chore: switch main to v2.0.0 GA (transition to v2)

Co-authored-by: Bo Yang <ybo@google.com>
Co-authored-by: Wei Sun (Jack) <weisun@google.com>
Co-authored-by: George Weale <gweale@google.com>
Co-authored-by: Swapnil Agarwal <swapnilag@google.com>
Co-authored-by: Xuan Yang <xygoogle@google.com>
Co-authored-by: Shangjie Chen <deanchen@google.com>
Co-authored-by: Yifan Wang <wanyif@google.com>
Co-authored-by: Kathy Wu <wukathy@google.com>

Author: 9 people

.agents/skills/adk-agent-builder/SKILL.md

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+---
+name: adk-agent-builder
+description: Central hub for building, testing, and iterating on ADK agents. Trigger this skill when the user wants to create a new agent, configure modes (task, single-turn), or build graph-based workflows.
+---
+
+# ADK Agent Builder
+
+This file serves as a directory of specialized reference guides for developing agents with ADK. To avoid context pollution, read only the relevant reference file based on your current task.
+
+## Core Concepts Directory
+
+Refer to these files for foundational knowledge:
+- **Getting Started & Basic Agents**: [getting-started.md](references/getting-started.md)
+  - Environment setup, API key configuration, and minimal agent definitions.
+- **Tool Catalog**: [tool-catalog.md](references/tool-catalog.md)
+  - How to bind function tools, MCP tools, OpenAPI specs, and Google API tools.
+- **Agent Modes (Task / Single-Turn)**: [task-mode.md](references/task-mode.md)
+  - Multi-turn structured delegation and autonomous single-turn execution patterns.
+
+## Workflow & Graph Orchestration
+
+Refer to these files when building complex graphs:
+- **Function Nodes**: [function-nodes.md](references/function-nodes.md)
+  - How to use functions as nodes, type resolution, and generators.
+- **Routing & Conditions**: [routing-and-conditions.md](references/routing-and-conditions.md)
+  - Edge patterns, dict-based routing, self-loops, and conditional execution.
+- **LLM Agent Nodes**: [llm-agent-nodes.md](references/llm-agent-nodes.md)
+  - How to use LLM agents as workflow nodes, task wrappers, and handling output schemas.
+
+## Advanced Orchestration Patterns
+
+- **Parallel Processing & Fan-Out**: [parallel-and-fanout.md](references/parallel-and-fanout.md)
+  - `ParallelWorker` for list splitting and concurrent processing, fan-out/join patterns.
+- **Human-in-the-Loop**: [human-in-the-loop.md](references/human-in-the-loop.md)
+  - Pausing execution for user input, resumable workflows, and AuthConfig on nodes.
+- **Dynamic Nodes**: [dynamic-nodes.md](references/dynamic-nodes.md)
+  - Scheduling nodes at runtime dynamically via `ctx.run_node()`.
+
+## Infrastructure & Utilities
+
+- **State & Events**: [state-and-events.md](references/state-and-events.md)
+  - Using context API, sharing global state, and yield event structures.
+- **Multi-Agent Systems**: [multi-agent.md](references/multi-agent.md)
+  - Hierarchical execution (e.g., `SequentialAgent`, `LoopAgent`, `ParallelAgent`).
+- **Testing Strategies**: [testing.md](references/testing.md)
+  - Automated queries with `adk run`, unit tests, and integration testing with sample agents.
+
+## Standards & Guidelines
+
+- **Best Practices**: [best-practices.md](references/best-practices.md)
+  - Critical rules (Pydantic schemas, content events, state-based data flow).

