Migration from SequentialAgent to Workflow with AgentTools: Context is lost

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**Describe the Bug:**
I am migrating my SequentialAgent to the new Workflow. Agent 1 has AgentTools.

After migration the Agent calling an AgentTool restarts without context:
START -> Agent1 -> calling Tool "agentTool1" -> Back to Agent1 (but this time the agents starts without any context. It just has its system instructions available).

**Steps to Reproduce:**
Before:
```
sequential_agent = SequentialAgent(
name="Assistant",
description="Sequential agent that orchestrates work and synthesizes final response",
sub_agents=[orchestrator_agent, response_agent],
)
```
Iterating events:
`async for event in sequential_agent.run_async(ctx):`

After:
```
sequential_workflow = Workflow(
name="Assistant",
edges=[("START", orchestrator_agent, response_agent)],
)
```
Iterating events:
`async for event in sequential_workflow.run(ctx=Context(ctx), node_input=ctx.user_content):`

**Expected Behavior:**
Agent1 working on user query, calling agentTool1, returning to Agent1 with full context available (user query, tools calls, tool responses, etc), Agent1 continuing its task

**Observed Behavior:**
Agent1 working on user query, calling agentTool1, returning to Agent1 with no context available, therefore answering something like "Understood. Provide request"

In mlflow it can be seen, the user query is "Handle the requests as specified in the System Instruction.", which is inserted by litellm automatically, if no content parts are available.

**Environment Details:**

- ADK Library Version (pip show google-adk): 2.0.0
- Desktop OS:** macOS
- Python Version (python -V): 3.12.13

**Model Information:**

- Are you using LiteLLM: Yes
- Which model is being used: Mistral Models, but that's irrelevant

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## 🟡 Optional Information
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**Regression:**
It works with sequential agent, it does not with worflow

**Logs:**
n/a

**Screenshots / Video:**
n/a

**Additional Context:**
n/a

**Minimal Reproduction Code:**
n/a

**How often has this issue occurred?:**
- Always (100%)