feat(classifier): export/import a whole workspace; fix short-viewport welcome

The scan is the expensive part (minutes on cloud mounts), so a workspace is now
portable between browsers/machines without re-scanning:
- Per-workspace "Export" downloads the snapshot + classify map as one
  <name>.zddc-workspace.json (the source-directory handle is omitted — it can't
  be serialized across browsers).
- Landing-page "Import" recreates the workspace from that JSON; the user clicks
  "Connect directory" once on the new browser to re-attach the folder (no
  re-scan — the snapshot carries the 2-hour walk). A classification-dataset JSON
  is rejected with a pointer to the in-app Import.

Also fix the welcome screen clipping its top on short viewports: the base
.empty-state centers with align-items:center, which overflows symmetrically and
puts the card's top out of scroll reach. Center the inner card with auto margins
instead — they collapse when it's taller than the viewport, keeping the top
reachable.

Test: workspace import recreates a transferable record (snapshot + map, no handle); 46 green.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

classifier/css/layout.css

@@ -287,7 +287,12 @@
 }
 
 /* ── Welcome screen (intro + tutorial) ─────────────────────────────────── */
+/* Scroll when the viewport is short. The inner card uses auto margins instead
+   of the base .empty-state's align-items:center so it centers when it fits but
+   collapses to the top when taller than the viewport — otherwise centering
+   clips the top of the card and it can't be scrolled into view. */
 .empty-state--overlay { overflow-y: auto; }
+.empty-state--overlay > .empty-state__inner { margin: auto; }
 .welcome { max-width: 900px; padding: 1.5rem 0.5rem 2.5rem; }
 .welcome__title { font-size: 2.6rem; line-height: 1.1; margin: 0 0 0.6rem; }
 .welcome__lede {
@@ -322,7 +327,8 @@
 
 /* ── Workspaces (welcome manager) ──────────────────────────────────────── */
 .workspaces { text-align: left; margin: 1.5rem 0 0.5rem; }
-.ws-head { display: flex; align-items: center; justify-content: space-between; gap: 1rem; }
+.ws-head { display: flex; align-items: center; justify-content: space-between; gap: 1rem; flex-wrap: wrap; }
+.ws-head__actions { display: flex; gap: 0.5rem; }
 .ws-head h2 { margin: 0; font-size: 1.4rem; }
 .ws-list { display: flex; flex-direction: column; gap: 0.4rem; }
 .ws-empty { color: var(--text-muted); font-size: 0.85rem; padding: 0.75rem; border: 1px dashed var(--border); border-radius: var(--radius); }

classifier/js/workspace.js

@@ -35,6 +35,8 @@
             newBtn: document.getElementById('newWorkspaceBtn'),
             wsBtn: document.getElementById('workspacesBtn'),
             connectBtn: document.getElementById('connectDirBtn'),
+            importBtn: document.getElementById('importWorkspaceBtn'),
+            importInput: document.getElementById('importWorkspaceInput'),
         };
         if (!P() || !P().available) {
             // No IndexedDB → hide the workspace UI; legacy rename path still works.
@@ -46,6 +48,11 @@
         if (els.wsBtn) els.wsBtn.addEventListener('click', showWelcome);
         if (els.connectBtn) els.connectBtn.addEventListener('click', function () { tryReconnect(false); });
         if (els.list) els.list.addEventListener('click', onListClick);
+        if (els.importBtn) els.importBtn.addEventListener('click', function () { els.importInput.click(); });
+        if (els.importInput) els.importInput.addEventListener('change', function () {
+            if (this.files && this.files[0]) importWorkspace(this.files[0]);
+            this.value = '';
+        });
 
         // Autosave the active workspace whenever the map changes.
         C().on(scheduleAutosave);
@@ -101,7 +108,7 @@
 
         var actions = document.createElement('div');
         actions.className = 'ws-row__actions';
-        [['open', 'Open'], ['rename', 'Rename'], ['delete', 'Delete']].forEach(function (a) {
+        [['open', 'Open'], ['rename', 'Rename'], ['export', 'Export'], ['delete', 'Delete']].forEach(function (a) {
             var b = document.createElement('button');
             b.className = 'btn btn-sm ' + (a[0] === 'open' ? 'btn-primary' : 'btn-secondary');
             b.dataset.act = a[0]; b.textContent = a[1];
@@ -118,9 +125,74 @@
         if (!id) return;
         if (btn.dataset.act === 'open') openWorkspace(id);
         else if (btn.dataset.act === 'rename') renameWorkspace(id);
+        else if (btn.dataset.act === 'export') exportWorkspace(id);
         else if (btn.dataset.act === 'delete') deleteWorkspace(id);
     }
 
