diff --git a/docs/architecture/07-naming-and-relationships.md b/docs/architecture/07-naming-and-relationships.md
index d7bc136..0fda734 100644
--- a/docs/architecture/07-naming-and-relationships.md
+++ b/docs/architecture/07-naming-and-relationships.md
@@ -286,42 +286,44 @@ reactive code.
 
 ## 5. Import: auto-suffix collisions, then report
 
-On import we never overwrite an existing dataset. A dataset whose name collides
+On import we never overwrite an existing record. A record whose name collides
 is renamed to a unique name via `makeUniqueName`, and **every rename is
 collected and reported to the user** (toast / summary) so the change is never
 silent. Crucially, names are reserved _as we go_ — within a single import, two
 incoming `Sales` datasets become `Sales 2` and `Sales 3`, not two `Sales 2`.
+The helper is generic over `{ name: string }` because two record kinds key on a
+unique name: datasets and custom chart themes (only dataset renames need
+propagation — nothing references a theme by name).
 
 ```ts
 // src/core/import-normalize.ts
 
 import { makeUniqueName } from './naming';
-import type { Dataset } from './dataset';
 
-export interface DatasetRename {
+export interface NameRename {
   from: string;
   to: string;
 }
 
 /**
- * Returns incoming datasets with collision-free names, plus the renames applied.
- * `existing` are names already in the library; `incoming` are datasets to add.
+ * Returns incoming records with collision-free names, plus the renames applied.
+ * `existing` are names already in the collection; `incoming` are records to add.
  */
-export function dedupeIncomingDatasetNames(
+export function dedupeIncomingNames<T extends { name: string }>(
   existing: ReadonlyArray<string>,
-  incoming: ReadonlyArray<Dataset>,
-): { datasets: Dataset[]; renames: DatasetRename[] } {
+  incoming: ReadonlyArray<T>,
+): { records: T[]; renames: NameRename[] } {
   const reserved = new Set(existing.map((n) => n.toLowerCase()));
-  const renames: DatasetRename[] = [];
+  const renames: NameRename[] = [];
 
-  const datasets = incoming.map((d) => {
-    const unique = makeUniqueName(d.name, reserved);
+  const records = incoming.map((r) => {
+    const unique = makeUniqueName(r.name, reserved);
     reserved.add(unique.toLowerCase()); // reserve so later imports don't collide
-    if (unique !== d.name) renames.push({ from: d.name, to: unique });
-    return unique === d.name ? d : { ...d, name: unique };
+    if (unique !== r.name) renames.push({ from: r.name, to: unique });
+    return unique === r.name ? r : { ...r, name: unique };
   });
 
-  return { datasets, renames };
+  return { records, renames };
 }
 ```
 
@@ -471,7 +473,7 @@ user action — there is no separate coordinator module to call.
 | `renameDatasetInSpec`                                                    | `src/core/spec-refs.ts`          | yes                 | unit        |
 | `snippetsReferencingDataset`, `datasetUsageCounts` (reverse-lookup scan) | `src/core/relationships.ts`      | yes                 | unit        |
 | `renameDatasetRefs` → updated count (rename propagation)                 | `src/app/stores/SnippetStore.ts` | no (mutates stores) | integration |
-| `dedupeIncomingDatasetNames`                                             | `src/core/import-normalize.ts`   | yes                 | unit        |
+| `dedupeIncomingNames` (datasets + custom themes)                         | `src/core/import-normalize.ts`   | yes                 | unit        |
 
 The dividing line: anything that takes plain data and returns plain data is
 **core** and unit-tested in isolation; anything that reaches into a Zustand store
diff --git a/docs/chart-theming-scope.md b/docs/chart-theming-scope.md
index 40b506f..e1d7134 100644
--- a/docs/chart-theming-scope.md
+++ b/docs/chart-theming-scope.md
@@ -142,7 +142,7 @@ ships, it is an explicit per-font user action, never automatic.
    (spec §03G): bake the active theme into `spec.config` (existing keys win,
    render-identical), or lift `spec.config` out to the clipboard (copy before remove —
    a failed copy aborts).
-4. **Custom named themes** ✅ (2026-06-12, except export/import) — IndexedDB entity
+4. **Custom named themes** ✅ (2026-06-12) — IndexedDB entity
    `{ id, name, config }` (`core/custom-theme.ts`, themes store @ DB v2) + the **Theme
    Builder** modal: theme list, JSON config editor, a font control that populates one
    family across every font slot (`applyFontToConfig`), and a live multi-chart gallery
@@ -151,8 +151,9 @@ ships, it is an explicit per-font user action, never automatic.
    theme (house/preset/custom) or via the editor's **Extract Config to New Theme**
    action (spec §03G); appears in the selector as `custom:<id>` (the "Edit themes…"
    action row sits right after the customs, before the preset roster); deleting the
-   active one falls back to Astrolabe. **Remaining:** export/import as JSON alongside
-   the library (touches the §08 envelope + import-normalize atomicity).
+   active one falls back to Astrolabe. Custom themes travel in the §08 workspace
+   export/import envelope (additive `themes` array, name auto-suffix on clash, ids
+   reassigned by the store, rolled back with datasets on a failed import).
 5. **Shipped font roster** — fontsource packages, `@font-face` registration, selector
    metadata (which themes/fonts pair), `document.fonts.load` gate in the render path,
    precache strategy above. Roster finalized via visual specimen.
@@ -166,6 +167,16 @@ it without a second mechanism).
 
 ## 5. Status log
 
+- **2026-06-12 (slice 4 close-out)** — **custom themes in the §08 envelope.** The
+  workspace export now writes a `themes` array (additive — no format bump; importers
+  treat it as optional, so pre-theme envelopes stay valid). Import normalizes each
+  record (`normalizeCustomTheme`), auto-suffixes name clashes via the generalized
+  `dedupeIncomingNames` (the dataset dedupe, now shared), reassigns ids through
+  `CustomThemeStore.addThemes` (selection untouched), and rolls themes back together
+  with datasets when the atomic snippet write fails. Toast counts gain a theme
+  clause. Spec §08 updated ("Dataset conflicts" → "Name conflicts"). Slice 4 is now
+  fully done; next is slice 5 (shipped font roster).
+
 - **2026-06-12 (slice 4)** — **custom named themes + Theme Builder shipped.**
   `CustomTheme` entity through the full stack (core → theme-store @ DB v2 →
   CustomThemeStore → theme-persistence → startup hydrate); selection model extended to
diff --git a/docs/spec/08-import-export.md b/docs/spec/08-import-export.md
index 9fb05ac..2830f10 100644
--- a/docs/spec/08-import-export.md
+++ b/docs/spec/08-import-export.md
@@ -6,17 +6,17 @@ Separately, a single chart can be exported on its own — its spec or its render
 
 ## Export
 
-Export produces one downloadable JSON file containing every snippet (see _Snippet Library_) and every dataset (see _Datasets_), wrapped in an envelope carrying format metadata.
+Export produces one downloadable JSON file containing every snippet (see _Snippet Library_), every dataset (see _Datasets_), and every custom chart theme (see _Live Preview → Chart theme_), wrapped in an envelope carrying format metadata.
 
