feat: epoch-based interruption

[crepererum]

Closes #15.

[Copilot]

Pull Request Overview

This PR implements epoch-based interruption for WebAssembly execution to prevent malicious or buggy WASM payloads from hanging the host system. The implementation uses Wasmtime's epoch interruption feature combined with a background timer to periodically check and interrupt long-running WASM code.

Key changes:

• Added epoch-based interruption with configurable tick times and timeout thresholds
• Implemented timeout handling for blocking operations in sync contexts
• Refactored test infrastructure to properly separate I/O and CPU runtimes
• Added comprehensive test coverage for various spin/hang scenarios

Reviewed Changes

Copilot reviewed 16 out of 16 changed files in this pull request and generated 3 comments.

Show a summary per file

File	Description
host/src/lib.rs	Implements epoch timer background task, adds timeout configuration to WasmPermissions, updates engine configuration to enable epoch interruption, and adds comprehensive documentation on async/blocking behavior
host/src/tokio_helpers.rs	Adds timeout support and runtime flavor validation to async_in_sync_context helper function
host/tests/integration_tests/rust.rs	Refactors tests to use helper functions for UDF creation, adds tests for runtime context validation
host/tests/integration_tests/evil/test_utils.rs	Adds dedicated I/O runtime for evil tests to properly test epoch-based interruption
host/tests/integration_tests/evil/spin.rs	New test suite verifying that spinning WASM payloads timeout correctly across different UDF operations
host/tests/integration_tests/evil/mod.rs	Adds spin module to test structure
guests/evil/src/lib.rs	Registers new spin test payloads for various UDF operations
guests/evil/src/common.rs	Adds common helper functions for empty root and UDF lists
guests/evil/src/spin/mod.rs	Implements spin function that creates CPU-intensive loop for testing interruption
guests/evil/src/spin/root.rs	Test payload that spins during root filesystem retrieval
guests/evil/src/spin/udf_invoke.rs	Test payload that spins during UDF invocation
guests/evil/src/spin/udf_name.rs	Test payload that spins during UDF name retrieval
guests/evil/src/spin/udf_return_type_exact.rs	Test payload that spins during return_type call with exact signature
guests/evil/src/spin/udf_return_type_other.rs	Test payload that spins during return_type call with non-exact signature
guests/evil/src/spin/udf_signature.rs	Test payload that spins during signature retrieval
guests/evil/src/spin/udfs.rs	Test payload that spins during UDF list retrieval

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