.agents/skills/adk-agent-builder/references/advanced-patterns.md

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+# Advanced Workflow Patterns Reference
+
+Nested workflows, dynamic nodes, retry configuration, custom node types, and graph construction.
+
+## 📋 Agent Verification Checklist (Advanced Patterns)
+Use this checklist when implementing complex workflows:
+- [ ] **Validation**: Does your graph follow all 7 validation rules? (e.g., no unconditional cycles)
+- [ ] **Custom Nodes**: If creating a custom node, did you override `get_name()` and `run()`?
+- [ ] **Dynamic Execution**: If using `run_node`, did you follow the rules in the dedicated dynamic-nodes reference?
+- [ ] **Waiting State**: Did you use `wait_for_output=True` if the node should stay in WAITING state until output is yielded?
+
+## 💡 Quick Reference
+- **Retry**: `RetryConfig(max_attempts=5, initial_delay=1.0)`
+- **Custom Node Fields**: `rerun_on_resume`, `wait_for_output`, `retry_config`, `timeout`
+
+## Nested Workflows
+
+A `Workflow` is both an agent and a node. Use one workflow inside another:
+
+```python
+from google.adk.workflow import Workflow
+
+# Inner workflow
+inner = Workflow(
+    name="inner_pipeline",
+    edges=[
+        ('START', step_a),
+        (step_a, step_b),
+    ],
+)
+
+# Outer workflow using inner as a node
+outer = Workflow(
+    name="outer_pipeline",
+    edges=[
+        ('START', pre_process),
+        (pre_process, inner),      # Nested workflow
+        (inner, post_process),
+    ],
+)
+```
+
+The inner workflow receives the predecessor's output as its START input and its terminal output flows to the next node in the outer workflow.
+
+## Dynamic Node Scheduling
+
+Schedule nodes at runtime using `ctx.run_node()`.
+
+See the dedicated [Dynamic Node Scheduling Reference](file:///Users/deanchen/Desktop/adk-workflow/.agents/skills/adk-workflow/references/dynamic-nodes.md) for detailed rules, examples, and best practices.
+
+## Retry Configuration
+
+Configure automatic retry for nodes that may fail:
+
+```python
+from google.adk.workflow import RetryConfig
+from google.adk.workflow import FunctionNode
+
+retry = RetryConfig(
+    max_attempts=5,         # Max attempts (default: 5). 0 or 1 = no retry
+    initial_delay=1.0,      # Seconds before first retry (default: 1.0)
+    max_delay=60.0,         # Max seconds between retries (default: 60.0)
+    backoff_factor=2.0,     # Delay multiplier per attempt (default: 2.0)
+    jitter=1.0,             # Randomness factor (default: 1.0, 0.0 = none)
+    exceptions=None,        # Exception types to retry (None = all)
+)
+
+node = FunctionNode(
+    flaky_api_call,
+    name="api_call",
+    retry_config=retry,
+)
+```
+
+### Retry delay formula
+
+```
+delay = initial_delay * (backoff_factor ^ attempt)
+delay = min(delay, max_delay)
+delay = delay * (1 + random(0, jitter))
+```
+
+### Accessing retry count
+
+```python
+def my_node(ctx: Context, node_input: str) -> str:
+  if ctx.retry_count > 0:
+    print(f"Retry attempt {ctx.retry_count}")
+  return "result"
+```
+
+## Custom Node Types
+
+Subclass `BaseNode` for custom behavior:
+
+```python
+from google.adk.workflow import BaseNode
+from google.adk.events.event import Event
+from google.adk.agents.context import Context
+from pydantic import ConfigDict, Field
+from typing import Any, AsyncGenerator
+from typing_extensions import override
+
+class BatchProcessorNode(BaseNode):
+  """Processes items in batches."""
+  model_config = ConfigDict(arbitrary_types_allowed=True)
+
+  name: str = Field(default="batch_processor")
+  batch_size: int = Field(default=10)
+
+  def __init__(self, *, name: str = "batch_processor", batch_size: int = 10):
+    super().__init__()
+    object.__setattr__(self, 'name', name)
+    object.__setattr__(self, 'batch_size', batch_size)
+
+  @override
+  def get_name(self) -> str:
+    return self.name
+
+  @override
+  async def run(
+      self,
+      *,
+      ctx: Context,
+      node_input: Any,
+  ) -> AsyncGenerator[Any, None]:
+    items = node_input if isinstance(node_input, list) else [node_input]
+    results = []
+    for i in range(0, len(items), self.batch_size):
+      batch = items[i:i + self.batch_size]
+      batch_result = await process_batch(batch)
+      results.extend(batch_result)
+    yield Event(output=results)
+```
+
+### BaseNode Fields
+
+| Field | Default | Description |
+|-------|---------|-------------|
+| `rerun_on_resume` | `False` | Whether to rerun after HITL interrupt |
+| `wait_for_output` | `False` | Node stays in WAITING state until it yields output (see below) |
+| `retry_config` | `None` | Retry configuration on failure |
+| `timeout` | `None` | Max seconds for node to complete |
+
+### wait_for_output
+
+When `wait_for_output=True`, a node that finishes without yielding an `Event` with output moves to **WAITING** state instead of COMPLETED. Downstream nodes are **not** triggered. The node can then be re-triggered by upstream predecessors.
