tty: coalesce queued input events into one frame; tracy zones behind -Dtracy

The tty shell rendered (core.render + full vaxis repaint + tree-sitter
re-highlight of the visible window) after EVERY event, so a wheel flick over a
highlighted file was 150 re-parses and 150 terminal repaints; the gui shell
drains the SDL queue before drawing and never had the issue. Now the tty loop
applies every queued input event, then renders once (batch cap 64; pty output
keeps a frame per chunk so progress paints and transient-state waits behave
exactly as before). Measured with tracy on a 2400-line .zig scroll script:
150 highlightFileRange calls at 1.85ms mean -> 4; render pipeline total
730ms -> 64ms; 364 frames -> 39. Snap suite 18/18.

Tracy: -Dtracy=<path-to-tracy-checkout> compiles TracyClient.cpp into the
binary and turns src/tracy.zig zones live (default off, all no-ops). Sampling,
callstacks, system tracing and the crash handler are disabled: tracy's symbol
worker SIGSEGVs on this binary's debug info and its crash handler then parks
every thread before the first frame. Capture: tracy-capture -o t.tracy; export:
tracy-csvexport t.tracy.

1 files changed, 25 insertions, 0 deletions

diff --git a/build.zig b/build.zig
index 22dd7158..41f4c0ec 100644
--- a/build.zig
+++ b/build.zig
@@ -16,6 +16,7 @@ pub fn build(b: *std.Build) void {
     const optimize = if (is_emscripten) .ReleaseSmall else requested_optimize;
     const default_grammars: TreeSitterGrammars = if (is_emscripten) .minimal else .full;
     const tree_sitter_grammars = b.option(TreeSitterGrammars, "tree-sitter", "tree-sitter grammar set: disabled, minimal, full") orelse default_grammars;
+    const tracy = b.option([]const u8, "tracy", "enable Tracy profiling; supply the path to a Tracy source checkout");
 
     // the browser shell: zig object + emcc link + html, installed to zig-out/web
     const web_step = b.step("web", "build the browser shell into zig-out/web (-Dplatform=web -Dtarget=wasm32-emscripten -Ddump=<dump.zon>)");
@@ -64,8 +65,32 @@ pub fn build(b: *std.Build) void {
     opts.addOption(bool, "syntax_highlighting", tree_sitter_grammars != .disabled);
     opts.addOption(bool, "syntax_minimal_grammars", tree_sitter_grammars != .disabled);
     opts.addOption(bool, "syntax_full_grammars", tree_sitter_grammars == .full);
+    opts.addOption(bool, "enable_tracy", tracy != null);
     root_mod.addOptions("pardes_config", opts);
 
+    // Tracy zones (src/tracy.zig): compile the client into the binary only when
+    // -Dtracy=<path> names a Tracy checkout; otherwise every zone is a no-op.
+    // Sampling/callstacks/system tracing stay off: tracy's symbol worker
+    // SIGSEGVs on this binary's debug info, and its crash handler then parks
+    // every thread — the app wedges before the first frame. Zones don't need
+    // any of it.
+    if (tracy) |tracy_path| {
+        root_mod.addIncludePath(.{ .cwd_relative = tracy_path });
+        root_mod.addCSourceFile(.{
+            .file = .{ .cwd_relative = b.pathJoin(&.{ tracy_path, "public", "TracyClient.cpp" }) },
+            .flags = &.{
+                "-DTRACY_ENABLE=1",
+                "-DTRACY_NO_SAMPLING",
+                "-DTRACY_NO_CALLSTACK",
+                "-DTRACY_NO_SYSTEM_TRACING",
+                "-DTRACY_NO_CRASH_HANDLER",
+                "-DTRACY_NO_CODE_TRANSFER",
+                "-fno-sanitize=undefined",
+            },
+        });
+        root_mod.link_libcpp = true;
+    }
+
     // tree-sitter: the zig bindings + C runtime, one static lib per grammar,
     // and each grammar's highlights.scm slurped at build time into the
     // ts_queries options module (codegen consumed by comptime in syntax.zig).