diff --git a/packages/web/src/app/api/orgs/[orgSlug]/dashboard/sessions/csv-field.ts b/packages/web/src/app/api/orgs/[orgSlug]/dashboard/sessions/csv-field.ts
new file mode 100644
index 00000000..b049d175
--- /dev/null
+++ b/packages/web/src/app/api/orgs/[orgSlug]/dashboard/sessions/csv-field.ts
@@ -0,0 +1,14 @@
+const FORMULA_PREFIX = /^[\s]*[=+\-@\t\r\n＝＋－＠]/u
+
+/**
+ * Encode one session-export field without letting untrusted text become a spreadsheet formula.
+ * Numeric metrics remain numeric; text still uses RFC-style quote doubling when CSV syntax requires it.
+ */
+export function csvField(value: string | number | null | undefined) {
+  if (value === null || value === undefined) return ''
+  let text = String(value)
+  if (typeof value !== 'number' && FORMULA_PREFIX.test(text)) {
+    text = "'" + text
+  }
+  return /[",\r\n]/.test(text) ? `"${text.replaceAll('"', '""')}"` : text
+}
diff --git a/packages/web/src/app/api/orgs/[orgSlug]/dashboard/sessions/route.test.ts b/packages/web/src/app/api/orgs/[orgSlug]/dashboard/sessions/route.test.ts
new file mode 100644
index 00000000..1be8941c
--- /dev/null
+++ b/packages/web/src/app/api/orgs/[orgSlug]/dashboard/sessions/route.test.ts
@@ -0,0 +1,41 @@
+import { expect, test } from 'vitest'
+import { csvField } from './csv-field'
+
+test('csvField handles null/undefined', () => {
+  expect(csvField(null)).toBe('')
+  expect(csvField(undefined)).toBe('')
+})
+
+test('csvField handles normal strings', () => {
+  expect(csvField('hello')).toBe('hello')
+  expect(csvField('hello world')).toBe('hello world')
+})
+
+test('csvField handles numbers', () => {
+  expect(csvField(123)).toBe('123')
+  expect(csvField(-5)).toBe('-5')
+  expect(csvField(0)).toBe('0')
+})
+
+test('csvField handles quotes and delimiters without opening a new cell', () => {
+  expect(csvField('hello, world')).toBe('"hello, world"')
+  expect(csvField('hello"world')).toBe('"hello""world"')
+  expect(csvField('hello\nworld')).toBe('"hello\nworld"')
+  expect(csvField('safe",=1+1')).toBe('"safe"",=1+1"')
+})
+
+test('csvField neutralizes spreadsheet formula prefixes', () => {
+  expect(csvField('=1+1')).toBe("'=1+1")
+  expect(csvField('+1+1')).toBe("'+1+1")
+  expect(csvField('-1+1')).toBe("'-1+1")
+  expect(csvField('@1+1')).toBe("'@1+1")
+  expect(csvField('\t1+1')).toBe("'\t1+1")
+  expect(csvField('\r1+1')).toBe('"\'\r1+1"')
+  expect(csvField('\n=1+1')).toBe('"\'\n=1+1"')
+  expect(csvField(' =1+1')).toBe("' =1+1")
+  expect(csvField('\uFEFF=1+1')).toBe("'\uFEFF=1+1")
+  expect(csvField('＝1+1')).toBe("'＝1+1")
+  expect(csvField('＋1+1')).toBe("'＋1+1")
+  expect(csvField('－1+1')).toBe("'－1+1")
+  expect(csvField('＠1+1')).toBe("'＠1+1")
+})
diff --git a/packages/web/src/app/api/orgs/[orgSlug]/dashboard/sessions/route.ts b/packages/web/src/app/api/orgs/[orgSlug]/dashboard/sessions/route.ts
index 7d6a4d4a..34230d6e 100644
--- a/packages/web/src/app/api/orgs/[orgSlug]/dashboard/sessions/route.ts
+++ b/packages/web/src/app/api/orgs/[orgSlug]/dashboard/sessions/route.ts
@@ -10,6 +10,7 @@ import {
   resolveOrgScopedProjectIds,
 } from '@/lib/server/dashboard-route-helper'
 import { canAccessIndividualData, forbiddenByRole } from '@/lib/server/rbac'
+import { csvField } from './csv-field'
 
 export const runtime = 'nodejs'
 export const dynamic = 'force-dynamic'
@@ -71,12 +72,6 @@ function mapSessionItem(session: SessionWithInclude): SessionItem {
   }
 }
 
-function csvField(value: string | number | null | undefined) {
-  if (value === null || value === undefined) return ''
-  const text = String(value)
-  return /[",\r\n]/.test(text) ? `"${text.replaceAll('"', '""')}"` : text
-}
-
 function buildSessionsCsv(sessions: SessionWithInclude[]) {
   const headers = [
     'Session ID',