diff --git a/docs/architecture/07-naming-and-relationships.md b/docs/architecture/07-naming-and-relationships.md
index c69bf78..7ada1a1 100644
--- a/docs/architecture/07-naming-and-relationships.md
+++ b/docs/architecture/07-naming-and-relationships.md
@@ -132,9 +132,14 @@ always mirrors the dataset names actually referenced in the published spec.
 ### 3.1 Extracting referenced names from a spec (pure — `src/core/spec-refs.ts`)
 
 A Vega-Lite spec can reference named data in several places: the top-level
-`data`, per-layer `data`, `data` inside `spec`/`facet`/`hconcat`/`vconcat`, and
-named entries in top-level `datasets`. Rather than enumerate Vega-Lite's grammar,
-we walk the spec recursively and collect every `{ data: { name } }` we find.
+`data`, per-layer `data`, `data` inside `spec`/`facet`/`hconcat`/`vconcat`, and a
+lookup transform's `from.data`. A spec may also define its OWN inline datasets via
+a top-level `datasets` map — those are self-defined, not library references.
+Rather than enumerate Vega-Lite's grammar, we walk the spec recursively and
+collect every `{ data: { name } }` — but **prune two keys**: never recurse into a
+`data` object's payload (its `values`/rows) or the top-level `datasets` map,
+because those hold user data, not nested specs. Without the prune, a data _row_
+carrying a field literally named `data: { name: "x" }` is misread as a reference.
 This is pure, deterministic, and the most heavily unit-tested function here.
 
 ```ts
@@ -142,8 +147,10 @@ This is pure, deterministic, and the most heavily unit-tested function here.
 
 type Json = unknown;
 
-/** Collects every dataset name referenced by `{ data: { name } }` anywhere in the spec. */
+/** Collects every library dataset name referenced by `{ data: { name } }`, excluding self-defined ones. */
 export function extractDatasetRefs(spec: Json): string[] {
+  const root = typeof spec === 'string' ? safeParse(spec) : spec;
+  const selfDefined = selfDefinedNames(root); // names from the spec's own top-level `datasets`
   const names = new Set<string>();
 
   const walk = (node: Json): void => {
@@ -155,13 +162,17 @@ export function extractDatasetRefs(spec: Json): string[] {
       const obj = node as Record<string, Json>;
       const data = obj.data as Record<string, Json> | undefined;
       if (data && typeof data === 'object' && typeof data.name === 'string') {
-        names.add(data.name);
+        if (!selfDefined.has(data.name)) names.add(data.name);
+      }
+      // Prune: a `data` payload and the `datasets` map hold user data, not refs.
+      for (const key of Object.keys(obj)) {
+        if (key === 'data' || key === 'datasets') continue;
+        walk(obj[key]);
       }
-      for (const key of Object.keys(obj)) walk(obj[key]);
     }
   };
 
-  walk(typeof spec === 'string' ? safeParse(spec) : spec);
+  walk(root);
   return [...names];
 }
 
@@ -193,11 +204,20 @@ export function recomputeDatasetRefs(spec: Json): string[] {
   agreeing with what the renderer actually resolves.
 - Recompute and store `datasetRefs` on **publish**, not on every keystroke —
   the draft can be transiently invalid, and only the published spec is shared.
+- Prune the **same two keys** (`data`, `datasets`) in all three ref walks —
+  extraction here, `renameDatasetInSpec`, and the renderer's `resolveDatasetRefs`
+  (`src/core/rendering.ts`). They must agree on what counts as a reference; if one
+  descends into data payloads and another doesn't, extraction and rendering
+  disagree and a row field named `data` either gets counted, rewritten, or throws
+  `DatasetNotFoundError`.
 
 **Don't**
 
 - Don't let two code paths each have their own idea of "referenced names".
-  Renamer and ref-recomputer must use the same extractor.
+  Renamer, ref-recomputer, and renderer must use the same walk shape.
+- Don't "enumerate the grammar" (scope the walk to a fixed list of container
+  keys) to fix the payload-descent problem — pruning the two data-bearing keys
+  stays correct as Vega-Lite's composition grammar grows; an allow-list rots.
 
 ---
 
@@ -323,19 +343,21 @@ The spec rewrite is pure; the orchestration reads and writes stores.
