[Bug]: SendMessage does not return an error when taskId and contextId are mismatched

[jmesnil]

What happened?

Summary

The SUT accepts a SendMessage request with a taskId and a mismatching contextId instead of rejecting it with an error (JSON-RPC transport).

Requirement

• ID: CORE-MULTI-006
• Section: 3.4.3 — Multi-Turn Conversation Patterns
• Level: MUST
• Spec: specification.md#343-multi-turn-conversation-patterns

Specification

Agents MUST reject messages containing mismatching contextId and taskId (i.e., the provided contextId is different from that of the referenced Task).

Expected behavior

When a client sends a SendMessage with a taskId referencing an existing task and a contextId that does not match that task's context, the agent must return an error.

Actual behavior

The SUT accepts the message and returns a success response instead of an error.

Reproducer

# Step 1: Create a task to get a valid taskId and contextId
curl -s -X POST http://localhost:9999 \
  -H "Content-Type: application/json" \
  -d '{
    "jsonrpc": "2.0",
    "id": 1,
    "method": "SendMessage",
    "params": {
      "message": {
        "role": "ROLE_USER",
        "parts": [{"text": "hello"}],
        "messageId": "tck-setup-001"
      }
    }
  }'
# Note the taskId and contextId from the response.

# Step 2: Send a follow-up with the correct taskId but a WRONG contextId
# Replace <TASK_ID> with the taskId from Step 1.
curl -s -X POST http://localhost:9999 \
  -H "Content-Type: application/json" \
  -d '{
    "jsonrpc": "2.0",
    "id": 2,
    "method": "SendMessage",
    "params": {
      "message": {
        "role": "ROLE_USER",
        "parts": [{"text": "Mismatched context test"}],
        "messageId": "tck-mismatch-001",
        "taskId": "<TASK_ID>",
        "contextId": "wrong-context-does-not-exist"
      }
    }
  }'
# Expected: a JSON-RPC error response
# Actual:   a success response with a Task/StatusEvent

TCK test

tests/compatibility/core_operations/test_task_lifecycle.py::TestMultiTurn::test_reject_mismatching_context

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