diff --git a/app/components/DefectForm.vue b/app/components/DefectForm.vue
new file mode 100644
index 0000000..db79d4e
--- /dev/null
+++ b/app/components/DefectForm.vue
@@ -0,0 +1,114 @@
+<script setup lang="ts">
+// File a defect against a board section (C3, F2). Driven by `sectionId`: when a
+// section is clicked the modal opens pre-targeted to it; pick a project, type
+// what's wrong, submit. Reporter and timestamp are added server-side.
+import { sections } from '~/board/definition'
+
+interface Project {
+  id: string
+  name: string
+}
+
+interface Defect {
+  id: string
+  sectionId: string
+  projectId: string
+  verbatim: string
+}
+
+const props = defineProps<{ sectionId: string | null }>()
+const emit = defineEmits<{ close: []; filed: [Defect] }>()
+
+const project = ref<Project | null>(null)
+const verbatim = ref('')
+const busy = ref(false)
+const error = ref('')
+
+const sectionLabel = computed(
+  () => sections.find((s) => s.id === props.sectionId)?.label ?? '',
+)
+const canSubmit = computed(
+  () => project.value !== null && verbatim.value.trim().length > 0,
+)
+
+// Each time a (new) section opens, start from a clean form.
+watch(
+  () => props.sectionId,
+  () => {
+    project.value = null
+    verbatim.value = ''
+    error.value = ''
+  },
+)
+
+async function submit() {
+  if (!canSubmit.value || busy.value || !props.sectionId) return
+  busy.value = true
+  error.value = ''
+  try {
+    const defect = await $fetch<Defect>('/api/defects', {
+      method: 'POST',
+      body: {
+        sectionId: props.sectionId,
+        projectId: project.value!.id,
+        verbatim: verbatim.value.trim(),
+      },
+    })
+    emit('filed', defect)
+  } catch {
+    error.value = 'Could not file the defect. Please try again.'
+  } finally {
+    busy.value = false
+  }
+}
+</script>
+
+<template>
+  <dialog class="modal" :class="{ 'modal-open': sectionId !== null }">
+    <div class="modal-box">
+      <h3 class="text-lg font-bold">Report a problem — {{ sectionLabel }}</h3>
+
+      <form class="mt-4 flex flex-col gap-4" @submit.prevent="submit">
+        <fieldset class="fieldset">
+          <legend class="fieldset-legend">Project</legend>
+          <ProjectAutocomplete v-model="project" />
+        </fieldset>
+
+        <fieldset class="fieldset">
+          <legend class="fieldset-legend">What's wrong?</legend>
+          <textarea
+            v-model="verbatim"
+            class="textarea textarea-bordered w-full"
+            rows="3"
+            placeholder="Describe the problem in your own words…"
+            data-test="verbatim"
+          />
+        </fieldset>
+
+        <p v-if="error" class="text-error text-sm" role="alert">{{ error }}</p>
+
+        <div class="modal-action">
+          <button type="button" class="btn btn-ghost" @click="emit('close')">
+            Cancel
+          </button>
+          <button
+            type="submit"
+            class="btn btn-primary"
+            :disabled="!canSubmit || busy"
+            data-test="submit"
+          >
+            {{ busy ? 'Filing…' : 'File defect' }}
+          </button>
+        </div>
+      </form>
+    </div>
+
+    <!-- Click the backdrop to dismiss. -->
+    <button
+      type="button"
+      class="modal-backdrop"
+      aria-label="Close"
+      @click="emit('close')"
+    />
+  </dialog>
+</template>
diff --git a/app/pages/index.vue b/app/pages/index.vue
index 4065dd3..170dac1 100644
--- a/app/pages/index.vue
+++ b/app/pages/index.vue
@@ -1,13 +1,33 @@
 <script setup lang="ts">
-const selected = ref<string | null>(null)
+// Andon reporting view (F2): the board is the entry point — clicking a section
+// opens the defect form for it.
+const selectedSectionId = ref<string | null>(null)
+const confirmation = ref<string | null>(null)
+
+function onFiled() {
+  selectedSectionId.value = null
+  confirmation.value = 'Thanks — your report was filed.'
+  setTimeout(() => (confirmation.value = null), 4000)
+}
 </script>
 
 <template>
-  <main>
-    <h1>Andon — report a board problem</h1>
-    <BoardView @select="(id) => (selected = id)" />
-    <p v-if="selected">
-      Selected section: <code>{{ selected }}</code> — the defect form arrives in Task 5.
