rob thijssen
495d3f7c05
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The single-GPU dense load of Qwen/Qwen3.5-0.8B succeeded but the first
inference forward bombed with `dtype mismatch in mul, lhs: F32, rhs:
BF16`. Trace through the recurrent delta-rule loop:
let q = (q.to_dtype(F32)? * scale)?; // F32
let k = k.to_dtype(F32)?; // F32
let v = v.to_dtype(F32)?; // F32
// g built from A_log/dt_bias // F32
// beta = sigmoid(b) // BF16 (sigmoid preserves dtype)
...
let delta = (v_t - kv_mem)?.broadcast_mul(&beta_col)?;
^^^^^^^^^^^^^ ^^^^^^^^^
F32 BF16 ← mismatch
`g` was already F32 because it was constructed from `a_log.to_dtype(F32)`
+ `dt_bias.to_dtype(F32)` earlier in the function. `beta` came from
`sigmoid(b)` where `b` was the model dtype (BF16), so beta stayed BF16
and the multiplication tripped candle's dtype-mismatch check.
Promote beta to F32 at the same point we promote q/k/v.
Caught by the validate-neuron.sh probe against Qwen/Qwen3.5-0.8B on
beast — load returned 200, then `POST /v1/chat/completions` returned
the dtype error.
Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>