fix(tags): preserve leading zeros in bulk tag CSV uploads and wire up drag-and-drop

landlord_property_id values like "07510027001" were being read via SheetJS
without raw:false, so CSV parsing coerced numeric-looking cells to numbers
and dropped leading zeros. Also wires up drag-and-drop on the bulk tag
upload dropzone, which was styled as one but only supported click-to-browse.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

src/app/portfolio/[slug]/components/BulkTagUploadModal.tsx

@@ -1,8 +1,7 @@
 "use client";
 
-import { useState } from "react";
+import { useRef, useState, DragEvent } from "react";
 import { useMutation } from "@tanstack/react-query";
-import * as XLSX from "xlsx";
 import {
   Dialog,
   DialogContent,
@@ -12,7 +11,11 @@ import {
   DialogFooter,
 } from "@/app/shadcn_components/ui/dialog";
 import { Button } from "@/app/shadcn_components/ui/button";
-import { parseTagIdentifierRows, IdentifierKey } from "@/lib/tags/bulkAssign";
+import {
+  parseTagIdentifierRows,
+  readIdentifierRows,
+  IdentifierKey,
+} from "@/lib/tags/bulkAssign";
 import { Tag, useInvalidateTagSurfaces, usePortfolioTags } from "./useTags";
 import { TagChip } from "./TagChip";
 
@@ -69,6 +72,8 @@ export function BulkTagUploadModal({
   const { data: tags = [] } = usePortfolioTags(portfolioId);
   const invalidate = useInvalidateTagSurfaces(portfolioId);
 
+  const fileInputRef = useRef<HTMLInputElement>(null);
+  const [isDragging, setIsDragging] = useState(false);
   const [fileName, setFileName] = useState<string | null>(null);
   const [parsed, setParsed] = useState<Parsed | null>(null);
   const [parseError, setParseError] = useState<string | null>(null);
@@ -76,6 +81,7 @@ export function BulkTagUploadModal({
   const [summary, setSummary] = useState<AssignSummary | null>(null);
 
   function reset() {
+    setIsDragging(false);
     setFileName(null);
     setParsed(null);
     setParseError(null);
@@ -91,13 +97,7 @@ export function BulkTagUploadModal({
     setFileName(file.name);
     try {
       const buf = await file.arrayBuffer();
-      const wb = XLSX.read(buf, { type: "array" });
-      const sheet = wb.Sheets[wb.SheetNames[0]];
-      const rows = XLSX.utils.sheet_to_json(sheet, { header: 1 }) as (
-        | string
-        | number
-        | null
-      )[][];
+      const rows = readIdentifierRows(buf);
       const result = parseTagIdentifierRows(rows);
       if (!result.ok) {
         setParseError(result.error);
@@ -109,6 +109,22 @@ export function BulkTagUploadModal({
     }
   }
 
+  function handleDragOver(e: DragEvent<HTMLLabelElement>) {
+    e.preventDefault();
+    setIsDragging(true);
+  }
+
+  function handleDragLeave() {
+    setIsDragging(false);
+  }
+
+  function handleDrop(e: DragEvent<HTMLLabelElement>) {
+    e.preventDefault();
+    setIsDragging(false);
+    const f = e.dataTransfer.files?.[0];
+    if (f) onFile(f);
+  }
+
   const assign = useMutation<AssignSummary, Error, void>({
     mutationFn: async () => {
       if (!parsed || !targetTag) throw new Error("Pick a file and a tag first");
@@ -198,14 +214,24 @@ export function BulkTagUploadModal({
           </div>
         ) : (
           <div className="space-y-4">
-            <label className="flex cursor-pointer flex-col items-center gap-1 rounded-xl border-2 border-dashed border-slate-200 bg-slate-50 px-4 py-6 text-center transition hover:border-slate-300">
+            <label
+              onDragOver={handleDragOver}
+              onDragLeave={handleDragLeave}
+              onDrop={handleDrop}
+              className={`flex cursor-pointer flex-col items-center gap-1 rounded-xl border-2 border-dashed px-4 py-6 text-center transition ${
+                isDragging
+                  ? "border-brandmidblue bg-blue-50"
+                  : "border-slate-200 bg-slate-50 hover:border-slate-300"
+              }`}
+            >
               <span className="text-sm font-semibold text-slate-600">
-                {fileName ?? "Choose a CSV or Excel file"}
+                {fileName ?? "Choose or drop a CSV or Excel file"}
               </span>
               <span className="text-xs text-slate-400">
                 First row must be a header
               </span>
               <input
+                ref={fileInputRef}
                 type="file"
                 accept=".csv,.xlsx,.xls"
                 className="hidden"

src/lib/tags/bulkAssign.test.ts

@@ -1,5 +1,9 @@
 import { describe, expect, it } from "vitest";
-import { parseTagIdentifierRows, MAX_BULK_TAG_ROWS } from "./bulkAssign";
+import {
+  parseTagIdentifierRows,
+  readIdentifierRows,
+  MAX_BULK_TAG_ROWS,
+} from "./bulkAssign";
 
 describe("parseTagIdentifierRows", () => {
   it("extracts landlord property ids from a landlord_property_id column", () => {
@@ -61,3 +65,22 @@ describe("parseTagIdentifierRows", () => {
     );
   });
 });
+
+describe("readIdentifierRows", () => {
+  it("preserves leading zeros in a numeric-looking landlord_property_id from a CSV", () => {
+    // A real uploaded CSV arrives as raw bytes/text, not a pre-typed SheetJS
+    // cell — that's exactly where SheetJS's numeric-inference kicks in and
+    // drops leading zeros unless the reader is told to keep displayed text.
+    const csvText = "landlord_property_id\n07510027001\n";
+    const buf = new TextEncoder().encode(csvText).buffer;
+
+    const rows = readIdentifierRows(buf);
+    const result = parseTagIdentifierRows(rows);
+
+    expect(result).toEqual({
+      ok: true,
+      key: "landlord_property_id",
+      identifiers: ["07510027001"],
+    });
+  });
+});

src/lib/tags/bulkAssign.ts

@@ -6,6 +6,8 @@
  * runs in the browser before anything is sent to the server.
  */
 
+import * as XLSX from "xlsx";
+
 /** Upper bound on rows per upload ("relatively small file", ADR-0013). */
 export const MAX_BULK_TAG_ROWS = 10_000;
 
@@ -17,6 +19,22 @@ export type ParsedIdentifiers =
 
 type Cell = string | number | null | undefined;
 
+/**
+ * Read an uploaded CSV/Excel file's first sheet into rows of cell text.
+ * raw: false forces SheetJS to hand back each cell's displayed text rather
+ * than its inferred type, so a numeric-looking id like "07510027001" survives
+ * instead of being coerced to the number 7510027001 (leading zeros dropped).
+ */
+export function readIdentifierRows(buf: ArrayBuffer): Cell[][] {
+  const wb = XLSX.read(buf, { type: "array" });
+  const sheet = wb.Sheets[wb.SheetNames[0]];
+  return XLSX.utils.sheet_to_json(sheet, {
+    header: 1,
+    raw: false,
+    defval: "",
+  }) as Cell[][];
+}
+
 /** Normalise a header cell: trimmed, lowercased, spaces/hyphens → underscores. */
 function normaliseHeader(cell: Cell): string {
   return String(cell ?? "")