diff --git a/src/views/TimesheetView.vue b/src/views/TimesheetView.vue
index 0d902de..0e8a933 100644
--- a/src/views/TimesheetView.vue
+++ b/src/views/TimesheetView.vue
@@ -8,29 +8,60 @@
         <button
           @click="prevWeek"
           class="p-1.5 text-text-secondary hover:text-text-primary transition-colors duration-150"
-          title="Previous week"
+          aria-label="Previous week"
         >
-          <ChevronLeft class="w-5 h-5" :stroke-width="2" />
+          <ChevronLeft class="w-5 h-5" :stroke-width="2" aria-hidden="true" />
         </button>
 
         <button
           @click="goToThisWeek"
-          class="px-3 py-1.5 text-xs text-text-secondary border border-border-subtle rounded-lg hover:text-text-primary hover:bg-bg-elevated transition-colors duration-150"
+          class="px-3 py-1.5 text-xs text-text-secondary border border-border-subtle rounded-lg hover:text-text-primary hover:bg-bg-elevated transition-colors duration-150 focus-visible:outline-2 focus-visible:outline-offset-2 focus-visible:outline-accent"
         >
           This Week
         </button>
 
         <button
-          @click="nextWeek"
-          class="p-1.5 text-text-secondary hover:text-text-primary transition-colors duration-150"
-          title="Next week"
+          @click="copyLastWeekStructure"
+          :disabled="isCurrentWeekLocked"
+          class="px-3 py-1.5 text-xs text-text-secondary border border-border-subtle rounded-lg hover:text-text-primary hover:bg-bg-elevated transition-colors duration-150 disabled:opacity-40 disabled:cursor-not-allowed focus-visible:outline-2 focus-visible:outline-offset-2 focus-visible:outline-accent"
         >
-          <ChevronRight class="w-5 h-5" :stroke-width="2" />
+          Copy Last Week
         </button>
 
-        <span class="text-[0.8125rem] text-text-primary font-medium ml-2">
+        <button
+          @click="nextWeek"
+          class="p-1.5 text-text-secondary hover:text-text-primary transition-colors duration-150"
+          aria-label="Next week"
+        >
+          <ChevronRight class="w-5 h-5" :stroke-width="2" aria-hidden="true" />
+        </button>
+
+        <span class="text-[0.8125rem] text-text-primary font-medium ml-2" role="status" aria-live="polite">
           {{ weekRangeLabel }}
         </span>
+
+        <!-- Lock status + button -->
+        <template v-if="isCurrentWeekLocked">
+          <span class="flex items-center gap-1 text-[0.6875rem] text-amber-500 ml-3">
+            <Lock class="w-3.5 h-3.5" :stroke-width="2" aria-hidden="true" />
+            Locked
+          </span>
+          <button
+            @click="showUnlockConfirm = true"
+            class="ml-1 px-2.5 py-1 text-[0.6875rem] text-text-secondary border border-border-subtle rounded-lg hover:text-text-primary hover:bg-bg-elevated transition-colors duration-150"
+          >
+            Unlock
+          </button>
+        </template>
+        <template v-else-if="canLock">
+          <button
+            @click="showLockConfirm = true"
+            class="ml-3 flex items-center gap-1 px-2.5 py-1 text-[0.6875rem] text-text-secondary border border-border-subtle rounded-lg hover:text-text-primary hover:bg-bg-elevated transition-colors duration-150"
+          >
+            <Lock class="w-3.5 h-3.5" :stroke-width="2" aria-hidden="true" />
+            Lock Week
+          </button>
+        </template>
       </div>
     </div>
 
