feat: session file registry with drag-and-drop on day view

Adds a FileDropZone at the bottom of the day view where users can
drop all session files at once. Filenames are regex-matched to
subjects using their animal_id_string (word-boundary aware, so
"2852" won't match "28520"). Only metadata is recorded — files
are never uploaded.

Backend: new session_files table (id, daily_status_id, filename,
file_size BIGINT, file_type, last_modified, notes). Routes:
  POST /api/daily-statuses/:id/files  (batch create)
  GET  /api/daily-statuses/:id/files
  DELETE /api/session-files/:id

Frontend: FileDropZone shows per-subject match groups, unmatched
files, and a warning for subjects with no match. After saving,
registered files are displayed with delete capability.

test-files/: generate_test_files.sh creates 4 dummy files per
subject (2×bin, 2×csv) with correct naming for drag-and-drop
testing. Pre-generated for 2026-04-23 with IDs 2852/3076/3077/3078.

Tests: 19 tests covering drag state, regex matching, save payload,
partial-overlap prevention, multi-subject batching, and delete.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

backend/prisma/migrations/20250423000000_add_session_files/migration.sql

@@ -0,0 +1,18 @@
+CREATE TABLE "session_files" (
+    "id"              TEXT         NOT NULL,
+    "daily_status_id" TEXT         NOT NULL,
+    "filename"        TEXT         NOT NULL,
+    "file_size"       BIGINT       NOT NULL,
+    "file_type"       TEXT,
+    "last_modified"   BIGINT,
+    "notes"           TEXT,
+    "created_at"      TIMESTAMP(3) NOT NULL DEFAULT CURRENT_TIMESTAMP,
+
+    CONSTRAINT "session_files_pkey" PRIMARY KEY ("id")
+);
+
+ALTER TABLE "session_files"
+    ADD CONSTRAINT "session_files_daily_status_id_fkey"
+    FOREIGN KEY ("daily_status_id")
+    REFERENCES "daily_statuses"("id")
+    ON DELETE CASCADE ON UPDATE CASCADE;

backend/prisma/schema.prisma

@@ -43,10 +43,25 @@ model DailyStatus {
   analysis_summary       Json?
   animal                 Animal          @relation(fields: [animal_id], references: [id], onDelete: Cascade)
   analyses               DailyAnalysis[]
+  session_files          SessionFile[]
 
   @@map("daily_statuses")
 }
 
+model SessionFile {
+  id              String      @id @default(uuid())
+  daily_status_id String
+  daily_status    DailyStatus @relation(fields: [daily_status_id], references: [id], onDelete: Cascade)
+  filename        String
+  file_size       BigInt
+  file_type       String?
+  last_modified   BigInt?
+  notes           String?
+  created_at      DateTime    @default(now())
+
+  @@map("session_files")
+}
+
 model DailyAnalysis {
   id                String      @id @default(uuid())
   daily_status_id   String

backend/src/app.js

@@ -10,6 +10,7 @@ const animalsRouter = require('./routes/animals');
 const dailyStatusesRouter = require('./routes/dailyStatuses');
 const auditLogsRouter = require('./routes/auditLogs');
 const analysesRouter = require('./routes/analyses');
+const sessionFilesRouter = require('./routes/sessionFiles');
 
 const app = express();
 
@@ -63,6 +64,7 @@ app.use('/api/animals', animalsRouter);
 app.use('/api/daily-statuses', dailyStatusesRouter);
 app.use('/api/audit-logs', auditLogsRouter);
 app.use('/api', analysesRouter);
+app.use('/api', sessionFilesRouter);
 
 app.use((req, res) => {
   res.status(404).json({ error: `Route ${req.method} ${req.path} not found` });

backend/src/routes/sessionFiles.js

@@ -0,0 +1,77 @@
+const router = require('express').Router();
+const prisma = require('../lib/prisma');
+
+// POST /api/daily-statuses/:id/files  — register file metadata (batch)
+// Body: [{ filename, file_size, file_type, last_modified, notes }, ...]
+router.post('/daily-statuses/:id/files', async (req, res, next) => {
+  try {
+    const status = await prisma.dailyStatus.findUnique({ where: { id: req.params.id } });
+    if (!status) return res.status(404).json({ error: 'Daily status not found' });
+
+    const files = req.body;
+    if (!Array.isArray(files) || files.length === 0)
+      return res.status(422).json({ error: 'Request body must be a non-empty array of file metadata' });
+
+    if (files.length > 200)
+      return res.status(422).json({ error: 'At most 200 files per request' });
+
+    for (const f of files) {
+      if (!f.filename || typeof f.filename !== 'string' || !f.filename.trim())
+        return res.status(422).json({ error: 'Each file must have a non-empty filename' });
+      if (f.file_size == null || typeof f.file_size !== 'number' || f.file_size < 0)
+        return res.status(422).json({ error: `file_size must be a non-negative number (got: ${f.file_size})` });
+    }
+
+    const created = await prisma.$transaction(
+      files.map((f) =>
+        prisma.sessionFile.create({
+          data: {
+            daily_status_id: req.params.id,
+            filename:      f.filename.trim(),
+            file_size:     BigInt(Math.round(f.file_size)),
+            file_type:     f.file_type ?? null,
+            last_modified: f.last_modified != null ? BigInt(Math.round(f.last_modified)) : null,
+            notes:         f.notes ?? null,
+          },
+        })
+      )
+    );
+
+    res.status(201).json(created.map(serializeFile));
+  } catch (err) { next(err); }
+});
+
+// GET /api/daily-statuses/:id/files
+router.get('/daily-statuses/:id/files', async (req, res, next) => {
+  try {
+    const status = await prisma.dailyStatus.findUnique({ where: { id: req.params.id } });
+    if (!status) return res.status(404).json({ error: 'Daily status not found' });
+
+    const files = await prisma.sessionFile.findMany({
+      where: { daily_status_id: req.params.id },
+      orderBy: { created_at: 'asc' },
+    });
+    res.json(files.map(serializeFile));
+  } catch (err) { next(err); }
+});
+
+// DELETE /api/session-files/:id
+router.delete('/session-files/:id', async (req, res, next) => {
+  try {
+    const file = await prisma.sessionFile.findUnique({ where: { id: req.params.id } });
+    if (!file) return res.status(404).json({ error: 'Session file not found' });
+    await prisma.sessionFile.delete({ where: { id: req.params.id } });
+    res.status(204).send();
+  } catch (err) { next(err); }
+});
+
+// BigInt fields must be serialized to strings to survive JSON.stringify
+function serializeFile(f) {
+  return {
+    ...f,
+    file_size:     f.file_size.toString(),
+    last_modified: f.last_modified != null ? f.last_modified.toString() : null,
+  };
+}
+
+module.exports = router;

frontend/src/api/client.js

@@ -69,6 +69,13 @@ export const systemApi = {
   info: () => api.get('/info').then((r) => r.data),
 };
 