+
+This is how `JoinNode` works internally — it runs once per predecessor, storing partial inputs, and only yields output (triggering downstream) when all predecessors have completed. `LlmAgentWrapper` in `task` mode also sets `wait_for_output=True` automatically.
+
+```python
+from google.adk.workflow import BaseNode
+
+class CollectorNode(BaseNode):
+  wait_for_output: bool = True  # Stay in WAITING until output is yielded
+
+  async def run(self, *, ctx, node_input):
+    # Store partial input, don't yield output yet
+    collected = ctx.state.get("collected", [])
+    collected.append(node_input)
+    yield Event(state={"collected": collected})
+
+    # Only yield output when we have enough
+    if len(collected) >= 3:
+      yield Event(output=collected)
+      # Now node transitions to COMPLETED and triggers downstream
+```
+
+Nodes with `wait_for_output=True` default:
+- `JoinNode`: `True` (waits for all predecessors)
+- `LlmAgentWrapper` (task mode): `True` (set in `model_post_init`)
+- All other nodes: `False`
+
+### Required Methods
+
+| Method | Description |
+|--------|-------------|
+| `get_name() -> str` | Return the node name |
+| `run(*, ctx, node_input) -> AsyncGenerator` | Execute the node, yield events |
+
+## ToolNode
+
+Wrap an ADK tool as a workflow node:
+
+```python
+from google.adk.workflow._tool_node import _ToolNode as ToolNode
+from google.adk.tools.function_tool import FunctionTool
+
+def search(query: str) -> str:
+  """Search for information."""
+  return f"Results for: {query}"
+
+tool = FunctionTool(search)
+tool_node = ToolNode(tool, name="search_node")
+
+agent = Workflow(
+    name="with_tool",
+    edges=[
+        ('START', prepare_query),
+        (prepare_query, tool_node),  # Input must be dict (tool args) or None
+        (tool_node, process_results),
+    ],
+)
+```
+
+**Important**: ToolNode input must be a dictionary of tool arguments or None.
+
+## AgentNode
+
+Wrap any `BaseAgent` (not just LlmAgent) as a workflow node:
+
+```python
+from google.adk.workflow._agent_node import AgentNode
+from google.adk.agents.loop_agent import LoopAgent
+
+loop = LoopAgent(
+    name="refine_loop",
+    sub_agents=[writer, reviewer],
+    max_iterations=3,
+)
+
+loop_node = AgentNode(agent=loop, name="refinement")
+
+agent = Workflow(
+    name="with_loop",
+    edges=[
+        ('START', loop_node),
+        (loop_node, final_step),
+    ],
+)
+```
+
+## Graph Validation Rules
+
+The workflow graph is validated on construction. These rules are enforced:
+
+1. START node must exist
+2. START node must not have incoming edges
+3. All non-START nodes must be reachable (appear as `to_node` in some edge)
+4. No duplicate node names
+5. No duplicate edges
+6. At most one `__DEFAULT__` route per node
+7. No unconditional cycles (cycles must have at least one routed edge)
+
+## Edge Construction Patterns
+
+```python
+from google.adk.workflow import Edge
+from google.adk.workflow._workflow_graph import WorkflowGraph
+
+# Tuple syntax (most common)
+edges = [
+    ('START', node_a),                    # Simple edge
+    (node_a, node_b, "route"),            # Routed edge
+    (node_a, (node_b, node_c)),           # Fan-out
+    ((node_b, node_c), join_node),        # Fan-in
+]
+
+# Sequence shorthand (tuple with 3+ elements creates chain)
+edges = [('START', node_a, node_b, node_c)]
+# Equivalent to: [('START', node_a), (node_a, node_b), (node_b, node_c)]
+
+# Routing map (dict syntax)
+edges = [
+    (classifier, {"success": handler_a, "error": handler_b}),
+]
+
+# Edge objects (explicit)
+edges = [
+    Edge(START, node_a),
+    Edge(node_a, node_b, route="success"),
+]
+
+# Edge.chain helper
+edges = Edge.chain('START', node_a, node_b, node_c)
+# Returns: [(START, node_a), (node_a, node_b), (node_b, node_c)]
+
+# WorkflowGraph.from_edge_items
+graph = WorkflowGraph.from_edge_items([
+    ('START', node_a),
+    (node_a, node_b),
+])
+agent = Workflow(name="my_workflow", graph=graph)
+```
+
+## Source File Locations
+
+| Component | File |
+|-----------|------|
+| Workflow | `src/google/adk/workflow/_workflow.py` |
+| WorkflowGraph, Edge | `src/google/adk/workflow/_workflow_graph.py` |
+| Context | `src/google/adk/agents/context.py` |
+| FunctionNode | `src/google/adk/workflow/_function_node.py` |
+| _LlmAgentWrapper | `src/google/adk/workflow/_llm_agent_wrapper.py` |
+| AgentNode | `src/google/adk/workflow/_agent_node.py` |
+| _ToolNode | `src/google/adk/workflow/_tool_node.py` |
+| JoinNode | `src/google/adk/workflow/_join_node.py` |
+| ParallelWorker | `src/google/adk/workflow/_parallel_worker.py` |
+| BaseNode, START | `src/google/adk/workflow/_base_node.py` |
+| @node decorator | `src/google/adk/workflow/_node.py` |
+| RetryConfig | `src/google/adk/workflow/_retry_config.py` |
+| Event | `src/google/adk/events/event.py` |
+| RequestInput | `src/google/adk/events/request_input.py` |