 - **Trigger**: the **Export** header control runs the export immediately (no intermediate dialog).
-- **Contents**: all snippets and all datasets currently stored, plus envelope metadata.
-- **Empty workspace**: if there are no snippets, the user is informed ("No snippets to export") and no file is downloaded — even if datasets exist.
+- **Contents**: all snippets, datasets, and custom chart themes currently stored, plus envelope metadata.
+- **Empty workspace**: if there are no snippets, the user is informed ("No snippets to export") and no file is downloaded — even if datasets or themes exist.
 - **Filename**: `astrolabe-project-YYYY-MM-DD.json`, where the date is today's date (export day).
-- **Feedback**: on success a toast reports the counts, e.g. "Exported 4 snippets and 2 datasets" (the dataset clause is omitted when there are no datasets; singular/plural wording adapts to the counts).
+- **Feedback**: on success a toast reports the counts, e.g. "Exported 4 snippets, 2 datasets and 1 theme" (the dataset and theme clauses are omitted when their counts are zero; singular/plural wording adapts to the counts).
 
 ### Export envelope shape
 
-The downloaded file is a single JSON object: an envelope with a format `version`, an export timestamp, an exporter tag, and the two data arrays.
+The downloaded file is a single JSON object: an envelope with a format `version`, an export timestamp, an exporter tag, and the data arrays.
 
 ```json
 {
@@ -28,6 +28,9 @@ The downloaded file is a single JSON object: an envelope with a format `version`
   ],
   "datasets": [
     /* full dataset objects (see Data Model) */
+  ],
+  "themes": [
+    /* full custom chart theme objects (see Data Model) */
   ]
 }
 ```
@@ -35,7 +38,7 @@ The downloaded file is a single JSON object: an envelope with a format `version`
 - `version` — export format version (currently `"1.0"`).
 - `exportedAt` — ISO 8601 timestamp of the export.
 - `exportedBy` — fixed identifier `"Astrolabe"`.
-- `snippets` / `datasets` — arrays of complete records as defined in _Data Model_, each including its record `version` field. (This is the per-record schema version, not the envelope `version` above.)
+- `snippets` / `datasets` / `themes` — arrays of complete records as defined in _Data Model_, each including its record `version` field. (This is the per-record schema version, not the envelope `version` above.) `themes` is additive: exports always write it, and importers treat it as optional, so pre-theme envelopes remain valid `"1.0"` files.
 
 ## Per-chart export
 
@@ -70,8 +73,8 @@ Import lets the user pick a JSON file from their device; its contents are normal
 
 The importer recognizes several shapes so that both Astrolabe exports and looser snippet files work:
 
-- **Astrolabe export envelope** — an object with a `version` and a `snippets` array; an optional `datasets` array is imported too.
-- **Bare array of snippets** — a top-level JSON array is treated as a list of snippets (no datasets).
+- **Astrolabe export envelope** — an object with a `version` and a `snippets` array; optional `datasets` and `themes` arrays are imported too.
+- **Bare array of snippets** — a top-level JSON array is treated as a list of snippets (no datasets or themes).
 - **Single snippet object** — any other object is treated as one snippet.
 - **Older / foreign snippet shapes** — snippets that do not match the current model are normalized onto it:
   - Alternative field names are mapped: `content` → spec, `draft` → draft spec, `createdAt` → creation timestamp.
@@ -85,14 +88,16 @@ A snippet is treated as already in current Astrolabe format when it carries an I
 
 - Imported snippets are **appended** to the existing library; nothing is overwritten or removed.
 - **ID collisions** (an incoming snippet whose id already exists) are resolved by assigning the incoming snippet a fresh unique id; the original snippet keeps its id.
-- Datasets are imported **before** snippets so that snippet dataset references can resolve.
+- Datasets and custom themes are imported **before** snippets so that snippet dataset references can resolve.
+- Imported custom themes always receive fresh ids from the theme library; an envelope's theme ids never displace existing records.
 
-### Dataset conflicts
+### Name conflicts (datasets and themes)
 
-When an imported dataset's name already exists in the library, it is auto-renamed to a unique name rather than overwriting the existing one (see _Datasets_).
+When an imported dataset's or custom theme's name already exists in the library, it is auto-renamed to a unique name rather than overwriting the existing one (see _Datasets_).
 
 - A numeric suffix is appended to the original name; further suffixes are added until the name is unique.
-- The renamed datasets are reported to the user via a warning toast listing each `original -> new` rename.
+- The renamed records are reported to the user via a warning toast listing each `original -> new` rename.
+- A dataset rename is propagated into the imported snippets that reference it; theme renames need no propagation (nothing references a theme by name).
 - If a single dataset fails to import, it is skipped and the rest of the import continues.
 
 ### Storage limit handling
@@ -105,8 +110,8 @@ Snippet storage has an approximate 5 MB budget (see _Snippet Library_ storage mo
 
 ### Feedback
 
-- **Success**: a toast reports how many snippets (and datasets, when any) were imported, e.g. "Imported 4 snippets and 2 datasets".
-- **Renames**: when datasets were renamed, the success message is shown as a warning toast that also lists the renames.
-- **Empty file**: if no snippets are found in the file, the user is informed ("No snippets found in file") and nothing is imported.
+- **Success**: a toast reports how many snippets (and datasets and themes, when any) were imported, e.g. "Imported 4 snippets, 2 datasets and 1 theme".
+- **Renames**: when datasets or themes were renamed, the success message is shown as a warning toast that also lists the renames.
+- **Empty file**: if no snippets are found in the file, the user is informed ("No snippets found in file") and nothing is imported — even if the file carries datasets or themes.
 - **Quota failure**: a clear error advising the user to delete snippets and retry.
 - **Invalid file**: a non-JSON or unparseable file produces a clear error ("Failed to import. Please check that the file is valid JSON."); an unreadable file produces a read error. In all error cases the existing workspace is left unchanged.
diff --git a/src/app/services/transfer.test.ts b/src/app/services/transfer.test.ts
index 1d990f0..0980515 100644
--- a/src/app/services/transfer.test.ts
+++ b/src/app/services/transfer.test.ts
@@ -20,10 +20,12 @@ vi.mock('../infrastructure/snippet-store', async (importOriginal) => {
   };
 });
 
+import { createCustomTheme } from '@core/custom-theme';
 import { createDataset } from '@core/dataset';
 import { createSnippet } from '@core/snippet';
 import { downloadJson, readTextFile } from '../infrastructure/file-transfer';
 import { deleteSnippet, saveSnippet, StorageQuotaError } from '../infrastructure/snippet-store';
+import { useCustomThemeStore } from '../stores/CustomThemeStore';
 import { useDatasetStore } from '../stores/DatasetStore';
 import { useNotificationStore } from '../stores/NotificationStore';
 import { useSnippetStore } from '../stores/SnippetStore';
@@ -50,6 +52,7 @@ beforeEach(() => {
   vi.clearAllMocks();
   useSnippetStore.getState().reset();
   useDatasetStore.getState().reset();
+  useCustomThemeStore.getState().reset();
   useNotificationStore.getState().clear();
 });
 
