harden: mix random bits into migration ID generation#125
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when SystemTime::now() is unavailable (returns Duration::ZERO via unwrap_or_default), migration IDs degenerated to just the slot number, causing collisions if the same slot was migrated more than once. mix 16 bits of randomness into the upper bits of the ID so uniqueness doesn't depend solely on clock availability.
kacy
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Feb 19, 2026
…#125) when SystemTime::now() is unavailable (returns Duration::ZERO via unwrap_or_default), migration IDs degenerated to just the slot number, causing collisions if the same slot was migrated more than once. mix 16 bits of randomness into the upper bits of the ID so uniqueness doesn't depend solely on clock availability.
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summary
mixes 16 bits of randomness into migration IDs to prevent collisions when
the system clock is unavailable.
previously,
MigrationId::new()usedunwrap_or_default()onSystemTime::now(), which returnsDuration::ZEROon clock failure. thismade the ID degenerate to just the slot number (
0 ^ slot), so twomigrations of the same slot would produce identical IDs.
now the ID combines timestamp, slot, and random bits:
ts ^ (slot as u64) ^ ((noise as u64) << 48)randwas already a dependency of ember-cluster.what was tested
all 59 ember-cluster tests pass.