stillwater-sc / universal / 27468758182

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feat(elreal): online div host-floor lift + dense Newton-Raphson reciprocal (#1061) (#1069)

* fix(elreal): lift the online div host-floor for wide hosts (#1061)

The lazy, pull-driven div_online had an un-gated host_exp_floor =
min_exp + 2k in twoDivZBCL, truncating a single-block quotient at
~17 blocks / ~260 digits on a double host -- ~33 digits short of the
eager div(), whose floor was already gated to narrow hosts (divide.hpp).

block_two_div_rem is scale-invariant: the quotient/remainder
significands stay in [1,2) (always normal) and the scale is carried
symbolically in the wide block exponent (integer<256>, #1066), so on a
wide host (k>=24) the floor is defensive, not load-bearing. Gate it to
narrow hosts only, mirroring divide.hpp's exp_floor. div_online(1,3)
now refines to double's natural ~19-component ceiling (~293 digits) on
demand, matching eager div() block-for-block.

Add verify_div_deep_reach to online_muldiv.cpp: asserts >=19 blocks,
lastE <= -950, 0-overlap, and lazy == eager over the shared prefix via
the exact dyadic oracle. Verified to fail without the gating (negative
control: 17 blocks, lastE=-866). PASS on gcc 13.3 and clang 18.1.

Single-block and sparse divisors now reach the host ceiling; the dense
multi-block deep case (streaming products newfs/newdiv) keeps the floor
and remains the open "div floor rework" -- banner updated accordingly.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

* feat(elreal): dense online div via Newton-Raphson reciprocal (#1061, #1068)

The faithful McCleeary long division (divideHelper, 4.2.6) is correct for a
dense multi-block divisor but COST-EXPLODES: newfs = mul_online(fs, divisorTail)
grows fs every level and infsumRec's cancellation region pulls an unbounded
prefix of that growing stream per emitted block. Measured: correct through
depth 7 (~28ms) then non-terminating at depth 8, at exponent ~ -340 (far above
any host floor) -- so the prior banner's "dense host-floor" f... (continued)

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