fix(server): resolve agent cwd to absolute path at creation time

Relative paths like "." resolve differently depending on where the
server is started, causing agent history files to be stored under
different directories. This fixes the empty state issue when loading
agents created with relative paths.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

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

packages/server/src/server/agent/agent-manager.ts

@@ -1,4 +1,5 @@
 import { randomUUID } from "node:crypto";
+import { resolve } from "node:path";
 
 import type {
   AgentCapabilityFlags,
@@ -773,6 +774,12 @@ export class AgentManager {
     config: AgentSessionConfig
   ): Promise<AgentSessionConfig> {
     const normalized: AgentSessionConfig = { ...config };
+
+    // Always resolve cwd to absolute path for consistent history file lookup
+    if (normalized.cwd) {
+      normalized.cwd = resolve(normalized.cwd);
+    }
+
     const resolvedModel = await resolveAgentModel({
       provider: normalized.provider,
       requestedModel: normalized.model,