feat: add context parameter to prompt handlers

[hashwnath]

Summary

Closes #707

• Add optional context parameter to prompt handlers for SDK parity with TypeScript
• Use inspect.signature introspection to detect handler arity, supporting both old-style (args) and new-style (context, args) signatures for backward compatibility
• Pass the per-request Context (from get_current_model_context()) through PromptManager.get_prompt to PromptHandler.get_messages
• Update type annotations from Callable[[dict[str, str]], list[PromptMessage]] to Callable[..., list[PromptMessage]] across prompt manager, server, and MCPApp

New prompt handler pattern

# New style - receives context (context first, matching tools)
async def greeting(context: Context, args: dict[str, str]) -> list[PromptMessage]:
    await context.log.info("Generating greeting")
    return [PromptMessage(role="user", content=f"Hello {args['name']}")]

# Old style - still works (backward compatible)
async def greeting(args: dict[str, str]) -> list[PromptMessage]:
    return [PromptMessage(role="user", content=f"Hello {args['name']}")]

Test plan

• New-style handler with context receives the context object
• Old-style handler without context still works when context is provided (backward compat)
• Old-style handler works when no context is provided at all
• Default handler (no user handler) works with context
• Synchronous handler with context works
• Signature introspection correctly detects 1-param vs 2-param handlers
• All 14 existing prompt tests pass unchanged

Generated with Claude Code

---

Note

Low Risk
Additive API with signature-based dispatch; existing single-argument handlers are unchanged, and context is only injected on the prompts/get path.

Overview
Adds optional per-request Context to MCP prompt handlers so Python SDK behavior aligns with tools and the TypeScript SDK.

PromptHandler uses inspect.signature at registration time: handlers with two required positional parameters (after self) are invoked as (context, args); single-parameter handlers still receive only args. PromptManager.get_prompt and MCPServer._handle_get_prompt pass context from get_current_model_context() into that path. Handler type hints widen to Callable[..., list[PromptMessage]] on the manager, server, and MCPApp prompts API.

Tests cover context-aware async/sync handlers, backward compatibility when context is omitted or ignored, default handlers, and the introspection helper.

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Context not forwarded through Prompts.get() call path

Medium Severity

The _prompt_manager.get_prompt call in context.py:557 (Prompts.get()) was not updated to pass the context parameter, even though self._ctx (the Context object) is readily available. Prompt handlers that accept context will receive None when invoked through this path (e.g., a tool calling a prompt via context.prompts.get()), while the same handler called via the MCP protocol (_handle_get_prompt) correctly receives context.

Additional Locations (1)

• libs/arcade-mcp-server/arcade_mcp_server/managers/prompt.py#L97-L102

 

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