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fix: pass the request seed to the sampler, and survive a negative one - #220
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The samplers draw from their own RandomState, which only GenerateParameters.seed seeds. Seeding MLX's global generator alone left the request's `seed` without effect: the same seeded request sampled differently every time. Both handlers now set GenerateParameters.seed; the global seed call stays for the paths that use MLXRandom directly. UInt64(seed) trapped on a negative value, so `"seed": -1` took the whole server down. samplingSeed(_:) takes the bit pattern instead. Closes SharpAI#219.
This was referenced Oct 9, 2026
HamedShams
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Oct 10, 2026
Both SharpAI#220 and this branch added a block before the results footer of tests/test-contract.sh. The seed assertions keep their numbers (9, 9b); the request-shape assertions move to 10 and 10b.
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Closes #219.
What
seednow reaches the sampler. Both handlers setGenerateParameters.seed, which is whatTopPSampler/CategoricalSampleractually use; the globalMLXRandom.seedcall stays for the paths that callMLXRandomdirectly.UInt64(seed)trapped on it ("Negative value is not representable",Server.swift:2387); the newsamplingSeed(_:)takes the bit pattern instead, so every distinctIntis still a distinct seed.Behaviour without a
seedis unchanged: the sampler keeps its entropy-seededRandomState.Why
The samplers draw from their own
RandomState, seeded only throughGenerateParameters.seed. Seeding MLX's global generator alone meantseedwas accepted and silently ignored: the same request withseed: 42three times gave three different answers. And since OpenAI'sseedis a plain integer, a client sending-1took the whole server down with one request (crash report in #219).Verified
SamplingSeedTests(new): theInt → UInt64mapping, and that two samplers built with the sameGenerateParameters.seeddraw the same tokens while different seeds differ. Red onmainfor the negative-seed case (trap) and green here.tests/test-contract.shgained two assertions: the same seeded request twice returns the identical message, and"seed": -1answers 200 with/healthstill responding. Both fail onmain(the second one by killing the server).swift test --filter SwiftLMTests: 280 tests green locally (M1 Max, Xcode 27 / Swift 6.4).tests/test-contract.shagainst the CI model (mlx-community/Qwen2.5-0.5B-Instruct-4bit): 12 passed, 0 failed, 2 skipped (the script's own tool-call / JSON capability skips).