@@ -41,7 +72,10 @@
         <thead>
           <tr class="border-b border-border-subtle">
             <th class="px-3 py-2 text-left text-[0.6875rem] text-text-tertiary uppercase tracking-[0.08em] font-medium w-56">
-              Project / Task
+              <span class="flex items-center gap-1.5">
+                Project / Task
+                <Lock v-if="isCurrentWeekLocked" class="w-3 h-3 text-amber-500" :stroke-width="2" aria-label="Week is locked" />
+              </span>
             </th>
             <th
               v-for="(day, i) in dayHeaders"
@@ -61,13 +95,16 @@
           <tr
             v-for="(row, rowIndex) in rows"
             :key="rowIndex"
-            class="border-b border-border-subtle hover:bg-bg-elevated transition-colors duration-150"
+            class="border-b border-border-subtle transition-colors duration-150"
+            :class="isCurrentWeekLocked ? 'bg-bg-inset' : 'hover:bg-bg-elevated'"
+            :title="isCurrentWeekLocked ? 'This week is locked' : undefined"
           >
             <td class="px-3 py-2">
               <div class="flex items-center gap-2">
                 <div
                   class="w-2 h-2 rounded-full shrink-0"
                   :style="{ backgroundColor: row.color }"
+                  aria-hidden="true"
                 />
                 <span class="text-[0.75rem] text-text-primary truncate">{{ row.project_name }}</span>
                 <span v-if="row.task_name" class="text-[0.75rem] text-text-tertiary truncate">/ {{ row.task_name }}</span>
@@ -76,10 +113,32 @@
             <td
               v-for="(seconds, dayIndex) in row.days"
               :key="dayIndex"
-              class="px-3 py-2 text-right text-[0.75rem] font-mono"
-              :class="seconds > 0 ? 'text-accent-text' : 'text-text-tertiary'"
+              @click="startEdit(rowIndex, dayIndex)"
+              @keydown.enter="startEdit(rowIndex, dayIndex)"
+              tabindex="0"
+              role="gridcell"
+              :aria-label="'Hours for ' + row.project_name + ' on ' + getDayLabel(dayIndex) + ': ' + formatHM(seconds)"
+              class="px-3 py-2 text-right text-[0.75rem] font-mono transition-colors duration-150"
+              :class="[
+                seconds > 0 ? 'text-accent-text' : 'text-text-tertiary',
+                !isCurrentWeekLocked ? 'cursor-pointer hover:bg-bg-elevated' : ''
+              ]"
             >
-              {{ formatHM(seconds) }}
+              <template v-if="editingCell?.rowIdx === rowIndex && editingCell?.dayIdx === dayIndex">
+                <input
+                  ref="editInputRef"
+                  v-model="editValue"
+                  @blur="saveEdit()"
+                  @keydown.enter.prevent="saveEdit()"
+                  @keydown.escape.prevent="cancelEdit()"
+                  @keydown.tab="saveEdit()"
+                  class="w-full text-right text-[0.75rem] font-mono bg-transparent border-b-2 border-accent outline-none text-text-primary"
+                  aria-label="Enter hours (decimal or H:MM)"
+                />
+              </template>
+              <template v-else>
+                {{ formatHM(seconds) }}
+              </template>
             </td>
             <td class="px-3 py-2 text-right text-[0.75rem] font-mono text-accent-text font-medium">
               {{ formatHM(rowTotal(row)) }}
@@ -99,6 +158,7 @@
                     placeholder="Select project"
                     :placeholder-value="null"
                     :searchable="true"
+                    aria-label="Select project"
                   />
                 </div>
                 <div class="w-48">
@@ -111,6 +171,7 @@
                     :placeholder-value="null"
                     :searchable="true"
                     :disabled="!newRowProjectId"
+                    aria-label="Select task"
                   />
                 </div>
                 <button
@@ -132,8 +193,22 @@
 
