Tick/toc instrumentation across build + test + mesh phases

run.sh:
  - phase() wrapper logs elapsed seconds per build step.
  - Tracks total build+startup at the end.
  - Output is "==> phase / [Ns] phase" so the slow steps are obvious.

test/run.py:
  - Per-step time.perf_counter() around each scenario step.
  - "slowest steps" summary printed at the end so the worst
    offenders are immediately visible.
  - Total wall-clock time at scenario end.

src/render/mod.rs:
  - browser_now() helper: web_sys::performance().now() on wasm,
    Instant-based on native. Monotonic ms timestamps for tick/toc.
  - Renderer::rebuild_chunk wraps build_chunk_mesh in a t0/t1
    measurement and logs anything over 5ms with vertex/index counts.
    Surfaces sky_visibility cost in the browser console.

web/main.js:
  - Exposes window.voxel_game = wasm after init so the test
    harness can drive scenarios declaratively (set_scene_time,
    teleport, look_at, get_position, etc.).

src/shader.wgsl:
  - Fix duplicate `let to_eye` declaration introduced in Round D
    (specular's normalized to_eye conflicted with fog's raw version).
    Renamed fog's local to_eye_raw. The test harness caught this
    immediately — first WGSL compile error, first scenario run.

Findings from running scenarios/lighting-times-of-day.yaml:
  - 289 chunks × ~100ms avg = ~29s mesh-build on main thread.
  - Page-ready latency dominated by this. window.voxel_game appears
    almost immediately (init resolves before chunks build), but
    the world is invisible until meshes are uploaded.
  - sky_visibility (8 cosine rays × HashMap voxel lookups) is the
    hot path inside build_chunk_mesh.

Next: make chunk-mesh build progressive (one or two chunks per tick
instead of all up-front), so the world becomes visible immediately
and pops in over a few seconds.

run.sh

@@ -20,17 +20,33 @@ for arg in "$@"; do
   esac
 done
 
+# tick/toc — measure each build phase so we know where time goes.
+# Bash arithmetic on $SECONDS gives whole-second resolution; cheap and
+# portable. For sub-second jobs use `time` directly.
+phase() {
+  local label="$1"; shift
+  local start=$SECONDS
+  echo "==> $label"
+  "$@"
+  local elapsed=$((SECONDS - start))
+  echo "    [${elapsed}s] $label"
+}
+
+TOTAL_START=$SECONDS
+
 if [[ $DO_BUILD -eq 1 ]]; then
-  echo "==> running unit tests (proves spawn / collision / mesh invariants)"
-  cargo test --lib
+  phase "running unit tests (proves spawn / collision / mesh invariants)" \
+    cargo test --lib
 
-  echo "==> building wasm client (release)"
-  cargo build --target wasm32-unknown-unknown --release --lib
-  ~/.cargo/bin/wasm-bindgen --target web --out-dir web --no-typescript \
-    target/wasm32-unknown-unknown/release/voxel_game.wasm
+  phase "building wasm client (release)" \
+    cargo build --target wasm32-unknown-unknown --release --lib
 
-  echo "==> building server (release)"
-  (cd server && cargo build --release)
+  phase "wasm-bindgen → web/" \
+    ~/.cargo/bin/wasm-bindgen --target web --out-dir web --no-typescript \
+      target/wasm32-unknown-unknown/release/voxel_game.wasm
+
+  phase "building server (release)" \
+    bash -c "cd server && cargo build --release"
 
   # Catch JS no-undef / parse errors before they hit the browser. eslint
   # is optional: warns if absent so this step never blocks an emergency
@@ -68,6 +84,8 @@ for i in {1..20}; do
   sleep 0.2
 done
 
+echo "==> total build+startup: $((SECONDS - TOTAL_START))s"
+
 if [[ $DO_TUNNEL -eq 0 ]]; then
   echo "==> server running at http://localhost:8080  (no tunnel)"
   wait $SERVER_PID

src/render/mod.rs

@@ -484,7 +484,22 @@ impl Renderer {
         let Some(chunk) = world.chunks.get(&coord) else {
             return;
         };
+        // tick/toc — mesh build (esp. the sky_visibility hemisphere
+        // raycasts) is the suspected hot path on world init. Times
+        // come through the browser console for now; once we have a
+        // real perf overlay they'll go there.
+        let t0 = browser_now();
         let mesh = build_chunk_mesh(world, chunk);
+        let mesh_ms = browser_now() - t0;
+        if mesh_ms > 5.0 {
+            log::info!(
+                "rebuild_chunk {:?}: {:.1}ms ({} verts, {} idx)",
+                coord,
+                mesh_ms,
+                mesh.vertices.len(),
+                mesh.indices.len()
+            );
+        }
         if mesh.indices.is_empty() {
             self.chunk_buffers.remove(&coord);
             return;
@@ -627,6 +642,29 @@ impl Renderer {
     }
 }
 
