test: add e2e session/sandbox lifecycle tests

Add session_lifecycle_test.go covering the scenarios from issue #103:

- A1 (TestAgentRuntimeSessionCreationAndReuse): verifies that a first
  invocation without x-agentcube-session-id returns HTTP 200 plus a
  non-empty session ID header, and that a second invocation using that
  ID returns the same session ID (reuse).

- A2 (TestAgentRuntimeMissingRuntime): asserts that calling a
  non-existent AgentRuntime returns HTTP 404 with a clear error body.

- A3 (TestSessionSandboxLifecycleTTL): smoke test for idle-TTL
  semantics; creates a session, confirms it is still alive before TTL,
  then waits past TTL + GC window and asserts the session is gone.
  Skipped automatically under go test -short.

- B1 (TestCodeInterpreterSessionAutoCreation): verifies that the Router
  auto-creates a session when no x-agentcube-session-id is sent, and
  sets the header in the response.

- B2 (TestCodeInterpreterStatefulSession): verifies that state written
  to the shared workspace in one call is visible in the next call of
  the same session.

Also adds echo_agent_short_ttl.yaml, an AgentRuntime CR identical to
echo-agent but with sessionTimeout: 30s, required by the A3 TTL test.

Fixes #103

Signed-off-by: Jagjeevan Kashid <jagjeevandev97@gmail.com>

Author: JagjeevanAK

test/e2e/echo_agent_short_ttl.yaml

@@ -0,0 +1,104 @@
+apiVersion: runtime.agentcube.volcano.sh/v1alpha1
+kind: AgentRuntime
+metadata:
+  name: echo-agent-short-ttl
+  namespace: agentcube
+spec:
+  targetPort:
+    - pathPrefix: "/echo"
+      port: 8080
+      protocol: "HTTP"
+  podTemplate:
+    labels:
+      app: echo-agent-short-ttl
+      test: e2e
+    spec:
+      containers:
+        - name: echo-server
+          image: python:3.9-slim
+          ports:
+            - containerPort: 8080
+              protocol: TCP
+          readinessProbe:
+            httpGet:
+              path: /echo
+              port: 8080
+            initialDelaySeconds: 5
+            periodSeconds: 5
+            timeoutSeconds: 3
+            successThreshold: 1
+            failureThreshold: 3
+          livenessProbe:
+            httpGet:
+              path: /echo
+              port: 8080
+            initialDelaySeconds: 10
+            periodSeconds: 10
+            timeoutSeconds: 5
+            successThreshold: 1
+            failureThreshold: 3
+          command: ["python3", "-c"]
+          args:
+            - |
+              import http.server
+              import socketserver
+              import json
+              import sys
+
+              class EchoHandler(http.server.BaseHTTPRequestHandler):
+                  def do_POST(self):
+                      if self.path.startswith('/echo'):
+                          try:
+                              content_length = int(self.headers['Content-Length'])
+                              post_data = self.rfile.read(content_length)
+                              request_data = json.loads(post_data.decode('utf-8'))
+                              input_text = request_data.get('input', '')
+
+                              response = {
+                                  'output': f'echo: {input_text}',
+                                  'metadata': {
+                                      'echoed': True,
+                                      'original_input': input_text
+                                  }
+                              }
+
+                              self.send_response(200)
+                              self.send_header('Content-Type', 'application/json')
+                              self.end_headers()
+                              self.wfile.write(json.dumps(response).encode('utf-8'))
+                          except Exception as e:
+                              self.send_response(400)
+                              self.send_header('Content-Type', 'application/json')
+                              self.end_headers()
+                              self.wfile.write(json.dumps({'error': str(e)}).encode('utf-8'))
+                      else:
+                          self.send_response(404)
+                          self.send_header('Content-Type', 'application/json')
+                          self.end_headers()
+                          self.wfile.write(b'{"error": "Not found"}')
+
+                  def do_GET(self):
+                      if self.path == '/echo':
+                          # Health check for livenessProbe and readinessProbe
+                          self.send_response(200)
+                          self.send_header('Content-Type', 'application/json')
+                          self.end_headers()
+                          self.wfile.write(b'{"status": "healthy"}')
+                      else:
+                          self.send_response(404)
+                          self.send_header('Content-Type', 'application/json')
+                          self.end_headers()
+                          self.wfile.write(b'{"error": "Not found"}')
+
+                  def log_message(self, format, *args):
+                      # Suppress server logs
+                      pass
+
+              with socketserver.TCPServer(("0.0.0.0", 8080), EchoHandler) as httpd:
+                  print("Echo server started on port 8080")
+                  httpd.serve_forever()
+  # Very short idle TTL – used by TestSessionSandboxLifecycleTTL (A3) to verify
+  # that expired sessions are properly invalidated by the garbage collector.
+  sessionTimeout: "30s"
+  maxSessionDuration: "8h"
+status: {}