           <!-- Empty state -->
           <tr v-if="rows.length === 0 && !showAddRow">
-            <td colspan="9" class="px-3 py-8 text-center">
-              <p class="text-[0.75rem] text-text-tertiary">No timesheet data for this week</p>
+            <td colspan="9" class="px-3 py-12">
+              <div class="flex flex-col items-center justify-center">
+                <ClockIcon class="w-10 h-10 text-text-tertiary" :stroke-width="1.5" aria-hidden="true" />
+                <p class="text-sm text-text-secondary mt-3">No timesheet data for this week</p>
+                <p class="text-xs text-text-tertiary mt-1">Start tracking time to see your weekly timesheet.</p>
+                <router-link to="/timer" class="mt-3 px-4 py-1.5 bg-accent text-bg-base text-xs font-medium rounded-lg hover:bg-accent-hover transition-colors">
+                  Go to Timer
+                </router-link>
+                <button
+                  v-if="onboardingStore.isVisible"
+                  @click="tourStore.start(TOURS.timer)"
+                  class="mt-2 text-[0.6875rem] text-accent-text hover:underline"
+                >
+                  Show me how
+                </button>
+              </div>
             </td>
           </tr>
         </tbody>
@@ -163,22 +238,93 @@
     <button
       v-if="!showAddRow"
       @click="startAddRow"
-      class="mt-3 flex items-center gap-1.5 text-text-secondary text-xs hover:text-text-primary transition-colors duration-150"
+      :disabled="isCurrentWeekLocked"
+      class="mt-3 flex items-center gap-1.5 text-text-secondary text-xs hover:text-text-primary transition-colors duration-150 disabled:opacity-40 disabled:cursor-not-allowed"
+      :title="isCurrentWeekLocked ? 'Cannot add rows to a locked week' : undefined"
     >
-      <Plus class="w-4 h-4" :stroke-width="2" />
+      <Plus class="w-4 h-4" :stroke-width="2" aria-hidden="true" />
       Add Row
     </button>
+
+    <!-- Lock Confirmation Dialog -->
+    <Transition name="modal">
+    <div
+      v-if="showLockConfirm"
+      class="fixed inset-0 bg-black/70 backdrop-blur-[4px] flex items-center justify-center p-4 z-50"
+      @click.self="showLockConfirm = false"
+    >
+      <div class="bg-bg-surface border border-border-subtle rounded-lg shadow-[0_1px_3px_rgba(0,0,0,0.3)] w-full max-w-sm p-6" role="alertdialog" aria-modal="true" aria-labelledby="lock-title" aria-describedby="lock-desc">
+        <h2 id="lock-title" class="text-[1.125rem] font-semibold font-[family-name:var(--font-heading)] text-text-primary mb-2">Lock Week</h2>
+        <p id="lock-desc" class="text-[0.75rem] text-text-secondary mb-6">
+          Locking this week will prevent any changes to time entries within it. You can unlock it later if needed.
+        </p>
+        <div class="flex justify-end gap-3">
+          <button
+            @click="showLockConfirm = false"
+            class="px-4 py-2 border border-border-subtle text-text-secondary rounded-lg hover:bg-bg-elevated transition-colors duration-150"
+          >
+            Cancel
+          </button>
+          <button
+            @click="lockWeek"
+            class="px-4 py-2 bg-accent text-bg-base font-medium rounded-lg hover:bg-accent-hover transition-colors duration-150"
+          >
+            Lock
+          </button>
+        </div>
+      </div>
+    </div>
+    </Transition>
+
+    <!-- Unlock Confirmation Dialog -->
+    <Transition name="modal">
+    <div
+      v-if="showUnlockConfirm"
+      class="fixed inset-0 bg-black/70 backdrop-blur-[4px] flex items-center justify-center p-4 z-50"
+      @click.self="showUnlockConfirm = false"
+    >
+      <div class="bg-bg-surface border border-border-subtle rounded-lg shadow-[0_1px_3px_rgba(0,0,0,0.3)] w-full max-w-sm p-6" role="alertdialog" aria-modal="true" aria-labelledby="unlock-title" aria-describedby="unlock-desc">
+        <h2 id="unlock-title" class="text-[1.125rem] font-semibold font-[family-name:var(--font-heading)] text-text-primary mb-2">Unlock Week</h2>
+        <p id="unlock-desc" class="text-[0.75rem] text-text-secondary mb-6">
+          Unlocking this week will allow changes to time entries. Are you sure?
+        </p>
+        <div class="flex justify-end gap-3">
+          <button
+            @click="showUnlockConfirm = false"
+            class="px-4 py-2 border border-border-subtle text-text-secondary rounded-lg hover:bg-bg-elevated transition-colors duration-150"
+          >
+            Cancel
+          </button>
+          <button
+            @click="unlockWeek"
+            class="px-4 py-2 border border-status-error text-status-error font-medium rounded-lg hover:bg-status-error/10 transition-colors duration-150"
+          >
+            Unlock
+          </button>
+        </div>
+      </div>
+    </div>
+    </Transition>
+
+    <div class="sr-only" aria-live="polite" aria-atomic="true">{{ liveAnnouncement }}</div>
   </div>
 </template>
 
 <script setup lang="ts">
-import { ref, computed, watch, onMounted } from 'vue'
-import { ChevronLeft, ChevronRight, Plus } from 'lucide-vue-next'
+import { ref, computed, watch, onMounted, nextTick } from 'vue'
+import { ChevronLeft, ChevronRight, Plus, Lock, Clock as ClockIcon } from 'lucide-vue-next'
 import { invoke } from '@tauri-apps/api/core'
 import AppSelect from '../components/AppSelect.vue'
 import { useProjectsStore, type Task } from '../stores/projects'
+import { useToastStore } from '../stores/toast'
+import { useOnboardingStore } from '../stores/onboarding'
+import { useTourStore } from '../stores/tour'
+import { TOURS } from '../utils/tours'
 
 const projectsStore = useProjectsStore()
+const toast = useToastStore()
+const onboardingStore = useOnboardingStore()
+const tourStore = useTourStore()
 