@@ -68,18 +71,25 @@ describe('exportWorkspace', () => {
       .addDatasets([
         createDataset({ name: 'Sales', data: [{ a: 1 }], format: 'json', source: 'inline' }),
       ]);
+    useCustomThemeStore.getState().addThemes([createCustomTheme({ name: 'Brand', config: {} })]);
 
     exportWorkspace(new Date('2026-06-07T12:00:00.000Z'));
 
     expect(mockedDownload).toHaveBeenCalledTimes(1);
     const [filename, json] = mockedDownload.mock.calls[0];
     expect(filename).toBe('astrolabe-project-2026-06-07.json');
-    const env = JSON.parse(json) as { version: string; snippets: unknown[]; datasets: unknown[] };
+    const env = JSON.parse(json) as {
+      version: string;
+      snippets: unknown[];
+      datasets: unknown[];
+      themes: unknown[];
+    };
     expect(env.version).toBe('1.0');
     expect(env.snippets).toHaveLength(1);
     expect(env.datasets).toHaveLength(1);
+    expect(env.themes).toHaveLength(1);
     expect(lastNote()).toMatchObject({ kind: 'success' });
-    expect(lastNote().message).toBe('Exported 1 snippet and 1 dataset');
+    expect(lastNote().message).toBe('Exported 1 snippet, 1 dataset and 1 theme');
   });
 });
 
@@ -153,6 +163,33 @@ describe('importWorkspace', () => {
     expect(lastNote().message).toContain('Sales → Sales 2');
   });
 
+  it('merges envelope themes: ids reassigned, clashing names auto-suffixed and reported', async () => {
+    const existing = useCustomThemeStore
+      .getState()
+      .add(createCustomTheme({ name: 'Brand', config: { background: '#000' } }));
+
+    await importJson(
+      JSON.stringify({
+        version: '1.0',
+        snippets: [{ id: 's1', created: '2026-01-01T00:00:00.000Z', name: 'A', spec: '{}' }],
+        themes: [
+          { id: existing.id, name: 'Brand', config: { background: '#fff' } },
+          { id: 99, name: 'Mono', config: { font: 'Courier' } },
+        ],
+      }),
+    );
+
+    const themes = useCustomThemeStore.getState().themes;
+    expect(themes.map((t) => t.name).sort()).toEqual(['Brand', 'Brand 2', 'Mono']);
+    // The existing record is untouched; incoming ids were reassigned past it.
+    expect(themes.find((t) => t.id === existing.id)!.config).toEqual({ background: '#000' });
+    expect(new Set(themes.map((t) => t.id)).size).toBe(3);
+
+    expect(lastNote()).toMatchObject({ kind: 'warning' });
+    expect(lastNote().message).toContain('Imported 1 snippet and 2 themes');
+    expect(lastNote().message).toContain('Brand → Brand 2');
+  });
+
   it('reassigns a colliding snippet id, keeping the existing one', async () => {
     useSnippetStore.getState().hydrate([createSnippet({ id: 's1', name: 'Existing' })]);
 
@@ -224,8 +261,8 @@ describe('importWorkspace', () => {
       expect(mockedDelete).toHaveBeenCalledTimes(1);
     });
 
-    it('rolls back datasets added to the store before the snippet write failed', async () => {
-      // The import contains both a dataset and a snippet; the snippet write fails.
+    it('rolls back datasets and themes added to the store before the snippet write failed', async () => {
+      // The import contains a dataset, a theme, and a snippet; the snippet write fails.
       mockedSave.mockRejectedValueOnce(new StorageQuotaError());
 
       await importJson(
@@ -235,12 +272,14 @@ describe('importWorkspace', () => {
             { id: 's1', created: '2026-01-01T00:00:00.000Z', name: 'S', spec: '{"mark":"bar"}' },
           ],
           datasets: [{ id: 1, name: 'DS', data: [{ x: 1 }], format: 'json', source: 'inline' }],
+          themes: [{ id: 1, name: 'T', config: {} }],
         }),
       );
 
-      // Neither snippets nor datasets should persist in the store.
+      // Neither snippets, datasets, nor themes should persist in the store.
       expect(useSnippetStore.getState().snippets).toHaveLength(0);
       expect(useDatasetStore.getState().datasets).toHaveLength(0);
+      expect(useCustomThemeStore.getState().themes).toHaveLength(0);
     });
 
     it('surfaces a quota error as a clear actionable notification without a detail field', async () => {
diff --git a/src/app/services/transfer.ts b/src/app/services/transfer.ts
index 62aea29..8ff58c7 100644
--- a/src/app/services/transfer.ts
+++ b/src/app/services/transfer.ts
@@ -5,24 +5,24 @@
  * in `@core/import-normalize` and `@core/export-envelope`; this layer reads the
  * stores, drives the browser file adapter, commits the merge, and reports.
  *
- * Order matters on import (spec §08 → Merge): datasets are committed **before**
- * snippets so a snippet's by-name reference resolves against the just-added
- * dataset (whose name may have been auto-suffixed to avoid a clash).
+ * Order matters on import (spec §08 → Merge): datasets and custom themes are
+ * committed **before** snippets so a snippet's by-name reference resolves
+ * against the just-added dataset (whose name may have been auto-suffixed to
+ * avoid a clash).
  *
  * Atomicity (spec §08 → Storage limit handling / spec §10 → Non-destructive
  * import): snippet writes are performed directly to IDB before touching the
  * Zustand store. If any write fails the already-written IDB records are deleted
- * and the just-added datasets are rolled back from the store, so neither the
- * store nor IDB retains a partial import. The write-through subscriber sees
+ * and the just-added datasets/themes are rolled back from the store, so neither
+ * the store nor IDB retains a partial import. The write-through subscriber sees
  * store changes only after all IDB writes succeed; because `put` is idempotent
  * the second (subscriber) write of each record is a harmless no-op.
  */
 
-import { buildExportEnvelope, exportFilename, exportSummaryMessage } from '@core/export-envelope';
+import { buildExportEnvelope, exportFilename, transferSummaryMessage } from '@core/export-envelope';
 import {
   applyDatasetRenamesToSnippets,
-  dedupeIncomingDatasetNames,
-  importSummaryMessage,
+  dedupeIncomingNames,
   normalizeImport,
   reassignCollidingSnippetIds,
 } from '@core/import-normalize';
@@ -31,6 +31,7 @@ import { humanizeBytes } from '@core/storage-estimate';
 import { downloadJson, readTextFile } from '../infrastructure/file-transfer';
 import { deleteSnippet, saveSnippet, StorageQuotaError } from '../infrastructure/snippet-store';
 import { notify } from '../stores/NotificationStore';
+import { useCustomThemeStore } from '../stores/CustomThemeStore';
 import { useDatasetStore } from '../stores/DatasetStore';
 import { useSnippetStore } from '../stores/SnippetStore';
 
@@ -48,6 +49,7 @@ export function exportWorkspace(now: Date = new Date()): void {
 
   const snippets = useSnippetStore.getState().snippets;
   const datasets = useDatasetStore.getState().datasets;
+  const themes = useCustomThemeStore.getState().themes;
 
   if (snippets.length === 0) {
     notify({
@@ -58,13 +60,13 @@ export function exportWorkspace(now: Date = new Date()): void {
     return;
   }
 
-  const envelope = buildExportEnvelope(snippets, datasets, { now });
+  const envelope = buildExportEnvelope(snippets, datasets, themes, { now });
   downloadJson(exportFilename(now), JSON.stringify(envelope, null, 2));
 
   notify({
     kind: 'success',
     title: 'Workspace exported',
-    message: exportSummaryMessage(snippets.length, datasets.length),
+    message: transferSummaryMessage('Exported', snippets.length, datasets.length, themes.length),
   });
 }
 
@@ -99,7 +101,11 @@ export async function importWorkspace(file: File): Promise<void> {
     return;
   }
 