+    // ── transfer (export / import a whole workspace as JSON) ─────────────────
+    // The scan is the expensive part (minutes on cloud mounts), so a workspace
+    // is portable: its snapshot + classify map travel as one JSON. The source
+    // directory HANDLE can't cross browsers, so an imported workspace has none —
+    // "Connect directory" re-attaches the folder once, without re-scanning.
+    async function exportWorkspace(id) {
+        var rows = await P().listWorkspaces();
+        var meta = rows.filter(function (r) { return r.id === id; })[0];
+        var rec = await P().getWorkspace(id);
+        if (!meta || !rec) { window.zddc.toast('Could not load that workspace to export.', 'error'); return; }
+        var payload = {
+            zddcWorkspace: 1,
+            exportedAt: new Date().toISOString(),
+            meta: { name: meta.name, rootName: meta.rootName, createdAt: meta.createdAt, updatedAt: meta.updatedAt, summary: meta.summary },
+            tree: rec.tree || [],          // the scanned snapshot (no re-scan on the other side)
+            classify: rec.classify || {},  // assignments + target trees
+        };
+        var blob = new Blob([JSON.stringify(payload)], { type: 'application/json' });
+        var url = URL.createObjectURL(blob);
+        var a = document.createElement('a');
+        a.href = url;
+        a.download = String(meta.name || 'workspace').replace(/[^\w.-]+/g, '_') + '.zddc-workspace.json';
+        document.body.appendChild(a); a.click(); a.remove();
+        URL.revokeObjectURL(url);
+        window.zddc.toast('Exported “' + meta.name + '”. Import it in another browser to skip the re-scan.', 'success');
+    }
+
+    function importWorkspace(file) {
+        return new Promise(function (resolve) {
+            var reader = new FileReader();
+            reader.onload = function () {
+                var obj;
+                try { obj = JSON.parse(reader.result); }
+                catch (e) { window.zddc.toast('Import failed — not valid JSON.', 'error'); resolve(null); return; }
+                if (!obj || !obj.zddcWorkspace) {
+                    window.zddc.toast(obj && obj.zddcClassifierFiles
+                        ? 'That’s a classification dataset, not a workspace — open a workspace and use Import in the toolbar.'
+                        : 'Import failed — not a ZDDC workspace export.', 'error');
+                    resolve(null); return;
+                }
+                var m = obj.meta || {};
+                var id = uid();
+                var meta = {
+                    id: id,
+                    name: m.name || 'Imported workspace',
+                    rootName: m.rootName || '',
+                    createdAt: m.createdAt || now(),
+                    updatedAt: now(),
+                    summary: m.summary || { files: 0, done: 0, excluded: 0 },
+                };
+                // No rootHandle — it can't be serialized across browsers; the
+                // user re-attaches via "Connect directory" after opening.
+                P().putWorkspace(meta, { id: id, rootHandle: null, tree: obj.tree || [], classify: obj.classify || {} })
+                    .then(function () {
+                        renderList();
+                        window.zddc.toast('Imported “' + meta.name + '”. Open it, then “Connect directory” to re-attach the source folder for preview/copy.', 'success', { durationMs: 8000 });
+                        resolve(id);
+                    });
+            };
+            reader.onerror = function () { window.zddc.toast('Import failed — could not read the file.', 'error'); resolve(null); };
+            reader.readAsText(file);
+        });
+    }
+
     // ── summary ───────────────────────────────────────────────────────────
     function allFiles() {
         var out = [];
@@ -297,6 +369,8 @@
         showWelcome: showWelcome,
         newWorkspace: newWorkspace,
         openWorkspace: openWorkspace,
+        exportWorkspace: exportWorkspace,
+        importWorkspace: importWorkspace,
         onRescanned: onRescanned,
         renderList: renderList,
         activeId: function () { return activeId; },

classifier/template.html

@@ -208,7 +208,11 @@
                     <section id="workspacesSection" class="workspaces">
                         <div class="ws-head">
                             <h2>Your workspaces</h2>
-                            <button id="newWorkspaceBtn" class="btn btn-primary">+ New workspace</button>
+                            <div class="ws-head__actions">
+                                <button id="importWorkspaceBtn" class="btn btn-secondary" title="Import a workspace exported from another browser (.json) — restores the scanned snapshot so you don't re-scan">⭱ Import</button>
+                                <button id="newWorkspaceBtn" class="btn btn-primary">+ New workspace</button>
+                            </div>
+                            <input type="file" id="importWorkspaceInput" accept="application/json,.json" hidden>
                         </div>
                         <div id="workspaceList" class="ws-list"><!-- rendered --></div>
                     </section>

tests/classify.spec.js

@@ -883,3 +883,32 @@ test('copy: a zip member is extracted from its archive and written out', async (
     expect(res.wrote).toBe(true);
     expect(res.content).toBe('ZIPBYTES');
 });
+
+test('workspace: import recreates a transferable record (snapshot + map, no handle)', async ({ page }) => {
+    const r = await page.evaluate(async () => {
+        const ws = window.app.modules.workspace, P = window.app.modules.persist;
+        const json = JSON.stringify({
+            zddcWorkspace: 1,
+            meta: { name: 'Transferred', rootName: 'BigProject', summary: { files: 3, done: 1, excluded: 0 } },
+            tree: [{ n: 'BigProject', p: 'BigProject', f: [{ o: 'a', e: 'pdf', p: 'BigProject' }] }],
+            classify: {
+                assignments: { 'a.pdf': { trackingNodeId: null, transmittalNodeId: null, excluded: true, titleOverride: null } },
+                trackingTree: [], transmittalTree: [],
+            },
+        });
+        const file = new File([json], 'x.zddc-workspace.json', { type: 'application/json' });
+        const id = await ws.importWorkspace(file);
+        const rec = id && await P.getWorkspace(id);
+        const rows = await P.listWorkspaces();
+        return {
+            listed: rows.some((x) => x.id === id && x.name === 'Transferred' && x.rootName === 'BigProject'),
+            hasTree: !!(rec && rec.tree && rec.tree.length),
+            excluded: !!(rec && rec.classify && rec.classify.assignments['a.pdf'] && rec.classify.assignments['a.pdf'].excluded),
+            noHandle: rec ? (rec.rootHandle == null) : false,
+        };
+    });
+    expect(r.listed).toBe(true);     // appears in the welcome list
+    expect(r.hasTree).toBe(true);    // the expensive scan came across
+    expect(r.excluded).toBe(true);   // classifications came across
+    expect(r.noHandle).toBe(true);   // source handle intentionally absent (re-attach on this browser)
+});