From ac1799db38661e07a855653f86feb3e66081102e Mon Sep 17 00:00:00 2001
From: "Dylan M. Taylor" <dylan@dylanmtaylor.com>
Date: Mon, 2 Nov 2026 22:50:58 -0500
Subject: [PATCH] web: ?bench runs on demo photos in an unsaved library, never
 the stored one (#3646)

A navigation link with ?bench opened the first photo of the library in
browser storage and committed Exposure edits to it, finishing at 0 instead
of the photo's own value. ?bench now implies ?store=memory and loads the
generated demo photos, so the benchmark cannot edit stored photos.
---
 apps/lightcraft-web/src/bench.rs |  3 +++
 apps/lightcraft-web/src/lib.rs   |  3 ++-
 apps/lightcraft-web/src/web.rs   | 11 +++++++++--
 docs/web.md                      |  3 ++-
 4 files changed, 16 insertions(+), 4 deletions(-)

diff --git a/apps/lightcraft-web/src/bench.rs b/apps/lightcraft-web/src/bench.rs
index 484c0041f6..4864834c75 100644
--- a/apps/lightcraft-web/src/bench.rs
+++ b/apps/lightcraft-web/src/bench.rs
@@ -2,6 +2,9 @@
 //! control exactly like a slider drag (begin interaction → N `develop.set` → end) and time each
 //! step from the command to the moment the new loupe texture is ready. Results go to the log
 //! (the browser console on the web) as one `lightcraft-bench {…json…}` line.
+//!
+//! The web host runs it only on the generated demo photos in an unsaved library (`?bench` implies `?store=memory`): it
+//! commits edits to the photo it opens, which must never be one in the user's stored library.
 
 use lightcraft_ui_egui::LightcraftApp;
 use lightcraft_ui_egui::render::Slot;
diff --git a/apps/lightcraft-web/src/lib.rs b/apps/lightcraft-web/src/lib.rs
index 5d3c011589..6a6b83b728 100644
--- a/apps/lightcraft-web/src/lib.rs
+++ b/apps/lightcraft-web/src/lib.rs
@@ -11,7 +11,8 @@
 //! - export downloads the file through the browser.
 //!
 //! `?bench` in the URL runs a scripted first-paint / slider-latency measurement and logs it to the
-//! console (see [`bench`]); `?store=idb` forces the IndexedDB backend, `?store=memory` disables
+//! console (see [`bench`]) on the generated demo photos in an unsaved library (it implies `?store=memory`, so it never edits
+//! the library in browser storage); `?store=idb` forces the IndexedDB backend, `?store=memory` disables
 //! persistence and `?workers=0` renders on the main thread.
 #![forbid(unsafe_code)]
 #![deny(clippy::unwrap_used, clippy::expect_used, clippy::panic, clippy::unimplemented, clippy::todo, clippy::unreachable)]
diff --git a/apps/lightcraft-web/src/web.rs b/apps/lightcraft-web/src/web.rs
index bd5215e4d4..da71c592a8 100644
--- a/apps/lightcraft-web/src/web.rs
+++ b/apps/lightcraft-web/src/web.rs
@@ -90,9 +90,12 @@ impl Options {
             })
             .collect();
         let get = |k: &str| params.iter().find(|(n, _)| n == k).map(|(_, v)| v.clone());
+        let bench = get("bench").is_some();
         Options {
-            bench: get("bench").is_some(),
-            store: get("store").filter(|s| s == "idb" || s == "memory").unwrap_or_else(|| "opfs".into()),
+            bench,
+            // the benchmark edits the first photo it finds: a link with `?bench` must never reach
+            // the library in browser storage, so it always runs on the demo photos in an unsaved library
+            store: if bench { "memory".into() } else { get("store").filter(|s| s == "idb" || s == "memory").unwrap_or_else(|| "opfs".into()) },
             workers: get("workers").and_then(|v| v.parse().ok()),
             reset: get("reset").is_some(),
         }
@@ -496,6 +499,10 @@ impl WebApp {
                 });
             }
         }
+        // `?bench` never has storage (see `Options::from_url`): it measures the generated demo photos
+        if opts.bench && backend.is_none() && session.catalog.len() == 0 {
+            lightcraft_engine::demo::load(&mut session);
+        }
         if backend.is_some() {
             notice(
                 "LightCraft in the browser is experimental. Your library is kept in this browser's storage: keep your original photos \
diff --git a/docs/web.md b/docs/web.md
index 76b84cd7c0..d8065dd766 100644
--- a/docs/web.md
+++ b/docs/web.md
@@ -188,7 +188,8 @@ are the same in every version, so serve them with `Cache-Control: no-cache` (not
 
 ## Measuring
 
-Open `http://127.0.0.1:8080/?bench` to run a scripted measurement:
+Open `http://127.0.0.1:8080/?bench` to run a scripted measurement. It always runs on the generated demo photos in an unsaved library
+(`?bench` implies `?store=memory`), so it never edits the library kept in browser storage:
 
 1. Wait for the grid thumbnails.
 2. Open the first photo in Detail.