feat(strands-py-wasm): add DecoratedTool for host-side Python tools

strands-py-wasm/pyproject.toml

@@ -28,8 +28,8 @@ classifiers = [
     "Topic :: Software Development :: Libraries :: Python Modules",
 ]
 dependencies = [
-    # Imports as `wasmtime`. Pinned to pgrayy/wasm-deps git URL until upstream PRs land.
-    "pgrayy-wasmtime @ git+https://github.com/pgrayy/wasm-deps.git@4b5dc41512109ebafe4c4f1edd592c739872c640#subdirectory=wasmtime-py",
+    # Imports as `wasmtime`. Pinned to a pgrayy/wasm-deps release wheel until upstream PRs land.
+    "pgrayy-wasmtime @ https://github.com/pgrayy/wasm-deps/releases/download/wasmtime-v46.0.7/pgrayy_wasmtime-46.0.7-py3-none-macosx_11_0_arm64.whl",
     "botocore>=1.29.0,<2.0.0",
 ]
 

strands-py-wasm/src/strands/__init__.py

@@ -266,40 +266,24 @@ def __init__(self, *, interrupt_id: str, response: Any) -> None:
         super().__init__(interrupt_id=interrupt_id, response=payload)
 
 
-class PydanticTool:
-    """Tool whose input schema is derived from a pydantic ``BaseModel``."""
+class DecoratedTool:
+    """A Python function exposed to the agent as a tool.
 
-    def __init__(
-        self,
-        *,
-        name: str,
-        description: str,
-        input_model: type,
-        func: Callable[..., Any],
-    ) -> None:
-        if not hasattr(input_model, "model_json_schema") or not hasattr(input_model, "model_validate"):
-            raise TypeError(f"input_model must be a pydantic BaseModel subclass; got {input_model!r}")
-        self.name = name
-        self.description = description
-        self._input_model = input_model
-        self.input_schema = input_model.model_json_schema()
-        self.func = func
+    Build one with the ``@tool`` decorator, then pass it to
+    :class:`Agent` via ``tools=[...]``. The agent will call the function
+    when the model invokes the tool by name.
 
-    def to_spec(self) -> types.ToolSpec:
-        return types.ToolSpec(
-            name=self.name,
-            description=self.description,
-            input_schema=json.dumps(self.input_schema),
-        )
+    Callbacks must be synchronous. Async functions are not yet supported.
 
-    def invoke(self, raw_input: str) -> list[Any]:
-        payload = json.loads(raw_input) if raw_input else {}
-        validated = self._input_model.model_validate(payload)
-        return _coerce_tool_result(self.func(validated))
+    Example::
 
+        @tool
+        def get_weather(city: str) -> str:
+            \"\"\"Return the current weather for a city.\"\"\"
+            return f"It is 72F and sunny in {city}."
 
-class Tool:
-    """Registered tool: spec plus Python callable."""
+        agent = Agent(model=BedrockModel(...), tools=[get_weather])
+    """
 
     def __init__(
         self,
@@ -321,12 +305,13 @@ def to_spec(self) -> types.ToolSpec:
             input_schema=json.dumps(self.input_schema),
         )
 
-    def invoke(self, raw_input: str) -> list[Any]:
+    def invoke(self, raw_input: str) -> list[types.ToolResultContent]:
+        """Run the tool with a JSON object of keyword arguments."""
         kwargs = json.loads(raw_input) if raw_input else {}
-        return _coerce_tool_result(self.func(**kwargs))
+        return _normalize_tool_result(self.func(**kwargs))
 
 
-def _coerce_tool_result(result: Any) -> list[Any]:
+def _normalize_tool_result(result: Any) -> list[types.ToolResultContent]:
     if isinstance(result, str):
         return [types.ToolResultContent.Text(types.TextBlock(text=result))]
     if isinstance(result, types.TextBlock):
@@ -348,9 +333,12 @@ def tool(
     name: str | None = None,
     description: str | None = None,
 ) -> Any:
-    """Decorator that turns a Python function into a :class:`Tool`."""
+    """Decorator that turns a Python function into a :class:`DecoratedTool`.
+
+    Only synchronous functions are supported at this time.
+    """
 
