use single quote to toggle last symbol in tui

TODO.md

@@ -554,11 +554,6 @@ so they don't get lost; pick up opportunistically.
   the interaction model — e.g. allow specifying an expiration date,
   showing all monthlies expanded by default, or filtering by strategy
   (covered calls, spreads).
-- **TUI: toggle to last symbol keybind.** A single-key toggle that
-  flips between the current symbol and the previously selected one
-  (like `cd -` in bash or `Ctrl+^` in vim). Store `last_symbol` on
-  `App`; on symbol change, stash the previous. Useful for
-  eyeball-comparing performance/risk data between two symbols.
 
 ### Options / valuation
 

src/tui.zig

@@ -258,6 +258,57 @@ pub fn buildHelpLines(
     return lines.toOwnedSlice(arena);
 }
 
+/// Decide whether the outgoing active symbol should be stashed as the
+/// "last symbol" when switching to `incoming`. Stash only a non-empty
+/// symbol that actually differs (case-insensitively) from the one
+/// we're switching to, so `toggle_last_symbol` never records the
+/// symbol you're already on as the thing to flip back to.
+fn shouldStashSymbol(outgoing: []const u8, incoming: []const u8) bool {
+    return outgoing.len > 0 and !std.ascii.eqlIgnoreCase(outgoing, incoming);
+}
+
+/// Post-swap state from `computeSymbolToggle`: the new active symbol
+/// and the new last symbol, each slicing into the buffer passed for it.
+const SymbolToggle = struct {
+    current: []const u8,
+    last: []const u8,
+};
+
+/// Swap the active symbol with the last-active symbol, writing the
+/// results into the two backing buffers and returning slices into
+/// them. Returns `null` when there is no previous symbol to toggle to
+/// (`last` empty).
+///
+/// Aliasing-safe: `current` and/or `last` may already point into
+/// `current_buf` / `last_buf`. The outgoing current is copied to a
+/// stack temp before either buffer is overwritten, so the swap holds
+/// regardless of where the inputs live. Inputs longer than a buffer
+/// are clamped to the buffer length (symbols are <= 16 bytes in
+/// practice; the clamp just prevents an out-of-bounds copy).
+fn computeSymbolToggle(
+    current: []const u8,
+    last: []const u8,
+    current_buf: *[16]u8,
+    last_buf: *[16]u8,
+) ?SymbolToggle {
+    if (last.len == 0) return null;
+
+    // SAFETY: only tmp[0..cur_len] is written (below) before being
+    // read back; the tail is never observed.
+    var tmp: [16]u8 = undefined;
+    const cur_len = @min(current.len, tmp.len);
+    @memcpy(tmp[0..cur_len], current[0..cur_len]);
+
+    const new_cur_len = @min(last.len, current_buf.len);
+    @memcpy(current_buf[0..new_cur_len], last[0..new_cur_len]);
+    @memcpy(last_buf[0..cur_len], tmp[0..cur_len]);
+
+    return .{
+        .current = current_buf[0..new_cur_len],
+        .last = last_buf[0..cur_len],
+    };
+}
+
 /// Per-tab state, owned by `App` and accessed as `app.states.<tab>`.
 ///
 /// Per-tab private state aggregator, derived at comptime from the
@@ -454,6 +505,14 @@ pub const App = struct {
     // is unobservable.
     symbol_buf: [16]u8 = undefined,
     symbol_owned: bool = false,
+    /// The previously-active symbol, for the `toggle_last_symbol`
+    /// keybind (flip between current and prior, like `cd -`). Empty
+    /// until at least one symbol change has occurred. Bytes live in
+    /// `last_symbol_buf`.
+    last_symbol: []const u8 = "",
+    // SAFETY: paired with `last_symbol`; only the prefix
+    // last_symbol_buf[0..last_symbol.len] is ever read.
+    last_symbol_buf: [16]u8 = undefined,
     /// Symbol the overlay popup is currently showing details for.
     /// Empty when the overlay is closed. Bytes live in
     /// `overlay_symbol_buf`. Set/cleared via `toggleOverlay`.
@@ -978,14 +1037,10 @@ pub const App = struct {
             .edited => return ctx.consumeAndRedraw(),
             .ignored => {},
             .committed => {
-                // Commit: uppercase the input, set as active symbol, switch to quote tab
+                // Commit: set as active symbol (uppercased + stashed
+                // by setActiveSymbol), then switch to the quote tab.
                 if (self.input_len > 0) {
-                    for (self.input_buf[0..self.input_len]) |*ch| ch.* = std.ascii.toUpper(ch.*);
+                    self.setActiveSymbol(self.input_buf[0..self.input_len]);
-                    @memcpy(self.symbol_buf[0..self.input_len], self.input_buf[0..self.input_len]);
-                    self.symbol = self.symbol_buf[0..self.input_len];
-                    self.symbol_owned = true;
-                    self.has_explicit_symbol = true;
-                    self.resetSymbolData();
                     self.active_tab = .quote;
                     self.loadTabData();
                     ctx.queueRefresh() catch |err| std.log.debug("queueRefresh failed: {t}", .{err});
@@ -1022,6 +1077,13 @@ pub const App = struct {
                 self.input_len = 0;
                 return ctx.consumeAndRedraw();
             },
+            .toggle_last_symbol => {
+                if (self.toggleLastSymbol()) {
+                    self.loadTabData();
+                    ctx.queueRefresh() catch |err| std.log.debug("queueRefresh failed: {t}", .{err});
+                }
+                return ctx.consumeAndRedraw();
+            },
             .refresh => {
                 // Two-phase so the "Refreshing..." indicator paints
                 // before the (blocking) refresh runs. Flag it and
@@ -1201,6 +1263,13 @@ pub const App = struct {
     }
 