+// ── Session Files ─────────────────────────────────────────────────────────────
+export const sessionFilesApi = {
+  list:   (statusId) => api.get(`/daily-statuses/${statusId}/files`).then((r) => r.data),
+  create: (statusId, files) => api.post(`/daily-statuses/${statusId}/files`, files).then((r) => r.data),
+  delete: (id) => api.delete(`/session-files/${id}`),
+};
+
 // ── Analyses ──────────────────────────────────────────────────────────────────
 export const analysesApi = {
   listForStatus: (statusId) => api.get(`/daily-statuses/${statusId}/analyses`).then((r) => r.data),

frontend/src/components/FileDropZone.jsx

@@ -0,0 +1,385 @@
+import React, { useCallback, useEffect, useRef, useState } from 'react';
+import { sessionFilesApi } from '../api/client';
+
+// ── Helpers ───────────────────────────────────────────────────────────────────
+
+function escapeRegex(str) {
+  return str.replace(/[.*+?^${}()|[\]\\]/g, '\\$&');
+}
+
+/**
+ * Build a regex that matches an animal's identifier in a filename.
+ * Matches only when the ID is not surrounded by other alphanumeric chars,
+ * so "2852" matches "rat_2852_session" but not "28520" or "X2852Y".
+ */
+function buildAnimalRegex(animal) {
+  const ids = [];
+  if (animal.animal_id_string) ids.push(escapeRegex(animal.animal_id_string));
+  if (animal.animal_name)      ids.push(escapeRegex(animal.animal_name));
+  if (ids.length === 0) return null;
+  return new RegExp(`(?<![a-zA-Z0-9])(${ids.join('|')})(?![a-zA-Z0-9])`, 'i');
+}
+
+function classifyFile(filename) {
+  const ext = filename.split('.').pop().toLowerCase();
+  const MAP = { csv: 'CSV', tsv: 'TSV', h5: 'HDF5', hdf5: 'HDF5', nwb: 'NWB', bin: 'Binary', dat: 'Binary', raw: 'Binary', npy: 'NumPy', npz: 'NumPy', mat: 'MATLAB', pkl: 'Pickle' };
+  return MAP[ext] ?? 'Binary';
+}
+
+function fmtBytes(n) {
+  const num = typeof n === 'bigint' ? Number(n) : Number(n);
+  if (num >= 1e9)  return `${(num / 1e9).toFixed(1)} GB`;
+  if (num >= 1e6)  return `${(num / 1e6).toFixed(1)} MB`;
+  if (num >= 1e3)  return `${(num / 1e3).toFixed(1)} KB`;
+  return `${num} B`;
+}
+
+/** Match an array of File objects against animals. Returns { matched: Map<animalId, File[]>, unmatched: File[] } */
+function matchFilesToAnimals(files, animals) {
+  const patterns = animals.map((a) => ({ animal: a, re: buildAnimalRegex(a) })).filter((x) => x.re);
+  const matched = new Map(animals.map((a) => [a.id, []]));
+  const unmatched = [];
+
+  for (const file of files) {
+    const hit = patterns.find(({ re }) => re.test(file.name));
+    if (hit) {
+      matched.get(hit.animal.id).push(file);
+    } else {
+      unmatched.push(file);
+    }
+  }
+  return { matched, unmatched };
+}
+
+// ── Sub-components ────────────────────────────────────────────────────────────
+
+function FileRow({ file, onRemove }) {
+  return (
+    <div className="flex items-center justify-between py-1 gap-2 text-xs">
+      <span className="font-mono text-gray-700 truncate min-w-0 flex-1">{file.name}</span>
+      <span className="text-gray-400 shrink-0">{fmtBytes(file.size)}</span>
+      <span className="text-gray-400 shrink-0 w-12 text-right">{classifyFile(file.name)}</span>
+      {onRemove && (
+        <button type="button" onClick={onRemove}
+          className="text-red-300 hover:text-red-500 transition-colors shrink-0 ml-1">✕</button>
+      )}
+    </div>
+  );
+}
+
+function SavedFileRow({ file, onDelete, deleting }) {
+  const size = typeof file.file_size === 'string' ? BigInt(file.file_size) : file.file_size;
+  return (
+    <div className="flex items-center justify-between py-1 gap-2 text-xs">
+      <span className="font-mono text-gray-600 truncate min-w-0 flex-1">{file.filename}</span>
+      <span className="text-gray-400 shrink-0">{fmtBytes(size)}</span>
+      <span className="text-gray-400 shrink-0 w-12 text-right">{file.file_type ?? '?'}</span>
+      <button type="button" onClick={onDelete} disabled={deleting}
+        className="text-red-300 hover:text-red-500 transition-colors shrink-0 ml-1 disabled:opacity-40">✕</button>
+    </div>
+  );
+}
+
+// ── Main component ────────────────────────────────────────────────────────────
+
+/**
+ * FileDropZone
+ *
+ * Props:
+ *   rows      — array of { animal, status } from ExperimentDayView
+ *               (only rows with a status are shown; status.id is required to save files)
+ *   date      — YYYY-MM-DD string, shown in naming hint
+ */
+export default function FileDropZone({ rows, date }) {
+  const [isDragging, setIsDragging] = useState(false);
+  const [dropped, setDropped]       = useState(null);   // { matched: Map, unmatched: File[] } | null
+  const [saving, setSaving]         = useState(false);
+  const [saveError, setSaveError]   = useState(null);
+  const [savedByStatus, setSavedByStatus] = useState({}); // statusId → SavedFile[]
+  const [loadingIds, setLoadingIds]       = useState(new Set());
+  const [deletingId, setDeletingId]       = useState(null);
+  const dragCounter = useRef(0);
+
+  const statusRows = rows.filter((r) => r.status);
+  const animals    = statusRows.map((r) => r.animal);
+
+  // Load existing saved files for all statuses in this day view
+  useEffect(() => {
+    if (statusRows.length === 0) return;
+    const ids = statusRows.map((r) => r.status.id);
+    setLoadingIds(new Set(ids));
+    Promise.all(
