diff --git a/www/index.html b/www/index.html
index 2e39476..5df99b2 100644
--- a/www/index.html
+++ b/www/index.html
@@ -7,10 +7,20 @@
     <meta name="viewport" content="user-scalable=no">
     <title>OMORI</title>
     <script>
-        if (window.nw.App.argv.length < 1) {
-            alert("OMORI must be launched directly from Steam.");
-            process.exit(0);
-        }
+        // Only the Steam build needs the launch argument: it carries the asset decryption
+        // key. Non-Steam builds ship plaintext assets and are launched without arguments,
+        // so gating them here would make the game unstartable.
+        (function () {
+            var fs = require('fs');
+            var path = require('path');
+            var base = path.dirname(process.mainModule.filename);
+            var isSteamBuild = fs.existsSync(path.join(base, "data", "System.KEL"));
+
+            if (isSteamBuild && window.nw.App.argv.length < 1) {
+                alert("OMORI must be launched directly from Steam.");
+                process.exit(0);
+            }
+        })();
     </script>
 
     <script src="modloader/lib/fast-json-patch.min.js"></script>
diff --git a/www/modloader/_oneloader_configuration.js b/www/modloader/_oneloader_configuration.js
index 7fd7275..26831a8 100644
--- a/www/modloader/_oneloader_configuration.js
+++ b/www/modloader/_oneloader_configuration.js
@@ -1,18 +1,39 @@
-if (window.nw.App.argv[0] !== "test") {
-    console.log("Loading basic oneloader configuration.");
-    const MAX_MANIFEST_VERSION = 1;
-    const ID_BLACKLIST = ["gomori"];
-    const EXTENSION_RULES = {
-        "png": { "encrypt": "rpgmaker", "target_extension": "rpgmvp", "raw": ["img/system/window.png", "img/system/loading.png"]  },
-        "ogg": { "encrypt": "rpgmaker", "target_extension": "rpgmvo" }
-    };
+/*
+ * Which injection targets and which encryption layer are correct depends on how the copy of
+ * the game was distributed:
+ *
+ *   steam     - assets are AES encrypted and renamed (data/System.KEL, js/plugins/*.OMORI).
+ *   plaintext - any non-Steam build: stock RPG Maker MV layout, nothing encrypted.
+ *   test      - RPG Maker playtest. Also plaintext, but changes more than this file.
+ *
+ * "test" is detected from argv because $modLoader.isInTestMode alters URL handling in the web
+ * VFS too. "steam" is detected from the presence of the encrypted System file rather than from
+ * argv, so a non-Steam copy is not required to be launched with a decryption key it lacks.
+ */
+var $ONELOADER_INSTALL_TYPE = (function () {
+    const fs = require("fs");
+    const path = require("path");
+    const base = path.dirname(process.mainModule.filename);
+
+    if (window.nw.App.argv[0] === "test") return "test";
+    if (fs.existsSync(path.join(base, "data", "System.KEL"))) return "steam";
+    return "plaintext";
+})();
+
+/*
+ * Language folder that text mods are mounted into, read from the game's own
+ * Text_Language_Processor parameters so mods land where the game will look for them.
+ */
+var $ONELOADER_LANGUAGE = (function () {
+    const fs = require("fs");
+    const path = require("path");
+    const base = path.dirname(process.mainModule.filename);
 
-    let LANGUAGE = "en";
+    let language = "en";
     try {
-        const fs = require("fs");
-        const js = fs.readFileSync("www/js/plugins.js", "utf8")
-        eval(js.replace("var $plugins", "window.___tmp_plugins"))
-        LANGUAGE = window.___tmp_plugins.filter(
+        const js = fs.readFileSync(path.join(base, "js", "plugins.js"), "utf8");
+        eval(js.replace("var $plugins", "window.___tmp_plugins"));
+        language = window.___tmp_plugins.filter(
             a => a.name.toLowerCase() === "text_language_processor"
         )[0].parameters["Default Language"];
     } catch (error) {
@@ -21,6 +42,18 @@ if (window.nw.App.argv[0] !== "test") {
     } finally {
         window.___tmp_plugins = undefined;
     }
+    return language;
+})();
+
+if ($ONELOADER_INSTALL_TYPE === "steam") {
+    console.log("Loading basic oneloader configuration.");
+    const MAX_MANIFEST_VERSION = 1;
+    const ID_BLACKLIST = ["gomori"];
+    const IMAGE_EXTENSION = "rpgmvp";
+    const EXTENSION_RULES = {
+        "png": { "encrypt": "rpgmaker", "target_extension": "rpgmvp", "raw": ["img/system/window.png", "img/system/loading.png"]  },
+        "ogg": { "encrypt": "rpgmaker", "target_extension": "rpgmvo" }
+    };
 