 /** Returns a copy of `spec` with every data.name === oldName replaced by newName. */
 export function renameDatasetInSpec(spec: Json, oldName: string, newName: string): Json {
   const obj = typeof spec === 'string' ? safeParse(spec) : spec;
+  const selfDefined = selfDefinedNames(obj); // never rename a spec's own inline dataset name
 
   const rewrite = (node: Json): Json => {
     if (Array.isArray(node)) return node.map(rewrite);
     if (node && typeof node === 'object') {
       const out: Record<string, Json> = {};
       for (const [k, v] of Object.entries(node as Record<string, Json>)) {
-        if (
-          k === 'data' &&
-          v &&
-          typeof v === 'object' &&
-          (v as Record<string, Json>).name === oldName
-        ) {
-          out[k] = { ...(v as object), name: newName };
+        // A `data` object is a reference site: rename a matching name, but never
+        // recurse into its payload. `datasets` (self-defined inline data) is left
+        // whole. Same prune as extractDatasetRefs — see §3.1.
+        if (k === 'data' && v && typeof v === 'object' && !Array.isArray(v)) {
+          const dv = v as Record<string, Json>;
+          out[k] = dv.name === oldName && !selfDefined.has(oldName) ? { ...dv, name: newName } : dv;
+        } else if (k === 'data' || k === 'datasets') {
+          out[k] = v;
         } else {
           out[k] = rewrite(v);
         }
diff --git a/docs/architecture/10-interaction-and-feedback.md b/docs/architecture/10-interaction-and-feedback.md
index 4d1b72a..0be59bd 100644
--- a/docs/architecture/10-interaction-and-feedback.md
+++ b/docs/architecture/10-interaction-and-feedback.md
@@ -43,6 +43,28 @@ nature of the message, not by convenience.
   consent-for-destruction in a toast.
 - **Errors persist; success fades.** An error/warning toast waits for the user (a critical
   message must not vanish on a timer); success/info auto-dismiss (~6s).
+- **Toasts sit bottom-right**, not top-right. Carbon's default is the top, but our header's
+  action cluster (Publish/Revert, theme/datasets) lives top-right — a toast there covers the
+  control the user just used. Bottom-anchored, the stack grows upward with the newest toast
+  nearest the corner, and still clears the centered confirm dialog. (`Toaster.module.css`.)
+- **Toast copy: title states it, message adds to it.** Every toast renders a `title` and a
+  `message`. The title is the short headline — the action or what stopped, **no terminal
+  period** ("Snippet published", "Storage full"). The message is **one short sentence that
+  must not paraphrase the title** (Carbon, `components/notification/usage.mdx` §Body
+  content: _"Don't repeat or paraphrase the title"_); it carries the **consequence** for a
+  success ("Your draft is now the published version") or the **next step** for a fixable
+  error. Name the specific item in the message when toasts can stack — a delete confirms
+  _which_ one went ("…removed `\"Sales\"`…").
+- **Toast only what the user can't already see.** A success toast is for an outcome with no
+  strong on-screen cue: a **side effect** (Extract creates a dataset off-screen while the
+  user is in the editor), a **disappearance** (delete), or a **state flip** (publish/revert).
+  An action whose result is immediately visible — a created snippet opening in the editor, a
+  new dataset shown selected — is confirmed by that visible change; adding a toast is noise
+  (NN/g aesthetic-and-minimalist; Carbon `notification/usage.mdx` "Deciding what to use").
+  An **invisible** outcome that still shouldn't toast is **copy-to-clipboard**: confirm it
+  _inline on the control_ ("Copied") with a polite `aria-live` announcement for assistive
+  tech, never a toast-per-copy. This refines the spec's earlier blanket "every action
+  toasts" (spec §01F/§02/§05, reconciled).
 - **The same failure can light up two channels.** An unrenderable spec shows the _same_
   message inline in both the editor (§03E) and the preview (§04) — one producer
   (`PreviewStore`), two subscribers. That's intentional, not duplication.
diff --git a/docs/spec/01-application-shell.md b/docs/spec/01-application-shell.md
index 616e313..4be85b5 100644
--- a/docs/spec/01-application-shell.md
+++ b/docs/spec/01-application-shell.md
@@ -99,13 +99,17 @@ Transient toast messages appear in a corner of the screen to confirm actions or
 - Each toast auto-dismisses after a few seconds, and can also be dismissed manually via its close control.
 - Multiple toasts stack rather than replacing one another, and appear/disappear with a brief fade.