-  const { snippets: normSnippets, datasets: normDatasets } = normalizeImport(parsed);
+  const {
+    snippets: normSnippets,
+    datasets: normDatasets,
+    themes: normThemes,
+  } = normalizeImport(parsed);
 
   if (normSnippets.length === 0) {
     notify({
@@ -112,23 +118,33 @@ export async function importWorkspace(file: File): Promise<void> {
 
   // Datasets first: de-dupe their names against the library (and within the batch),
   // then propagate any rename into the imported snippets so their references still
-  // resolve (spec §08 → Dataset conflicts; docs/architecture/07 §5–6).
+  // resolve (spec §08 → Name conflicts; docs/architecture/07 §5–6).
   const existingDatasetNames = useDatasetStore.getState().datasets.map((d) => d.name);
-  const { datasets: dedupedDatasets, renames } = dedupeIncomingDatasetNames(
+  const { records: dedupedDatasets, renames } = dedupeIncomingNames(
     existingDatasetNames,
     normDatasets,
   );
   const renamedSnippets = applyDatasetRenamesToSnippets(normSnippets, renames);
 
+  // Themes key on a unique name too, but nothing references them by name, so a
+  // rename needs no propagation — only reporting (spec §08 → Name conflicts).
+  const existingThemeNames = useCustomThemeStore.getState().themes.map((t) => t.name);
+  const { records: dedupedThemes, renames: themeRenames } = dedupeIncomingNames(
+    existingThemeNames,
+    normThemes,
+  );
+
   // Reassign incoming snippet ids that clash with the library (spec §08 → ID collisions).
   const existingSnippetIds = useSnippetStore.getState().snippets.map((s) => s.id);
   const finalSnippets = reassignCollidingSnippetIds(existingSnippetIds, renamedSnippets);
 
-  // Commit datasets BEFORE snippets so by-name references resolve (spec §08).
-  // Record which dataset ids existed before the add so we can roll them back if
-  // the subsequent snippet writes fail.
+  // Commit datasets and themes BEFORE snippets so by-name references resolve
+  // (spec §08). Record which ids existed before the add so we can roll them back
+  // if the subsequent snippet writes fail.
   const datasetIdsBefore = new Set(useDatasetStore.getState().datasets.map((d) => d.id));
   useDatasetStore.getState().addDatasets(dedupedDatasets);
+  const themeIdsBefore = new Set(useCustomThemeStore.getState().themes.map((t) => t.id));
+  useCustomThemeStore.getState().addThemes(dedupedThemes);
 
   // Storage budget pre-check (spec §08 → Storage limit handling): warn on overage
   // but still attempt the save.
@@ -156,14 +172,20 @@ export async function importWorkspace(file: File): Promise<void> {
     // Roll back: delete every IDB record we already wrote.
     await Promise.allSettled(writtenSnippetIds.map((id) => deleteSnippet(id)));
 
-    // Roll back: remove the datasets we just added to the store so neither
-    // store nor IDB retains any trace of this import.
+    // Roll back: remove the datasets and themes we just added to the store so
+    // neither store nor IDB retains any trace of this import.
     const addedDatasets = useDatasetStore
       .getState()
       .datasets.filter((d) => !datasetIdsBefore.has(d.id));
     for (const d of addedDatasets) {
       useDatasetStore.getState().remove(d.id);
     }
+    const addedThemes = useCustomThemeStore
+      .getState()
+      .themes.filter((t) => !themeIdsBefore.has(t.id));
+    for (const t of addedThemes) {
+      useCustomThemeStore.getState().remove(t.id);
+    }
 
     // Surface a clear, actionable error (spec §08 "Quota failure"; NN/g #9 /
     // GOV.UK plain language — no codes, tell the user what to do next).
@@ -192,13 +214,19 @@ export async function importWorkspace(file: File): Promise<void> {
   // All IDB writes succeeded — now make the snippets visible in the store.
   useSnippetStore.getState().addSnippets(finalSnippets);
 
-  // Feedback (spec §08 → Feedback): one summary toast; a warning when datasets were
+  // Feedback (spec §08 → Feedback): one summary toast; a warning when records were
   // renamed or storage is over budget, otherwise a success.
-  const summary = importSummaryMessage(finalSnippets.length, dedupedDatasets.length);
+  const summary = transferSummaryMessage(
+    'Imported',
+    finalSnippets.length,
+    dedupedDatasets.length,
+    dedupedThemes.length,
+  );
   const clauses: string[] = [];
-  if (renames.length > 0) {
+  const allRenames = [...renames, ...themeRenames];
+  if (allRenames.length > 0) {
     clauses.push(
-      `Renamed to avoid clashes: ${renames.map((r) => `${r.from} → ${r.to}`).join(', ')}.`,
+      `Renamed to avoid clashes: ${allRenames.map((r) => `${r.from} → ${r.to}`).join(', ')}.`,
     );
   }
   if (overage > 0) {
diff --git a/src/app/stores/CustomThemeStore.test.ts b/src/app/stores/CustomThemeStore.test.ts
index 064f16c..9cd37fa 100644
--- a/src/app/stores/CustomThemeStore.test.ts
+++ b/src/app/stores/CustomThemeStore.test.ts
@@ -37,6 +37,33 @@ describe('createTheme', () => {
   });
 });
 
+describe('addThemes (import batch)', () => {
+  it('reassigns ids from the store id authority and appends', () => {
+    const existing = store().createTheme('Existing', {});
+    store().addThemes([
+      { id: existing.id, version: 1, name: 'A', config: {}, created: 'x', modified: 'x' },
+      { id: existing.id, version: 1, name: 'B', config: {}, created: 'x', modified: 'x' },
+    ]);
+    const themes = store().themes;
+    expect(themes.map((t) => t.name)).toEqual(['Existing', 'A', 'B']);
+    expect(new Set(themes.map((t) => t.id)).size).toBe(3);
+  });
+
+  it('does not touch the builder selection or draft', () => {
+    store().createTheme('Open', {});
+    const before = store().selectedId;
+    store().addThemes([{ id: 9, version: 1, name: 'A', config: {}, created: 'x', modified: 'x' }]);
+    expect(store().selectedId).toBe(before);
+    expect(store().draft?.name).toBe('Open');
+  });
+
+  it('is a no-op for an empty batch (no state churn)', () => {
+    const before = store().themes;
+    store().addThemes([]);
+    expect(store().themes).toBe(before);
+  });
+});
+
 describe('draft editing', () => {
   beforeEach(() => store().createTheme('Brand', { font: 'Helvetica' }));
 
diff --git a/src/app/stores/CustomThemeStore.ts b/src/app/stores/CustomThemeStore.ts
index 19a748e..9d701f6 100644
--- a/src/app/stores/CustomThemeStore.ts
+++ b/src/app/stores/CustomThemeStore.ts
@@ -72,6 +72,12 @@ export interface CustomThemeState {
 
   /** Low-level: add a fully-formed theme and select it. Returns the record with its assigned id. */
   add: (theme: CustomTheme) => CustomTheme;
+  /**
+   * Low-level batch add (import path): reassign ids from the store's id
+   * authority and append, WITHOUT touching the builder selection — an import
+   * must not hijack an open Theme Builder draft.
+   */
+  addThemes: (incoming: CustomTheme[]) => void;
   /** Low-level: merge a patch into a theme, advancing `modified`. */
   update: (id: number, patch: Partial<CustomTheme>, now?: Date) => void;
   /**
@@ -208,6 +214,15 @@ export const useCustomThemeStore = create<CustomThemeState>((set, get) => ({
     return withId;
   },
 
