Add execution field to base Tool class

[chrisguidry]

The base Tool class now has an optional execution field for storing task execution metadata (SEP-1686). This lets gateways/proxies preserve execution info when forwarding tools from backends - previously this metadata was lost because Tool had no way to store it.

When a gateway receives tools from a backend with execution metadata (e.g., taskSupport: "optional"), it can now store that in a Tool object and have it survive the round-trip through to_mcp_tool().

# Gateway can now preserve execution metadata from backends
tool = Tool(
    name="backend_tool",
    parameters={...},
    execution=ToolExecution(taskSupport="optional"),
)

# Metadata preserved when converting back to MCP
mcp_tool = tool.to_mcp_tool()
assert mcp_tool.execution.taskSupport == "optional"

FunctionTool continues to derive execution from task_config as before - this only affects the base Tool class.

🤖 Generated with Claude Code

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Walkthrough

This change adds an optional execution field to the Tool class in src/fastmcp/tools/tool.py to carry task execution configuration settings. The field is typed as ToolExecution | None and defaults to None. During Tool to MCP Tool conversion, the implementation now preserves the tool's execution value as a default when no override is explicitly provided, using execution=overrides.get("execution", self.execution) in the conversion logic.

Pre-merge checks and finishing touches

✅ Passed checks (3 passed)

Check name	Status	Explanation
Title check	✅ Passed	The pull request title accurately and concisely describes the main change: adding an execution field to the base Tool class, which is the primary modification in the changeset.
Description check	✅ Passed	The description provides clear context about the change (storing task execution metadata), includes a practical example, notes the scope limitation to the base Tool class, and discloses the use of Claude Code for generation. However, it does not include the required Contributors/Review checklists from the template.
Docstring Coverage	✅ Passed	Docstring coverage is 100.00% which is sufficient. The required threshold is 80.00%.

✨ Finishing touches

• 📝 Generate docstrings

🧪 Generate unit tests (beta)

• Create PR with unit tests
• Post copyable unit tests in a comment
• Commit unit tests in branch tool-execution-field

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Actionable comments posted: 0

🧹 Nitpick comments (1)

src/fastmcp/tools/tool.py (1)

136-193: Execution metadata field and propagation logic look correct; consider cloning behavior

The new execution field on Tool and its propagation via execution=overrides.get("execution", self.execution) into MCPTool look solid: typing is appropriate (ToolExecution | None), precedence is consistent with other fields (overrides win over the instance default), and FunctionTool.to_mcp_tool still correctly respects explicit execution overrides while deriving execution from task_config otherwise.

One optional thing to double‑check: any helper paths that wrap/clone tools (e.g., via Tool.from_tool / TransformedTool.from_tool or similar) should also preserve the execution value from the source tool so this metadata isn’t silently dropped in those flows.

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Reviewing files that changed from the base of the PR and between 659ec38 and 17520ec.

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• src/fastmcp/tools/tool.py (2 hunks)

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src/**/*.py

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Files:

• src/fastmcp/tools/tool.py

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