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+---
+epic: 11
+story: 11.4
+title: "Interactive REPL"
+status: draft
+---
+
+## Epic 11 — CLI Tool
+**Goal:** Command-line tool for scripting and automation, same Rust engine.
+
+### Story 11.4: Interactive REPL
+
+As a power user,
+I want an interactive CalcPad session in my terminal,
+So that I can iteratively build up calculations with persistent variables.
+
+**Acceptance Criteria:**
+
+**Given** the user runs `calcpad --repl`
+**When** the REPL starts
+**Then** a prompt is displayed (e.g., `> `) indicating readiness for input
+**And** the REPL session begins with a clean variable scope
+
+**Given** the user is in the REPL
+**When** they type `x = 10` and press Enter, then type `x * 5` and press Enter
+**Then** the first line outputs `10` and the second line outputs `50`
+**And** variables persist for the duration of the session
+
+**Given** the user is in the REPL
+**When** they press the Up arrow key
+**Then** the previous expression is recalled into the input line
+**And** history navigation (up/down) works via rustyline or equivalent library
+
+**Given** the user is in the REPL
+**When** they type `exit`, `quit`, or press `Ctrl+D`
+**Then** the REPL session ends cleanly
+**And** the process exits with code 0
+
+**Given** the user enters an invalid expression in the REPL
+**When** they press Enter
+**Then** an error message is displayed inline
+**And** the REPL continues to accept input (does not crash or exit)