+  addThemes: (incoming) => {
+    if (incoming.length === 0) return;
+    set((s) => {
+      let nextId = nextThemeId(s.themes);
+      const withIds = incoming.map((t) => ({ ...t, id: nextId++ }));
+      return { themes: [...s.themes, ...withIds] };
+    });
+  },
+
   update: (id, patch, now) => {
     const modified = patch.modified ?? (now ?? new Date()).toISOString();
     set((s) => ({
diff --git a/src/core/export-envelope.test.ts b/src/core/export-envelope.test.ts
index 731978b..b179111 100644
--- a/src/core/export-envelope.test.ts
+++ b/src/core/export-envelope.test.ts
@@ -1,11 +1,12 @@
 import { describe, it, expect } from 'vitest';
 
+import { createCustomTheme, type CustomTheme } from './custom-theme';
 import { createDataset, type Dataset } from './dataset';
 import {
   EXPORT_ENVELOPE_VERSION,
   buildExportEnvelope,
   exportFilename,
-  exportSummaryMessage,
+  transferSummaryMessage,
   type ExportEnvelope,
 } from './export-envelope';
 import { createSnippet, type Snippet } from './snippet';
@@ -16,6 +17,14 @@ function makeSnippet(overrides: Partial<Snippet> = {}): Snippet {
   return { ...createSnippet({ now: FIXED_NOW, id: 's1' }), ...overrides };
 }
 
+function makeTheme(overrides: Partial<CustomTheme> = {}): CustomTheme {
+  return {
+    ...createCustomTheme({ name: 'T1', config: { background: '#fff' }, now: FIXED_NOW }),
+    id: 1,
+    ...overrides,
+  };
+}
+
 function makeDataset(overrides: Partial<Dataset> = {}): Dataset {
   return {
     ...createDataset({
@@ -38,7 +47,7 @@ describe('EXPORT_ENVELOPE_VERSION', () => {
 
 describe('buildExportEnvelope', () => {
   it('stamps version, ISO timestamp, and the fixed exporter tag', () => {
-    const env = buildExportEnvelope([], [], { now: FIXED_NOW });
+    const env = buildExportEnvelope([], [], [], { now: FIXED_NOW });
     expect(env.version).toBe('1.0');
     expect(env.exportedAt).toBe('2026-06-03T12:00:00.000Z');
     expect(env.exportedBy).toBe('Astrolabe');
@@ -47,13 +56,15 @@ describe('buildExportEnvelope', () => {
   it('produces the full envelope shape (matches spec §08 example fields)', () => {
     const snippet = makeSnippet();
     const dataset = makeDataset();
-    const env = buildExportEnvelope([snippet], [dataset], { now: FIXED_NOW });
+    const theme = makeTheme();
+    const env = buildExportEnvelope([snippet], [dataset], [theme], { now: FIXED_NOW });
     const expected: ExportEnvelope = {
       version: '1.0',
       exportedAt: '2026-06-03T12:00:00.000Z',
       exportedBy: 'Astrolabe',
       snippets: [snippet],
       datasets: [dataset],
+      themes: [theme],
     };
     expect(env).toEqual(expected);
   });
@@ -61,17 +72,21 @@ describe('buildExportEnvelope', () => {
   it('carries the records through unchanged', () => {
     const snippet = makeSnippet();
     const dataset = makeDataset();
-    const env = buildExportEnvelope([snippet], [dataset], { now: FIXED_NOW });
+    const theme = makeTheme();
+    const env = buildExportEnvelope([snippet], [dataset], [theme], { now: FIXED_NOW });
     expect(env.snippets[0]).toBe(snippet);
     expect(env.datasets[0]).toBe(dataset);
+    expect(env.themes[0]).toBe(theme);
   });
 
   it("preserves each record's own version field", () => {
     const snippet = makeSnippet({ version: 1 });
     const dataset = makeDataset({ version: 1 });
-    const env = buildExportEnvelope([snippet], [dataset], { now: FIXED_NOW });
+    const theme = makeTheme({ version: 1 });
+    const env = buildExportEnvelope([snippet], [dataset], [theme], { now: FIXED_NOW });
     expect(env.snippets[0].version).toBe(1);
     expect(env.datasets[0].version).toBe(1);
+    expect(env.themes[0].version).toBe(1);
     // The per-record version is distinct from the envelope's file-format version.
     expect(env.version).toBe('1.0');
   });
@@ -79,19 +94,23 @@ describe('buildExportEnvelope', () => {
   it("does not alias the caller's arrays (mutating inputs afterward is inert)", () => {
     const snippets = [makeSnippet()];
     const datasets = [makeDataset()];
-    const env = buildExportEnvelope(snippets, datasets, { now: FIXED_NOW });
+    const themes = [makeTheme()];
+    const env = buildExportEnvelope(snippets, datasets, themes, { now: FIXED_NOW });
 
     snippets.push(makeSnippet({ id: 's2' }));
     datasets.push(makeDataset({ id: 2, name: 'D2' }));
+    themes.push(makeTheme({ id: 2, name: 'T2' }));
 
     expect(env.snippets).toHaveLength(1);
     expect(env.datasets).toHaveLength(1);
+    expect(env.themes).toHaveLength(1);
   });
 
   it('handles empty arrays', () => {
-    const env = buildExportEnvelope([], [], { now: FIXED_NOW });
+    const env = buildExportEnvelope([], [], [], { now: FIXED_NOW });
     expect(env.snippets).toEqual([]);
     expect(env.datasets).toEqual([]);
+    expect(env.themes).toEqual([]);
   });
 });
 
@@ -106,24 +125,30 @@ describe('exportFilename', () => {
   });
 });
 
-describe('exportSummaryMessage', () => {
-  it('reports both counts (plural)', () => {
-    expect(exportSummaryMessage(4, 2)).toBe('Exported 4 snippets and 2 datasets');
+describe('transferSummaryMessage (shared by export and import feedback)', () => {
+  it('reports snippet and dataset counts (plural)', () => {
+    expect(transferSummaryMessage('Exported', 4, 2, 0)).toBe('Exported 4 snippets and 2 datasets');
   });
 
-  it('omits the dataset clause when there are no datasets', () => {
-    expect(exportSummaryMessage(4, 0)).toBe('Exported 4 snippets');
+  it('omits the dataset and theme clauses when their counts are zero', () => {
+    expect(transferSummaryMessage('Exported', 4, 0, 0)).toBe('Exported 4 snippets');
   });
 
   it('uses singular wording for counts of 1', () => {
-    expect(exportSummaryMessage(1, 1)).toBe('Exported 1 snippet and 1 dataset');
+    expect(transferSummaryMessage('Imported', 1, 1, 0)).toBe('Imported 1 snippet and 1 dataset');
   });
 
-  it('singular snippet with omitted dataset clause', () => {
-    expect(exportSummaryMessage(1, 0)).toBe('Exported 1 snippet');
+  it('pluralizes zero counts (and omits the other clauses)', () => {
+    expect(transferSummaryMessage('Imported', 0, 0, 0)).toBe('Imported 0 snippets');
   });
 
