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+---
+epic: 10
+story: 10.5
+title: "Line Numbers"
+status: draft
+---
+
+## Epic 10 — Notepad UX (Cross-Platform Spec)
+**Goal:** Consistent editor behavior specified once, implemented per platform.
+
+### Story 10.5: Line Numbers
+
+As a user,
+I want optional line numbers in the editor gutter,
+So that I can reference specific lines when collaborating or reviewing.
+
+**Acceptance Criteria:**
+
+**Given** the user enables line numbers in settings
+**When** the editor renders a sheet
+**Then** a gutter column on the left displays sequential line numbers starting at 1
+**And** the line numbers are rendered in a dimmed/muted color to avoid visual clutter
+
+**Given** line numbers are enabled
+**When** the user inserts or deletes lines
+**Then** all line numbers update immediately to reflect the new sequence
+
+**Given** line numbers are enabled
+**When** the user toggles line numbers off in settings
+**Then** the gutter column is hidden
+**And** the input column expands to reclaim the gutter space
+
+**Given** the user has toggled line numbers on or off
+**When** they reopen the app
+**Then** their line number preference is remembered and applied