chat: put the session list cwd in the url, not a panel channel

Which project group you are looking at is addressable state, so /chat?cwd=<dir> has to be a
link anyone can hand out — it survives a refresh and an agent run can point straight at its
own runs directory. Was usePanelChannel('chat:active-cwd'), which per the navigation audit is
for signals and refresh buses only. Row links and New Chat now carry the query string along.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

src/apps/officer-web/Screens/Dashboard/ChatHistory/index.tsx

@@ -1,5 +1,5 @@
 import { useEffect, useMemo, useRef } from 'react';
-import { useParams, useNavigate } from 'react-router';
+import { useParams, useNavigate, useSearchParams } from 'react-router';
 import type { LayoutNode, SelectedSession } from 'officerdev';
 import { WorkspaceView } from 'officerdev';
 import { useIsMobile } from 'hooks/useIsMobile';
@@ -38,7 +38,7 @@ type SessionListPageProps = {
 export const SessionListPage = ({ isNew }: SessionListPageProps) => {
   const { sessionId } = useParams<{ sessionId: string }>();
   const [selected, setSelected] = usePanelChannel<SelectedSession>('chat:selected-session', null);
-  const [, setActiveCwd] = usePanelChannel<string | null>('chat:active-cwd', null);
+  const [, setSearchParams] = useSearchParams();
   const client = useClient();
   const selectedRef = useRef(selected);
   selectedRef.current = selected;
@@ -78,7 +78,16 @@ export const SessionListPage = ({ isNew }: SessionListPageProps) => {
       try {
         const detail = await client.get<ClaudeSessionDetail>(`/chat/sessions/${sessionId}?limit=${CHAT_TAIL}`);
         if (cancelled) return;
-        setActiveCwd(detail.cwd || null);
+        // replace: resolving a deep link is a canonicalisation, not a navigation the back button owes you.
+        setSearchParams(
+          (prev) => {
+            const next = new URLSearchParams(prev);
+            if (detail.cwd) next.set('cwd', detail.cwd);
+            else next.delete('cwd');
+            return next;
+          },
+          { replace: true },
+        );
         setSelected({
           id: sessionId,
           model: detail.model,