-    </p>
+  <main class="mx-auto flex max-w-5xl flex-col items-center gap-6 p-6">
+    <header class="text-center">
+      <h1>Andon — report a board problem</h1>
+      <p class="opacity-70">Click a section to report a problem.</p>
+    </header>
+
+    <BoardView @select="(id) => (selectedSectionId = id)" />
+
+    <DefectForm
+      :section-id="selectedSectionId"
+      @close="selectedSectionId = null"
+      @filed="onFiled"
+    />
+
+    <div v-if="confirmation" class="toast toast-end">
+      <div class="alert alert-success">{{ confirmation }}</div>
+    </div>
   </main>
 </template>
diff --git a/server/api/defects.post.ts b/server/api/defects.post.ts
new file mode 100644
index 0000000..dc20d19
--- /dev/null
+++ b/server/api/defects.post.ts
@@ -0,0 +1,15 @@
+import { type } from 'arktype'
+import { getDb } from '../db/client'
+import { createDefect } from '../db/repositories/defects'
+import { DefectInput } from '../utils/defectInput'
+import { getReporter } from '../utils/getReporter'
+
+// File a defect against a board section (F2). Reporter comes from the seam,
+// not the client; the timestamp defaults in the DB.
+export default defineEventHandler(async (event) => {
+  const input = DefectInput(await readBody(event))
+  if (input instanceof type.errors) {
+    throw createError({ statusCode: 400, statusMessage: input.summary })
+  }
+  return createDefect(getDb(), { ...input, reporterEmail: getReporter(event) })
+})
diff --git a/server/utils/defectInput.ts b/server/utils/defectInput.ts
new file mode 100644
index 0000000..9ff27ed
--- /dev/null
+++ b/server/utils/defectInput.ts
@@ -0,0 +1,17 @@
+import { type } from 'arktype'
+import { sectionIds } from '../../app/board/definition'
+
+// Validated request body for filing a defect (F2). The reporter is resolved
+// server-side via the session seam, never trusted from the client. Verbatim is
+// trimmed; the section must be one defined on the canonical board (C1).
+export const DefectInput = type({
+  sectionId: type('string').narrow(
+    (id, ctx) => sectionIds.has(id) || ctx.reject('a known board section id'),
+  ),
+  projectId: 'string.uuid',
+  verbatim: type('string')
+    .pipe((s) => s.trim())
+    .narrow((s, ctx) => s.length > 0 || ctx.reject('non-empty text')),
+})
+
+export type DefectInputData = typeof DefectInput.infer
diff --git a/server/utils/getReporter.ts b/server/utils/getReporter.ts
new file mode 100644
index 0000000..0bcdda3
--- /dev/null
+++ b/server/utils/getReporter.ts
@@ -0,0 +1,10 @@
+import type { H3Event } from 'h3'
+
+/**
+ * Resolves the reporter's email — the one seam between filing and auth (ADR
+ * 0002). For now it returns a fixed dev identity so the filing slice works
+ * before OAuth exists; Task 9 swaps this to read the verified session email.
+ */
+export function getReporter(_event: H3Event): string {
+  return process.env.DEV_REPORTER_EMAIL ?? 'dev@theodo.com'
+}
diff --git a/tasks/todo.md b/tasks/todo.md
index 2326148..92c73e0 100644
--- a/tasks/todo.md
+++ b/tasks/todo.md
@@ -12,7 +12,7 @@ review.
 ## Phase 2 — File a defect (G1)
 - [x] **T3** Postgres schema + migrations (C8) (S) — _deps: T1_
 - [x] **T4** Projects API + ProjectAutocomplete (C4) — F3 (M) — _deps: T3_
-- [ ] **T5** File a defect: POST /api/defects + DefectForm (C3) — F2 (M) — _deps: T2, T3, T4_
+- [x] **T5** File a defect: POST /api/defects + DefectForm (C3) — F2 (M) — _deps: T2, T3, T4_
 - [ ] ⛳ **Checkpoint:** defect files end-to-end (dev auth), tests pass, human review
 
 ## Phase 3 — See weak points (G2)
diff --git a/tests/defect-filing.spec.ts b/tests/defect-filing.spec.ts
new file mode 100644
index 0000000..3873bea
--- /dev/null
+++ b/tests/defect-filing.spec.ts
@@ -0,0 +1,80 @@
+import { describe, it, expect, beforeAll, beforeEach, afterAll } from 'vitest'
+import { type } from 'arktype'
+import { setupTestDb, truncateAll, type TestDb } from './helpers/db'
+import { createProject } from '../server/db/repositories/projects'
+import { createDefect, listRecentDefects } from '../server/db/repositories/defects'
+import { DefectInput } from '../server/utils/defectInput'
+
+const UUID = '3f0a27a7-81c0-43fa-9b42-c2864ddc569b'
+
+describe('defect input validation', () => {
+  it('accepts a valid defect and trims the verbatim', () => {
+    const result = DefectInput({
+      sectionId: 'macroplan',
+      projectId: UUID,
+      verbatim: '  builds are flaky  ',
+    })
+    expect(result).toMatchObject({
+      sectionId: 'macroplan',
+      projectId: UUID,
+      verbatim: 'builds are flaky',
+    })
+  })
+
+  it('rejects an unknown section id', () => {