+      ids.map((sid) => sessionFilesApi.list(sid).then((files) => ({ sid, files })))
+    ).then((results) => {
+      const map = {};
+      results.forEach(({ sid, files }) => { map[sid] = files; });
+      setSavedByStatus(map);
+      setLoadingIds(new Set());
+    }).catch(() => setLoadingIds(new Set()));
+  }, [statusRows.map((r) => r.status?.id).join(',')]); // eslint-disable-line react-hooks/exhaustive-deps
+
+  // ── Drag handlers ──────────────────────────────────────────────────────────
+
+  const onDragEnter = useCallback((e) => {
+    e.preventDefault();
+    dragCounter.current += 1;
+    if (dragCounter.current === 1) setIsDragging(true);
+  }, []);
+
+  const onDragLeave = useCallback((e) => {
+    e.preventDefault();
+    dragCounter.current -= 1;
+    if (dragCounter.current === 0) setIsDragging(false);
+  }, []);
+
+  const onDragOver = useCallback((e) => { e.preventDefault(); }, []);
+
+  const onDrop = useCallback((e) => {
+    e.preventDefault();
+    dragCounter.current = 0;
+    setIsDragging(false);
+    const files = Array.from(e.dataTransfer.files);
+    if (files.length === 0) return;
+    setDropped(matchFilesToAnimals(files, animals));
+    setSaveError(null);
+  }, [animals]);
+
+  function removeMatchedFile(animalId, fileIdx) {
+    setDropped((prev) => {
+      const next = new Map(prev.matched);
+      const arr = [...next.get(animalId)];
+      arr.splice(fileIdx, 1);
+      next.set(animalId, arr);
+      return { matched: next, unmatched: prev.unmatched };
+    });
+  }
+
+  function removeUnmatched(idx) {
+    setDropped((prev) => {
+      const u = [...prev.unmatched];
+      u.splice(idx, 1);
+      return { matched: prev.matched, unmatched: u };
+    });
+  }
+
+  // ── Save ───────────────────────────────────────────────────────────────────
+
+  async function save() {
+    if (!dropped) return;
+    setSaving(true);
+    setSaveError(null);
+    try {
+      const results = await Promise.all(
+        statusRows.map(async ({ animal, status }) => {
+          const files = dropped.matched.get(animal.id) ?? [];
+          if (files.length === 0) return { statusId: status.id, saved: [] };
+          const payload = files.map((f) => ({
+            filename:      f.name,
+            file_size:     f.size,
+            file_type:     classifyFile(f.name),
+            last_modified: f.lastModified ?? null,
+          }));
+          const saved = await sessionFilesApi.create(status.id, payload);
+          return { statusId: status.id, saved };
+        })
+      );
+      setSavedByStatus((prev) => {
+        const next = { ...prev };
+        results.forEach(({ statusId, saved }) => {
+          next[statusId] = [...(next[statusId] ?? []), ...saved];
+        });
+        return next;
+      });
+      setDropped(null);
+    } catch (err) {
+      setSaveError(err.message ?? 'Failed to save file metadata');
+    } finally {
+      setSaving(false);
+    }
+  }
+
+  // ── Delete ─────────────────────────────────────────────────────────────────
+
+  async function deleteFile(fileId, statusId) {
+    setDeletingId(fileId);
+    try {
+      await sessionFilesApi.delete(fileId);
+      setSavedByStatus((prev) => ({
+        ...prev,
+        [statusId]: prev[statusId].filter((f) => f.id !== fileId),
+      }));
+    } catch {
+      // silently ignore — UI stays consistent, user can retry
+    } finally {
+      setDeletingId(null);
+    }
+  }
+
+  // ── Derived counts ─────────────────────────────────────────────────────────
+
+  const totalDropped       = dropped ? [...dropped.matched.values()].reduce((n, a) => n + a.length, 0) : 0;
+  const totalUnmatched     = dropped?.unmatched.length ?? 0;
+  const totalSaved         = Object.values(savedByStatus).reduce((n, a) => n + a.length, 0);
+  const hasSaved           = totalSaved > 0;
+  const hasMatchedDropped  = totalDropped > 0;
+
+  // Hint string for naming convention
+  const sampleId = animals[0]?.animal_id_string || animals[0]?.animal_name || '<id>';
+  const namingHint = `${date}_${sampleId}_session1.csv`;
+
+  return (
+    <div className="mt-8">
+      <h3 className="text-sm font-semibold text-gray-700 mb-3">Session File Registry</h3>
+      <p className="text-xs text-gray-400 mb-4">
+        Drop all session files here. Filenames are matched to subjects by ID —
+        only metadata (name, size) is recorded; files are never uploaded.
+        <br />
+        Naming convention: <span className="font-mono text-gray-500">{namingHint}</span>
+      </p>
+
+      {/* Drop zone */}
+      <div
+        onDragEnter={onDragEnter}
+        onDragLeave={onDragLeave}
+        onDragOver={onDragOver}
+        onDrop={onDrop}
+        data-testid="drop-zone"
+        className={[
+          'border-2 border-dashed rounded-xl px-6 py-10 text-center transition-all cursor-default select-none',
+          isDragging
+            ? 'border-blue-400 bg-blue-50'
+            : 'border-gray-200 bg-gray-50 hover:border-gray-300',
+        ].join(' ')}
+      >
+        {isDragging ? (
+          <p className="text-blue-600 font-medium text-sm">Release to register files</p>
+        ) : (
+          <>
+            <p className="text-gray-400 text-sm">Drag &amp; drop session files here</p>
+            <p className="text-gray-300 text-xs mt-1">All subjects at once · files are not uploaded</p>
+          </>
