chat session context scoping, fix sandboxed pi config mounts, dedupe zai/opencode providers

- Add context/contextId fields to session types, storage, and index
- Filter sessions by context (project, workspace, or default chat)
- Pass context through websocket, REST API, and frontend hooks
- Mount ~/.pi/agent into sandboxed containers for auth + writable sessions
- Remove PI_CODING_AGENT_DIR override so container pi uses ~/.pi/agent
- Deduplicate zai/opencode models (same service, show as opencode)

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

src/servers/api/pi/storage.ts

@@ -251,6 +251,8 @@ export function messagesToJnlEntries(messages: Message[], meta: SessionMeta): Jn
       messageCount: meta.messageCount,
       createdAt: meta.createdAt,
       updatedAt: meta.updatedAt,
+      context: meta.context,
+      contextId: meta.contextId,
     },
   };
   entries.push(infoEntry);
@@ -357,6 +359,8 @@ function indexEntryToMeta(sessionId: string, entry: SessionIndexEntry): SessionM
     messageCount: entry.messageCount,
     cost: entry.cost,
     groupSlug: entry.groupSlug ?? null,
+    context: entry.context,
+    contextId: entry.contextId,
   };
 }
 
@@ -371,6 +375,8 @@ function metaToIndexEntry(meta: SessionMeta, relFile: string): SessionIndexEntry
     messageCount: meta.messageCount,
     cost: meta.cost,
     groupSlug: meta.groupSlug ?? null,
+    context: meta.context,
+    contextId: meta.contextId,
   };
 }
 
@@ -495,14 +501,28 @@ export async function deleteSession(
   await saveIndex(baseCwd, index);
 }
 
-export async function listUserSessions(baseCwd: string): Promise<SessionMeta[]> {
+type SessionFilter = {
+  context?: string;
+  contextId?: string;
+};
+
+export async function listUserSessions(baseCwd: string, filter?: SessionFilter): Promise<SessionMeta[]> {
   let index = await loadIndex(baseCwd);
 
   if (Object.keys(index).length === 0) {
     index = await rebuildIndex(baseCwd);
   }
 
-  const sessions: SessionMeta[] = Object.entries(index).map(([id, entry]) => indexEntryToMeta(id, entry));
+  let sessions: SessionMeta[] = Object.entries(index).map(([id, entry]) => indexEntryToMeta(id, entry));
+
+  if (filter?.context) {
+    if (filter.context === 'chat') {
+      // 'chat' matches sessions with no context or context='chat'
+      sessions = sessions.filter((s) => !s.context || s.context === 'chat');
+    } else {
+      sessions = sessions.filter((s) => s.context === filter.context && s.contextId === filter.contextId);
+    }
+  }
 
   sessions.sort((a, b) => b.updatedAt - a.updatedAt);
   return sessions;
@@ -748,6 +768,8 @@ export async function rebuildIndex(baseCwd: string): Promise<SessionIndex> {
         let createdAt = new Date(header.timestamp).getTime();
         let updatedAt = createdAt;
         let groupSlug: string | null = null;
+        let context: string | undefined;
+        let contextId: string | undefined;
 
         // Count message entries and find session_info
         for (const entry of entries) {
@@ -763,6 +785,8 @@ export async function rebuildIndex(baseCwd: string): Promise<SessionIndex> {
               createdAt = info.officer.createdAt;
               updatedAt = info.officer.updatedAt;
               groupSlug = info.officer.groupSlug ?? null;
+              context = info.officer.context;
+              contextId = info.officer.contextId;
             }
           }
         }
@@ -777,6 +801,8 @@ export async function rebuildIndex(baseCwd: string): Promise<SessionIndex> {
           messageCount,
           cost,
           groupSlug,
+          context,
+          contextId,
         };
       } catch {
         continue;