+    const result = DefectInput({ sectionId: 'not-a-section', projectId: UUID, verbatim: 'x' })
+    expect(result instanceof type.errors).toBe(true)
+  })
+
+  it('rejects empty / whitespace-only verbatim', () => {
+    const result = DefectInput({ sectionId: 'macroplan', projectId: UUID, verbatim: '   ' })
+    expect(result instanceof type.errors).toBe(true)
+  })
+
+  it('rejects a non-uuid project id', () => {
+    const result = DefectInput({ sectionId: 'macroplan', projectId: 'nope', verbatim: 'x' })
+    expect(result instanceof type.errors).toBe(true)
+  })
+})
+
+describe('defects repository', () => {
+  let db: TestDb
+  let pool: { end: () => Promise<void> }
+
+  beforeAll(async () => {
+    const setup = await setupTestDb()
+    db = setup.db
+    pool = setup.pool
+  })
+
+  afterAll(async () => {
+    await pool.end()
+  })
+
+  beforeEach(async () => {
+    await truncateAll(db)
+  })
+
+  it('persists a filed defect with section, project, verbatim and reporter', async () => {
+    const project = await createProject(db, 'Acme')
+    const row = await createDefect(db, {
+      sectionId: 'macroplan',
+      projectId: project.id,
+      verbatim: 'login is flaky',
+      reporterEmail: 'dev@theodo.com',
+    })
+
+    expect(row).toMatchObject({
+      sectionId: 'macroplan',
+      projectId: project.id,
+      verbatim: 'login is flaky',
+      reporterEmail: 'dev@theodo.com',
+    })
+    expect(row.id).toBeDefined()
+    expect(row.createdAt).toBeInstanceOf(Date)
+
+    const recent = await listRecentDefects(db)
+    expect(recent).toHaveLength(1)
+    expect(recent[0]!.id).toBe(row.id)
+  })
+})
diff --git a/tests/defect-form.nuxt.spec.ts b/tests/defect-form.nuxt.spec.ts
new file mode 100644
index 0000000..75b1d8f
--- /dev/null
+++ b/tests/defect-form.nuxt.spec.ts
@@ -0,0 +1,73 @@
+// @vitest-environment nuxt
+import { describe, it, expect, beforeEach, vi } from 'vitest'
+import { mountSuspended, registerEndpoint } from '@nuxt/test-utils/runtime'
+import { flushPromises } from '@vue/test-utils'
+import { defineEventHandler, readBody } from 'h3'
+import DefectForm from '../app/components/DefectForm.vue'
+
+let filed: { sectionId: string; projectId: string; verbatim: string } | null
+
+beforeEach(() => {
+  filed = null
+  registerEndpoint(
+    '/api/projects',
+    defineEventHandler(() => [{ id: 'p1', name: 'Acme' }]),
+  )
+  registerEndpoint(
+    '/api/defects',
+    defineEventHandler(async (event) => {
+      filed = await readBody(event)
+      return { id: 'd1', ...filed, reporterEmail: 'dev@theodo.com' }
+    }),
+  )
+})
+
+async function pickProject(wrapper: Awaited<ReturnType<typeof mountSuspended>>) {
+  await wrapper.find('[data-test="project-input"]').trigger('focus')
+  await wrapper.find('[data-test="project-option"]').trigger('click')
+}
+
+describe('DefectForm', () => {
+  it('opens for the clicked section and shows its name', async () => {
+    const wrapper = await mountSuspended(DefectForm, { props: { sectionId: 'macroplan' } })
+    await flushPromises()
+
+    expect(wrapper.find('dialog').classes()).toContain('modal-open')
+    expect(wrapper.text()).toContain('Macroplan')
+  })
+
+  it('is closed when no section is selected', async () => {
+    const wrapper = await mountSuspended(DefectForm, { props: { sectionId: null } })
+    expect(wrapper.find('dialog').classes()).not.toContain('modal-open')
+  })
+
+  it('cannot submit until both a project and verbatim are provided', async () => {
+    const wrapper = await mountSuspended(DefectForm, { props: { sectionId: 'macroplan' } })
+    await flushPromises()
+
+    expect(wrapper.find('[data-test="submit"]').attributes('disabled')).toBeDefined()
+
+    await pickProject(wrapper)
+    // project but no verbatim → still blocked
+    expect(wrapper.find('[data-test="submit"]').attributes('disabled')).toBeDefined()
+
+    await wrapper.find('[data-test="verbatim"]').setValue('builds are flaky')
+    expect(wrapper.find('[data-test="submit"]').attributes('disabled')).toBeUndefined()
+  })
+
+  it('files the defect with the section, chosen project and verbatim, then emits filed', async () => {
+    const wrapper = await mountSuspended(DefectForm, { props: { sectionId: 'macroplan' } })
+    await flushPromises()
+
+    await pickProject(wrapper)
+    await wrapper.find('[data-test="verbatim"]').setValue('builds are flaky')
+    await wrapper.find('form').trigger('submit')
+
+    await vi.waitFor(() => expect(wrapper.emitted('filed')).toBeTruthy())
+    expect(filed).toEqual({
+      sectionId: 'macroplan',
+      projectId: 'p1',
+      verbatim: 'builds are flaky',
+    })
+  })
+})