-  it('pluralizes zero counts (and omits the dataset clause)', () => {
-    expect(exportSummaryMessage(0, 0)).toBe('Exported 0 snippets');
+  it('reports all three counts with comma-and joining', () => {
+    expect(transferSummaryMessage('Exported', 4, 2, 1)).toBe(
+      'Exported 4 snippets, 2 datasets and 1 theme',
+    );
+  });
+
+  it('joins snippets and themes with "and" when there are no datasets', () => {
+    expect(transferSummaryMessage('Imported', 4, 0, 3)).toBe('Imported 4 snippets and 3 themes');
   });
 });
diff --git a/src/core/export-envelope.ts b/src/core/export-envelope.ts
index 7447ce0..1b6e672 100644
--- a/src/core/export-envelope.ts
+++ b/src/core/export-envelope.ts
@@ -12,6 +12,7 @@
  * migration target — see snippet.ts / dataset.ts).
  */
 
+import type { CustomTheme } from './custom-theme';
 import type { Dataset } from './dataset';
 import type { Snippet } from './snippet';
 
@@ -24,8 +25,9 @@ export const EXPORT_ENVELOPE_VERSION = '1.0';
 
 /**
  * The downloaded file's top-level shape (spec §08 → Export envelope shape): format
- * metadata plus the two complete-record arrays. Each record keeps its own `version`
- * field unchanged.
+ * metadata plus the complete-record arrays. Each record keeps its own `version`
+ * field unchanged. `themes` is additive (always written, optional on read) so
+ * pre-theme envelopes and importers remain compatible without a format bump.
  */
 export interface ExportEnvelope {
   /** Export format version (currently `"1.0"`). */
@@ -38,6 +40,8 @@ export interface ExportEnvelope {
   snippets: Snippet[];
   /** All datasets, as complete records (each including its record `version`). */
   datasets: Dataset[];
+  /** All custom chart themes, as complete records (each including its record `version`). */
+  themes: CustomTheme[];
 }
 
 /**
@@ -50,6 +54,7 @@ export interface ExportEnvelope {
 export function buildExportEnvelope(
   snippets: ReadonlyArray<Snippet>,
   datasets: ReadonlyArray<Dataset>,
+  themes: ReadonlyArray<CustomTheme>,
   opts: { now: Date },
 ): ExportEnvelope {
   return {
@@ -58,6 +63,7 @@ export function buildExportEnvelope(
     exportedBy: 'Astrolabe',
     snippets: [...snippets],
     datasets: [...datasets],
+    themes: [...themes],
   };
 }
 
@@ -82,12 +88,21 @@ function countClause(count: number, noun: string): string {
 }
 
 /**
- * Success-toast message reporting the export counts (spec §08 → Feedback), e.g.
- * "Exported 4 snippets and 2 datasets". The dataset clause is omitted entirely when
- * there are no datasets; singular/plural wording adapts to the counts.
+ * Success-toast message reporting transfer counts (spec §08 → Feedback) for both
+ * directions, e.g. "Exported 4 snippets, 2 datasets and 1 theme" / "Imported 1
+ * snippet". The dataset and theme clauses are omitted entirely when their counts
+ * are zero; singular/plural wording adapts. One builder for export and import so
+ * a new record kind or wording change lands in both messages at once.
  */
-export function exportSummaryMessage(snippetCount: number, datasetCount: number): string {
-  const snippets = countClause(snippetCount, 'snippet');
-  if (datasetCount === 0) return `Exported ${snippets}`;
-  return `Exported ${snippets} and ${countClause(datasetCount, 'dataset')}`;
+export function transferSummaryMessage(
+  verb: 'Exported' | 'Imported',
+  snippetCount: number,
+  datasetCount: number,
+  themeCount: number,
+): string {
+  const clauses = [countClause(snippetCount, 'snippet')];
+  if (datasetCount > 0) clauses.push(countClause(datasetCount, 'dataset'));
+  if (themeCount > 0) clauses.push(countClause(themeCount, 'theme'));
+  const last = clauses.pop()!;
+  return clauses.length === 0 ? `${verb} ${last}` : `${verb} ${clauses.join(', ')} and ${last}`;
 }
diff --git a/src/core/import-normalize.test.ts b/src/core/import-normalize.test.ts
index e1c5405..c4dee65 100644
--- a/src/core/import-normalize.test.ts
+++ b/src/core/import-normalize.test.ts
@@ -1,10 +1,10 @@
 import { describe, expect, it } from 'vitest';
 
+import { CURRENT_THEME_VERSION } from './custom-theme';
 import { CURRENT_DATASET_VERSION, type Dataset } from './dataset';
 import {
   applyDatasetRenamesToSnippets,
-  dedupeIncomingDatasetNames,
-  importSummaryMessage,
+  dedupeIncomingNames,
   normalizeImport,
   reassignCollidingSnippetIds,
 } from './import-normalize';
@@ -107,10 +107,11 @@ describe('normalizeImport — shape detection', () => {
   });
 
   it('returns empty for null / non-object / non-array junk', () => {
-    expect(normalizeImport(null)).toEqual({ snippets: [], datasets: [] });
-    expect(normalizeImport(42)).toEqual({ snippets: [], datasets: [] });
-    expect(normalizeImport('hello')).toEqual({ snippets: [], datasets: [] });
-    expect(normalizeImport(undefined)).toEqual({ snippets: [], datasets: [] });
+    const empty = { snippets: [], datasets: [], themes: [] };
+    expect(normalizeImport(null)).toEqual(empty);
+    expect(normalizeImport(42)).toEqual(empty);
+    expect(normalizeImport('hello')).toEqual(empty);
+    expect(normalizeImport(undefined)).toEqual(empty);
   });
 
   it('ignores a non-array datasets field on the envelope', () => {
@@ -118,6 +119,26 @@ describe('normalizeImport — shape detection', () => {
     const result = normalizeImport(parsed, { now: FIXED_NOW });
     expect(result.datasets).toEqual([]);
   });
+
+  it('reads an optional themes array on the envelope (absent → empty)', () => {
+    const withThemes = {
+      version: '1.0',
+      snippets: [currentSnippetRecord()],
+      themes: [{ id: 7, name: 'Corporate', config: { background: '#fff' } }],
+    };
+    expect(normalizeImport(withThemes, { now: FIXED_NOW }).themes).toHaveLength(1);
+
+    const without = { version: '1.0', snippets: [currentSnippetRecord()] };
+    expect(normalizeImport(without, { now: FIXED_NOW }).themes).toEqual([]);
+
+    const junkThemes = { version: '1.0', snippets: [currentSnippetRecord()], themes: 'nope' };
+    expect(normalizeImport(junkThemes, { now: FIXED_NOW }).themes).toEqual([]);
+  });
+
+  it('does not read themes from bare-array or single-object shapes', () => {
+    expect(normalizeImport([currentSnippetRecord()], { now: FIXED_NOW }).themes).toEqual([]);
+    expect(normalizeImport(currentSnippetRecord(), { now: FIXED_NOW }).themes).toEqual([]);
+  });
 });
 
 describe('normalizeImport — snippet normalization', () => {
@@ -287,31 +308,74 @@ describe('normalizeImport — dataset normalization', () => {
   });
 });
 