 // ── Types ──────────────────────────────────────────────────────────────
 
@@ -296,9 +442,90 @@ async function fetchTimesheetData() {
   }
 }
 
+// Persist current row structure to backend
+async function persistRows() {
+  try {
+    const rowData = rows.value.map((r, i) => ({
+      project_id: r.project_id,
+      task_id: r.task_id,
+      sort_order: i,
+    }))
+    await invoke('save_timesheet_rows', { weekStart: weekStart.value, rows: rowData })
+  } catch {
+    // Silent failure - row persistence is a convenience feature
+  }
+}
+
+// Load previous week's row structure if current week has no rows
+async function maybeLoadPreviousStructure() {
+  if (rows.value.length > 0) return
+  try {
+    const prevRows = await invoke<any[]>('get_previous_week_structure', { currentWeekStart: weekStart.value })
+    if (prevRows.length > 0) {
+      for (const pr of prevRows) {
+        const project = projectsStore.projects.find(p => p.id === pr.project_id)
+        if (!project) continue
+        let taskName: string | null = null
+        if (pr.task_id) {
+          const tasks = await projectsStore.fetchTasks(pr.project_id)
+          taskName = tasks.find(t => t.id === pr.task_id)?.name ?? null
+        }
+        rows.value.push({
+          project_id: pr.project_id,
+          project_name: project.name,
+          color: project.color,
+          task_id: pr.task_id || null,
+          task_name: taskName,
+          days: [0, 0, 0, 0, 0, 0, 0],
+        })
+      }
+    }
+  } catch {
+    // No previous structure
+  }
+}
+
+// Copy previous week's row structure into current week
+async function copyLastWeekStructure() {
+  try {
+    const prevRows = await invoke<any[]>('get_previous_week_structure', { currentWeekStart: weekStart.value })
+    if (prevRows.length === 0) {
+      toast.info('No rows found in previous week')
+      return
+    }
+    for (const pr of prevRows) {
+      const project = projectsStore.projects.find(p => p.id === pr.project_id)
+      if (!project) continue
+      // Skip if already exists
+      const exists = rows.value.some(
+        r => r.project_id === pr.project_id && r.task_id === (pr.task_id || null)
+      )
+      if (exists) continue
+      let taskName: string | null = null
+      if (pr.task_id) {
+        const tasks = await projectsStore.fetchTasks(pr.project_id)
+        taskName = tasks.find(t => t.id === pr.task_id)?.name ?? null
+      }
+      rows.value.push({
+        project_id: pr.project_id,
+        project_name: project.name,
+        color: project.color,
+        task_id: pr.task_id || null,
+        task_name: taskName,
+        days: [0, 0, 0, 0, 0, 0, 0],
+      })
+    }
+    await persistRows()
+    toast.success('Copied row structure from last week')
+  } catch {
+    toast.error('Failed to copy last week structure')
+  }
+}
+
 // Re-fetch whenever weekStart changes
-watch(weekStart, () => {
-  fetchTimesheetData()
+watch(weekStart, async () => {
+  await fetchTimesheetData()
+  await maybeLoadPreviousStructure()
 })
 
 // ── Totals ─────────────────────────────────────────────────────────────
@@ -330,6 +557,91 @@ function formatHM(seconds: number): string {
   return `${h}:${String(m).padStart(2, '0')}`
 }
 
