add axis labels to return backtest

src/charts/forecast_chart.zig

@@ -97,9 +97,12 @@ pub fn renderConvergenceChart(
     };
 }
 
-/// Thin RGB wrapper over `renderBacktestToSurface` for the TUI's
+/// RGB wrapper over `renderBacktestToSurface` for the inline kitty
-/// kitty path: renders without axis labels, extracts RGB, frees the
+/// path (CLI + TUI). Renders WITH axis labels baked in: unlike the
-/// surface.
+/// projection chart - whose callers stamp their own labels into the
+/// cell grid - nothing draws the forecast chart's labels separately,
+/// so the percent y-ticks + date x-endpoints go into the surface here
+/// (matching the PNG export) to show the divergence magnitude.
 pub fn renderBacktestChart(
     io: std.Io,
     alloc: std.mem.Allocator,
@@ -108,7 +111,7 @@ pub fn renderBacktestChart(
     height_px: u32,
     th: theme.Theme,
 ) !ChartResult {
-    var rendered = try renderBacktestToSurface(io, alloc, anchors, width_px, height_px, th, false);
+    var rendered = try renderBacktestToSurface(io, alloc, anchors, width_px, height_px, th, true);
     defer rendered.deinit(alloc);
     return .{
         .rgb_data = try rendered.extractRgb(alloc),

src/charts/text.zig

@@ -11,7 +11,7 @@
 //!   2. It keeps a ~hundreds-of-KB TTF (and its license) out of the repo.
 //!
 //! The glyph set is intentionally minimal - just what axis labels and
-//! chart legends need: digits, `$`, `.`, `,`, `-`, the `T`/`B`/`M`
+//! chart legends need: digits, `$`, `.`, `,`, `-`, `%`, the `T`/`B`/`M`
 //! magnitude suffixes emitted by `format.fmtLargeNum`, and the
 //! lowercase letters `t`/`h`/`e`/`n`/`o`/`w` for the comparison
 //! chart's "then"/"now" legend. Space and unknown chars render blank.
@@ -57,6 +57,7 @@ const glyph_dollar: Glyph = .{ 0x04, 0x0E, 0x14, 0x0E, 0x05, 0x0E, 0x04 };
 const glyph_period: Glyph = .{ 0x00, 0x00, 0x00, 0x00, 0x00, 0x06, 0x06 };
 const glyph_comma: Glyph = .{ 0x00, 0x00, 0x00, 0x00, 0x06, 0x06, 0x08 };
 const glyph_minus: Glyph = .{ 0x00, 0x00, 0x00, 0x0E, 0x00, 0x00, 0x00 };
+const glyph_percent: Glyph = .{ 0x19, 0x1A, 0x02, 0x04, 0x08, 0x13, 0x03 };
 const glyph_T: Glyph = .{ 0x1F, 0x04, 0x04, 0x04, 0x04, 0x04, 0x04 };
 const glyph_B: Glyph = .{ 0x1E, 0x11, 0x11, 0x1E, 0x11, 0x11, 0x1E };
 const glyph_M: Glyph = .{ 0x11, 0x1B, 0x15, 0x15, 0x11, 0x11, 0x11 };
@@ -80,6 +81,7 @@ fn glyphFor(ch: u8) Glyph {
         '.' => glyph_period,
         ',' => glyph_comma,
         '-' => glyph_minus,
+        '%' => glyph_percent,
         'T' => glyph_T,
         'B' => glyph_B,
         'M' => glyph_M,
@@ -237,3 +239,12 @@ test "drawText renders the lowercase legend letters (then/now)" {
     drawText(&sfc, 1, 1, 1, white, "thenow");
     try testing.expect(draw.countColor(&sfc, white) > 30);
 }
+
+test "drawText renders the percent glyph (for return-rate axis labels)" {
+    const alloc = testing.allocator;
+    var sfc = try Surface.init(.image_surface_rgb, alloc, 16, 16);
+    defer sfc.deinit(alloc);
+    const white = [3]u8{ 0xFF, 0xFF, 0xFF };
+    drawText(&sfc, 1, 1, 1, white, "%");
+    try testing.expect(draw.countColor(&sfc, white) > 0);
+}