-describe('dedupeIncomingDatasetNames', () => {
+describe('normalizeImport — custom themes', () => {
+  const envelope = (themes: unknown[]) => ({
+    version: '1.0',
+    snippets: [currentSnippetRecord()],
+    themes,
+  });
+
+  it('preserves a complete record and stamps the current version', () => {
+    const [t] = normalizeImport(
+      envelope([
+        {
+          id: 7,
+          version: 99,
+          name: 'Corporate',
+          config: { background: '#fff', font: 'Georgia' },
+          created: '2025-03-01T00:00:00.000Z',
+          modified: '2025-03-02T00:00:00.000Z',
+        },
+      ]),
+      { now: FIXED_NOW },
+    ).themes;
+    expect(t.id).toBe(7);
+    expect(t.version).toBe(CURRENT_THEME_VERSION);
+    expect(t.name).toBe('Corporate');
+    expect(t.config).toEqual({ background: '#fff', font: 'Georgia' });
+    expect(t.created).toBe('2025-03-01T00:00:00.000Z');
+    expect(t.modified).toBe('2025-03-02T00:00:00.000Z');
+  });
+
+  it('fills gaps with defaults (junk record)', () => {
+    const [t] = normalizeImport(envelope(['junk']), { now: FIXED_NOW }).themes;
+    expect(t.id).toBe(0);
+    expect(t.version).toBe(CURRENT_THEME_VERSION);
+    expect(t.name).toBe('Untitled');
+    expect(t.config).toEqual({});
+    expect(t.created).toBe(FIXED_NOW_ISO);
+    expect(t.modified).toBe(FIXED_NOW_ISO);
+  });
+
+  it('coerces a non-object config to {} and derives modified from created', () => {
+    const [t] = normalizeImport(
+      envelope([{ name: 'Odd', config: [1, 2], created: '2025-03-01T00:00:00.000Z' }]),
+      { now: FIXED_NOW },
+    ).themes;
+    expect(t.config).toEqual({});
+    expect(t.modified).toBe('2025-03-01T00:00:00.000Z');
+  });
+});
+
+describe('dedupeIncomingNames', () => {
   it('returns names unchanged when there are no collisions', () => {
-    const { datasets, renames } = dedupeIncomingDatasetNames(
-      ['Other'],
-      [datasetRecord({ name: 'Sales' })],
-    );
-    expect(datasets[0].name).toBe('Sales');
+    const { records, renames } = dedupeIncomingNames(['Other'], [datasetRecord({ name: 'Sales' })]);
+    expect(records[0].name).toBe('Sales');
     expect(renames).toEqual([]);
   });
 
   it('suffixes a collision with an existing library name', () => {
-    const { datasets, renames } = dedupeIncomingDatasetNames(
-      ['Sales'],
-      [datasetRecord({ name: 'Sales' })],
-    );
-    expect(datasets[0].name).toBe('Sales 2');
+    const { records, renames } = dedupeIncomingNames(['Sales'], [datasetRecord({ name: 'Sales' })]);
+    expect(records[0].name).toBe('Sales 2');
     expect(renames).toEqual([{ from: 'Sales', to: 'Sales 2' }]);
   });
 
   it('reserves names as-you-go so intra-batch dupes become Sales 2, Sales 3', () => {
-    const { datasets, renames } = dedupeIncomingDatasetNames(
+    const { records, renames } = dedupeIncomingNames(
       ['Sales'],
       [datasetRecord({ name: 'Sales' }), datasetRecord({ name: 'Sales' })],
     );
-    expect(datasets.map((d) => d.name)).toEqual(['Sales 2', 'Sales 3']);
+    expect(records.map((d) => d.name)).toEqual(['Sales 2', 'Sales 3']);
     expect(renames).toEqual([
       { from: 'Sales', to: 'Sales 2' },
       { from: 'Sales', to: 'Sales 3' },
@@ -319,18 +383,24 @@ describe('dedupeIncomingDatasetNames', () => {
   });
 
   it('matches collisions case-insensitively (Sales vs sales)', () => {
-    const { datasets, renames } = dedupeIncomingDatasetNames(
-      ['Sales'],
-      [datasetRecord({ name: 'sales' })],
-    );
-    expect(datasets[0].name).toBe('sales 2'); // preserves incoming casing
+    const { records, renames } = dedupeIncomingNames(['Sales'], [datasetRecord({ name: 'sales' })]);
+    expect(records[0].name).toBe('sales 2'); // preserves incoming casing
     expect(renames).toEqual([{ from: 'sales', to: 'sales 2' }]);
   });
 
-  it('only clones datasets whose name changed', () => {
+  it('only clones records whose name changed', () => {
     const keep = datasetRecord({ name: 'Untouched' });
-    const { datasets } = dedupeIncomingDatasetNames(['Sales'], [keep]);
-    expect(datasets[0]).toBe(keep);
+    const { records } = dedupeIncomingNames(['Sales'], [keep]);
+    expect(records[0]).toBe(keep);
+  });
+
+  it('works for any named record (custom themes)', () => {
+    const { records, renames } = dedupeIncomingNames(
+      ['Corporate'],
+      [{ name: 'Corporate', config: {} }],
+    );
+    expect(records[0].name).toBe('Corporate 2');
+    expect(renames).toEqual([{ from: 'Corporate', to: 'Corporate 2' }]);
   });
 });
 
@@ -457,21 +527,3 @@ describe('applyDatasetRenamesToSnippets', () => {
     expect(out.datasetRefs).toEqual(['Regions 2', 'Sales 2']);
   });
 });
-
-describe('importSummaryMessage', () => {
-  it('pluralizes snippets and includes the dataset clause', () => {
-    expect(importSummaryMessage(4, 2)).toBe('Imported 4 snippets and 2 datasets');
-  });
-
-  it('uses singular wording for counts of 1', () => {
-    expect(importSummaryMessage(1, 1)).toBe('Imported 1 snippet and 1 dataset');
-  });
-
-  it('omits the dataset clause when datasetCount is 0', () => {
-    expect(importSummaryMessage(3, 0)).toBe('Imported 3 snippets');
-  });
-
-  it('pluralizes zero counts correctly', () => {
-    expect(importSummaryMessage(0, 0)).toBe('Imported 0 snippets');
-  });
-});
diff --git a/src/core/import-normalize.ts b/src/core/import-normalize.ts
index 09ea657..6e03ceb 100644
--- a/src/core/import-normalize.ts
+++ b/src/core/import-normalize.ts
@@ -6,18 +6,21 @@
  * data in, plain data out. The app's ImportService orchestrates the file read,
  * store reads (for existing names/ids), and the commit; everything *deterministic*
  * about an import — recognizing the file shape, coercing each record onto the
- * current `Snippet`/`Dataset` shape, de-duping names, reassigning colliding ids,
- * and propagating renames into specs — lives here so it can be unit-tested hardest.
+ * current `Snippet`/`Dataset`/`CustomTheme` shape, de-duping names, reassigning
+ * colliding ids, and propagating renames into specs — lives here so it can be
+ * unit-tested hardest.
  *
  * `crypto.randomUUID` is a platform global (like in snippet.ts), allowed in core.
  * Both id generators are injectable so tests can assert deterministically.
  */
 
+import { CURRENT_THEME_VERSION, type CustomTheme } from './custom-theme';
 import { CURRENT_DATASET_VERSION, type DataSource, type Dataset } from './dataset';
 import type { DataFormat } from './format-detection';
 import { makeUniqueName } from './naming';
 import type { ColumnStats } from './profile';
 import { CURRENT_SNIPPET_VERSION, type Snippet } from './snippet';
+import { isJsonObject } from './spec-config';
 import { extractDatasetRefs, recomputeDatasetRefs, renameDatasetInSpec } from './spec-refs';
 import type { ColumnType } from './type-inference';
 
@@ -28,10 +31,11 @@ const IMPORTED_TAG = 'imported';
 export interface NormalizedImport {
   snippets: Snippet[];
   datasets: Dataset[];
+  themes: CustomTheme[];
 }
 
