Remove deprecated FastMCP() constructor kwargs

[jlowin]

FastMCP v1 conflated server identity, transport config, and global settings into a single FastMCP() constructor — v2 deprecated the transport params but kept them for backwards compat, resulting in a 34-parameter __init__ with a _deprecated_settings indirection layer bridging old kwargs to transport methods.

This removes all 16 deprecated kwargs and replaces them with a **kwargs catch that raises TypeError with specific migration instructions. Users passing host= get told to use run_http_async(host=...) or FASTMCP_HOST; users passing include_tags= get told to use server.enable(tags=..., only=True). Environment variables continue to work — transport methods now read directly from fastmcp.settings instead of the deleted per-instance _deprecated_settings.

# Before: 34-param constructor with deprecated indirection
mcp = FastMCP("server", host="0.0.0.0", port=8080, include_tags={"public"})

# After: clean constructor, settings where they belong
mcp = FastMCP("server")
mcp.enable(tags={"public"}, only=True)
mcp.run_http(host="0.0.0.0", port=8080)

# Helpful error if you forget:
# TypeError: FastMCP() no longer accepts `host`. Pass `host` to `run_http_async()`, or set FASTMCP_HOST.

Also deletes ExperimentalSettings (dead code) and fixes mcp_config.py which was passing include_tags/exclude_tags through create_proxy() to the now-strict constructor.

[coderabbitai]

Walkthrough

This PR removes multiple deprecated FastMCP constructor kwargs and centralizes removal checks via a _REMOVED_KWARGS checker; FastMCP.init signature no longer accepts legacy transport/server, tag-filtering, tool-serialization, and transformation kwargs. Tag filtering is applied post-proxy-creation via enable/disable calls. The MCP Apps decorator parameter is renamed from ui= to app= and a new public AppConfig replaces ToolUI/ResourceUI (wire format unchanged). ExperimentalSettings and related deprecation plumbing were removed. HTTP transport code now reads configuration directly from fastmcp.settings. Several documentation anchors were updated.

Possibly related PRs

• #2836: Removes passing tool_transformations into proxy creation and applies transforms post-creation, matching transformation-wiring changes in this PR.
• #3117: Introduces AppConfig and renames decorator parameter from ui= to app=, the same breaking API change implemented here.
• #2581: Removes deprecated settings shims and simplifies access to the global settings object, relating to the migration to fastmcp.settings used in transport code.

🚥 Pre-merge checks | ✅ 2 | ❌ 1

❌ Failed checks (1 warning)

Check name	Status	Explanation	Resolution
Docstring Coverage	⚠️ Warning	Docstring coverage is 62.50% which is insufficient. The required threshold is 80.00%.	Write docstrings for the functions missing them to satisfy the coverage threshold.

✅ Passed checks (2 passed)

Check name	Status	Explanation
Title check	✅ Passed	The title 'Remove deprecated FastMCP() constructor kwargs' clearly and concisely summarizes the main change: removal of deprecated kwargs from the constructor.
Description check	✅ Passed	The PR description is comprehensive and well-structured, explaining the motivation, implementation details, before/after examples, and migration guidance for users. It follows good practices by being specific about changes and providing concrete examples.

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✨ 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 remove-deprecated-init-kwargs

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[jlowin]

@coderabbitai review

[coderabbitai]

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[chatgpt-codex-connector]

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[chatgpt-codex-connector]

Handle empty include_tags when configuring proxy filters

Using a truthiness check here changes behavior for include_tags=set(): the filter is now skipped entirely, so the proxy exposes all components, whereas the previous path (FastMCP(..., include_tags=set())) still applied allowlist mode and resulted in no components being enabled. This can silently broaden access when config generation produces an empty include list; check for is not None instead so an explicit empty set remains an explicit filter.

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[coderabbitai]

Actionable comments posted: 1

🧹 Nitpick comments (1)

src/fastmcp/server/mixins/transport.py (1)

240-242: port or will swallow an explicit port=0 (OS-assigned port)

port = port or fastmcp.settings.port treats 0 as falsy. If a caller passes port=0 to let the OS assign a port, it silently falls back to the settings default. This is likely a pre-existing issue, but worth noting since the function signature accepts int | None.

Suggested fix

-        host = host or fastmcp.settings.host
-        port = port or fastmcp.settings.port
+        host = host if host is not None else fastmcp.settings.host
+        port = port if port is not None else fastmcp.settings.port