 
+Toasts confirm outcomes the user **cannot already see** — a side effect, a disappearance, or a state change with no strong on-screen cue. An action whose result is immediately visible (a newly created snippet opening in the editor; a new dataset shown selected in its detail pane) is confirmed by that visible change, not by an added toast, which would only be noise (Nielsen Norman "aesthetic and minimalist design"; Carbon notification usage; see _docs/architecture/10 → Toast copy_). Assistive-technology users still receive an announcement on the changed region.
+
 Events that raise toasts include:
 
-- Snippet actions: creating, duplicating, deleting, publishing a draft, and reverting/discarding a draft.
-- Dataset actions: creating, deleting, and extracting inline data into a dataset.
+- Snippet actions: **duplicating** (the copy is easily mistaken for an edit of the original), **deleting** (the snippet disappears), **publishing** a draft, and **reverting** a draft. _Creating_ a snippet opens it in the editor and needs no toast.
+- Dataset actions: **deleting**, and **extracting** inline data into a dataset (the dataset is created off-screen while the user is in the editor). _Creating_ a dataset in the Datasets modal is confirmed by the new dataset appearing selected.
 - Import/Export: results of an import (success/partial/failure) and confirmation of an export.
 - Errors: spec/data validation failures and local-storage capacity warnings.
 
+**Copy Reference** (Datasets) is the exception that proves the rule: a clipboard write is invisible, but the universal pattern confirms it _inline on the control_ ("Copied"), announced politely to assistive tech — a toast per copy would be noise.
+
 ## G. Offline & Installable
 
 Astrolabe is local-first and usable without a network connection.
diff --git a/docs/spec/02-snippet-library.md b/docs/spec/02-snippet-library.md
index fcc2627..3288653 100644
--- a/docs/spec/02-snippet-library.md
+++ b/docs/spec/02-snippet-library.md
@@ -57,9 +57,9 @@ When a snippet is active, a metadata panel (within the left pane) exposes its ed
 
 ## Snippet Operations
 
-The library provides the lifecycle operations for snippets. Each operation gives clear feedback via a toast notification (see _Application Shell & Navigation_).
+The library provides the lifecycle operations for snippets. An operation whose outcome the user can't already see confirms it with a toast; an operation whose result is immediately visible needs none (see _Application Shell & Navigation_ → Toasts).
 
-- **Create New**: starts a new snippet from a small sample Vega-Lite bar-chart template (a few inline category/value rows), assigns it an auto-generated default name (see _Naming & Tags_), saves it, and makes it the active snippet.
+- **Create New**: starts a new snippet from a small sample Vega-Lite bar-chart template (a few inline category/value rows), assigns it an auto-generated default name (see _Naming & Tags_), saves it, and makes it the active snippet. Opening in the editor _is_ the confirmation, so no toast is raised.
 - **Duplicate**: creates an independent copy of the active snippet with a name suffixed "(copy)". The copy carries over the specification, comment, tags, and dataset references, gets fresh created/modified timestamps and a new identity, and becomes the active snippet. A success toast confirms the duplication.
 - **Delete**: permanently removes the active snippet after the user confirms a warning that the action cannot be undone. After deletion no snippet is active. A toast confirms the deletion.
 - These operations never affect other snippets.
diff --git a/docs/spec/05-datasets.md b/docs/spec/05-datasets.md
index b6e3d9a..df6dc72 100644
--- a/docs/spec/05-datasets.md
+++ b/docs/spec/05-datasets.md
@@ -84,11 +84,12 @@ The detail pane for a selected dataset shows:
 
 ## Actions
 
-Each action raises a confirming toast (or an error toast on failure).
+A destructive or off-screen outcome raises a confirming toast; an action whose result is immediately visible is confirmed by that change. Any action may raise an error toast on failure (see _Application Shell & Navigation_ → Toasts).
 
 - **Copy Reference** — copies the by-name reference object to the clipboard, ready to paste into a spec:
   `{ "data": { "name": "MyDataset" } }`
-- **New / Create New** — opens the create form in the detail pane with fields: **name** (required, unique), **source** toggle (Inline / URL), the **data** (a paste area for inline, a URL field for URL source), and an optional **comment**. Save is disabled until a name and valid data/URL are present. On success the new dataset is selected.
+  The clipboard write is invisible, so it is confirmed _inline on the control_ ("Copied"), announced politely to assistive technology — not a toast.
