diff --git a/README.md b/README.md
index 056bfed..7c4baa1 100644
--- a/README.md
+++ b/README.md
@@ -195,6 +195,7 @@ SQLite migration rule:
 - Workspace reads are resolved through API requests in `WorkspaceQueryService`; browser interop stays focused on auth forms, session storage, SSE wiring, and small DOM helpers.
 - Interactive authenticated startup begins in `WorkspaceRouteView.razor` after first render because `RpgRollerApiClient` still depends on JS interop-backed `fetch`.
 - Workspace startup diagnostics now log route initialization, route-content render phases, and browser-side workspace mutation snapshots to help isolate the remaining Firefox startup crash documented in `POSTMORTEM.md`.
+- Pre-Blazor diagnostics also watch the static `#rr-interactive-host` container before `_framework/blazor.web.js` connects, so extension-driven DOM mutations can be compared against the first failing interactive batch.
 - Live workspace refresh compares separate roster, per-character sheet, and log versions so unrelated changes do not trigger full reloads.
 - Campaign log data is loaded in bounded slices: campaign summaries, one selected roster, one selected character sheet, and a 25-row incremental log window from `/api/campaigns/{campaignId}/log/page`.
 - Log rows return compact summary data first and lazy-load full detail from `/api/rolls/{rollId}` when expanded.
diff --git a/RpgRoller/Components/App.razor b/RpgRoller/Components/App.razor
index 73e211d..9c1bffa 100644
--- a/RpgRoller/Components/App.razor
+++ b/RpgRoller/Components/App.razor
@@ -25,11 +25,16 @@
 }
 else
 {
-    <Routes @rendermode="@(new InteractiveServerRenderMode(prerender: false))"/>
+    <div id="rr-interactive-host" data-request-path="@RequestPath">
+        <Routes @rendermode="@(new InteractiveServerRenderMode(prerender: false))"/>
+    </div>
 }
 <script src="js/rpgroller-api.js"></script>
 @if (UseInteractiveApp)
 {
+    <script>
+        window.rpgRollerApi.bootstrapPreBlazorDiagnostics("@RequestPath");
+    </script>
     <script src="_framework/blazor.web.js"></script>
 }
 </body>
@@ -55,6 +60,8 @@ else
 
     private bool AuthStatusIsError => string.Equals(ReadAuthQueryValue("kind"), "error", StringComparison.OrdinalIgnoreCase);
 
+    private string RequestPath => HttpContext?.Request.Path.Value ?? "/";
+
     private string BaseHref
     {
         get
diff --git a/RpgRoller/wwwroot/js/rpgroller-api.js b/RpgRoller/wwwroot/js/rpgroller-api.js
index 478c1ad..f465970 100644
--- a/RpgRoller/wwwroot/js/rpgroller-api.js
+++ b/RpgRoller/wwwroot/js/rpgroller-api.js
@@ -13,6 +13,7 @@ window.rpgRollerApi = (() => {
         observer: null,
         route: null,
         globalHandlersInstalled: false,
+        domOperationDiagnosticsInstalled: false,
         mutationBatchCount: 0
     };
 
@@ -24,6 +25,14 @@ window.rpgRollerApi = (() => {
         console.warn(debugPrefix, new Date().toISOString(), ...args);
     }
 
+    function summarizeChildren(element) {
+        if (!element || !element.childNodes) {
+            return [];
+        }
+
+        return Array.from(element.childNodes).slice(0, 20).map(summarizeNode);
+    }
+
     function summarizeNode(node) {
         if (!node) {
             return "<null>";
@@ -117,6 +126,53 @@ window.rpgRollerApi = (() => {
         });
     }
 
+    function installDomOperationDiagnostics() {
+        if (workspaceDiagnostics.domOperationDiagnosticsInstalled) {
+            return;
+        }
+
+        workspaceDiagnostics.domOperationDiagnosticsInstalled = true;
+        const originalInsertBefore = Node.prototype.insertBefore;
+        const originalAppendChild = Node.prototype.appendChild;
+        const originalRemoveChild = Node.prototype.removeChild;
+        const originalReplaceChild = Node.prototype.replaceChild;
+
+        Node.prototype.insertBefore = function (newNode, referenceNode) {
+            debug("dom insertBefore", {
+                parent: summarizeNode(this),
+                newNode: summarizeNode(newNode),
+                referenceNode: summarizeNode(referenceNode),
+                referenceParent: referenceNode ? summarizeNode(referenceNode.parentNode) : null
+            });
+            return originalInsertBefore.call(this, newNode, referenceNode);
+        };
+
+        Node.prototype.appendChild = function (child) {
+            debug("dom appendChild", {
+                parent: summarizeNode(this),
+                child: summarizeNode(child)
+            });
+            return originalAppendChild.call(this, child);
+        };
+
+        Node.prototype.removeChild = function (child) {
+            debug("dom removeChild", {
+                parent: summarizeNode(this),
+                child: summarizeNode(child)
+            });
+            return originalRemoveChild.call(this, child);
+        };
+
+        Node.prototype.replaceChild = function (newChild, oldChild) {
+            debug("dom replaceChild", {
+                parent: summarizeNode(this),
+                newChild: summarizeNode(newChild),
+                oldChild: summarizeNode(oldChild)
+            });
+            return originalReplaceChild.call(this, newChild, oldChild);
+        };
+    }
+
     function summarizeMutation(mutation) {
         return {
             type: mutation.type,
@@ -181,6 +237,79 @@ window.rpgRollerApi = (() => {
         logWorkspaceSnapshot(`phase:${label}`);
     }
 
