler and sampler one click away, in a thin window over the timeline. Same settings as Engine ▸ Sampling,
-// same values tree, so the two cannot disagree. Absent when no installed module has a sampling setting.
+// "⏱ Sampler": the pipeline's steps, sampler and scheduler (the inputs its preset marks as sampling) and Engine ▸ Sampling's
+// settings, one click away in a thin window over the timeline. Same pipeline and values tree as those pages, so they cannot
+// disagree. Absent when the pipeline marks no sampling input and no module has a sampling setting.
 import { offer } from "../../shell/actions.js";
 import { composer as c } from "../../composer/composer.js";
 import { settingRow, whenSatisfied } from "../settings/field.js";
+import { widgetControl } from "../settings/models.js";
 
 export default {
   id: "sampler",
@@ -10,9 +12,20 @@ export default {
   needs: ["pipeline"],
   setup({ host, app }) {
     const ps = app.pipeline;
-    let pop = null;
-    const sampling = () => ps.activeModules().filter((m) => (m.category || "") === "sampling" && Object.keys(m.settings || {}).length);
-    const button = c.button.sm({ label: "⏱ Sampler", tone: "neutral", title: "Steps, scheduler and sampler: one click, no modal.", onClick: () => (pop ? pop.close() : open()) });
+    let pop = null, specs = {};
+    const sampling = () => ps.activeModules().filter((m) => (m.category || "") === "sampling" && Object.keys(m.settings || {}).length && ps.useful(m));
+    const marked = () => (ps.slots() || []).flatMap((slot) => (slot.roles || []).filter((r) => r.at === "generation.sampling" && r.input && !Array.isArray((slot.inputs || {})[r.input])).map((role) => ({ slot, role })));
+    const describe = async () => {
+      const missing = [...new Set(marked().map(({ slot }) => slot.node))].filter((n) => !(n in specs));
+      if (missing.length) try { Object.assign(specs, (await app.api.describeNodes(missing)).nodes || {}); } catch { /* the rows just stay out until the next change */ }
+    };
+    const inputRow = ({ slot, role }) => {
+      const w = ((specs[slot.node] || {}).widgets || []).find((x) => x.name === role.input);
+      if (!w) return null;
+      const set = async (v) => { if (JSON.stringify((slot.inputs || {})[role.input]) !== JSON.stringify(v)) await ps.save({ inputs: { [slot.id]: { [role.input]: v } } }); };
+      return c.settingsRow.default({ label: role.label || w.name, hint: w.tooltip || "", control: widgetControl({ ...w, name: role.label || w.name }, (slot.inputs || {})[role.input] ?? w.default, set) });
+    };
+    const button = c.button.sm({ label: "⏱ Sampler", tone: "neutral", title: "Steps, sampler, scheduler and sampling settings: one click, no modal.", onClick: () => (pop ? pop.close() : open()) });
     button.node.hidden = true;
     host.append(button.node);
 
@@ -22,18 +35,19 @@ export default {
       if (ps.loadError()) return body.set([c.banner.warn({ text: `Could not load: ${ps.loadError()}` })]);
       const mods = sampling(), values = ps.currentValues();
       const change = async (id, name, value) => { await ps.setModuleValue(id, name, value); draw(); };
-      body.set(mods.flatMap((m) => [mods.length > 1 ? c.label.section({ text: m.title || m.id }) : null,
-        ...Object.entries(m.settings).filter(([, spec]) => whenSatisfied(values, m.id, spec.when)).map(([name, spec]) => settingRow(m.id, name, spec, values, change))]).filter(Boolean));
+      body.set([...marked().map(inputRow), ...mods.flatMap((m) => [mods.length > 1 ? c.label.section({ text: m.title || m.id }) : null,
+        ...Object.entries(m.settings).filter(([, spec]) => whenSatisfied(values, m.id, spec.when)).map(([name, spec]) => settingRow(m.id, name, spec, values, change))])].filter(Boolean));
     };
     const typing = () => body.node.contains(document.activeElement) && /^(input|textarea)$/i.test(document.activeElement.tagName);
-    const off = ps.subscribe(() => { if (pop && !typing()) draw(); });
-    const show = () => { button.node.hidden = !sampling().length; if (button.node.hidden && pop) pop.close(); };
+    const off = ps.subscribe(() => { if (pop && !typing()) describe().then(draw); });
+    const show = () => { button.node.hidden = !sampling().length && !marked().length; if (button.node.hidden && pop) pop.close(); };
     ps.ensureLoaded().then(show);
     const offShow = ps.subscribe(show);
 
     function open() {
       draw();
       pop = c.popover.anchored({ anchor: button, body, side: "top", align: "end", onClose: () => { pop = null; } });
+      describe().then(() => { if (pop) draw(); });
     }
     const offered = offer(app, { id: "sampler", label: "Sampler", icon: "⏱", run: () => { if (!button.node.hidden) (pop ? pop.close() : open()); } });
     return () => { off(); offShow(); offered(); if (pop) pop.close(); button.node.remove(); };
diff --git a/app/ui/features/settings/models.js b/app/ui/features/settings/models.js
index 41cd68a4..f37e171e 100644
--- a/app/ui/features/settings/models.js
+++ b/app/ui/features/settings/models.js
@@ -7,7 +7,7 @@ import { labelOf, shownValues, sourcesFor } from "./wiring.js";
 const SEP = "\0", NEW_GROUP = "\0new";
 const fed = (v) => Array.isArray(v);
 
