diff --git a/src/configuration.h b/src/configuration.h
index 84dabee4e..efd9ddcf7 100644
--- a/src/configuration.h
+++ b/src/configuration.h
@@ -499,6 +499,7 @@ along with this program.  If not, see <http://www.gnu.org/licenses/>.
 #define MESHTASTIC_EXCLUDE_PKI 1
 #define MESHTASTIC_EXCLUDE_POWER_FSM 1
 #define MESHTASTIC_EXCLUDE_TZ 1
+#define MESHTASTIC_EXCLUDE_PKT_HISTORY_HASH 1
 #endif
 
 // Turn off all optional modules
diff --git a/src/mesh/NextHopRouter.cpp b/src/mesh/NextHopRouter.cpp
index 13f948a7b..e8613d457 100644
--- a/src/mesh/NextHopRouter.cpp
+++ b/src/mesh/NextHopRouter.cpp
@@ -101,9 +101,12 @@ void NextHopRouter::sniffReceived(const meshtastic_MeshPacket *p, const meshtast
             if (origTx) {
                 // Either relayer of ACK was also a relayer of the packet, or we were the *only* relayer and the ACK came
                 // directly from the destination
-                bool wasAlreadyRelayer = wasRelayer(p->relay_node, p->decoded.request_id, p->to);
+                // Single lookup for both relayer checks on the same (request_id, to) pair
+                bool wasAlreadyRelayer = false;
                 bool weWereSoleRelayer = false;
-                bool weWereRelayer = wasRelayer(ourRelayID, p->decoded.request_id, p->to, &weWereSoleRelayer);
+                bool weWereRelayer = false;
+                checkRelayers(p->relay_node, ourRelayID, p->decoded.request_id, p->to, &wasAlreadyRelayer, &weWereRelayer,
+                              &weWereSoleRelayer);
                 if ((weWereRelayer && wasAlreadyRelayer) || (getHopsAway(*p) == 0 && weWereSoleRelayer)) {
                     if (origTx->next_hop != p->relay_node) { // Not already set
                         LOG_INFO("Update next hop of 0x%x to 0x%x based on ACK/reply (was relayer %d we were sole %d)", p->from,
diff --git a/src/mesh/PacketHistory.cpp b/src/mesh/PacketHistory.cpp
index 845a936d4..8289f0078 100644
--- a/src/mesh/PacketHistory.cpp
+++ b/src/mesh/PacketHistory.cpp
@@ -1,6 +1,7 @@
 #include "PacketHistory.h"
 #include "configuration.h"
 #include "mesh-pb-constants.h"
+#include "meshUtils.h"
 
 #ifdef ARCH_PORTDUINO
 #include "platform/portduino/PortduinoGlue.h"
@@ -23,6 +24,14 @@ PacketHistory::PacketHistory(uint32_t size) : recentPacketsCapacity(0), recentPa
         size = PACKETHISTORY_MAX; // Use default size if invalid
     }
 
+#if !MESHTASTIC_EXCLUDE_PKT_HISTORY_HASH
+    // Ensure capacity fits in uint16_t hash index (HASH_EMPTY = 0xFFFF is the sentinel)
+    if (size >= HASH_EMPTY) {
+        LOG_WARN("Packet History - Clamping size %d to %d (hash index limit)", size, HASH_EMPTY - 1);
+        size = HASH_EMPTY - 1;
+    }
+#endif
+
     // Allocate memory for the recent packets array
     recentPacketsCapacity = size;
     recentPackets = new PacketRecord[recentPacketsCapacity];
@@ -35,6 +44,20 @@ PacketHistory::PacketHistory(uint32_t size) : recentPacketsCapacity(0), recentPa
 
     // Initialize the recent packets array to zero
     memset(recentPackets, 0, sizeof(PacketRecord) * recentPacketsCapacity);
+
+#if !MESHTASTIC_EXCLUDE_PKT_HISTORY_HASH
+    // Allocate hash index with load factor <= 0.5 for short probe chains
+    hashCapacity = nextPowerOf2(recentPacketsCapacity * 2);
+    hashMask = hashCapacity - 1;
+    hashIndex = new uint16_t[hashCapacity];
+    if (!hashIndex) {
+        LOG_ERROR("Packet History - Hash index allocation failed for %d entries", hashCapacity);
+        hashCapacity = 0;
+        hashMask = 0;
+        return;
+    }
+    memset(hashIndex, 0xFF, sizeof(uint16_t) * hashCapacity); // Fill with HASH_EMPTY (0xFFFF)
+#endif
 }
 
 PacketHistory::~PacketHistory()
@@ -42,6 +65,12 @@ PacketHistory::~PacketHistory()
     recentPacketsCapacity = 0;
     delete[] recentPackets;
     recentPackets = NULL;
+#if !MESHTASTIC_EXCLUDE_PKT_HISTORY_HASH
+    delete[] hashIndex;
+    hashIndex = NULL;
+    hashCapacity = 0;
+    hashMask = 0;
+#endif
 }
 