     const DATA_RULES = [
         {
@@ -50,7 +83,7 @@ if (window.nw.App.argv[0] !== "test") {
                 "yamld": { target: "HERO", delta: true, delta_method: "yaml", encrypt: true },
                 "hero": { target: "HERO", delta: false, encrypt: false }
             },
-            mountPoint: "languages/" + LANGUAGE
+            mountPoint: "languages/" + $ONELOADER_LANGUAGE
         },
         {
             jsonKeys: [
@@ -79,12 +112,14 @@ if (window.nw.App.argv[0] !== "test") {
     ];
 
     window.$ONELOADER_CONFIG = {
-        MAX_MANIFEST_VERSION, ID_BLACKLIST, EXTENSION_RULES, DATA_RULES
+        MAX_MANIFEST_VERSION, ID_BLACKLIST, EXTENSION_RULES, DATA_RULES, IMAGE_EXTENSION,
+        INSTALL_TYPE: $ONELOADER_INSTALL_TYPE
     };
 } else {
-    console.log("Loading playtest configuration");
+    console.log("Loading plaintext configuration");
     const MAX_MANIFEST_VERSION = 1;
     const ID_BLACKLIST = ["gomori"];
+    const IMAGE_EXTENSION = "png";
     const EXTENSION_RULES = {
         "png": { "encrypt": "rpgmaker", "target_extension": "png" },
         "ogg": { "encrypt": "rpgmaker", "target_extension": "ogg" }
@@ -118,7 +153,7 @@ if (window.nw.App.argv[0] !== "test") {
                 "yamld": { target: "yaml", delta: true, delta_method: "yaml", encrypt: true },
                 "hero": { target: "HERO", delta: false, encrypt: false } // Mods that ship encrypted files WILL fail. Don't do that. Not cool.
             },
-            mountPoint: "languages/en"
+            mountPoint: "languages/" + $ONELOADER_LANGUAGE
         },
         {
             jsonKeys: [
@@ -147,6 +182,7 @@ if (window.nw.App.argv[0] !== "test") {
     ];
 
     window.$ONELOADER_CONFIG = {
-        MAX_MANIFEST_VERSION, ID_BLACKLIST, EXTENSION_RULES, DATA_RULES
+        MAX_MANIFEST_VERSION, ID_BLACKLIST, EXTENSION_RULES, DATA_RULES, IMAGE_EXTENSION,
+        INSTALL_TYPE: $ONELOADER_INSTALL_TYPE
     };
-}
\ No newline at end of file
+}
diff --git a/www/modloader/early_loader.js b/www/modloader/early_loader.js
index a6f0fad..49beae3 100644
--- a/www/modloader/early_loader.js
+++ b/www/modloader/early_loader.js
@@ -77,10 +77,18 @@
     /* Install the argv handler and shadow the true argv object to allow the base game to work normally */ {
         let key = window.nw.App.argv[0];
         $modLoader.realArgv = window.nw.App.argv;
+        /*
+         * A non-Steam copy is launched with no arguments at all, so there is no key to keep.
+         * Shadowing with [undefined] would still report a length of 1, and every caller of
+         * Utils.isOptionValid does `nw.App.argv[0].split('&')` once the length check passes -
+         * which throws before Graphics exists and takes the whole boot down. Hide an empty
+         * argv as an empty array instead.
+         */
+        let shadowedArgv = (key === undefined) ? [] : [key];
         window.nw.App = new Proxy(window.nw.App, {
             get(t, p, r) {
                 if (p === "argv") {
-                    return [key];
+                    return shadowedArgv;
                 } else {
                     return Reflect.get(...arguments);
                 }
diff --git a/www/modloader/encryption.js b/www/modloader/encryption.js
index 28e3a54..5239131 100644
--- a/www/modloader/encryption.js
+++ b/www/modloader/encryption.js
@@ -1,5 +1,8 @@
 const crypto = require('crypto');
-if (window.nw.App.argv[0] !== "test")
+// Only the Steam build is encrypted. Playtest and non-Steam builds keep plaintext assets,
+// so they get the pass-through implementation below instead of an AES layer keyed on a
+// Steam launch argument they were never given.
+if (window.$ONELOADER_CONFIG.INSTALL_TYPE === "steam")
 {
     window._modloader_encryption = new (class Encryption {
         constructor() {
@@ -85,7 +88,7 @@ if (window.nw.App.argv[0] !== "test")
         }
     })();
 } else {
-    console.log("Loading fallback encryption system for test mode");
+    console.log("Loading pass-through encryption system for a plaintext install");
     window._modloader_encryption = new (class BSEncryption {
         decrypt(buffer) { return buffer; }
         encrypt(buffer) { return buffer; }
diff --git a/www/modloader/imagedelta_applier.js b/www/modloader/imagedelta_applier.js
index 15f99ac..974186d 100644
--- a/www/modloader/imagedelta_applier.js
+++ b/www/modloader/imagedelta_applier.js
@@ -31,6 +31,10 @@ async function __modloader_image_delta(knownMods) {
 
