Show an event's entrypoint and request headers in the event log and on its page (closes #389)

The receiver stored each event's request headers and entrypoint, but no page showed them, so with several entrypoints the operator could not tell which sender sent an event. An expanded event in the event log, and the event's own page, now show the entrypoint by its description ("Entrypoint" without one, "deleted entrypoint" once deleted), never its URL, and the headers as one escaped block, sorted, whitespace kept. A resubmitted copy says the request it copies arrived there. The event log reads at most 32 KiB of headers per event, the body's limit, and links to the event's page beyond it. Both pages share one template, `event_request.html`.

Model: opus-5-5

templates/event_detail.html

@@ -50,6 +50,15 @@
         </dl>
     </div>
 
+    <div class="card mt-6">
+        <div class="p-4 border-b border-gray-200">
+            <h2 class="text-lg font-medium text-gray-900">Request</h2>
+        </div>
+        <div class="p-4">
+            {{template "event_request" .}}
+        </div>
+    </div>
+
     <div class="card mt-6">
         <div class="p-4 border-b border-gray-200">
             <h2 class="text-lg font-medium text-gray-900">Body</h2>

templates/event_request.html

@@ -0,0 +1,22 @@
+{{define "event_request"}}
+<!-- The entrypoint an event arrived at and its request headers, as
+     handlers.EventLogView carries them: the same in the event log and
+     the event's own page. The entrypoint's URL is never shown. A
+     resubmitted copy, even a copy of a copy, did not arrive at an
+     entrypoint; the request it copies did. -->
+<div class="space-y-2 text-xs">
+    {{if .ResubmittedFrom}}
+    <p class="text-gray-500">The request it copies arrived at <span class="text-gray-900">{{.Entrypoint}}</span></p>
+    {{else}}
+    <p class="text-gray-500">Arrived at <span class="text-gray-900">{{.Entrypoint}}</span></p>
+    {{end}}
+    {{if .HeadersCut}}
+    <p class="text-gray-500">The request headers are larger than the event log shows. <a href="{{.Body.EventURL}}" class="btn-small">Show the request headers</a></p>
+    {{else if .Headers}}
+    <p class="text-gray-500">Request headers</p>
+    <pre class="rounded-md border border-gray-200 bg-white p-2 text-xs text-gray-700 overflow-x-auto whitespace-pre-wrap break-all">{{.Headers}}</pre>
+    {{else}}
+    <p class="text-gray-500">No request headers.</p>
+    {{end}}
+</div>
+{{end}}

templates/source_logs.html

@@ -55,6 +55,9 @@
                             <button type="submit" class="btn-small" title="Submit this event again as a new event, to every currently active target">Resubmit</button>
                         </form>
                     </div>
+                    <div class="mb-3">
+                        {{template "event_request" .}}
+                    </div>
                     {{template "event_body" .Body}}
 
                     {{if .Deliveries}}