diff --git a/clippy.toml b/clippy.toml
index 4b6c79f..8b8bc5a 100644
--- a/clippy.toml
+++ b/clippy.toml
@@ -2,3 +2,11 @@ allow-unwrap-in-tests = true
 allow-expect-in-tests = true
 allow-panic-in-tests = true
 allow-indexing-slicing-in-tests = true
+
+# The web app (wasm32-unknown-unknown) has no clock: these trap (`RuntimeError: unreachable`)
+# instead of returning. Read the clock only off wasm (`cfg(not(target_arch = "wasm32"))` or
+# `cfg!`) and allow the lint at that call.
+disallowed-methods = [
+    { path = "std::time::Instant::now", reason = "traps on wasm; read the clock only off wasm" },
+    { path = "std::time::SystemTime::now", reason = "traps on wasm; read the clock only off wasm" },
+]
diff --git a/crates/calc/src/recalc.rs b/crates/calc/src/recalc.rs
index 13b47c4..a15bec9 100644
--- a/crates/calc/src/recalc.rs
+++ b/crates/calc/src/recalc.rs
@@ -553,6 +553,7 @@ impl Calc {
 }
 
 /// Local date-time as a serial (1900 system). Wasm without a clock returns a fixed date.
+#[allow(clippy::disallowed_methods)] // the clock is read only off wasm
 pub fn now_serial() -> f64 {
     #[cfg(not(target_arch = "wasm32"))]
     {
@@ -592,6 +593,7 @@ pub fn evaluate_expr(wb: &Workbook, sheet: usize, at: CellRef, expr: &Expr) -> V
     ev.value(expr)
 }
 
+#[allow(clippy::disallowed_methods)] // the clock is read only off wasm
 fn prof_now() -> f64 {
     #[cfg(not(target_arch = "wasm32"))]
     {
diff --git a/crates/core/src/parse.rs b/crates/core/src/parse.rs
index b08cf2a..217c45b 100644
--- a/crates/core/src/parse.rs
+++ b/crates/core/src/parse.rs
@@ -275,6 +275,7 @@ fn valid_ymd(sys: DateSystem, y: i64, m: i64, d: i64) -> Option<f64> {
 
 /// The year used for dates typed without one. Fixed per process from the system clock when
 /// available (wasm without clock falls back to 2026).
+#[allow(clippy::disallowed_methods)] // the clock is read only off wasm
 pub fn current_year() -> i64 {
     #[cfg(not(target_arch = "wasm32"))]
     {
diff --git a/crates/engine/examples/perf.rs b/crates/engine/examples/perf.rs
index 2a533a2..61ecf56 100644
--- a/crates/engine/examples/perf.rs
+++ b/crates/engine/examples/perf.rs
@@ -1,6 +1,8 @@
 //! Performance scenarios on large workbooks (release build):
 //! `cargo run --release -p gridcraft-engine --example perf -- [rows]`
 
+#![allow(clippy::disallowed_methods)] // a native-only benchmark: wasm never runs it
+
 use std::time::Instant;
 
 use gridcraft_engine::Session;
diff --git a/crates/engine/src/cmd/mod.rs b/crates/engine/src/cmd/mod.rs
index 397a05c..530bc3a 100644
--- a/crates/engine/src/cmd/mod.rs
+++ b/crates/engine/src/cmd/mod.rs
@@ -217,8 +217,10 @@ pub(crate) fn edit<R>(s: &mut Session, f: impl FnOnce(&mut Ctx) -> Result<R>) ->
 }
 
 pub(crate) fn commit<R>(d: &mut DocState, f: impl FnOnce(&mut Ctx) -> Result<R>) -> Result<R> {
-    let prof = std::env::var_os("GRIDCRAFT_PROFILE").is_some();
-    let t0 = std::time::Instant::now();
+    // `GRIDCRAFT_PROFILE` timing. Read the clock only when profiling, and never on wasm: there
+    // `Instant::now` traps (`RuntimeError: unreachable`), which broke every edit in the web app.
+    #[allow(clippy::disallowed_methods)]
+    let t0 = if cfg!(target_arch = "wasm32") { None } else { std::env::var_os("GRIDCRAFT_PROFILE").map(|_| std::time::Instant::now()) };
     let mut sel = d.selection.clone();
     let mut ctx = Ctx { wb: (*d.wb).clone(), changed: Vec::new(), structural: false, sel: &mut sel, fit_rows: Vec::new() };
     let r = f(&mut ctx)?;
@@ -226,7 +228,7 @@ pub(crate) fn commit<R>(d: &mut DocState, f: impl FnOnce(&mut Ctx) -> Result<R>)
     if changed.len() <= 200_000 {
         fit_rows.extend(changed.iter().map(|(s, c)| (*s, c.row)));
     }
-    if prof {
+    if let Some(t0) = t0 {
         eprintln!("commit: edit {:?}, {} changed", t0.elapsed(), changed.len());
     }
     if structural {
@@ -234,7 +236,7 @@ pub(crate) fn commit<R>(d: &mut DocState, f: impl FnOnce(&mut Ctx) -> Result<R>)
     } else if !changed.is_empty() {
         d.calc.cells_changed(&mut wb, &changed);
     }
-    if prof {
+    if let Some(t0) = t0 {
         eprintln!("commit: + recalc {:?}", t0.elapsed());
     }
     fit_rows.sort_unstable();
@@ -242,7 +244,7 @@ pub(crate) fn commit<R>(d: &mut DocState, f: impl FnOnce(&mut Ctx) -> Result<R>)
     for (si, row) in fit_rows {
         auto_row_height(&mut wb, si, row);
     }
-    if prof {
+    if let Some(t0) = t0 {
         eprintln!("commit: + rows {:?}", t0.elapsed());
     }
     d.wb = std::sync::Arc::new(wb);
diff --git a/crates/ui-egui/src/lib.rs b/crates/ui-egui/src/lib.rs
index 8eb1eca..530097b 100644
--- a/crates/ui-egui/src/lib.rs
+++ b/crates/ui-egui/src/lib.rs
@@ -486,6 +486,7 @@ pub fn clean_error(e: &str) -> String {
     e.to_string()
 }
 
+#[allow(clippy::disallowed_methods)] // the clock is read only off wasm
 pub fn now_ms() -> f64 {
     #[cfg(not(target_arch = "wasm32"))]
     {