-/** A single dataset rename applied during dedupe (`from` original → `to` unique). */
-export interface DatasetRename {
+/** A single rename applied during name dedupe (`from` original → `to` unique). */
+export interface NameRename {
   from: string;
   to: string;
 }
@@ -198,6 +202,30 @@ function normalizeDataset(raw: unknown, nowIso: string): Dataset {
   };
 }
 
+/**
+ * Normalize one raw custom-theme record onto the current `CustomTheme` shape
+ * (spec §08 → Accepted inputs). Themes only travel inside Astrolabe envelopes,
+ * so this is gap-filling rather than foreign-shape mapping: a non-object
+ * `config` becomes `{}`, missing timestamps derive like datasets, and `version`
+ * is stamped current. Ids are provisional — the store's id authority reassigns
+ * them on insert, so collisions need no handling here.
+ */
+function normalizeCustomTheme(raw: unknown, nowIso: string): CustomTheme {
+  const r = isPlainObject(raw) ? raw : {};
+
+  const created = asNonEmptyString(r.created) ?? nowIso;
+  const modified = asNonEmptyString(r.modified) ?? created;
+
+  return {
+    id: typeof r.id === 'number' ? r.id : Number(r.id) || 0,
+    version: CURRENT_THEME_VERSION,
+    name: typeof r.name === 'string' ? r.name : 'Untitled',
+    config: isJsonObject(r.config) ? r.config : {},
+    created,
+    modified,
+  };
+}
+
 // ----------------------------------------------------------------------------
 // Shape detection (spec §08 "Accepted inputs")
 // ----------------------------------------------------------------------------
@@ -206,9 +234,9 @@ function normalizeDataset(raw: unknown, nowIso: string): Dataset {
  * Detect the import shape and normalize every record onto the current model.
  *
  *   - Envelope: object with a `version` AND a `snippets` array → its snippets
- *     (+ optional `datasets` array).
- *   - Bare array: a top-level array → a list of snippets, no datasets.
- *   - Single object: any other object → one snippet, no datasets.
+ *     (+ optional `datasets` and `themes` arrays).
+ *   - Bare array: a top-level array → a list of snippets, no datasets/themes.
+ *   - Single object: any other object → one snippet, no datasets/themes.
  *   - junk (null / non-object / non-array) → empty.
  */
 export function normalizeImport(
@@ -220,6 +248,7 @@ export function normalizeImport(
 
   let rawSnippets: unknown[] = [];
   let rawDatasets: unknown[] = [];
+  let rawThemes: unknown[] = [];
 
   if (Array.isArray(parsed)) {
     // Bare array of snippets.
@@ -229,16 +258,18 @@ export function normalizeImport(
     if (hasEnvelope) {
       rawSnippets = parsed.snippets as unknown[];
       if (Array.isArray(parsed.datasets)) rawDatasets = parsed.datasets;
+      if (Array.isArray(parsed.themes)) rawThemes = parsed.themes;
     } else {
       // Single snippet object.
       rawSnippets = [parsed];
     }
   }
-  // else: null / non-object / non-array junk → both stay empty.
+  // else: null / non-object / non-array junk → all stay empty.
 
   return {
     snippets: rawSnippets.map((s) => normalizeSnippet(s, nowIso, makeId)),
     datasets: rawDatasets.map((d) => normalizeDataset(d, nowIso)),
+    themes: rawThemes.map((t) => normalizeCustomTheme(t, nowIso)),
   };
 }
 
@@ -247,27 +278,28 @@ export function normalizeImport(
 // ----------------------------------------------------------------------------
 
 /**
- * De-dupe incoming dataset names against the existing library and within the
- * batch itself (architecture 07 §5). Names are reserved *as we go* so two incoming
- * `Sales` become `Sales 2`, `Sales 3` — never two `Sales 2`. Existing datasets are
- * never overwritten. Every rename is collected for reporting. Only datasets whose
+ * De-dupe incoming record names against the existing collection and within the
+ * batch itself (architecture 07 §5) — used for datasets and custom themes, both
+ * of which key on a unique name. Names are reserved *as we go* so two incoming
+ * `Sales` become `Sales 2`, `Sales 3` — never two `Sales 2`. Existing records are
+ * never overwritten. Every rename is collected for reporting. Only records whose
  * name actually changed are cloned.
  */
-export function dedupeIncomingDatasetNames(
+export function dedupeIncomingNames<T extends { name: string }>(
   existing: ReadonlyArray<string>,
-  incoming: ReadonlyArray<Dataset>,
-): { datasets: Dataset[]; renames: DatasetRename[] } {
+  incoming: ReadonlyArray<T>,
+): { records: T[]; renames: NameRename[] } {
   const reserved = new Set(existing.map((n) => n.toLowerCase()));
-  const renames: DatasetRename[] = [];
+  const renames: NameRename[] = [];
 
-  const datasets = incoming.map((d) => {
-    const unique = makeUniqueName(d.name, reserved);
+  const records = incoming.map((r) => {
+    const unique = makeUniqueName(r.name, reserved);
     reserved.add(unique.toLowerCase()); // reserve so later imports don't collide
-    if (unique !== d.name) renames.push({ from: d.name, to: unique });
-    return unique === d.name ? d : { ...d, name: unique };
+    if (unique !== r.name) renames.push({ from: r.name, to: unique });
+    return unique === r.name ? r : { ...r, name: unique };
   });
 
-  return { datasets, renames };
+  return { records, renames };
 }
 
 /**
@@ -297,7 +329,7 @@ export function reassignCollidingSnippetIds(
 }
 
 /**
- * Propagate dataset renames (from `dedupeIncomingDatasetNames`) into the imported
+ * Propagate dataset renames (from `dedupeIncomingNames`) into the imported
  * snippets that reference them (architecture 07 §6): for each rename, rewrite both
  * `spec` and `draftSpec` via `renameDatasetInSpec`, then recompute `datasetRefs`
  * from the rewritten draft — the draft is the source of truth, `datasetRefs`
@@ -309,7 +341,7 @@ export function reassignCollidingSnippetIds(
  */
 export function applyDatasetRenamesToSnippets(
   snippets: ReadonlyArray<Snippet>,
-  renames: ReadonlyArray<DatasetRename>,
+  renames: ReadonlyArray<NameRename>,
 ): Snippet[] {
   if (renames.length === 0) return snippets.slice();
 
@@ -344,22 +376,3 @@ export function applyDatasetRenamesToSnippets(
     return { ...snippet, spec, draftSpec, datasetRefs: recomputeDatasetRefs(draftSpec) };
   });
 }
-
-// ----------------------------------------------------------------------------
-// Feedback
-// ----------------------------------------------------------------------------
-
-/** Pluralize a count: `1 thing`, `0 things`, `4 things`. */
-function plural(count: number, noun: string): string {
-  return `${count} ${noun}${count === 1 ? '' : 's'}`;
-}
-
-/**
- * The import success message (spec §08 "Feedback"), e.g.
- * "Imported 4 snippets and 2 datasets". The dataset clause is omitted when
- * `datasetCount` is 0; singular/plural adapts for any counts ≥ 0.
- */
-export function importSummaryMessage(snippetCount: number, datasetCount: number): string {
-  const head = `Imported ${plural(snippetCount, 'snippet')}`;
-  return datasetCount > 0 ? `${head} and ${plural(datasetCount, 'dataset')}` : head;
-}