+- **New / Create New** — opens the create form in the detail pane with fields: **name** (required, unique), **source** toggle (Inline / URL), the **data** (a paste area for inline, a URL field for URL source), and an optional **comment**. Save is disabled until a name and valid data/URL are present. On success the new dataset is shown selected in the detail pane — that visible result is the confirmation, so no toast is raised (a dataset created _off-screen_ via Extract does toast; see _Spec Editor_).
 - **Edit** — rename, edit the comment, and update the data (re-paste inline data or refresh the URL). Updating inline data re-profiles it; the modified timestamp advances.
 - **Delete** — asks for confirmation ("Delete \"Name\"? This cannot be undone."), then removes the dataset and clears the selection.
 
diff --git a/src/app/components/DatasetsModal.tsx b/src/app/components/DatasetsModal.tsx
index 5b87459..b4ded64 100644
--- a/src/app/components/DatasetsModal.tsx
+++ b/src/app/components/DatasetsModal.tsx
@@ -191,8 +191,16 @@ function DatasetDetail({
       confirmLabel: 'Delete',
       danger: true,
     });
-    // TODO (M6, spec §05): success toast on delete.
-    if (ok) remove(dataset.id);
+    if (!ok) return;
+    const removedName = dataset.name;
+    remove(dataset.id);
+    // Confirm the deletion (spec §05). The message names which dataset went
+    // (council toast-copy rule, docs/architecture/10 → Toast copy).
+    notify({
+      kind: 'success',
+      title: 'Dataset deleted',
+      message: `"${removedName}" was permanently removed.`,
+    });
   };
 
   return (
@@ -203,6 +211,13 @@ function DatasetDetail({
           <button type="button" className={styles.action} onClick={() => void handleCopy()}>
             {copied ? 'Copied' : 'Copy Reference'}
           </button>
+          {/* The clipboard write is invisible, so the success is confirmed inline
+              ("Copied") rather than by a toast (docs/architecture/10 → Toast copy).
+              This polite live region announces it to assistive tech, which the
+              button's visual label swap alone would not reliably do. */}
+          <span role="status" className="visually-hidden">
+            {copied ? 'Reference copied to clipboard' : ''}
+          </span>
           <button type="button" className={styles.action} onClick={handleEdit}>
             Edit
           </button>
diff --git a/src/app/components/SnippetLibrary.tsx b/src/app/components/SnippetLibrary.tsx
index c326cd7..5ee4b9c 100644
--- a/src/app/components/SnippetLibrary.tsx
+++ b/src/app/components/SnippetLibrary.tsx
@@ -11,6 +11,7 @@
 import { useShallow } from 'zustand/react/shallow';
 import { formatSnippetSize, hasUnpublishedChanges, snippetSizeBytes } from '@core/snippet';
 import { confirm } from '../stores/ConfirmStore';
+import { notify } from '../stores/NotificationStore';
 import { useSnippetStore } from '../stores/SnippetStore';
 import styles from './SnippetLibrary.module.css';
 
@@ -73,18 +74,28 @@ export function SnippetLibrary() {
 
   const handleDelete = async (id: string, name: string) => {
     // In-app confirmation (docs/architecture/03 → confirmation dialogs).
-    // TODO: surface a deletion toast (spec §02) once the toast system lands (M6).
     const ok = await confirm({
       title: 'Delete snippet',
       message: `Delete "${name}"? This cannot be undone.`,
       confirmLabel: 'Delete',
       danger: true,
     });
-    if (ok) removeSnippet(id);
+    if (!ok) return;
+    removeSnippet(id);
+    // Confirm the deletion (spec §02). The message names which snippet went —
+    // useful when toasts stack (council toast-copy rule, docs/architecture/10).
+    notify({
+      kind: 'success',
+      title: 'Snippet deleted',
+      message: `"${name}" was permanently removed from your library.`,
+    });
   };
 
   return (
     <div className={styles.library}>
+      {/* Create raises no toast: the new snippet opens in the editor, so the
+          result is already on-screen (spec §02; docs/architecture/10 → Toast
+          copy). Delete/duplicate toast because the outcome isn't visible. */}
       <button className={styles.createNew} onClick={() => createSnippet()}>
         + Create New Snippet
       </button>
diff --git a/src/app/components/SpecEditor.tsx b/src/app/components/SpecEditor.tsx
index 9effc77..aa10e0b 100644
--- a/src/app/components/SpecEditor.tsx
+++ b/src/app/components/SpecEditor.tsx
@@ -27,6 +27,7 @@ import { openModal } from '../modals/ModalCoordinator';
 import { useAppStore } from '../stores/AppStore';
 import { confirm } from '../stores/ConfirmStore';
 import { hasInlineData } from '../stores/ExtractStore';
+import { notify } from '../stores/NotificationStore';
 import { usePreviewStore } from '../stores/PreviewStore';
 import { selectActiveSnippet, selectShownText, useSnippetStore } from '../stores/SnippetStore';
 import { SegmentedControl, type SegmentedOption } from './SegmentedControl';
@@ -64,7 +65,14 @@ function EditorToolbar() {
   const handlePublish = () => {
     if (!useSnippetStore.getState().activeSnippetId) return;
     useSnippetStore.getState().publish();
-    // TODO: success toast "Snippet published" once the toast system lands (M6, spec §03D).