 /** Update recentPackets and return true if we have already seen this packet */
@@ -194,7 +223,78 @@ bool PacketHistory::wasSeenRecently(const meshtastic_MeshPacket *p, bool withUpd
     return seenRecently;
 }
 
-/** Find a packet record in history.
+#if !MESHTASTIC_EXCLUDE_PKT_HISTORY_HASH
+// Hash function for (sender, id) pairs. Uses xor-shift mixing for good distribution.
+uint32_t PacketHistory::hashSlot(NodeNum sender, PacketId id) const
+{
+    uint32_t h = sender ^ (id * 0x9E3779B9); // Fibonacci hashing constant
+    h ^= h >> 16;
+    h *= 0x45d9f3b;
+    h ^= h >> 16;
+    return h & hashMask;
+}
+
+void PacketHistory::hashInsert(NodeNum sender, PacketId id, uint16_t slotIdx)
+{
+    if (!hashIndex)
+        return;
+    uint32_t bucket = hashSlot(sender, id);
+    // Guard against infinite loop if hash table is corrupted (no HASH_EMPTY slots)
+    for (uint32_t i = 0; i < hashCapacity; i++) {
+        if (hashIndex[bucket] == HASH_EMPTY) {
+            hashIndex[bucket] = slotIdx;
+            return;
+        }
+        bucket = (bucket + 1) & hashMask;
+    }
+    LOG_ERROR("Packet History - hashInsert: table full or corrupted, rebuilding");
+    hashRebuild();
+}
+
+void PacketHistory::hashRemove(NodeNum sender, PacketId id)
+{
+    if (!hashIndex)
+        return;
+    uint32_t bucket = hashSlot(sender, id);
+    for (uint32_t i = 0; i < hashCapacity; i++) {
+        if (hashIndex[bucket] == HASH_EMPTY)
+            return;
+        uint16_t idx = hashIndex[bucket];
+        if (idx < recentPacketsCapacity && recentPackets[idx].sender == sender && recentPackets[idx].id == id) {
+            // Found it — delete and re-insert subsequent entries to maintain probe chain integrity
+            hashIndex[bucket] = HASH_EMPTY;
+            uint32_t next = (bucket + 1) & hashMask;
+            for (uint32_t j = 0; j < hashCapacity; j++) {
+                if (hashIndex[next] == HASH_EMPTY)
+                    break;
+                uint16_t displaced = hashIndex[next];
+                hashIndex[next] = HASH_EMPTY;
+                if (displaced < recentPacketsCapacity) {
+                    const auto &rec = recentPackets[displaced];
+                    hashInsert(rec.sender, rec.id, displaced);
+                }
+                next = (next + 1) & hashMask;
+            }
+            return;
+        }
+        bucket = (bucket + 1) & hashMask;
+    }
+}
+
+void PacketHistory::hashRebuild()
+{
+    if (!hashIndex)
+        return;
+    memset(hashIndex, 0xFF, sizeof(uint16_t) * hashCapacity);
+    for (uint32_t i = 0; i < recentPacketsCapacity; i++) {
+        if (recentPackets[i].rxTimeMsec != 0)
+            hashInsert(recentPackets[i].sender, recentPackets[i].id, (uint16_t)i);
+    }
+}
+#endif
+
+/** Find a packet record in history using the hash index for O(1) average lookup.
+ * Falls back to linear scan if hash index is unavailable.
  * @return pointer to PacketRecord if found, NULL if not found */
 PacketHistory::PacketRecord *PacketHistory::find(NodeNum sender, PacketId id)
 {
@@ -205,23 +305,40 @@ PacketHistory::PacketRecord *PacketHistory::find(NodeNum sender, PacketId id)
         return NULL;
     }
 
