terminal: add persistent REPL history

Persists REPL history to .lp-history, except in script mode.

src/agent/Agent.zig

@@ -111,11 +111,15 @@ pub fn init(allocator: std.mem.Allocator, app: *App, opts: Config.Agent) !*Self
         return error.ToolInitFailed;
     };
 
+    // Persist REPL history in a cwd-relative `.lp-history`. Skipped in pure
+    // replay mode (no REPL is opened).
+    const history_path: ?[:0]const u8 = if (is_script_mode) null else ".lp-history";
+
     self.* = .{
         .allocator = allocator,
         .ai_client = ai_client,
         .tool_executor = tool_executor,
-        .terminal = Terminal.init(),
+        .terminal = Terminal.init(history_path),
         .cmd_executor = undefined,
         .recorder = Recorder.init(if (opts.save) opts.script_file else null),
         .messages = .empty,

src/agent/Terminal.zig

@@ -13,6 +13,8 @@ const ansi_green = "\x1b[32m";
 const ansi_yellow = "\x1b[33m";
 const ansi_red = "\x1b[31m";
 
+history_path: ?[:0]const u8,
+
 const CommandInfo = struct { name: [:0]const u8, hint: [:0]const u8 };
 
 const commands = [_]CommandInfo{
@@ -31,11 +33,14 @@ const commands = [_]CommandInfo{
     .{ .name = "EXIT", .hint = "" },
 };
 
-pub fn init() Self {
+pub fn init(history_path: ?[:0]const u8) Self {
     c.linenoiseSetMultiLine(1);
     c.linenoiseSetCompletionCallback(&completionCallback);
     c.linenoiseSetHintsCallback(&hintsCallback);
-    return .{};
+    if (history_path) |path| {
+        _ = c.linenoiseHistoryLoad(path.ptr);
+    }
+    return .{ .history_path = history_path };
 }
 
 fn completionCallback(buf: [*c]const u8, lc: [*c]c.linenoiseCompletions) callconv(.c) void {
@@ -63,11 +68,14 @@ fn hintsCallback(buf: [*c]const u8, color: [*c]c_int, bold: [*c]c_int) callconv(
     return null;
 }
 
-pub fn readLine(_: *Self, prompt: [*:0]const u8) ?[]const u8 {
+pub fn readLine(self: *Self, prompt: [*:0]const u8) ?[]const u8 {
     const line = c.linenoise(prompt) orelse return null;
     const slice = std.mem.sliceTo(line, 0);
     if (slice.len > 0) {
         _ = c.linenoiseHistoryAdd(line);
+        if (self.history_path) |path| {
+            _ = c.linenoiseHistorySave(path.ptr);
+        }
     }
     return slice;
 }