+    // Success confirmation (spec §03D). Per the council's toast-copy rule
+    // (docs/architecture/10 → Toast copy), the title states the action and the
+    // message adds the consequence rather than paraphrasing it.
+    notify({
+      kind: 'success',
+      title: 'Snippet published',
+      message: 'Your draft is now the published version.',
+    });
   };
 
   const handleRevert = async () => {
@@ -77,7 +85,11 @@ function EditorToolbar() {
     });
     if (ok) {
       useSnippetStore.getState().revert();
-      // TODO: success toast "Draft reverted" once the toast system lands (M6, spec §03D).
+      notify({
+        kind: 'success',
+        title: 'Draft reverted',
+        message: 'The editor was restored to the last published version.',
+      });
     }
   };
 
diff --git a/src/app/components/Toaster.module.css b/src/app/components/Toaster.module.css
index 119013d..c9d5bfb 100644
--- a/src/app/components/Toaster.module.css
+++ b/src/app/components/Toaster.module.css
@@ -1,10 +1,14 @@
 .region {
   position: fixed;
-  top: var(--space-5);
+  /* Bottom-right, not top-right: the header's action cluster (Publish/Revert,
+     theme/datasets controls) lives top-right, and a toast there lands on top of
+     the control the user just used. Bottom-anchored, the stack grows upward and
+     the newest toast sits nearest the corner (docs/architecture/10 → Toasts). */
+  bottom: var(--space-5);
   right: var(--space-5);
   /* Above the confirm backdrop (z 1000) so a failure stays visible and
-     dismissible even with a confirmation open; top-right won't block the
-     centered dialog. */
+     dismissible even with a confirmation open; the corner clears the centered
+     dialog. */
   z-index: 1100;
   display: flex;
   flex-direction: column;
diff --git a/src/app/components/Toaster.tsx b/src/app/components/Toaster.tsx
index 341c642..e785c57 100644
--- a/src/app/components/Toaster.tsx
+++ b/src/app/components/Toaster.tsx
@@ -2,8 +2,9 @@
  * Toaster — renders the NotificationStore as a stack of toasts (spec §10,
  * design language → Toasts). Mounted once at the app root, beside ConfirmDialog.
  *
- * The non-blocking counterpart to ConfirmDialog: top-right, stacked newest-last,
- * each dismissible. Error/warning toasts persist until dismissed (Carbon: a
+ * The non-blocking counterpart to ConfirmDialog: bottom-right, stacked
+ * newest-nearest-the-corner, each dismissible (placement rationale in
+ * Toaster.module.css). Error/warning toasts persist until dismissed (Carbon: a
  * critical message shouldn't vanish on a timer); success/info auto-dismiss. A
  * failure that carries diagnostic `detail` exposes it under a collapsed
  * "Technical details" disclosure — available to report, without shouting.
diff --git a/src/app/stores/DatasetStore.ts b/src/app/stores/DatasetStore.ts
index 842b84e..93a03b0 100644
--- a/src/app/stores/DatasetStore.ts
+++ b/src/app/stores/DatasetStore.ts
@@ -221,6 +221,10 @@ export const useDatasetStore = create<DatasetState>((set, get) => ({
       now,
     });
     get().add(dataset);
+    // Switching to the detail view with the new dataset selected IS the success
+    // confirmation, so no toast is raised — the result is on-screen (spec §05;
+    // docs/architecture/10 → Toast copy). Extract-to-dataset, which creates a
+    // dataset off-screen, does toast (see ExtractStore).