+        )}
+      </div>
+
+      {/* Dropped files preview */}
+      {dropped && (
+        <div className="mt-4 space-y-4" data-testid="drop-preview">
+
+          {/* Per-subject matched files */}
+          {statusRows.map(({ animal, status }) => {
+            const files = dropped.matched.get(animal.id) ?? [];
+            if (files.length === 0) return null;
+            return (
+              <div key={animal.id} className="bg-white border border-gray-200 rounded-xl p-4">
+                <div className="flex items-center justify-between mb-2">
+                  <span className="text-sm font-semibold text-gray-800">
+                    {animal.animal_name}
+                    {animal.animal_id_string && (
+                      <span className="ml-1.5 text-xs font-normal text-gray-400">{animal.animal_id_string}</span>
+                    )}
+                  </span>
+                  <span className="text-xs text-gray-400">{files.length} file{files.length !== 1 ? 's' : ''}</span>
+                </div>
+                <div className="divide-y divide-gray-50">
+                  {files.map((f, i) => (
+                    <FileRow key={f.name + i} file={f} onRemove={() => removeMatchedFile(animal.id, i)} />
+                  ))}
+                </div>
+              </div>
+            );
+          })}
+
+          {/* Subjects with no matched files */}
+          {statusRows.some(({ animal }) => (dropped.matched.get(animal.id) ?? []).length === 0) && (
+            <div className="bg-amber-50 border border-amber-100 rounded-xl p-4">
+              <p className="text-xs font-semibold text-amber-700 mb-1">No files matched for:</p>
+              {statusRows
+                .filter(({ animal }) => (dropped.matched.get(animal.id) ?? []).length === 0)
+                .map(({ animal }) => (
+                  <span key={animal.id} className="inline-block text-xs text-amber-600 bg-amber-100 rounded px-2 py-0.5 mr-1 mb-1 font-mono">
+                    {animal.animal_id_string || animal.animal_name}
+                  </span>
+                ))}
+            </div>
+          )}
+
+          {/* Unmatched files */}
+          {dropped.unmatched.length > 0 && (
+            <div className="bg-gray-50 border border-dashed border-gray-200 rounded-xl p-4">
+              <p className="text-xs font-semibold text-gray-500 mb-2">
+                Unmatched ({dropped.unmatched.length}) — no subject ID found in filename
+              </p>
+              <div className="divide-y divide-gray-100">
+                {dropped.unmatched.map((f, i) => (
+                  <FileRow key={f.name + i} file={f} onRemove={() => removeUnmatched(i)} />
+                ))}
+              </div>
+            </div>
+          )}
+
+          {saveError && (
+            <p className="text-xs text-red-500 px-1">{saveError}</p>
+          )}
+
+          {/* Action row */}
+          <div className="flex items-center gap-3 pt-1">
+            {hasMatchedDropped && (
+              <button
+                type="button"
+                onClick={save}
+                disabled={saving}
+                data-testid="save-btn"
+                className="px-4 py-2 rounded-lg text-sm font-medium bg-blue-600 text-white hover:bg-blue-700 disabled:opacity-50 transition-colors"
+              >
+                {saving ? 'Saving…' : `Register ${totalDropped} file${totalDropped !== 1 ? 's' : ''}`}
+              </button>
+            )}
+            <button
+              type="button"
+              onClick={() => { setDropped(null); setSaveError(null); }}
+              className="text-sm text-gray-400 hover:text-gray-600"
+            >
+              Clear
+            </button>
+          </div>
+        </div>
+      )}
+
+      {/* Saved files */}
+      {hasSaved && (
+        <div className="mt-6 space-y-3" data-testid="saved-files">
+          <p className="text-xs font-semibold text-gray-500 uppercase tracking-wide">
+            Registered files ({totalSaved})
+          </p>
+          {statusRows.map(({ animal, status }) => {
+            const files = savedByStatus[status.id] ?? [];
+            if (files.length === 0) return null;
+            return (
+              <div key={animal.id} className="bg-white border border-gray-200 rounded-xl p-4">
+                <div className="flex items-center justify-between mb-2">
+                  <span className="text-sm font-semibold text-gray-800">
+                    {animal.animal_name}
+                    {animal.animal_id_string && (
+                      <span className="ml-1.5 text-xs font-normal text-gray-400">{animal.animal_id_string}</span>
+                    )}
+                  </span>
+                  <span className="text-xs text-gray-400">{files.length} file{files.length !== 1 ? 's' : ''}</span>
+                </div>
+                <div className="divide-y divide-gray-50">
+                  {files.map((f) => (
+                    <SavedFileRow
+                      key={f.id}
+                      file={f}
+                      onDelete={() => deleteFile(f.id, status.id)}
+                      deleting={deletingId === f.id}
+                    />
+                  ))}
+                </div>
+              </div>
+            );
+          })}
+        </div>
+      )}
+    </div>
+  );
+}

