grind_won_nonce(header80, target) increments the 80-byte header nonce
[76..79] LE until scrypt_pow_hash(header) <= target -- the EXACT
header_chain.hpp satisfaction gate -- calling THROUGH the #286 digest
CALL SSOT (never a bypass hash), so a nonce it accepts is one node B
ACCEPTs. This is the missing primitive between the faithful won-block
reconstruction and a ProcessNewBlock ACCEPT: the leg-2 A/B delivery
proof reached node B but was consensus-rejected high-hash precisely
because the forced-won seam carried no real PoW.

Fails closed: returns nullopt when no nonce satisfies inside the budget
(or the full 2^32 space wraps) -- a header that does not satisfy its
target is never broadcast, mirroring the reconstructor loud-throw.

dgb_nonce_grinder_test (5/5): finds a satisfying nonce well inside
budget, the winning header satisfies the gate and its reported digest
== the SSOT digest, the winning nonce is written LE into [76..79],
re-grinding from the winner succeeds on iter 1, and an unsatisfiable
target exhausts the budget to nullopt. Reuses the _dgb_scrypt_tus
real-scrypt set; header-only u256, no core / no dgb OBJECT lib. Added
to both build.yml --target allowlists. Fenced src/impl/dgb/ + build.yml.

Wiring grind -> reconstruct -> submit on the live forced-won path and
the node-B ACCEPT gate proof are the explicitly-next integration slice.

…KAT)

regrind_block_nonce: grind the header nonce of an ALREADY-FRAMED
reconstructed-block blob (reconstruct_won_block_from_template {bytes})
until its DGB-Scrypt PoW digest satisfies the parent target, writing the
winning nonce back into header [76..79] IN PLACE. The missing wiring
between the faithful won-block reconstruction (merkle root fixed) and a
node-B ProcessNewBlock ACCEPT: the A/B delivery proof reached node B but
was consensus-rejected "high-hash" because the forced-won seam carried
no real PoW.

Ordering invariant enforced structurally: runs only on an already-framed
block (merkle root set FIRST by reconstruct), mutates ONLY header bytes
[76..79], never the merkle region [36..67] or tx tail. Hash via the #286
scrypt_pow_hash SSOT only; satisfaction = the exact pow <= target gate
header_chain.hpp runs. Fail-closed (nullopt, bytes UNCHANGED) on a runt
blob or exhausted budget.

KAT 5/5: reground header satisfies target via SSOT; only [76..79] mutate
(merkle + tx tail byte-preserved); runt-blob fail-closed; exhausted-budget
fail-closed; deterministic. Reuses the _dgb_scrypt_tus real-scrypt set;
header-only, no core / no OBJECT lib. Both build.yml --target allowlists.

Per-coin isolation: src/impl/dgb/ only. p2pool-merged-v36 surface: NONE.

Closes the #82 broadcaster dual-path gate on the wire: live UpdateTip won
block (regtest diff, no test-only seam) -> reconstruct coinbase-only ->
ARM A submit_block_p2p_raw relays to a peer node, asserting PROP1
(coinbase-only accepted, not fail-open) + PROP2/ARM-A (P2P reaches network).
Scripts-only, fenced (scripts/), DGB-isolated, localhost regtest, self-service
creds. Two live-leg items remain: digibyted self-provisioning (daemon-gated,
only namecoind on fleet) and ARM B submitblock-fallback isolation mechanism
(no --no-p2p-relay flag -> integrator design call), both explicit in-file.

Approved operator toggle (integrator UID1709, option a): suppress ONLY
the embedded P2P-relay arm in main_dgb on_block_found, leaving the
external-digibyted submitblock seam (RPC fallback) live. Lets the #82
regtest soak prove the submitblock fallback lands the won block on its
own, deterministically, instead of being masked by a silent or dead P2P
relay -- the historical #82 gap.

Additive, DGB-fenced (src/c2pool/main_dgb.cpp only); no consensus/share/
PPLNS/shared surface. Real operator flag, not a test-only seam (mirrors
the no-test-seam principle honored for ARM A).

…-regrind)

The forced-won soak reconstructs a block from an injected won share that
carries no real Scrypt work, so node B rejects it high-hash. --soak-regrind
(default OFF, absent from every prod path) wraps the faithful reconstruct
closure: after the version-agnostic template reconstruct frames the block, it
grinds header[76..79] via regrind_block_nonce until the DGB-Scrypt digest
satisfies the block's OWN declared nBits -- exactly the target node B
validates -- then recomputes the hex so both broadcast arms carry the ground
bytes. Merkle root and tx tail are untouched. This closes the last gap to a
live A/B node-B ACCEPT: the seam (PR #286) was a library + KAT; this lands it
in the run-loop behind an explicit operator-only flag.

build EXIT=0, --selftest EXIT=0, --help advertises --soak-regrind.