     const cache_base = path.join(base, '..', '.oneloader-image-cache');
 
+    // Pictures live under a different extension depending on how the game was distributed
+    // (rpgmvp when encrypted, png otherwise), so deltas have to target whichever is in use.
+    const imageTarget = i => i.replace(/\.png$/g, "." + $ONELOADER_CONFIG.IMAGE_EXTENSION);
+
     if (!native_fs.existsSync(cache_base)) {
         native_fs.mkdirSync(cache_base);
     }
@@ -86,7 +90,7 @@ async function __modloader_image_delta(knownMods) {
 
         if (deltas.length < 1) continue;
 
-        const image_data = _modloader_encryption.decryptAsset(await _vfs_resolve_file(image.replace(/\.png$/g, '.rpgmvp')));
+        const image_data = _modloader_encryption.decryptAsset(await _vfs_resolve_file(imageTarget(image)));
         
         job_id = `${job_id}+${shaDigest(image_data)}`;
         job_id = `${job_id}:${deltas.sort((a, b) => {return a.salt > b.salt?1:-1}).map(a => a.salt).join(":")}`;
@@ -163,8 +167,8 @@ async function __modloader_image_delta(knownMods) {
 
         $oneLoaderGui.inc();
 
-        let oDeep = _ensure_overlay_path($modLoader.overlayFS, image.replace(/\.png$/g, '.rpgmvp').toLowerCase());
-        let bruh = _overlay_fs_split_path(image.replace(/\.png$/g, '.rpgmvp').toLowerCase());
+        let oDeep = _ensure_overlay_path($modLoader.overlayFS, imageTarget(image).toLowerCase());
+        let bruh = _overlay_fs_split_path(imageTarget(image).toLowerCase());
         let lastFile = bruh[bruh.length - 1];
 
