Fonts: carry uploaded faces through export/import + embed in SVG export

docs/spec/08-import-export.md

@@ -6,13 +6,13 @@ 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_), every dataset (see _Datasets_), and every custom chart theme (see _Live Preview → Chart theme_), wrapped in an envelope carrying format metadata.
+Export produces one downloadable JSON file containing every snippet (see _Snippet Library_), every dataset (see _Datasets_), every custom chart theme (see _Live Preview → Chart theme_), and every uploaded font face (see _Live Preview → Chart theme → fonts_), wrapped in an envelope carrying format metadata.
 
 - **Trigger**: the **Export** header control runs the export immediately (no intermediate dialog).
-- **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.
+- **Contents**: all snippets, datasets, custom chart themes, and uploaded fonts 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, themes, or fonts 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, 2 datasets and 1 theme" (the dataset and theme clauses are omitted when their counts are zero; 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, theme, and font clauses are omitted when their counts are zero; singular/plural wording adapts to the counts).
 
 ### Export envelope shape
 
@@ -31,6 +31,9 @@ The downloaded file is a single JSON object: an envelope with a format `version`
   ],
   "themes": [
     /* full custom chart theme objects (see Data Model) */
+  ],
+  "fonts": [
+    /* uploaded font records, bytes base64-encoded (see Data Model) */
   ]
 }
 ```
@@ -39,6 +42,7 @@ The downloaded file is a single JSON object: an envelope with a format `version`
 - `exportedAt` — ISO 8601 timestamp of the export.
 - `exportedBy` — fixed identifier `"Astrolabe"`.
 - `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.
+- `fonts` — the uploaded font faces, each a complete record with its bytes **base64-encoded** (JSON cannot carry binary). Without this a theme or snippet referencing an uploaded font would import on another machine with only the family name, falling back to a system font. Like `themes`, `fonts` is additive — exports always write it, importers treat it as optional, so older envelopes remain valid `"1.0"` files.
 
 ## Per-chart export
 
@@ -53,7 +57,7 @@ A single chart can be exported on its own, separately from the whole-workspace E
 **Image** (available only when a chart is currently rendered — the actions are disabled, with an explanatory line, while the preview is empty or showing an error):
 
 - **Download PNG** — a rasterized image of the chart as shown.
-- **Download SVG** — a vector image of the chart as shown.
+- **Download SVG** — a vector image of the chart as shown. When the chart uses an **uploaded** font (not a built-in roster or system family), that face is embedded into the SVG as a base64 `@font-face` rule, so the file renders the right type off-app instead of falling back to a system font; this happens automatically, with no option to configure.
 - **Resolution** (PNG) — `1×` / `2×` / `3×`, default `1×`. These are multipliers **of the display's pixel density**, so `1×` already matches on-screen crispness on a high-DPI (Retina) display; higher values produce larger images for print or zoom. (SVG is resolution-independent and ignores this.)
 - **Background** — `Theme` (default) / `White` / `None`. The chart itself renders on a transparent background (so on screen it shows the pane colour); export therefore fills it: _Theme_ matches the active theme's background, _White_ is always white, _None_ keeps it transparent. Applies to both PNG and SVG.
 
@@ -73,8 +77,8 @@ 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; 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).
+- **Astrolabe export envelope** — an object with a `version` and a `snippets` array; optional `datasets`, `themes`, and `fonts` arrays are imported too.
+- **Bare array of snippets** — a top-level JSON array is treated as a list of snippets (no datasets, themes, or fonts).
 - **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.
@@ -88,10 +92,11 @@ 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 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.
+- Datasets, custom themes, and uploaded fonts are imported **before** snippets so that snippet dataset references resolve and the whole import rolls back together if the snippet write fails.
+- Imported custom themes (and fonts) always receive fresh ids from their library; an envelope's ids never displace existing records.
+- An unusable font record (missing family or bytes, or bytes that aren't valid base64) is skipped; the rest of the import continues.
 
-### Name conflicts (datasets and themes)
+### Name conflicts
 
 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_).
 
@@ -100,6 +105,8 @@ When an imported dataset's or custom theme's name already exists in the library,
 - 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.
 
+**Fonts conflict differently — skip, not rename.** A font is identified by its family, which is the key embedded directly in a config's font slots, so a same-named face already in the library satisfies any incoming reference. When an imported font's family already exists, the **incoming face is skipped** and the existing one is kept (the references resolve to it) — rather than renamed to a copy. This also means re-importing your own backup adds no duplicate "Font 2" copies. Skipped fonts are listed in the import's warning toast.
+
 ### Storage limit handling
 
 Snippet storage has an approximate 5 MB budget (see _Snippet Library_ storage monitor).
@@ -110,8 +117,8 @@ Snippet storage has an approximate 5 MB budget (see _Snippet Library_ storage mo
 
 ### Feedback
 
-- **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.
+- **Success**: a toast reports how many snippets (and datasets, themes, and fonts, when any) were imported, e.g. "Imported 4 snippets, 2 datasets and 1 theme".
+- **Renames / skips**: when datasets or themes were renamed, or fonts were skipped as already-present, the success message is shown as a warning toast that also lists the renames and skips.
+- **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, themes, or fonts.
 - **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.