-    def wrap(f: Callable[..., Any]) -> Tool:
+    def wrap(f: Callable[..., Any]) -> DecoratedTool:
         hints = get_type_hints(f)
         sig = inspect.signature(f)
         properties: dict[str, Any] = {}
@@ -362,7 +350,7 @@ def wrap(f: Callable[..., Any]) -> Tool:
         schema: dict[str, Any] = {"type": "object", "properties": properties}
         if required:
             schema["required"] = required
-        return Tool(
+        return DecoratedTool(
             name=name or f.__name__,
             description=description or (f.__doc__ or "").strip() or f.__name__,
             input_schema=schema,
@@ -372,19 +360,10 @@ def wrap(f: Callable[..., Any]) -> Tool:
     return wrap(func) if func is not None else wrap
 
 
-_ToolInput = Tool | PydanticTool | Callable[..., Any]
 # String shorthand picks a tool by name; otherwise pass a tagged ToolChoice arm.
 _ToolChoiceInput = str | types.ToolChoice | None
 
 
-def _coerce_tool(item: _ToolInput) -> Tool | PydanticTool:
-    if isinstance(item, (Tool, PydanticTool)):
-        return item
-    if callable(item):
-        return tool(item)
-    raise TypeError(f"unsupported tool: {type(item).__name__}")
-
-
 class Agent:
     """Strands agent. Construct once; call :meth:`invoke` or :meth:`stream_async`."""
 
@@ -394,7 +373,7 @@ def __init__(
         model: types.ModelInput | None = None,
         messages: list[types.Message] | None = None,
         system_prompt: PromptInput | None = None,
-        tools: list[_ToolInput] | None = None,
+        tools: list[DecoratedTool] | None = None,
         agent_tools: list[types.AgentAsToolConfig] | None = None,
         vended_tools: list[types.VendedToolInput] | None = None,
         vended_plugins: list[types.VendedPluginInput] | None = None,
@@ -413,7 +392,7 @@ def __init__(
         app_state: dict[str, Any] | None = None,
         model_state: dict[str, Any] | None = None,
     ) -> None:
-        self._tools: list[Tool | PydanticTool] = [_coerce_tool(t) for t in (tools or [])]
+        self._tools: list[DecoratedTool] = list(tools or [])
         identity = None
         if name is not None or id is not None or description is not None:
             identity = types.AgentIdentity(name=name, id=id, description=description)
@@ -467,7 +446,7 @@ async def _ensure_runtime_async(self) -> Any:
         await rt.async_init()
         return rt
 
-    def _lookup_tool(self, name: str) -> Tool | PydanticTool:
+    def _lookup_tool(self, name: str) -> DecoratedTool:
         for t in self._tools:
             if getattr(t, "name", None) == name:
                 return t
@@ -476,11 +455,11 @@ def _lookup_tool(self, name: str) -> Tool | PydanticTool:
     def _build_invoke_args(
         self,
         prompt: PromptInput,
-        tools: list[_ToolInput] | None,
+        tools: list[DecoratedTool] | None,
         tool_choice: _ToolChoiceInput,
         structured_output_schema: str | None,
     ) -> types.InvokeArgs:
-        extra_tools = [_coerce_tool(t).to_spec() for t in (tools or [])] or None
+        extra_tools = [t.to_spec() for t in (tools or [])] or None
         return types.InvokeArgs(
             input=_marshalling.coerce_prompt(prompt),
             tools=extra_tools,
@@ -492,7 +471,7 @@ async def stream_async(
         self,
         prompt: PromptInput,
         *,
-        tools: list[_ToolInput] | None = None,
+        tools: list[DecoratedTool] | None = None,
         tool_choice: _ToolChoiceInput = None,
         structured_output_schema: str | None = None,
     ) -> AsyncIterator[types.StreamEvent]:
@@ -507,7 +486,7 @@ async def invoke_async(
         self,
         prompt: PromptInput,
         *,
-        tools: list[_ToolInput] | None = None,
+        tools: list[DecoratedTool] | None = None,
         tool_choice: _ToolChoiceInput = None,
         structured_output_schema: str | None = None,
     ) -> AgentResult:
@@ -526,7 +505,7 @@ def invoke(
         self,
         prompt: PromptInput,
         *,
-        tools: list[_ToolInput] | None = None,
+        tools: list[DecoratedTool] | None = None,
         tool_choice: _ToolChoiceInput = None,
         structured_output_schema: str | None = None,
     ) -> AgentResult:

strands-py-wasm/tests/test_tools.py

@@ -0,0 +1,29 @@
+import pytest
+
+from strands import Agent, BedrockModel, tool
+
+
+@pytest.fixture
+def model():
+    return BedrockModel("us.anthropic.claude-haiku-4-5-20251001-v1:0")
+
+
+@pytest.fixture
+def weather_tool():
+    @tool
+    def get_weather(city: str) -> str:
+        """Return the current weather for a city."""
+        return f"It is 72F and sunny in {city}."
+
+    return get_weather
+
+
+@pytest.fixture
+def agent(model, weather_tool):
+    return Agent(model=model, tools=[weather_tool])
+
+
+@pytest.mark.asyncio
+async def test_decorated_tool_invocation(agent):
+    result = await agent.invoke_async("What is the weather in Seattle?")
+    assert "72" in str(result)

strands-wasm/entry.ts

@@ -18,7 +18,13 @@
 /// <reference path="./generated/interfaces/strands-agent-tool-provider.d.ts" />
 
 import type { AgentConfig, InvokeArgs, RespondArgs, AgentError } from 'strands:agent/api@0.1.0'
-import type { Message as WitMessage, PromptInput } from 'strands:agent/messages@0.1.0'
+import type {
+  ContentBlock as WitContentBlock,
+  Message as WitMessage,
+  PromptInput,
+  ToolResultBlock as WitToolResultBlock,
+  ToolResultContent as WitToolResultContent,
+} from 'strands:agent/messages@0.1.0'
 import type {
   StreamEvent as WitStreamEvent,
   StopEvent as WitStopEvent,
@@ -52,6 +58,8 @@ import type {
   ToolChoice,
   ModelStreamEvent,
   ContentBlock,
+  ToolResultBlock,
+  ToolResultContent,
   SaveLatestStrategy,
   JSONValue,
 } from '@strands-agents/sdk'
@@ -129,29 +137,62 @@ function mapMessage(message: Message): WitMessage {
   } as WitMessage
 }
 
-/** Serialize a TS SDK ContentBlock to the WIT tagged-variant shape. */
-function mapContentBlock(block: ContentBlock): import('strands:agent/messages@0.1.0').ContentBlock {
-  type WitBlock = import('strands:agent/messages@0.1.0').ContentBlock
-  // block.type is the SDK class discriminator; toJSON drops class identity but keeps fields.
+/**
+ * Serialize a TS SDK ContentBlock to the WIT `content-block` tagged variant.
+ *
+ * Most SDK blocks `toJSON()` to `{<discriminator>: <inner-data>}` (e.g.
+ * `{toolUse: {...}}`). The matching WIT record is the inner shape only;
+ * the discriminator already lives in `tag`. We strip that outer wrapper
+ * here so the WIT marshaler sees the right fields. `text` and `json` are
+ * the exception: their toJSON is already the inner shape.
+ */
+function mapContentBlock(block: ContentBlock): WitContentBlock {
   const payload = JSON.parse(JSON.stringify(block))
   switch (block.type) {
-    case 'textBlock': return { tag: 'text', val: payload } as WitBlock
-    case 'toolUseBlock': return { tag: 'tool-use', val: payload } as WitBlock
-    case 'toolResultBlock': return { tag: 'tool-result', val: payload } as WitBlock
-    case 'reasoningBlock': return { tag: 'reasoning', val: payload } as WitBlock
-    case 'cachePointBlock': return { tag: 'cache-point', val: payload } as WitBlock
-    case 'imageBlock': return { tag: 'image', val: payload } as WitBlock
-    case 'videoBlock': return { tag: 'video', val: payload } as WitBlock
-    case 'documentBlock': return { tag: 'document', val: payload } as WitBlock
-    case 'citationsBlock': return { tag: 'citations', val: payload } as WitBlock
-    case 'guardContentBlock': return { tag: 'guard-content', val: payload } as WitBlock
+    case 'textBlock': return { tag: 'text', val: payload } as WitContentBlock
+    case 'toolUseBlock':
+      return { tag: 'tool-use', val: { ...payload.toolUse, input: JSON.stringify(payload.toolUse.input) } } as WitContentBlock
+    case 'toolResultBlock':
+      return { tag: 'tool-result', val: mapToolResultBlock(block) } as WitContentBlock
+    case 'reasoningBlock': return { tag: 'reasoning', val: payload.reasoning } as WitContentBlock
+    case 'cachePointBlock': return { tag: 'cache-point', val: payload.cachePoint } as WitContentBlock
+    case 'imageBlock': return { tag: 'image', val: payload.image } as WitContentBlock
+    case 'videoBlock': return { tag: 'video', val: payload.video } as WitContentBlock
+    case 'documentBlock': return { tag: 'document', val: payload.document } as WitContentBlock
+    case 'citationsBlock': return { tag: 'citations', val: payload.citations } as WitContentBlock
+    case 'guardContentBlock': return { tag: 'guard-content', val: payload.guardContent } as WitContentBlock
     default: {
       block satisfies never
       throw new Error(`unknown content block: ${(block as { type: string }).type}`)
     }
   }
 }
 