frontend/src/pages/ExperimentDayView.jsx

@@ -10,6 +10,7 @@ import Button from '../components/ui/Button';
 import Modal from '../components/ui/Modal';
 import DailyStatusForm from '../components/DailyStatusForm';
 import Alert from '../components/ui/Alert';
+import FileDropZone from '../components/FileDropZone';
 
 const BUILTIN_KEYS_SET = new Set(['experiment_description', 'vitals', 'treatment', 'notes']);
 
@@ -367,6 +368,9 @@ export default function ExperimentDayView() {
         </div>
       )}
 
+      {/* Session file drop zone */}
+      <FileDropZone rows={rows} date={date} />
+
       {/* Edit modal (full row) */}
       {editStatus && (
         <Modal

frontend/tests/FileDropZone.test.jsx

@@ -0,0 +1,301 @@
+import React from 'react';
+import { render, screen, fireEvent, waitFor, act } from '@testing-library/react';
+import FileDropZone from '../src/components/FileDropZone';
+import { sessionFilesApi } from '../src/api/client';
+
+jest.mock('../src/api/client', () => ({
+  sessionFilesApi: {
+    list:   jest.fn(),
+    create: jest.fn(),
+    delete: jest.fn(),
+  },
+}));
+
+// ── Fixtures ───────────────────────────────────────────────────────────────────
+
+const DATE = '2026-04-23';
+
+const ANIMALS = [
+  { id: 'a1', animal_name: 'Rat 2852', animal_id_string: '2852' },
+  { id: 'a2', animal_name: 'Rat 3076', animal_id_string: '3076' },
+  { id: 'a3', animal_name: 'Rat 3077', animal_id_string: '3077' },
+];
+
+const STATUS_A1 = { id: 's-a1', animal_id: 'a1', date: `${DATE}T00:00:00.000Z` };
+const STATUS_A2 = { id: 's-a2', animal_id: 'a2', date: `${DATE}T00:00:00.000Z` };
+const STATUS_A3 = { id: 's-a3', animal_id: 'a3', date: `${DATE}T00:00:00.000Z` };
+
+const ROWS = [
+  { animal: ANIMALS[0], status: STATUS_A1 },
+  { animal: ANIMALS[1], status: STATUS_A2 },
+  { animal: ANIMALS[2], status: STATUS_A3 },
+];
+
+function makeFile(name, size = 1024, type = '') {
+  return new File(['x'], name, { type, lastModified: Date.now() });
+}
+
+function makeSavedFile(id, statusId, filename, fileSize = '10240') {
+  return { id, daily_status_id: statusId, filename, file_size: fileSize, file_type: 'CSV', last_modified: null, created_at: new Date().toISOString() };
+}
+
+function dropFiles(files) {
+  const zone = screen.getByTestId('drop-zone');
+  fireEvent.dragEnter(zone, { dataTransfer: { files } });
+  fireEvent.dragOver(zone, { dataTransfer: { files } });
+  fireEvent.drop(zone, { dataTransfer: { files } });
+}
+
+beforeEach(() => {
+  jest.clearAllMocks();
+  sessionFilesApi.list.mockResolvedValue([]);
+  sessionFilesApi.create.mockResolvedValue([]);
+  sessionFilesApi.delete.mockResolvedValue();
+});
+
+// ── Rendering ──────────────────────────────────────────────────────────────────
+
+describe('rendering', () => {
+  it('renders the drop zone', () => {
+    render(<FileDropZone rows={ROWS} date={DATE} />);
+    expect(screen.getByTestId('drop-zone')).toBeInTheDocument();
+    expect(screen.getByText(/drag.*drop session files/i)).toBeInTheDocument();
+  });
+
+  it('shows naming convention hint using first animal id', () => {
+    render(<FileDropZone rows={ROWS} date={DATE} />);
+    expect(screen.getByText(/2026-04-23_2852/)).toBeInTheDocument();
+  });
+
+  it('loads saved files on mount for each status', async () => {
+    sessionFilesApi.list.mockResolvedValue([]);
+    render(<FileDropZone rows={ROWS} date={DATE} />);
+    await waitFor(() => {
+      expect(sessionFilesApi.list).toHaveBeenCalledWith('s-a1');
+      expect(sessionFilesApi.list).toHaveBeenCalledWith('s-a2');
+      expect(sessionFilesApi.list).toHaveBeenCalledWith('s-a3');
+    });
+  });
+
+  it('shows saved files loaded from the API', async () => {
+    sessionFilesApi.list.mockImplementation((id) =>
+      id === 's-a1'
+        ? Promise.resolve([makeSavedFile('f1', 's-a1', `${DATE}_2852_trials.csv`)])
+        : Promise.resolve([])
+    );
+    render(<FileDropZone rows={ROWS} date={DATE} />);
+    await waitFor(() =>
+      expect(screen.getByText(`${DATE}_2852_trials.csv`)).toBeInTheDocument()
+    );
+    expect(screen.getByTestId('saved-files')).toBeInTheDocument();
+  });
+});
+
+// ── Drag state ─────────────────────────────────────────────────────────────────
+
+describe('drag interaction', () => {
+  it('highlights drop zone on dragenter', () => {
+    render(<FileDropZone rows={ROWS} date={DATE} />);
+    const zone = screen.getByTestId('drop-zone');
+    fireEvent.dragEnter(zone, { dataTransfer: { files: [] } });
+    expect(zone.className).toMatch(/border-blue-400/);
+    expect(screen.getByText(/release to register/i)).toBeInTheDocument();
+  });
+
+  it('removes highlight on dragleave', () => {
+    render(<FileDropZone rows={ROWS} date={DATE} />);
+    const zone = screen.getByTestId('drop-zone');
+    fireEvent.dragEnter(zone, { dataTransfer: { files: [] } });
+    fireEvent.dragLeave(zone, { dataTransfer: { files: [] } });
+    expect(zone.className).not.toMatch(/border-blue-400/);
+  });
+});
+
+// ── File matching ──────────────────────────────────────────────────────────────
+
+describe('filename-to-subject matching', () => {
+  it('matches files containing the animal_id_string to the correct subject', async () => {
+    render(<FileDropZone rows={ROWS} date={DATE} />);
+    dropFiles([
+      makeFile(`${DATE}_2852_ephys_raw.bin`, 10_000_000_000),
+      makeFile(`${DATE}_3076_trials.csv`, 10_000_000),
+    ]);
+    await waitFor(() => screen.getByTestId('drop-preview'));
+    expect(screen.getByText(/Rat 2852/)).toBeInTheDocument();
+    expect(screen.getByText(/Rat 3076/)).toBeInTheDocument();
+    expect(screen.getByText(`${DATE}_2852_ephys_raw.bin`)).toBeInTheDocument();
+    expect(screen.getByText(`${DATE}_3076_trials.csv`)).toBeInTheDocument();
+  });
+
+  it('shows unmatched section for files with no subject ID in name', async () => {
+    render(<FileDropZone rows={ROWS} date={DATE} />);
+    dropFiles([makeFile('unknown_file.csv', 1024)]);
+    await waitFor(() => screen.getByTestId('drop-preview'));
+    expect(screen.getByText(/unmatched/i)).toBeInTheDocument();
+    expect(screen.getByText('unknown_file.csv')).toBeInTheDocument();
+  });
+
+  it('does not match a partial numeric overlap (2852 should not match 28520)', async () => {
+    render(<FileDropZone rows={ROWS} date={DATE} />);
+    dropFiles([makeFile('session_28520_data.csv', 1024)]);
+    await waitFor(() => screen.getByTestId('drop-preview'));
+    expect(screen.getByText(/unmatched/i)).toBeInTheDocument();
+  });
+
+  it('shows warning for subjects with no matched files', async () => {
+    render(<FileDropZone rows={ROWS} date={DATE} />);
+    // Only drop file for 2852 — 3076 and 3077 get no match
+    dropFiles([makeFile(`${DATE}_2852_trials.csv`, 1024)]);
