Fixes for `Session::preprocess_message()` #93

Job	Run time
build-docs	38s
clippy	30s
semver	23s
rustfmt	11s
stable-test (x86_64-unknown-linux-gnu, 1.81.0)	39s
test-and-coverage	46s
wasm-build (1.81.0, wasm32-unknown-unknown)	27s
wasm-build (stable, wasm32-unknown-unknown)	29s
	4m 3s

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