+/** Serialize a TS SDK `ToolResultBlock` to the WIT `tool-result-block` record. */
+function mapToolResultBlock(block: ToolResultBlock): WitToolResultBlock {
+  return {
+    toolUseId: block.toolUseId,
+    status: block.status,
+    content: block.content.map(mapToolResultContent),
+  }
+}
+
+/** Serialize a TS SDK `ToolResultContent` to the WIT `tool-result-content` tagged variant. */
+function mapToolResultContent(block: ToolResultContent): WitToolResultContent {
+  const payload = JSON.parse(JSON.stringify(block))
+  switch (block.type) {
+    case 'textBlock': return { tag: 'text', val: payload } as WitToolResultContent
+    case 'jsonBlock': return { tag: 'json', val: payload } as WitToolResultContent
+    case 'imageBlock': return { tag: 'image', val: payload.image } as WitToolResultContent
+    case 'videoBlock': return { tag: 'video', val: payload.video } as WitToolResultContent
+    case 'documentBlock': return { tag: 'document', val: payload.document } as WitToolResultContent
+    default: {
+      block satisfies never
+      throw new Error(`unsupported tool-result-content type: ${(block as { type: string }).type}`)
+    }
+  }
+}
+
 //
 // --- stream event mapping ------------------------------------------------
 //
@@ -211,7 +252,7 @@ function mapEvent(event: AgentStreamEvent): WitStreamEvent | null {
             toolUseId: event.toolUse.toolUseId,
             input: JSON.stringify(event.toolUse.input ?? {}),
           },
-          toolResult: mapContentBlock(event.result) as unknown as import('strands:agent/messages@0.1.0').ToolResultBlock,
+          toolResult: mapToolResultBlock(event.result),
           error: event.error ? { tag: 'execution-failed', val: event.error.message } : undefined,
         },
       }
@@ -225,7 +266,7 @@ function mapEvent(event: AgentStreamEvent): WitStreamEvent | null {
     case 'toolResultEvent':
       return {
         tag: 'tool-result-hook',
-        val: { toolResult: mapContentBlock(event.result) as unknown as import('strands:agent/messages@0.1.0').ToolResultBlock },
+        val: { toolResult: mapToolResultBlock(event.result) },
       }
     case 'toolStreamUpdateEvent':
       return { tag: 'tool-update', val: { data: JSON.stringify(event.event.data ?? null) } }
@@ -365,8 +406,17 @@ function createTools(specs: ToolSpec[] | undefined): FunctionTool[] | undefined
               case 'data':
                 // Streaming tool progress is not surfaced to the SDK caller today.
                 continue
-              case 'complete':
-                return value.val as unknown as JSONValue
+              case 'complete': {
+                // The host pushes WIT `tool-result-content` variant arms; the
+                // TS FunctionTool expects the single-key data shape that
+                // `toolResultContentFromData` accepts. text/json arms already
+                // carry that shape inline; other arms need an explicit wrap.
+                const content = (value.val as Array<{ tag: string; val: unknown }>).map((c) => {
+                  if (c.tag === 'text' || c.tag === 'json') return c.val
+                  return { [c.tag]: c.val }
+                })
+                return content as unknown as JSONValue
+              }
               case 'error':
                 throw new Error(`tool ${spec.name} failed: ${value.val.tag}`)
             }