-const widgetControl = (w, current, set) => {
+export const widgetControl = (w, current, set) => {
   const label = w.name;
   if (w.type === "COMBO") {
     const choices = [...(w.choices || [])];
diff --git a/app/ui/shell/pipeline_link.js b/app/ui/shell/pipeline_link.js
index 8186e78d..765971af 100644
--- a/app/ui/shell/pipeline_link.js
+++ b/app/ui/shell/pipeline_link.js
@@ -1,16 +1,21 @@
 // The pipeline travels with the project: opening a project puts ITS pipeline over the session's, and
 // every landed pipeline edit becomes the project's copy (project.models). One writer -- the pipeline state.
 export function linkPipeline({ project, pipeline, onOpen, say = () => {} }) {
-  let adopted = true;        // false while the open project's pipeline is not the live one: its copy is not rewritten
-  let retries = 0;
+  // The id of the project the live pipeline belongs to, or null while one is being put in (or could not be): only
+  // it is written. A project opened while an open or a save is still in flight must never receive the other's pipeline.
+  // An id, not the object: Undo puts a copy of the same project in place.
+  let owner = null;
+  let retries = 0, opens = 0;
   // Only a real change is written: opening a project must not rewrite its file.
-  const store = (base, slots) => {
+  const store = (base, slots, opening) => {
     const next = { ...base, slots: JSON.parse(JSON.stringify(slots || [])), removed: pipeline.removedIds(), unwired: pipeline.unwiredMap(), whole: pipeline.whole() };
-    if (!("whole" in base) && !next.whole) delete next.whole;     // an older file reads as not whole anyway: no rewrite just to say so
+    if (opening && !("whole" in base)) delete next.whole;          // an older file is not rewritten just to record the guess; an edit records it
     if (JSON.stringify(next) !== JSON.stringify(project.project.models || {})) project.setField("models", next, { quiet: true });
   };
 
   async function adopt() {
+    owner = null;
+    const mine = ++opens, target = project.project && project.project.id;
     const saved = project.project && project.project.models || {};
     const own = (saved.slots || []).length > 0 || (saved.removed || []).length > 0;
     let ok = false, timer;
@@ -18,11 +23,12 @@ export function linkPipeline({ project, pipeline, onOpen, say = () => {} }) {
       // Bounded: a hung request must not hold the project behind it.
       ok = await Promise.race([pipeline.adopt(saved.slots || [], saved.removed, saved.unwired, saved.whole, project.fresh), new Promise((r) => { timer = setTimeout(() => r(false), 20000); })]);
     } catch { ok = false; } finally { clearTimeout(timer); }
-    adopted = Boolean(ok && pipeline.slots());
-    if (adopted) {
+    if (mine !== opens) return;                                  // opened again meanwhile (another project, or this one): the latest open handles it
+    if (ok && pipeline.slots()) {
+      owner = target;
       retries = 0;
       // An old project with nothing saved runs the default and stays as it is on disk; a new one keeps what it took.
-      if (own || project.fresh) store(saved, pipeline.slots());
+      if (own || project.fresh) store(saved, pipeline.slots(), true);
     } else if (retries++ < 3) {
       setTimeout(adopt, 5000);
     } else {
@@ -31,7 +37,7 @@ export function linkPipeline({ project, pipeline, onOpen, say = () => {} }) {
   }
 
