feat(mlkem_top): KeyGen stages 2a-2c (G, SampleNTT A_hat, CBD s/e)
Fresh valid/ready KeyGen FSM for ML-KEM-512 (K=2, eta1=3). Independent
keccak per consumer (no arbiter). Verified stage-by-stage vs ml-kem-r golden:
- 2a G(d||K): rho/sigma exact (d byte0-low, K at byte32, no reversal).
- 2b SampleNTT: A_hat[i][j] from seed rho||j||i, 1024/1024 coeffs exact.
- 2c CBD: s[i]=CBD3(PRF(sigma,i)), e[i]=CBD3(PRF(sigma,K+i)); signed->mod-q
(+Q when negative); 2048/2048 (A+s+e) coeffs exact.
polymem register array (10 slots x 256), debug readback tap (dbg_slot/idx ->
coeff, rho/sigma taps) for stage TBs. a_busy/c_busy guards (defensive after
sample_ntt fix). FSM: IDLE->G->A->C->DONE (datapath extended in later stages).
Plan + progress doc in .claude/plans/keygen_plan.md.
FallenSigh
2f206a6bc5