+/// Cross-platform "now" in milliseconds — uses the browser's
+/// `performance.now()` on wasm, `Instant::now()` on native. Always
+/// monotonic. Pairs with `browser_now()` calls to give tick/toc
+/// elapsed times for instrumenting hot paths (mesh build, etc.).
+fn browser_now() -> f64 {
+    #[cfg(target_arch = "wasm32")]
+    {
+        web_sys::window()
+            .and_then(|w| w.performance())
+            .map(|p| p.now())
+            .unwrap_or(0.0)
+    }
+    #[cfg(not(target_arch = "wasm32"))]
+    {
+        use std::time::Instant;
+        // The "0.0 epoch" is the first call; subsequent diffs are correct.
+        thread_local! {
+            static EPOCH: Instant = Instant::now();
+        }
+        EPOCH.with(|e| (Instant::now() - *e).as_secs_f64() * 1000.0)
+    }
+}
+
 /// Run a single full-screen-triangle render pass: clear target if
 /// `clear` is `Some`, load otherwise; set pipeline; bind groups in
 /// order; draw three vertices. Used for every post-chain step so the

src/shader.wgsl

@@ -386,9 +386,11 @@ fn fs_main(in: VsOut) -> @location(0) vec4<f32> {
         lit = lit + in.color * sun_col * trans;
     }
 
-    let to_eye   = eye_world() - in.world_pos;
-    let dist     = length(to_eye);
-    let view_dir = -to_eye / max(dist, 0.0001);
+    // Reuse `to_eye` from the specular block (normalized eye-to-fragment).
+    // Fog needs the *raw* distance though, so recompute that here.
+    let to_eye_raw = eye_world() - in.world_pos;
+    let dist     = length(to_eye_raw);
+    let view_dir = -to_eye_raw / max(dist, 0.0001);
 
     let color = apply_fog(lit, dist, view_dir);
     return vec4<f32>(color, 1.0);

test/run.py

@@ -166,25 +166,39 @@ def main() -> int:
 
     p, browser, page = attach_page()
     failures = 0
+    total_start = time.perf_counter()
+    timings: list[tuple[str, float]] = []
     try:
         for i, step in enumerate(scenario.get("steps", [])):
+            step_summary = next(iter(step.keys())) if step else f"step{i}"
             print(f"step {i}:")
+            step_start = time.perf_counter()
             try:
                 ok = run_step(page, step, name, args.halt_on_fail)
+                step_ms = (time.perf_counter() - step_start) * 1000
+                timings.append((step_summary, step_ms))
+                print(f"  [{step_ms:6.1f}ms]")
                 if not ok:
                     failures += 1
                     if args.halt_on_fail:
                         break
             except Exception as e:  # noqa: BLE001
+                step_ms = (time.perf_counter() - step_start) * 1000
+                timings.append((step_summary, step_ms))
                 print(f"  [!] step error: {e}", file=sys.stderr)
                 failures += 1
                 if args.halt_on_fail:
                     break
+        total_ms = (time.perf_counter() - total_start) * 1000
         print()
-        if failures == 0:
-            print(f"# {name}: OK ({len(scenario.get('steps', []))} steps)")
-        else:
-            print(f"# {name}: FAILED ({failures} step(s))", file=sys.stderr)
+        print(f"# {name}: {len(scenario.get('steps', []))} steps in {total_ms / 1000:.2f}s "
+              f"({failures} failure{'s' if failures != 1 else ''})")
+        # Per-step breakdown so the slowest steps are obvious.
+        if timings:
+            timings_sorted = sorted(enumerate(timings), key=lambda x: -x[1][1])
+            print("# slowest steps:")
+            for i, (kind, ms) in timings_sorted[:5]:
+                print(f"#   step {i:>2}  {kind:>12}  {ms:>7.1f}ms")
     finally:
         browser.close()
         p.stop()

web/main.js

@@ -22,6 +22,12 @@ function applyInputMode(mode) {
 }
 
 init().then(() => {
+  // Expose all wasm-bindgen exports on window.voxel_game so the
+  // Playwright test harness (test/run.py + scenarios) can drive the
+  // game declaratively from JS: set_scene_time, teleport, look_at,
+  // get_position, etc. Dev-affordance only; production users never
+  // touch this surface.
+  window.voxel_game = wasm;
   wasm.reset_input();
   setupTouch();
   setupGamepad();