+    await waitFor(() => screen.getByTestId('drop-preview'));
+    expect(screen.getByText(/no files matched/i)).toBeInTheDocument();
+    expect(screen.getByText('3076')).toBeInTheDocument();
+    expect(screen.getByText('3077')).toBeInTheDocument();
+  });
+
+  it('matches all four files per subject correctly', async () => {
+    render(<FileDropZone rows={[{ animal: ANIMALS[0], status: STATUS_A1 }]} date={DATE} />);
+    dropFiles([
+      makeFile(`${DATE}_2852_ephys_raw.bin`,    10_000_000_000),
+      makeFile(`${DATE}_2852_kilosort.h5`,       10_000_000_000),
+      makeFile(`${DATE}_2852_trials.csv`,            10_000_000),
+      makeFile(`${DATE}_2852_behavior_log.csv`,       10_000_000),
+    ]);
+    await waitFor(() => screen.getByTestId('drop-preview'));
+    // Save button label is the authoritative "all 4 matched" signal
+    expect(screen.getByTestId('save-btn')).toHaveTextContent('Register 4 files');
+  });
+
+  it('handles multiple subjects with 4 files each simultaneously', async () => {
+    render(<FileDropZone rows={ROWS} date={DATE} />);
+    dropFiles([
+      makeFile(`${DATE}_2852_ephys_raw.bin`,    10_000_000_000),
+      makeFile(`${DATE}_2852_kilosort.h5`,       10_000_000_000),
+      makeFile(`${DATE}_2852_trials.csv`,            10_000_000),
+      makeFile(`${DATE}_2852_behavior_log.csv`,       10_000_000),
+      makeFile(`${DATE}_3076_ephys_raw.bin`,    10_000_000_000),
+      makeFile(`${DATE}_3076_kilosort.h5`,       10_000_000_000),
+      makeFile(`${DATE}_3076_trials.csv`,            10_000_000),
+      makeFile(`${DATE}_3076_behavior_log.csv`,       10_000_000),
+    ]);
+    await waitFor(() => screen.getByTestId('drop-preview'));
+    const saveBtn = screen.getByTestId('save-btn');
+    expect(saveBtn.textContent).toMatch(/8 files/);
+  });
+});
+
+// ── Remove before saving ───────────────────────────────────────────────────────
+
+describe('remove files before saving', () => {
+  it('removes a matched file when ✕ is clicked', async () => {
+    render(<FileDropZone rows={ROWS} date={DATE} />);
+    dropFiles([makeFile(`${DATE}_2852_trials.csv`, 1024)]);
+    await waitFor(() => screen.getByText(`${DATE}_2852_trials.csv`));
+    fireEvent.click(screen.getAllByText('✕')[0]);
+    await waitFor(() =>
+      expect(screen.queryByText(`${DATE}_2852_trials.csv`)).not.toBeInTheDocument()
+    );
+  });
+});
+
+// ── Saving ─────────────────────────────────────────────────────────────────────
+
+describe('saving metadata', () => {
+  it('calls sessionFilesApi.create with correct payload for each subject', async () => {
+    const file = makeFile(`${DATE}_2852_trials.csv`); // size = 1 byte (content 'x')
+    const savedFile = makeSavedFile('f1', 's-a1', file.name, String(file.size));
+    sessionFilesApi.create.mockResolvedValue([savedFile]);
+
+    render(<FileDropZone rows={ROWS} date={DATE} />);
+    dropFiles([file]);
+    await waitFor(() => screen.getByTestId('save-btn'));
+    fireEvent.click(screen.getByTestId('save-btn'));
+
+    await waitFor(() =>
+      expect(sessionFilesApi.create).toHaveBeenCalledWith(
+        's-a1',
+        expect.arrayContaining([
+          expect.objectContaining({
+            filename:  `${DATE}_2852_trials.csv`,
+            file_size: file.size,
+            file_type: 'CSV',
+          }),
+        ])
+      )
+    );
+  });
+
+  it('does not call create for subjects with no matched files', async () => {
+    sessionFilesApi.create.mockResolvedValue([]);
+    render(<FileDropZone rows={ROWS} date={DATE} />);
+    // Only 2852 gets a file
+    dropFiles([makeFile(`${DATE}_2852_trials.csv`, 1024)]);
+    await waitFor(() => screen.getByTestId('save-btn'));
+    fireEvent.click(screen.getByTestId('save-btn'));
+
+    await waitFor(() => expect(sessionFilesApi.create).toHaveBeenCalledTimes(1));
+    expect(sessionFilesApi.create).toHaveBeenCalledWith('s-a1', expect.any(Array));
+  });
+
+  it('stores correct file_type classification from extension', async () => {
+    sessionFilesApi.create.mockResolvedValue([]);
+    render(<FileDropZone rows={[{ animal: ANIMALS[0], status: STATUS_A1 }]} date={DATE} />);
+    dropFiles([
+      makeFile(`${DATE}_2852_ephys.bin`,  10_000_000_000),
+      makeFile(`${DATE}_2852_spikes.h5`,  10_000_000_000),
+      makeFile(`${DATE}_2852_trials.csv`,     10_000_000),
+      makeFile(`${DATE}_2852_log.csv`,        10_000_000),
+    ]);
+    await waitFor(() => screen.getByTestId('save-btn'));
+    fireEvent.click(screen.getByTestId('save-btn'));
+
+    await waitFor(() => expect(sessionFilesApi.create).toHaveBeenCalled());
+    const [, files] = sessionFilesApi.create.mock.calls[0];
+    expect(files.find((f) => f.filename.endsWith('.bin')).file_type).toBe('Binary');
+    expect(files.find((f) => f.filename.endsWith('.h5')).file_type).toBe('HDF5');
+    expect(files.filter((f) => f.filename.endsWith('.csv'))).toHaveLength(2);
+    files.filter((f) => f.filename.endsWith('.csv')).forEach((f) => {
+      expect(f.file_type).toBe('CSV');
+    });
+  });
+
+  it('clears the drop preview after a successful save', async () => {
+    sessionFilesApi.create.mockResolvedValue([makeSavedFile('f1', 's-a1', `${DATE}_2852_trials.csv`)]);
+    render(<FileDropZone rows={ROWS} date={DATE} />);
+    dropFiles([makeFile(`${DATE}_2852_trials.csv`, 1024)]);
+    await waitFor(() => screen.getByTestId('save-btn'));
+    fireEvent.click(screen.getByTestId('save-btn'));
+    await waitFor(() =>
+      expect(screen.queryByTestId('drop-preview')).not.toBeInTheDocument()
+    );
+  });
+
+  it('shows an error message when create fails', async () => {
+    sessionFilesApi.create.mockRejectedValue({ message: 'Server error' });
+    render(<FileDropZone rows={ROWS} date={DATE} />);
+    dropFiles([makeFile(`${DATE}_2852_trials.csv`, 1024)]);
+    await waitFor(() => screen.getByTestId('save-btn'));
+    fireEvent.click(screen.getByTestId('save-btn'));
+    await waitFor(() => screen.getByText(/server error/i));
+  });
+});
+
+// ── Deleting saved files ───────────────────────────────────────────────────────
+
+describe('deleting saved files', () => {
+  it('removes a saved file when its ✕ is clicked', async () => {
+    sessionFilesApi.list.mockImplementation((id) =>
+      id === 's-a1'
+        ? Promise.resolve([makeSavedFile('f1', 's-a1', `${DATE}_2852_trials.csv`)])
+        : Promise.resolve([])
+    );
+    render(<FileDropZone rows={ROWS} date={DATE} />);
+    await waitFor(() => screen.getByText(`${DATE}_2852_trials.csv`));
+    fireEvent.click(screen.getAllByText('✕')[0]);
+    await waitFor(() =>
+      expect(sessionFilesApi.delete).toHaveBeenCalledWith('f1')
+    );
+    await waitFor(() =>
+      expect(screen.queryByText(`${DATE}_2852_trials.csv`)).not.toBeInTheDocument()
+    );
+  });
+});

