use arena allocator for cli commands

src/main.zig

@@ -145,12 +145,15 @@ fn resolveUserPath(
 }
 
 pub fn main() !u8 {
+    // Long-lived allocator for things that span the whole process. Only
+    // actually used for the early argsAlloc and the TUI path — CLI
+    // commands run under a per-invocation arena (see below).
     var gpa = std.heap.GeneralPurposeAllocator(.{}){};
     defer _ = gpa.deinit();
-    const allocator = gpa.allocator();
+    const gpa_alloc = gpa.allocator();
 
-    const args = try std.process.argsAlloc(allocator);
-    defer std.process.argsFree(allocator, args);
+    const args = try std.process.argsAlloc(gpa_alloc);
+    defer std.process.argsFree(gpa_alloc, args);
 
     // Single buffered writer for all stdout output
     var stdout_buf: [4096]u8 = undefined;
@@ -194,19 +197,38 @@ pub fn main() !u8 {
 
     const color = @import("format.zig").shouldUseColor(globals.no_color);
 
-    var config = zfin.Config.fromEnv(allocator);
-    defer config.deinit();
-
     const command = args[globals.cursor];
     const cmd_args = args[globals.cursor + 1 ..];
 
-    // Interactive TUI -- delegates to the TUI module (owns its own DataService).
+    // Interactive TUI: long-lived, per-frame allocations benefit from a
+    // real (non-arena) allocator. Runs against `gpa` directly.
     if (std.mem.eql(u8, command, "interactive") or std.mem.eql(u8, command, "i")) {
+        var tui_config = zfin.Config.fromEnv(gpa_alloc);
+        defer tui_config.deinit();
         try out.flush();
-        try tui.run(allocator, config, globals.portfolio_path, globals.watchlist_path, cmd_args);
+        try tui.run(gpa_alloc, tui_config, globals.portfolio_path, globals.watchlist_path, cmd_args);
         return 0;
     }
 
+    // ── Per-invocation arena ─────────────────────────────────────
+    //
+    // CLI commands do a batch of work then exit. Almost every allocation
+    // they make has the same lifetime (the invocation). An arena matched
+    // to that unit gives us three wins: skip per-allocation bookkeeping,
+    // ignore all the per-object `defer X.deinit()` calls (they become
+    // no-ops but remain correct code if the function is ever called from
+    // a non-arena context), and avoid gpa's leak-checking overhead for
+    // ephemeral state we're about to discard anyway.
+    //
+    // See models/portfolio.zig for the "match the arena to the unit of
+    // work" principle. Here the unit is one `zfin <subcommand>`.
+    var arena = std.heap.ArenaAllocator.init(std.heap.page_allocator);
+    defer arena.deinit();
+    const allocator = arena.allocator();
+
+    var config = zfin.Config.fromEnv(allocator);
+    defer config.deinit();
+
     // Version: doesn't need DataService; uses build_info + Config paths.
     if (std.mem.eql(u8, command, "version")) {
         commands.version.run(config, cmd_args, out) catch |err| switch (err) {