     pub fn setActiveSymbol(self: *App, sym: []const u8) void {
+        // Stash the outgoing symbol so `toggle_last_symbol` can flip
+        // back to it. Must run before symbol_buf is overwritten below.
+        if (shouldStashSymbol(self.symbol, sym)) {
+            const llen = @min(self.symbol.len, self.last_symbol_buf.len);
+            @memcpy(self.last_symbol_buf[0..llen], self.symbol[0..llen]);
+            self.last_symbol = self.last_symbol_buf[0..llen];
+        }
         const len = @min(sym.len, self.symbol_buf.len);
         @memcpy(self.symbol_buf[0..len], sym[0..len]);
         for (self.symbol_buf[0..len]) |*c| c.* = std.ascii.toUpper(c.*);
@@ -1210,6 +1279,28 @@ pub const App = struct {
         self.resetSymbolData();
     }
 
+    /// Flip the active symbol to the previously-active one (and vice
+    /// versa). Backs the `toggle_last_symbol` keybind. Returns false
+    /// when there's no previous symbol yet (nothing to toggle to).
+    ///
+    /// Does NOT route through `setActiveSymbol`: the swap inherently
+    /// stashes the outgoing symbol as the new `last_symbol`, so an
+    /// extra stash would be redundant (and would alias the buffers).
+    fn toggleLastSymbol(self: *App) bool {
+        const swapped = computeSymbolToggle(
+            self.symbol,
+            self.last_symbol,
+            &self.symbol_buf,
+            &self.last_symbol_buf,
+        ) orelse return false;
+        self.symbol = swapped.current;
+        self.last_symbol = swapped.last;
+        self.symbol_owned = true;
+        self.has_explicit_symbol = true;
+        self.resetSymbolData();
+        return true;
+    }
+
     /// Open / close / re-target the symbol-info overlay. Behavior:
     ///   - overlay closed                         → open with `sym`.
     ///   - overlay open, same `sym` as cursor     → close.
@@ -2722,6 +2813,68 @@ test "formatStatusHint: single fragment has no separator" {
     try testing.expectEqualStrings("ctrl+s save", out);
 }
 