+// ── Inline Editing ──────────────────────────────────────────────────────
+
+const editingCell = ref<{ rowIdx: number; dayIdx: number } | null>(null)
+const editValue = ref('')
+const editInputRef = ref<HTMLInputElement | null>(null)
+const liveAnnouncement = ref('')
+
+function startEdit(rowIdx: number, dayIdx: number) {
+  if (isCurrentWeekLocked.value) return
+  const row = rows.value[rowIdx]
+  if (!row) return
+  editingCell.value = { rowIdx, dayIdx }
+  const seconds = row.days[dayIdx]
+  editValue.value = seconds > 0 ? formatHoursDecimal(seconds) : ''
+  nextTick(() => {
+    editInputRef.value?.focus()
+    editInputRef.value?.select()
+  })
+}
+
+function cancelEdit() {
+  editingCell.value = null
+  editValue.value = ''
+}
+
+function formatHoursDecimal(seconds: number): string {
+  return (seconds / 3600).toFixed(2)
+}
+
+function parseTimeInput(input: string): number | null {
+  const trimmed = input.trim()
+  if (!trimmed) return 0
+
+  if (trimmed.includes(':')) {
+    const [h, m] = trimmed.split(':').map(Number)
+    if (isNaN(h) || isNaN(m) || h < 0 || m < 0 || m > 59) return null
+    const seconds = h * 3600 + m * 60
+    if (seconds > 86400) return null
+    return seconds
+  }
+
+  const num = parseFloat(trimmed)
+  if (isNaN(num) || num < 0 || num > 24) return null
+  return Math.round(num * 3600)
+}
+
+function getDayDate(dayIdx: number): string {
+  const dates = weekDates.value
+  if (dates[dayIdx]) return formatISODate(dates[dayIdx])
+  return ''
+}
+
+function getDayLabel(dayIdx: number): string {
+  const labels = ['Monday', 'Tuesday', 'Wednesday', 'Thursday', 'Friday', 'Saturday', 'Sunday']
+  return labels[dayIdx] || ''
+}
+
+async function saveEdit() {
+  if (!editingCell.value) return
+  const { rowIdx, dayIdx } = editingCell.value
+  const row = rows.value[rowIdx]
+  if (!row) { cancelEdit(); return }
+
+  const seconds = parseTimeInput(editValue.value)
+  if (seconds === null) { cancelEdit(); return }
+
+  const date = getDayDate(dayIdx)
+  if (!date) { cancelEdit(); return }
+
+  try {
+    await invoke('upsert_timesheet_entry', {
+      projectId: row.project_id,
+      taskId: row.task_id,
+      date,
+      durationSeconds: seconds,
+    })
+    row.days[dayIdx] = seconds
+    liveAnnouncement.value = `Saved ${formatHoursDecimal(seconds)} hours for ${row.project_name} on ${getDayLabel(dayIdx)}`
+  } catch (e) {
+    console.error('Failed to save timesheet entry:', e)
+    toast.error('Failed to save entry')
+  }
+  cancelEdit()
+}
+
 // ── Add Row ────────────────────────────────────────────────────────────
 
 const showAddRow = ref(false)
@@ -397,13 +709,68 @@ function confirmAddRow() {
     days: [0, 0, 0, 0, 0, 0, 0],
   })
 
+  persistRows()
   cancelAddRow()
 }
 
+// ── Timesheet locks ───────────────────────────────────────────────────
+
+interface TimesheetLock {
+  id: number
+  week_start: string
+  status: string
+  locked_at: string
+}
+
+const lockedWeeks = ref<Set<string>>(new Set())
+const showLockConfirm = ref(false)
+const showUnlockConfirm = ref(false)
+
+const isCurrentWeekLocked = computed(() => lockedWeeks.value.has(weekStart.value))
+
+const isPastWeek = computed(() => {
+  const currentMonday = formatISODate(getMonday(new Date()))
+  return weekStart.value < currentMonday
+})
+
+const canLock = computed(() => isPastWeek.value && !isCurrentWeekLocked.value)
+
+async function fetchLocks() {
+  try {
+    const locks = await invoke<TimesheetLock[]>('get_timesheet_locks')
+    lockedWeeks.value = new Set(locks.map(l => l.week_start))
+  } catch (error) {
+    console.error('Failed to fetch locks:', error)
+  }
+}
+
+async function lockWeek() {
+  try {
+    await invoke('lock_timesheet_week', { weekStart: weekStart.value })
+    lockedWeeks.value.add(weekStart.value)
+    toast.success('Week locked')
+  } catch (error) {
+    toast.error('Failed to lock week')
+  }
+  showLockConfirm.value = false
+}
+
+async function unlockWeek() {
+  try {
+    await invoke('unlock_timesheet_week', { weekStart: weekStart.value })
+    lockedWeeks.value.delete(weekStart.value)
+    toast.success('Week unlocked')
+  } catch (error) {
+    toast.error('Failed to unlock week')
+  }
+  showUnlockConfirm.value = false
+}
+
 // ── Init ───────────────────────────────────────────────────────────────
 
 onMounted(async () => {
   await projectsStore.fetchProjects()
-  goToThisWeek() // triggers watch → fetchTimesheetData
+  goToThisWeek() // triggers watch -> fetchTimesheetData
+  fetchLocks()
 })
 </script>