   pipeline.subscribe((slots) => {
-    if (!project.project || !adopted) return;
+    if (!project.project || project.project.id !== owner) return;
     store(project.project.models || {}, slots);
   });
   onOpen(adopt);
diff --git a/app/ui/shell/pipeline_state.js b/app/ui/shell/pipeline_state.js
index faef8298..08cb7842 100644
--- a/app/ui/shell/pipeline_state.js
+++ b/app/ui/shell/pipeline_state.js
@@ -26,11 +26,14 @@ export function createPipelineState(API) {
   // Which traits the pipeline's chosen model has; null when that is not knowable (no file, or no model
   // module recognised it, or the one that did names no traits): null means "do not filter", while a list,
   // even an empty one, hides every module needing a trait it lacks. undefined: the probe failed, try again.
+  let modelNote = null;       // why nothing is hidden for the chosen file, when no model module recognised it
   async function probeModelTraits(pipelineSlots) {
     const filename = currentModelFile(pipelineSlots);
+    modelNote = null;
     if (!filename) return null;
     try {
       const data = await API.probeFamily(filename);
+      if (!data.detected && data.reason) modelNote = `${data.reason}, so every module is offered, including ones this model cannot use.`;
       return data.detected && Array.isArray(data.traits) ? data.traits : null;
     } catch (_) {
       return undefined;
@@ -568,6 +571,6 @@ export function createPipelineState(API) {
     loading: () => loading,
     loadError: () => loadError,
     saving: () => saving,
-    saveNotes: () => saveNotes,
+    saveNotes: () => (modelNote ? [...saveNotes, modelNote] : saveNotes),
   };
 }
diff --git a/app/ui/shell/tests/pipeline_link.test.js b/app/ui/shell/tests/pipeline_link.test.js
index dc640d1a..3ae960cc 100644
--- a/app/ui/shell/tests/pipeline_link.test.js
+++ b/app/ui/shell/tests/pipeline_link.test.js
@@ -38,3 +38,47 @@ test("an older file with no whole flag is not rewritten just to add one", async
   await r.open();
   assert.equal(r.writes.length, 0);
 });
+
+test("an older file guessed whole is not rewritten to record the guess", async () => {
+  const writes = [];
+  let opened;
+  const project = { project: { models: { slots, removed: [], unwired: {} } }, setField: (k, v) => { writes.push(v); } };
+  const pipeline = { adopt: async () => true, slots: () => slots, removedIds: () => [], unwiredMap: () => ({}), whole: () => true, subscribe: () => {} };
+  linkPipeline({ project, pipeline, onOpen: (fn) => { opened = fn; } });
+  await opened();
+  assert.equal(writes.length, 0);
+});
+
+test("switching project while the first is still loading never writes into either the wrong pipeline", async () => {
+  const writes = [];
+  let opened, heard, release;
+  const A = { id: "a", models: { slots: [{ ...slots[0], inputs: { ckpt_name: "A" } }], removed: [], unwired: {}, whole: false } };
+  const B = { id: "b", models: { slots: [{ ...slots[0], inputs: { ckpt_name: "B" } }], removed: [], unwired: {}, whole: false } };
+  let live = A.models.slots;
+  const project = { project: A, setField: (k, v) => { writes.push([project.project.id, v.slots[0].inputs.ckpt_name]); project.project[k] = v; } };
+  const pipeline = {
+    adopt: async (saved) => { if (saved[0].inputs.ckpt_name === "A") await new Promise((r) => { release = r; }); live = saved; return true; },
+    slots: () => live, removedIds: () => [], unwiredMap: () => ({}), whole: () => false, subscribe: (fn) => { heard = fn; },
+  };
+  linkPipeline({ project, pipeline, onOpen: (fn) => { opened = fn; } });
+  const first = opened();
+  heard(live);                              // a pipeline change while A is still loading
+  project.project = B;
+  await opened();
+  release();
+  await first;                              // A's late finish must not touch B
+  heard([{ ...slots[0], inputs: { ckpt_name: "B2" } }]);
+  assert.deepStrictEqual(writes, [["b", "B2"]]);
+});
+
+test("an Undo copy of the same project keeps receiving edits", async () => {
+  const writes = [];
+  let opened, heard;
+  const project = { project: { id: "a", models: { slots, removed: [], unwired: {}, whole: false } }, setField: (k, v) => { writes.push(v); project.project[k] = v; } };
+  const pipeline = { adopt: async () => true, slots: () => slots, removedIds: () => [], unwiredMap: () => ({}), whole: () => false, subscribe: (fn) => { heard = fn; } };
+  linkPipeline({ project, pipeline, onOpen: (fn) => { opened = fn; } });
+  await opened();
+  project.project = JSON.parse(JSON.stringify(project.project));
+  heard([{ ...slots[0], inputs: { ckpt_name: "b" } }]);
+  assert.equal(writes.length, 1);
+});
diff --git a/app/ui/shell/tests/pipeline_state.test.js b/app/ui/shell/tests/pipeline_state.test.js
index 1ead9ed1..447d968b 100644
--- a/app/ui/shell/tests/pipeline_state.test.js
+++ b/app/ui/shell/tests/pipeline_state.test.js
@@ -349,3 +349,10 @@ test("a file picked in a save is announced after its modules are known", async (
   await PS.save({ inputs: { model: { ckpt_name: "picked" } } });
   assert.deepStrictEqual(seen, ["new"]);
 });
+
+test("a model file no module recognises says so, and why nothing is hidden", async () => {
+  const PS = withCheckpoint(load([]));
+  lastApi.probeFamily = async () => ({ detected: false, reason: "a.ckpt: only .safetensors can be inspected without loading it" });
+  await PS.ensureLoaded();
+  assert.match(PS.saveNotes().join(" "), /only \.safetensors.*every module is offered/);
+});