+// ── symbol toggle helpers ─────────────────────────────────────
+
+test "shouldStashSymbol: stashes a differing non-empty symbol" {
+    try testing.expect(shouldStashSymbol("AAPL", "MSFT"));
+}
+
+test "shouldStashSymbol: skips empty outgoing symbol" {
+    try testing.expect(!shouldStashSymbol("", "MSFT"));
+}
+
+test "shouldStashSymbol: skips when unchanged (case-insensitive)" {
+    try testing.expect(!shouldStashSymbol("AAPL", "aapl"));
+}
+
+test "computeSymbolToggle: null when there is no previous symbol" {
+    var cur = [_]u8{0} ** 16;
+    var last = [_]u8{0} ** 16;
+    try testing.expect(computeSymbolToggle("AAPL", "", &cur, &last) == null);
+}
+
+test "computeSymbolToggle: swaps non-aliased inputs" {
+    var cur = [_]u8{0} ** 16;
+    var last = [_]u8{0} ** 16;
+    const r = computeSymbolToggle("AAPL", "MSFT", &cur, &last).?;
+    try testing.expectEqualStrings("MSFT", r.current);
+    try testing.expectEqualStrings("AAPL", r.last);
+}
+
+test "computeSymbolToggle: aliasing-safe when slices point into the buffers" {
+    var cur = [_]u8{0} ** 16;
+    var last = [_]u8{0} ** 16;
+    @memcpy(cur[0..4], "AAPL");
+    @memcpy(last[0..4], "MSFT");
+    const r = computeSymbolToggle(cur[0..4], last[0..4], &cur, &last).?;
+    try testing.expectEqualStrings("MSFT", r.current);
+    try testing.expectEqualStrings("AAPL", r.last);
+}
+
+test "computeSymbolToggle: double toggle returns to the original" {
+    var cur = [_]u8{0} ** 16;
+    var last = [_]u8{0} ** 16;
+    @memcpy(cur[0..4], "AAPL");
+    @memcpy(last[0..4], "MSFT");
+
+    var r = computeSymbolToggle(cur[0..4], last[0..4], &cur, &last).?;
+    try testing.expectEqualStrings("MSFT", r.current);
+    try testing.expectEqualStrings("AAPL", r.last);
+
+    r = computeSymbolToggle(r.current, r.last, &cur, &last).?;
+    try testing.expectEqualStrings("AAPL", r.current);
+    try testing.expectEqualStrings("MSFT", r.last);
+}
+
+test "computeSymbolToggle: clamps inputs longer than the buffer" {
+    var cur = [_]u8{0} ** 16;
+    var last = [_]u8{0} ** 16;
+    const r = computeSymbolToggle("X", "ABCDEFGHIJKLMNOPQRSTUVWXYZ", &cur, &last).?;
+    try testing.expectEqual(@as(usize, 16), r.current.len);
+    try testing.expectEqualStrings("ABCDEFGHIJKLMNOP", r.current);
+    try testing.expectEqualStrings("X", r.last);
+}
+
 // ── interactive parseArgs ─────────────────────────────────────
 
 test "parseArgs: no args yields defaults" {

src/tui/keybinds.zig

@@ -25,6 +25,7 @@ pub const Action = enum {
     select_next,
     select_prev,
     symbol_input,
+    toggle_last_symbol,
     help,
     reload_portfolio,
 };
@@ -143,6 +144,7 @@ pub const global_default_bindings = [_]Binding{
     .{ .action = .select_prev, .key = .{ .codepoint = 'k' } },
     .{ .action = .select_prev, .key = .{ .codepoint = vaxis.Key.up } },
     .{ .action = .symbol_input, .key = .{ .codepoint = '/' } },
+    .{ .action = .toggle_last_symbol, .key = .{ .codepoint = '\'' } },
     .{ .action = .help, .key = .{ .codepoint = '?' } },
     .{ .action = .reload_portfolio, .key = .{ .codepoint = 'R' } },
 };
@@ -178,6 +180,7 @@ pub const action_labels = std.enums.EnumArray(Action, []const u8).init(.{
     .select_next = "Select next",
     .select_prev = "Select previous",
     .symbol_input = "Symbol input",
+    .toggle_last_symbol = "Toggle last symbol",
     .help = "Help",
     .reload_portfolio = "Reload portfolio",
 });