Own MCP connection request shutdown

[lynnswap]

Purpose

Prevent an MCP listener generation from shutting down its SwiftNIO event loop while accepted connections or already-admitted HTTP request tasks are still active.

Changes

• Add one network resource owner per listener generation and register accepted child channels before pipeline or task dispatch.
• Reserve each HTTP request operation and cancellation-aware work lease before creating its task.
• Preserve the first terminal cause across server stop, peer close, and transport failure.
• Close connection and request admission and signal child shutdown before awaiting close acknowledgements and shutting down the generation event-loop group.
• Add deterministic coverage for child close acknowledgement, pre-dispatch cancellation, late admission rejection, peer and error draining, generation replacement, and joined stop failures.

Testing

• MCP tests with SWIFTNIO_STRICT=1 (39 tests)
• Owner suite repeated 10 times
• Joined-stop failure test repeated 10 times
• Host tests (48 tests)
• swift test --build-system swiftbuild --no-parallel
• scripts/check-compatibility.sh
• ReviewMonitor xcodebuild test (15 tests)
• Independent concurrency and root scope audits

Screenshots

Not applicable.

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[lynnswap]

@codex review

[chatgpt-codex-connector]

Codex Review: Didn't find any major issues. Already looking forward to the next diff.

Reviewed commit: a9f341ea45

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