         oDeep[lastFile] = {
@@ -173,9 +177,9 @@ async function __modloader_image_delta(knownMods) {
                 type: "filesystem"
             },
             delta: false,
-            injectionPoint: image.replace(/\.png$/g, '.rpgmvp').toLowerCase(),
+            injectionPoint: imageTarget(image).toLowerCase(),
             mode: "rpgmaker",
-            ogName: path.basename(image.replace(/\.png$/g, '.rpgmvp'))
+            ogName: path.basename(imageTarget(image))
         };
     }
 }
\ No newline at end of file
diff --git a/www/modloader/start_game.js b/www/modloader/start_game.js
index a92662d..177c115 100644
--- a/www/modloader/start_game.js
+++ b/www/modloader/start_game.js
@@ -5,6 +5,9 @@ async function _start_game() {
         "js/libs/pixi.js",
         "js/libs/pixi-tilemap.js",
         "js/libs/pixi-picture.js",
+        // Part of the stock RPG Maker MV library set and shipped with the game, but absent
+        // from this list. Graphics._createFPSMeter uses the FPSMeter global it defines.
+        "js/libs/fpsmeter.js",
         "js/libs/lz-string.js",
         "js/libs/iphone-inline-video.browser.js",
         "js/rpg_core.js",
@@ -48,10 +51,35 @@ async function _start_game() {
             await p;
         }
     }
+    let pluginScriptLoads = [];
+
     for (let script of scripts) {
         $oneLoaderGui.inc();
         $oneLoaderGui.setHt("This may take up to 25 seconds", true);
         await rafResolve();
+
+        /*
+         * main.js calls PluginManager.setup, which appends one <script> per plugin. In an
+         * ordinary boot the browser's load event does not fire until those have executed, so
+         * every plugin is in place before SceneManager.run. Invoking window.onload() by hand
+         * throws that guarantee away: SceneManager.initialize then runs against a stock
+         * engine with none of the game's overrides applied. Record each plugin script as it
+         * is queued so the boot can wait for them below.
+         */
+        if (script === "js/main.js" && window.PluginManager && PluginManager.loadScript) {
+            const _oneloader_loadScript = PluginManager.loadScript;
+            PluginManager.loadScript = function (name) {
+                _oneloader_loadScript.call(this, name);
+                const el = document.body.lastChild;
+                if (el && el.tagName === "SCRIPT") {
+                    pluginScriptLoads.push(new Promise(resolve => {
+                        el.addEventListener("load", resolve);
+                        el.addEventListener("error", resolve); // a broken plugin must not stall the boot
+                    }));
+                }
+            };
+        }
+
         let s = document.createElement("script");
         s.src = script;
         document.body.appendChild(s);
@@ -60,8 +88,43 @@ async function _start_game() {
         })
     }
 
+    if (pluginScriptLoads.length > 0) {
+        $oneLoaderGui.setHt("Waiting for " + pluginScriptLoads.length + " plugin scripts");
+        window._logLine("Waiting for " + pluginScriptLoads.length + " plugin scripts to execute");
+        await Promise.race([
+            Promise.all(pluginScriptLoads),
+            new Promise(resolve => setTimeout(resolve, 60000)) // never hang the boot outright
+        ]);
+        window._logLine("Plugin scripts settled");
+    }
+
     await $modLoader.$runScripts("pre_window_onload", {});
 
+    /*
+     * Boot diagnostics.
+     *
+     * When the game throws before Graphics has finished initializing, SceneManager hands the
+     * error to Graphics.printError, which itself throws ("Cannot read property 'getContext'
+     * of undefined" in _clearUpperCanvas) because the canvases do not exist yet. That
+     * secondary TypeError is what propagates out, so the original cause is lost. Record the
+     * real error, plus any script that fails to load, before that happens.
+     */
+    window.addEventListener("error", function (e) {
+        if (e.target && e.target.tagName === "SCRIPT") {
+            window._logLine("[SCRIPT LOAD FAILED] " + (e.target.src || e.target._url || "unknown"));
+        } else if (e.error) {
+            window._logLine("[UNCAUGHT] " + (e.error.stack || e.error));
+        }
+    }, true);
+
+    if (window.SceneManager && SceneManager.catchException) {
+        const _oneloader_catchException = SceneManager.catchException;
+        SceneManager.catchException = function (e) {
+            window._logLine("[REAL BOOT ERROR] " + ((e && e.stack) ? e.stack : e));
+            return _oneloader_catchException.call(this, e);
+        };
+    }
+
     if ($modLoader.isInTestMode) {
         $oneLoaderGui.setHt("Playtest: Giving the game time to load plugins.");
         $oneLoaderGui.setPbMax(5);
@@ -72,7 +135,12 @@ async function _start_game() {
             $oneLoaderGui.setPbCurr(i + 1);
         }
     }
-    window.onload();
+    try {
+        window.onload();
+    } catch (e) {
+        window._logLine("[GAME BOOT THREW] " + ((e && e.stack) ? e.stack : e));
+        throw e;
+    }
 
     $oneLoaderGui.container.style.opacity = 0;
 }
\ No newline at end of file