     set({ view: 'detail', form: EMPTY_FORM, formError: null });
     return true;
   },
diff --git a/src/app/stores/ExtractStore.ts b/src/app/stores/ExtractStore.ts
index 3909668..cda40b5 100644
--- a/src/app/stores/ExtractStore.ts
+++ b/src/app/stores/ExtractStore.ts
@@ -17,6 +17,7 @@ import type { DataFormat } from '@core/format-detection';
 import { createDataset } from '@core/dataset';
 import { isNameTaken } from '@core/naming';
 import { useDatasetStore } from './DatasetStore';
+import { notify } from './NotificationStore';
 import { useSnippetStore } from './SnippetStore';
 
 /** The inline `data` block of a parsed spec, if it carries `values`. */
@@ -123,8 +124,14 @@ export const useExtractStore = create<ExtractState>((set, get) => ({
     spec.data = { name };
     useSnippetStore.getState().replaceActiveDraft(JSON.stringify(spec, null, 2), now);
 
-    // TODO (M6, spec §03F): success toast "Dataset created" — deferred with the
-    // other success toasts (see SnippetStore publish/revert breadcrumbs).
+    // Success confirmation (spec §03F). Title states the action; the message
+    // adds the consequence — the spec was rewritten to reference the new dataset
+    // by name (council toast-copy rule, docs/architecture/10 → Toast copy).
+    notify({
+      kind: 'success',
+      title: 'Dataset created',
+      message: `The spec now references "${name}" instead of its inline data.`,
+    });
     set(INITIAL);
     return true;
   },
diff --git a/src/core/rendering.test.ts b/src/core/rendering.test.ts
index 213c6d9..43e8d78 100644
--- a/src/core/rendering.test.ts
+++ b/src/core/rendering.test.ts
@@ -214,6 +214,25 @@ describe('prepareSpecForRender — dataset resolution (spec §04 Rendering Contr
     };
     expect(out.data).toEqual({ values: [{ a: 1 }], foo: 1 });
   });
+
+  test('a "data" field buried in inline rows is not resolved and does not throw', () => {
+    // The inline rows carry a column named `data` whose value looks like a
+    // reference object. It is payload; resolution must not descend into it.
+    const spec = { data: { values: [{ data: { name: 'Missing' } }] }, mark: 'bar' };
+    const out = prepareSpecForRender(spec, { datasets }) as { data: { values: unknown[] } };
+    expect(out.data.values).toEqual([{ data: { name: 'Missing' } }]);
+  });
+
+  test('resolves a reference inside a lookup transform (from.data)', () => {
+    const spec = {
+      data: { name: 'JsonDs' },
+      transform: [{ lookup: 'id', from: { data: { name: 'CsvDs' }, key: 'id', fields: ['x'] } }],
+    };
+    const out = prepareSpecForRender(spec, { datasets }) as unknown as {
+      transform: Array<{ from: { data: unknown } }>;
+    };
+    expect(out.transform[0].from.data).toEqual({ values: 'a,b\n1,2', format: { type: 'csv' } });
+  });
 });
 
 describe('escapeVegaField', () => {
diff --git a/src/core/rendering.ts b/src/core/rendering.ts
index 9bbb6f8..b5318bd 100644
--- a/src/core/rendering.ts
+++ b/src/core/rendering.ts
@@ -149,11 +149,12 @@ function resolvedData(dataset: ResolvableDataset, rest: SpecNode): SpecNode {
 
 /**
  * Replace every named-data reference in `node` with its library dataset's
- * contents, recursing through the entire spec (arrays and objects) so refs
- * anywhere are resolved — matching `extractDatasetRefs`. A self-defined name is
- * left untouched; an unknown library name throws `DatasetNotFoundError`. Matching
- * is case-insensitive, mirroring naming.ts. Mutates in place; the caller already
- * works on a copy.
+ * contents, recursing through the spec (arrays and objects) so refs anywhere are
+ * resolved — matching `extractDatasetRefs`, including pruning the `data` and
+ * top-level `datasets` payload keys so resolution never descends into user data
+ * rows. A self-defined name is left untouched; an unknown library name throws
+ * `DatasetNotFoundError`. Matching is case-insensitive, mirroring naming.ts.
+ * Mutates in place; the caller already works on a copy.