test-files/generate_test_files.sh

@@ -0,0 +1,75 @@
+#!/bin/bash
+# Generates dummy session files for drag-and-drop testing on the day view.
+# Files are tiny (just named correctly) — the browser File API only reads metadata.
+#
+# Usage:  bash generate_test_files.sh [DATE] [IDS...]
+#   DATE   defaults to today (YYYY-MM-DD)
+#   IDS    defaults to the three real subject IDs from the reach-task experiment
+#
+# Output: ./session_files/<DATE>/
+
+DATE=${1:-$(date +%Y-%m-%d)}
+shift
+SUBJECTS=("${@}")
+
+if [ ${#SUBJECTS[@]} -eq 0 ]; then
+  # Default IDs matching the real subjects in the experiments database
+  # (animal_id_string values visible on the day view)
+  SUBJECTS=("2852" "3076" "3077" "3078")
+fi
+
+OUTDIR="./session_files/${DATE}"
+mkdir -p "$OUTDIR"
+
+echo "Generating test files in ${OUTDIR}/ for subjects: ${SUBJECTS[*]}"
+echo ""
+
+for ID in "${SUBJECTS[@]}"; do
+  # File 1: large binary session recording (~placeholder, 0 bytes in test)
+  # Real file would be ~10 GB (e.g. raw ephys .bin)
+  BIN1="${OUTDIR}/${DATE}_${ID}_ephys_raw.bin"
+  touch "$BIN1"
+  echo "  [~10 GB] ${DATE}_${ID}_ephys_raw.bin"
+
+  # File 2: large HDF5 spike-sorted output (~placeholder, 0 bytes in test)
+  # Real file would be ~10 GB (e.g. kilosort output .h5)
+  BIN2="${OUTDIR}/${DATE}_${ID}_kilosort.h5"
+  touch "$BIN2"
+  echo "  [~10 GB] ${DATE}_${ID}_kilosort.h5"
+
+  # File 3: CSV trial events (~10 MB real, 1 KB here)
+  CSV1="${OUTDIR}/${DATE}_${ID}_trials.csv"
+  {
+    echo "trial_num,timestamp,outcome,reaction_time_ms,reward"
+    for i in $(seq 1 20); do
+      OUTCOME=$( [ $((RANDOM % 3)) -eq 0 ] && echo "Failure" || echo "Success" )
+      printf "%d,%.3f,%s,%d,%d\n" \
+        "$i" "$(echo "$i * 0.823 + 1.0" | bc -l 2>/dev/null || echo $i)" \
+        "$OUTCOME" "$((RANDOM % 400 + 50))" "$((RANDOM % 2))"
+    done
+  } > "$CSV1"
+  echo "  [~10 MB] ${DATE}_${ID}_trials.csv"
+
+  # File 4: CSV behavioral log (~10 MB real, small here)
+  CSV2="${OUTDIR}/${DATE}_${ID}_behavior_log.csv"
+  {
+    echo "ts,event,value,notes"
+    echo "0.000,session_start,1,"
+    echo "1.234,trial_start,1,"
+    echo "1.856,reach_onset,1,"
+    echo "2.102,reach_end,1,"
+    echo "2.103,outcome,Success,"
+    echo "3.500,trial_start,2,"
+    echo "4.100,reach_onset,1,"
+    echo "4.950,outcome,Failure,"
+    echo "9999.9,session_end,1,"
+  } > "$CSV2"
+  echo "  [~10 MB] ${DATE}_${ID}_behavior_log.csv"
+  echo ""
+done
+
+TOTAL=$(find "$OUTDIR" -type f | wc -l)
+echo "Done — ${TOTAL} files in ${OUTDIR}/"
+echo ""
+echo "Drag the entire '${DATE}' folder into the day-view drop zone at:"
+echo "  https://experiments.sam-tran.com/experiments/<id>/day/${DATE}?field=<fieldId>"

