chat: click-to-resume /chat sessions via Claude --resume

Clicking a session in the list loads its transcript (GET /chat/sessions/:id,
parsed from Claude's JSONL into display messages) and continues the actual Claude
session: a resumeSessionId is threaded chat handler -> send-claude-code -> sidecar
-> claude-manager, which passes --resume <uuid> (in-memory session mapping still
takes precedence for live turns). Parser verified against real transcripts.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

src/servers/sidecar/claude/claude-manager.ts

@@ -170,8 +170,12 @@ export async function spawnClaudeStreaming(
   const subModel = params.model?.split('/')[1];
   if (subModel) claudeArgs.push('--model', subModel);
 
-  if (existingSession) {
-    claudeArgs.push('--resume', existingSession);
+  // Resume: an in-memory mapping (subsequent turns of a live chat) takes precedence; otherwise a
+  // caller-supplied session uuid (reopening a session from the /chat list) resumes Claude's transcript.
+  const resumeId = existingSession ?? params.resumeSessionId;
+  if (resumeId) {
+    claudeArgs.push('--resume', resumeId);
+    if (!existingSession) setClaudeSession(sessionKey, resumeId);
   }
 
   const spawnCmd = isSuperAdmin ? claudeArgs : [...buildSandboxArgs(email), ...claudeArgs];

src/servers/sidecar/protocol.ts

@@ -73,6 +73,7 @@ export type ClaudeSpawnStreamingParams = {
   cwd?: string;
   model?: string;
   role?: string;
+  resumeSessionId?: string; // resume this Claude session uuid (from the /chat session list)
 };
 
 export type ClaudeCodeResult = {