  */
 function resolveDatasetRefs(
   node: unknown,
@@ -177,15 +178,16 @@ function resolveDatasetRefs(
     }
   }
 
-  // TODO: this walks EVERY key, so it also descends into inlined data payloads
-  // (the just-resolved `values`, a spec's `datasets`/`data.values`). That's
-  // wasteful for large inline data on every debounced render, and a row with a
-  // field literally named `data` holding `{ name: "x" }` would be spuriously
-  // resolved or throw DatasetNotFoundError. extractDatasetRefs shares this broad
-  // walk. A scoped walk (recurse only into the known sub-spec/container keys +
-  // `transform[].lookup.from`, never into data payloads) would be safer and
-  // faster — change deliberately, with tests for where refs may legally appear.
-  for (const key of Object.keys(node)) resolveDatasetRefs(node[key], byName, selfDefined);
+  // Recurse into every key except the two that hold data payloads (`data` —
+  // resolved/captured above; `datasets` — the spec's own inline data). Pruning
+  // them avoids descending into the just-resolved `values` and into user data
+  // rows, where a field named `data` holding `{ name: "x" }` would otherwise be
+  // spuriously resolved or throw DatasetNotFoundError. extractDatasetRefs prunes
+  // the same two keys so resolution and extraction stay in agreement.
+  for (const key of Object.keys(node)) {
+    if (key === 'data' || key === 'datasets') continue;
+    resolveDatasetRefs(node[key], byName, selfDefined);
+  }
 }
 
 /**
diff --git a/src/core/spec-refs.test.ts b/src/core/spec-refs.test.ts
index 1f60bc1..c4e89f1 100644
--- a/src/core/spec-refs.test.ts
+++ b/src/core/spec-refs.test.ts
@@ -47,6 +47,28 @@ describe('extractDatasetRefs', () => {
     // "foo" is self-defined and not a library dependency; "Library" is.
     expect(extractDatasetRefs(spec)).toEqual(['Library']);
   });
+
+  test('a data row carrying a field literally named "data" is not a reference', () => {
+    // The inline rows happen to have a column called `data` whose value looks
+    // like a reference object — it is payload, not a library dependency.
+    const spec = {
+      data: { values: [{ data: { name: 'NotARef' } }, { data: { name: 'AlsoNot' } }] },
+      mark: 'bar',
+    };
+    expect(extractDatasetRefs(spec)).toEqual([]);
+  });
+
+  test('does not descend into a self-defined datasets payload', () => {
+    const spec = { datasets: { local: [{ data: { name: 'Buried' } }] }, mark: 'bar' };
+    expect(extractDatasetRefs(spec)).toEqual([]);
+  });
+
+  test('collects a reference from a lookup transform (from.data)', () => {
+    const spec = {
+      transform: [{ lookup: 'id', from: { data: { name: 'Lookup' }, key: 'id', fields: ['x'] } }],
+    };
+    expect(extractDatasetRefs(spec)).toEqual(['Lookup']);
+  });
 });
 
 describe('recomputeDatasetRefs', () => {
@@ -105,4 +127,22 @@ describe('renameDatasetInSpec', () => {
     expect(out.data.name).toBe('Old'); // self-defined — left untouched
     expect(Object.keys(out.datasets)).toEqual(['Old']);
   });
+
+  test('does not rewrite a "data" field buried in inline data rows', () => {
+    const spec = {
+      data: { name: 'Old', values: [{ data: { name: 'Old' } }] },
+      mark: 'bar',
+    };
+    const out = renameDatasetInSpec(spec, 'Old', 'New');
+    expect(out.data.name).toBe('New'); // the real reference is renamed
+    expect(out.data.values[0].data.name).toBe('Old'); // the row payload is left alone
+  });
+
+  test('renames a reference inside a lookup transform (from.data)', () => {
+    const spec = {
+      transform: [{ lookup: 'id', from: { data: { name: 'Old' }, key: 'id' } }],
+    };
+    const out = renameDatasetInSpec(spec, 'Old', 'New');
+    expect(out.transform[0].from.data.name).toBe('New');
+  });
 });
diff --git a/src/core/spec-refs.ts b/src/core/spec-refs.ts
index 69b15ae..8227af4 100644
--- a/src/core/spec-refs.ts
+++ b/src/core/spec-refs.ts
@@ -4,10 +4,19 @@
  *
  * Portable core: no browser APIs, no React, no store access. A Vega-Lite spec
  * references named data through `{ "data": { "name": "MyDataset" } }`, which can
- * appear at the top level, per-layer, or inside `spec`/`facet`/concat children.
- * Rather than enumerate the grammar, we walk the spec recursively and collect
- * every `{ data: { name } }` we find — the single source of truth for "what does
- * this spec reference", which the renderer's resolution must agree with.
