diff --git a/AGENTS.md b/AGENTS.md
index 80c55db5..b2384311 100644
--- a/AGENTS.md
+++ b/AGENTS.md
@@ -81,7 +81,7 @@ code.
   L6 depends on egui/eframe/rfd/winit. **The UI crate is swappable.**
 - **The UI is thin**: panels read engine state and act through `app.run(id, params)` /
   `app.set_props(ids, props)`. Colours come from `theme::Tokens`.
-- **Time goes through `chrono`** (workspace dependency). Never hand-roll UTC/calendar conversion (days-to-date algorithms, leap-year math); a crate owns only its output format string. The one exception is range extension: past the years chrono can represent, shift the date by whole 400-year Gregorian cycles (146,097 days, after which the calendar repeats), let chrono compute the month, day and time, and add the cycles back to the year.
+- **Time goes through `chrono`** (workspace dependency). Never hand-roll UTC/calendar conversion (days-to-date algorithms, leap-year math); a crate owns only its output format string. The one exception is range extension: past the years chrono can represent, shift the date by whole 400-year Gregorian cycles (146,097 days, after which the calendar repeats), let chrono compute the month and day, and add the cycles back to the year (splitting seconds into hours, minutes and seconds is plain arithmetic).
 - **Rust only** (no handwritten JS/TS). **Never break wasm** (`cargo xtask wasm`).
 
 ### Quality gates (before every commit)
diff --git a/CLAUDE.md b/CLAUDE.md
index 80c55db5..b2384311 100644
--- a/CLAUDE.md
+++ b/CLAUDE.md
@@ -81,7 +81,7 @@ code.
   L6 depends on egui/eframe/rfd/winit. **The UI crate is swappable.**
 - **The UI is thin**: panels read engine state and act through `app.run(id, params)` /
   `app.set_props(ids, props)`. Colours come from `theme::Tokens`.
-- **Time goes through `chrono`** (workspace dependency). Never hand-roll UTC/calendar conversion (days-to-date algorithms, leap-year math); a crate owns only its output format string. The one exception is range extension: past the years chrono can represent, shift the date by whole 400-year Gregorian cycles (146,097 days, after which the calendar repeats), let chrono compute the month, day and time, and add the cycles back to the year.
+- **Time goes through `chrono`** (workspace dependency). Never hand-roll UTC/calendar conversion (days-to-date algorithms, leap-year math); a crate owns only its output format string. The one exception is range extension: past the years chrono can represent, shift the date by whole 400-year Gregorian cycles (146,097 days, after which the calendar repeats), let chrono compute the month and day, and add the cycles back to the year (splitting seconds into hours, minutes and seconds is plain arithmetic).
 - **Rust only** (no handwritten JS/TS). **Never break wasm** (`cargo xtask wasm`).
 
 ### Quality gates (before every commit)