Fixes for `Session::preprocess_message()` #92

Job	Run time
clippy	26s
rustfmt	13s
semver	23s
build-docs	35s
stable-test (x86_64-unknown-linux-gnu, 1.81.0)	39s
test-and-coverage	46s
wasm-build (1.81.0, wasm32-unknown-unknown)	29s
wasm-build (stable, wasm32-unknown-unknown)	29s
	4m 0s

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