test-files/session_files/2026-04-23/2026-04-23_2852_behavior_log.csv

@@ -0,0 +1,10 @@
+ts,event,value,notes
+0.000,session_start,1,
+1.234,trial_start,1,
+1.856,reach_onset,1,
+2.102,reach_end,1,
+2.103,outcome,Success,
+3.500,trial_start,2,
+4.100,reach_onset,1,
+4.950,outcome,Failure,
+9999.9,session_end,1,

test-files/session_files/2026-04-23/2026-04-23_2852_trials.csv

@@ -0,0 +1,21 @@
+trial_num,timestamp,outcome,reaction_time_ms,reward
+1,1.823,Failure,176,0
+2,2.646,Failure,378,0
+3,3.469,Failure,138,1
+4,4.292,Success,150,1
+5,5.115,Success,204,1
+6,5.938,Success,209,0
+7,6.761,Success,369,0
+8,7.584,Failure,84,0
+9,8.407,Failure,403,0
+10,9.230,Success,340,0
+11,10.053,Success,442,1
+12,10.876,Success,355,0
+13,11.699,Success,280,0
+14,12.522,Failure,430,1
+15,13.345,Success,60,1
+16,14.168,Failure,102,0
+17,14.991,Success,213,0
+18,15.814,Success,54,1
+19,16.637,Failure,88,0
+20,17.460,Failure,290,1

test-files/session_files/2026-04-23/2026-04-23_3076_behavior_log.csv

@@ -0,0 +1,10 @@
+ts,event,value,notes
+0.000,session_start,1,
+1.234,trial_start,1,
+1.856,reach_onset,1,
+2.102,reach_end,1,
+2.103,outcome,Success,
+3.500,trial_start,2,
+4.100,reach_onset,1,
+4.950,outcome,Failure,
+9999.9,session_end,1,

test-files/session_files/2026-04-23/2026-04-23_3076_trials.csv

@@ -0,0 +1,21 @@
+trial_num,timestamp,outcome,reaction_time_ms,reward
+1,1.823,Failure,56,0
+2,2.646,Failure,299,1
+3,3.469,Failure,335,0
+4,4.292,Failure,70,1
+5,5.115,Success,273,0
+6,5.938,Success,59,1
+7,6.761,Success,159,0
+8,7.584,Success,268,1
+9,8.407,Success,330,0
+10,9.230,Success,365,1
+11,10.053,Success,371,0
+12,10.876,Success,230,1
+13,11.699,Success,74,0
+14,12.522,Failure,381,1
+15,13.345,Success,70,1
+16,14.168,Failure,215,0
+17,14.991,Failure,310,0
+18,15.814,Success,78,1
+19,16.637,Success,79,1
+20,17.460,Failure,303,1

test-files/session_files/2026-04-23/2026-04-23_3077_behavior_log.csv

@@ -0,0 +1,10 @@
+ts,event,value,notes
+0.000,session_start,1,
+1.234,trial_start,1,
+1.856,reach_onset,1,
+2.102,reach_end,1,
+2.103,outcome,Success,
+3.500,trial_start,2,
+4.100,reach_onset,1,
+4.950,outcome,Failure,
+9999.9,session_end,1,

test-files/session_files/2026-04-23/2026-04-23_3077_trials.csv

@@ -0,0 +1,21 @@
+trial_num,timestamp,outcome,reaction_time_ms,reward
+1,1.823,Failure,169,1
+2,2.646,Success,127,0
+3,3.469,Failure,265,0
+4,4.292,Failure,266,1
+5,5.115,Success,295,1
+6,5.938,Success,94,1
+7,6.761,Failure,78,1
+8,7.584,Success,182,1
+9,8.407,Success,249,1
+10,9.230,Success,201,0
+11,10.053,Failure,167,0
+12,10.876,Failure,124,0
+13,11.699,Failure,361,0
+14,12.522,Success,306,1
+15,13.345,Failure,311,0
+16,14.168,Success,186,0
+17,14.991,Success,289,0
+18,15.814,Failure,152,0
+19,16.637,Failure,379,1
+20,17.460,Success,332,0

test-files/session_files/2026-04-23/2026-04-23_3078_behavior_log.csv

@@ -0,0 +1,10 @@
+ts,event,value,notes
+0.000,session_start,1,
+1.234,trial_start,1,
+1.856,reach_onset,1,
+2.102,reach_end,1,
+2.103,outcome,Success,
+3.500,trial_start,2,
+4.100,reach_onset,1,
+4.950,outcome,Failure,
+9999.9,session_end,1,

test-files/session_files/2026-04-23/2026-04-23_3078_trials.csv

@@ -0,0 +1,21 @@
+trial_num,timestamp,outcome,reaction_time_ms,reward
+1,1.823,Failure,81,1
+2,2.646,Success,243,0
+3,3.469,Success,218,1
+4,4.292,Success,348,1
+5,5.115,Failure,418,0
+6,5.938,Failure,249,1
+7,6.761,Success,133,0
+8,7.584,Success,386,1
+9,8.407,Failure,116,1
+10,9.230,Success,226,0
+11,10.053,Success,438,1
+12,10.876,Success,405,1
+13,11.699,Success,419,1
+14,12.522,Success,95,0
+15,13.345,Failure,89,1
+16,14.168,Success,360,1
+17,14.991,Failure,424,1
+18,15.814,Success,73,1
+19,16.637,Failure,269,0
+20,17.460,Success,236,0