stream: avoid duplicate writes in toWritable #6873

Job	Run time
Build slim tarball	1m 19s
aarch64-darwin: with shared libraries	26m 50s
x86_64-linux: with shared libraries	29m 26s
x86_64-darwin: with shared libraries	36m 59s
aarch64-linux: Cache V8 build	25s
aarch64-linux: with shared openssl-3.0.19	24m 20s
aarch64-linux: with shared boringssl-0.20260413.0	24m 51s
aarch64-linux: with shared openssl-1.1.1w	24m 56s
aarch64-linux: with shared openssl-4.0.0	25m 0s
aarch64-linux: with shared openssl-3.5.5	24m 17s
aarch64-linux: with shared openssl-3.6.1	25m 7s
Build slim tarball	1m 19s
aarch64-darwin: with shared libraries	26m 50s
x86_64-darwin: with shared libraries	36m 59s
x86_64-linux: with shared libraries	29m 26s
aarch64-linux: Cache V8 build	25s
aarch64-linux: with shared boringssl-0.20260413.0	24m 51s
aarch64-linux: with shared openssl-3.6.1	21m 29s
aarch64-linux: with shared openssl-1.1.1w	24m 56s
aarch64-linux: with shared openssl-3.0.19	24m 20s
aarch64-linux: with shared openssl-4.0.0	25m 0s
aarch64-linux: with shared openssl-3.5.5	24m 17s
	8h 3m 22s

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