diff --git a/src/impl/nmc/coin/header_chain.hpp b/src/impl/nmc/coin/header_chain.hpp
index bf06ccb93..d161e1e6f 100644
--- a/src/impl/nmc/coin/header_chain.hpp
+++ b/src/impl/nmc/coin/header_chain.hpp
@@ -646,6 +646,32 @@ class HeaderChain {
                                   header.m_bits);
     }
 
+    /// P1e: verdict for the activation-height admission gate.
+    enum class AdmitResult {
+        ADMIT,                    // height / auxpow-presence consistent (proof checked separately)
+        REJECT_PREMATURE_AUXPOW,  // header carries an AuxPow below the activation height
+        REJECT_MISSING_AUXPOW,    // no AuxPow at/after activation height (mainnet requirement)
+        REJECT_UNPINNED,          // activation height still the -1 sentinel - refuse to judge
+    };
+
+    /// P1e: the activation-height GATE, factored out for unit-testing
+    /// independent of the (still-deferred) storage path - the same pattern as
+    /// verify_auxpow_header(). Decides admissibility from the connected `height`
+    /// and whether the header carries an AuxPow, BEFORE the four-leg proof is
+    /// walked: below activation an AuxPow is premature, at/after activation
+    /// (mainnet) one is mandatory. While auxpow_activation_height is the
+    /// unpinned -1 sentinel it refuses to judge (REJECT_UNPINNED) so the P1 leaf
+    /// never renders an activation verdict off a placeholder constant.
+    AdmitResult check_activation_gate(int32_t height, bool has_auxpow) const {
+        if (m_params.auxpow_activation_height < 0)
+            return AdmitResult::REJECT_UNPINNED;          // TO-CONFIRM unpinned
+        if (!m_params.is_auxpow_active(height))
+            return has_auxpow ? AdmitResult::REJECT_PREMATURE_AUXPOW
+                              : AdmitResult::ADMIT;
+        return has_auxpow ? AdmitResult::ADMIT
+                          : AdmitResult::REJECT_MISSING_AUXPOW;
+    }
+
     /// Add a header that carries a merge-mining AuxPow proof.
     /// P1d: the AuxPow VERIFICATION GATE is now wired - check_proof() must
     /// return VALID or the header is rejected, so the (future) accept path can
diff --git a/src/impl/nmc/test/auxpow_merkle_test.cpp b/src/impl/nmc/test/auxpow_merkle_test.cpp
index 5ebc00f5f..dafadcb99 100644
--- a/src/impl/nmc/test/auxpow_merkle_test.cpp
+++ b/src/impl/nmc/test/auxpow_merkle_test.cpp
@@ -635,4 +635,65 @@ TEST(NmcP1dGate, MissingAuxBitsKeepsProofIncompleteAndRejected)
     EXPECT_FALSE(chain_.add_auxpow_header(h, ap));
 }
 
+// ---------------------------------------------------------------------------
+// P1e: activation-height admission gate KATs (NmcP1eActivationGate).
+// Exercise HeaderChain::check_activation_gate() - the height-derived MM
+// activation gate, factored like the P1d proof gate so it is testable without
+// the deferred storage path. The production activation height stays the -1
+// sentinel; these fixtures pin a TEST-only height (19200, the historically
+// cited NMC mainnet value) purely to drive the gate - no consensus promotion.
+// ---------------------------------------------------------------------------
+static NMCChainParams params_activation(int32_t act_height)
+{
+    NMCChainParams p = NMCChainParams::mainnet();
+    p.aux_chain_id = 1;
+    p.auxpow_activation_height = act_height;   // TEST-only pin; production stays -1
+    return p;
+}
+
+TEST(NmcP1eActivationGate, UnpinnedActivationRefusesToJudge)
+{
+    // mainnet() leaves auxpow_activation_height at -1: the gate must refuse
+    // rather than guess, regardless of whether the header carries an AuxPow.
+    HeaderChain chain_(params_chain_id_1());
+    EXPECT_EQ(chain_.check_activation_gate(50000, /*has_auxpow=*/true),
+              HeaderChain::AdmitResult::REJECT_UNPINNED);
+    EXPECT_EQ(chain_.check_activation_gate(50000, /*has_auxpow=*/false),
+              HeaderChain::AdmitResult::REJECT_UNPINNED);
+}
+
+TEST(NmcP1eActivationGate, AuxPowBelowActivationIsPremature)
+{
+    HeaderChain chain_(params_activation(19200));
+    EXPECT_EQ(chain_.check_activation_gate(19199, /*has_auxpow=*/true),
+              HeaderChain::AdmitResult::REJECT_PREMATURE_AUXPOW);
+    // a plain (non-MM) header below activation is admissible.
+    EXPECT_EQ(chain_.check_activation_gate(19199, /*has_auxpow=*/false),
+              HeaderChain::AdmitResult::ADMIT);
+}
+
+TEST(NmcP1eActivationGate, AuxPowRequiredAtAndAfterActivation)
+{
+    HeaderChain chain_(params_activation(19200));
+    // exactly at the activation height the AuxPow becomes mandatory.
+    EXPECT_EQ(chain_.check_activation_gate(19200, /*has_auxpow=*/false),
+              HeaderChain::AdmitResult::REJECT_MISSING_AUXPOW);
+    EXPECT_EQ(chain_.check_activation_gate(19200, /*has_auxpow=*/true),
+              HeaderChain::AdmitResult::ADMIT);
+    // and well past it.
+    EXPECT_EQ(chain_.check_activation_gate(250000, /*has_auxpow=*/true),
+              HeaderChain::AdmitResult::ADMIT);
+}
+
+TEST(NmcP1eActivationGate, ActivationBoundaryIsInclusive)
+{
+    HeaderChain chain_(params_activation(19200));
+    // height == activation-1 is still pre-activation (MM not yet required);
+    // height == activation flips MM to mandatory.
+    EXPECT_EQ(chain_.check_activation_gate(19199, /*has_auxpow=*/false),
+              HeaderChain::AdmitResult::ADMIT);
+    EXPECT_EQ(chain_.check_activation_gate(19200, /*has_auxpow=*/false),
+              HeaderChain::AdmitResult::REJECT_MISSING_AUXPOW);
+}
+
 } // namespace