+ * appear at the top level, per-layer, inside `spec`/`facet`/concat children, or in
+ * a lookup transform's `from.data`. Rather than enumerate the grammar, we walk the
+ * spec recursively and collect every `{ data: { name } }` we find — the single
+ * source of truth for "what does this spec reference", which the renderer's
+ * resolution must agree with.
+ *
+ * The walk recurses into every key EXCEPT two, which hold user data payloads
+ * rather than nested specs: a `data` object (its `name` is captured at the parent
+ * site; its `values`/`format` are payload, never a nested ref) and a top-level
+ * `datasets` map (the spec's own inline data). Pruning those is what keeps a data
+ * *row* that happens to carry a field literally named `data: { name: "x" }` from
+ * being misread as a library reference. The renderer's resolution prunes the same
+ * two keys so the two stay in lockstep.
  *
  * A spec may be stored as an **object** or as **JSON text** (see spec §09A); we
  * normalize once at the boundary (unparseable text → no refs / unchanged spec) so
@@ -66,12 +75,14 @@ export function extractDatasetRefs(spec: Json): string[] {
       if (data && typeof data === 'object' && typeof data.name === 'string') {
         if (!selfDefined.has(data.name)) names.add(data.name);
       }
-      // TODO: walks every key, so it also descends into data payloads
-      // (`data.values`, top-level `datasets`). A row with a field named `data`
-      // holding `{ name: "x" }` is falsely counted as a reference. Shared with
-      // rendering.ts resolveDatasetRefs — scope both to the keys where refs can
-      // legally appear, together and with tests. Benign for typical data.
-      for (const key of Object.keys(obj)) walk(obj[key]);
+      // Recurse into every key except the two that hold data payloads (`data` —
+      // captured above; `datasets` — the spec's own inline data). Pruning them
+      // keeps the walk out of user data rows, where a field named `data` would
+      // otherwise be misread as a reference. Kept in step with rendering.ts.
+      for (const key of Object.keys(obj)) {
+        if (key === 'data' || key === 'datasets') continue;
+        walk(obj[key]);
+      }
     }
   };
 
@@ -105,15 +116,16 @@ export function renameDatasetInSpec<T>(spec: T, oldName: string, newName: string
     if (node && typeof node === 'object') {
       const out: Record<string, Json> = {};
       for (const [k, v] of Object.entries(node as Record<string, Json>)) {
-        if (
-          k === 'data' &&
-          v &&
-          typeof v === 'object' &&
-          !Array.isArray(v) &&
-          (v as Record<string, Json>).name === oldName &&
-          !selfDefined.has(oldName)
-        ) {
-          out[k] = { ...v, name: newName };
+        // A `data` object is a reference site, not a container: rename a matching
+        // name and stop — never recurse into its payload. A `datasets` map is the
+        // spec's own inline data: leave it whole. Pruning both (mirroring
+        // extractDatasetRefs) keeps rename out of user data rows, where a field
+        // named `data` would otherwise be rewritten as if it were a reference.
+        if (k === 'data' && v && typeof v === 'object' && !Array.isArray(v)) {
+          const dv = v as Record<string, Json>;
+          out[k] = dv.name === oldName && !selfDefined.has(oldName) ? { ...dv, name: newName } : dv;
+        } else if (k === 'data' || k === 'datasets') {
+          out[k] = v;
         } else {
           out[k] = rewrite(v);
         }
diff --git a/styles/base.css b/styles/base.css
index b5932ae..f878665 100644
--- a/styles/base.css
+++ b/styles/base.css
@@ -63,3 +63,23 @@ body {
     transition-duration: 0.01ms !important;
   }
 }
+
+/*
+ * Visually-hidden but available to assistive tech — the standard sr-only recipe.
+ * Used for polite `aria-live`/`role="status"` announcements whose visible
+ * confirmation lives elsewhere (e.g. Copy Reference shows "Copied" on the button
+ * for sighted users; this announces it to a screen reader). See
+ * docs/architecture/10 → Toast copy (the "toast only what can't be seen" rule).
+ */
+.visually-hidden {
+  position: absolute;
+  width: 1px;
+  height: 1px;
+  margin: -1px;
+  padding: 0;
+  border: 0;
+  overflow: hidden;
+  clip: rect(0 0 0 0);
+  clip-path: inset(50%);
+  white-space: nowrap;
+}