+    function bootstrapPreBlazorDiagnostics(requestPath) {
+        installGlobalDiagnostics();
+        installDomOperationDiagnostics();
+
+        const host = document.getElementById("rr-interactive-host");
+        workspaceDiagnostics.route = requestPath;
+        debug("bootstrapPreBlazorDiagnostics", {
+            requestPath,
+            readyState: document.readyState,
+            bodyChildren: summarizeChildren(document.body),
+            host: summarizeNode(host),
+            hostChildren: summarizeChildren(host)
+        });
+
+        if (!host) {
+            warn("bootstrapPreBlazorDiagnostics missing host", { requestPath });
+            return;
+        }
+
+        const preconnectObserver = new MutationObserver((mutations) => {
+            debug("preblazor host mutations", {
+                requestPath,
+                mutations: mutations.slice(0, 20).map(summarizeMutation),
+                bodyChildren: summarizeChildren(document.body),
+                hostChildren: summarizeChildren(host)
+            });
+        });
+
+        preconnectObserver.observe(host, {
+            subtree: true,
+            childList: true,
+            attributes: true,
+            characterData: false
+        });
+
+        const bodyObserver = new MutationObserver((mutations) => {
+            debug("preblazor body mutations", {
+                requestPath,
+                mutations: mutations.slice(0, 20).map(summarizeMutation),
+                bodyChildren: summarizeChildren(document.body),
+                hostChildren: summarizeChildren(host)
+            });
+        });
+
+        bodyObserver.observe(document.body, {
+            subtree: false,
+            childList: true,
+            attributes: false
+        });
+
+        queueMicrotask(() => {
+            debug("preblazor microtask snapshot", {
+                requestPath,
+                bodyChildren: summarizeChildren(document.body),
+                hostChildren: summarizeChildren(host)
+            });
+        });
+        requestAnimationFrame(() => {
+            debug("preblazor raf snapshot", {
+                requestPath,
+                bodyChildren: summarizeChildren(document.body),
+                hostChildren: summarizeChildren(host)
+            });
+        });
+        setTimeout(() => {
+            debug("preblazor timeout50 snapshot", {
+                requestPath,
+                bodyChildren: summarizeChildren(document.body),
+                hostChildren: summarizeChildren(host)
+            });
+        }, 50);
+    }
+
     function toAppUrl(url) {
         if (!url || typeof url !== "string") {
             return url;
@@ -588,6 +717,7 @@ window.rpgRollerApi = (() => {
         scrollElementToBottom,
         clearInputValue,
         installWorkspaceDiagnostics,
-        markWorkspacePhase
+        markWorkspacePhase,
+        bootstrapPreBlazorDiagnostics
     };
 })();
diff --git a/TASKS.md b/TASKS.md
index 8bf8da2..400f869 100644
--- a/TASKS.md
+++ b/TASKS.md
@@ -24,6 +24,7 @@ The change is complete when a human can run the app, open `/`, observe the corre
 - [x] (2026-05-04 21:58Z) Removed shell-level `OnAfterRenderAsync` bootstrapping, moved the JS-dependent authenticated startup into a route-owned `WorkspaceRouteView`, removed shell-owned staged control renders, restored the missing development database fixture, and updated README to describe the completed route-first architecture.
 - [x] (2026-05-04) Updated host tests, Selenium smoke tests, and docs so the real-route model is the documented and verified Milestone 2 behavior.
 - [x] (2026-05-04) Added expanded workspace startup diagnostics across Blazor lifecycle logging, route-content render logging, and browser-side DOM mutation snapshots to narrow the remaining Firefox batch-2 crash.
+- [x] (2026-05-04) Extended the diagnostics to page-load time by wrapping the interactive host in a stable container and logging pre-Blazor body and host mutations before the first interactive batch applies.
 
 ## Surprises & Discoveries