-    PacketRecord *it = NULL;
-    for (it = recentPackets; it < (recentPackets + recentPacketsCapacity); ++it) {
-        if (it->id == id && it->sender == sender) {
+#if !MESHTASTIC_EXCLUDE_PKT_HISTORY_HASH
+    // Use hash index for O(1) lookup when available
+    if (hashIndex) {
+        uint32_t bucket = hashSlot(sender, id);
+        for (uint32_t i = 0; i < hashCapacity; i++) {
+            if (hashIndex[bucket] == HASH_EMPTY)
+                break;
+            uint16_t idx = hashIndex[bucket];
+            if (idx < recentPacketsCapacity && recentPackets[idx].id == id && recentPackets[idx].sender == sender) {
 #if VERBOSE_PACKET_HISTORY
-            LOG_DEBUG("Packet History - find: s=%08x id=%08x FOUND nh=%02x rby=%02x %02x %02x age=%d slot=%d/%d", it->sender,
-                      it->id, it->next_hop, it->relayed_by[0], it->relayed_by[1], it->relayed_by[2], millis() - (it->rxTimeMsec),
-                      it - recentPackets, recentPacketsCapacity);
+                LOG_DEBUG("Packet History - find: s=%08x id=%08x FOUND nh=%02x rby=%02x %02x %02x age=%d slot=%d/%d",
+                          recentPackets[idx].sender, recentPackets[idx].id, recentPackets[idx].next_hop,
+                          recentPackets[idx].relayed_by[0], recentPackets[idx].relayed_by[1], recentPackets[idx].relayed_by[2],
+                          millis() - (recentPackets[idx].rxTimeMsec), idx, recentPacketsCapacity);
 #endif
-            // only the first match is returned, so be careful not to create duplicate entries
-            return it; // Return pointer to the found record
+                return &recentPackets[idx];
+            }
+            bucket = (bucket + 1) & hashMask;
+        }
+#if VERBOSE_PACKET_HISTORY
+        LOG_DEBUG("Packet History - find: s=%08x id=%08x NOT FOUND", sender, id);
+#endif
+        return NULL;
+    }
+#endif
+
+    // Linear scan (sole path when hash excluded, fallback when hash allocation failed)
+    for (PacketRecord *it = recentPackets; it < (recentPackets + recentPacketsCapacity); ++it) {
+        if (it->id == id && it->sender == sender) {
+            return it;
         }
     }
 
-#if VERBOSE_PACKET_HISTORY
-    LOG_DEBUG("Packet History - find: s=%08x id=%08x NOT FOUND", sender, id);
-#endif
-    return NULL; // Not found
+    return NULL;
 }
 
 /** Insert/Replace oldest PacketRecord in recentPackets. */
@@ -327,8 +444,22 @@ void PacketHistory::insert(const PacketRecord &r)
         return; // Return early if we can't update the history
     }
 
+#if !MESHTASTIC_EXCLUDE_PKT_HISTORY_HASH
+    // Maintain hash index: remove old entry if evicting a different packet, then insert new entry
+    bool isMatchingSlot = (tu->id == r.id && tu->sender == r.sender);
+    if (!isMatchingSlot && tu->rxTimeMsec != 0) {
+        hashRemove(tu->sender, tu->id);
+    }
+
     *tu = r; // store the packet
 
+    if (!isMatchingSlot) {
+        hashInsert(r.sender, r.id, (uint16_t)(tu - recentPackets));
+    }
+#else
+    *tu = r; // store the packet
+#endif
+
 #if VERBOSE_PACKET_HISTORY
     LOG_DEBUG("Packet History - insert: Store slot@ %d/%d s=%08x id=%08x nh=%02x rby=%02x %02x %02x rxT=%d AFTER",
               tu - recentPackets, recentPacketsCapacity, tu->sender, tu->id, tu->next_hop, tu->relayed_by[0], tu->relayed_by[1],
@@ -396,6 +527,31 @@ bool PacketHistory::wasRelayer(const uint8_t relayer, const PacketRecord &r, boo
     return found;
 }
 
+// Check two relayers against the same packet record with a single find() call,
+// avoiding redundant O(N) lookups when both are checked for the same (id, sender) pair.
+void PacketHistory::checkRelayers(uint8_t relayer1, uint8_t relayer2, uint32_t id, NodeNum sender, bool *r1Result, bool *r2Result,
+                                  bool *r2WasSole)
+{
+    *r1Result = false;
+    *r2Result = false;
+    if (r2WasSole)
+        *r2WasSole = false;
+
+    if (!initOk()) {
+        LOG_ERROR("PacketHistory - checkRelayers: NOT INITIALIZED!");
+        return;
+    }
+
+    const PacketRecord *found = find(sender, id);
+    if (!found)
+        return;
+
+    if (relayer1 != 0)
+        *r1Result = wasRelayer(relayer1, *found);
+    if (relayer2 != 0)
+        *r2Result = wasRelayer(relayer2, *found, r2WasSole);
+}
+
 // Remove a relayer from the list of relayers of a packet in the history given an ID and sender
 void PacketHistory::removeRelayer(const uint8_t relayer, const uint32_t id, const NodeNum sender)
 {
diff --git a/src/mesh/PacketHistory.h b/src/mesh/PacketHistory.h
index 9b6a93280..a11e2d038 100644
--- a/src/mesh/PacketHistory.h
+++ b/src/mesh/PacketHistory.h
@@ -28,6 +28,22 @@ class PacketHistory
         0; // Can be set in constructor, no need to recompile. Used to allocate memory for mx_recentPackets.
     PacketRecord *recentPackets = NULL; // Simple and fixed in size. Debloat.
 
+#if !MESHTASTIC_EXCLUDE_PKT_HISTORY_HASH
+    // Open-addressing hash table for O(1) lookup in find(), replacing the O(N) linear scan.
+    // Maps (sender, id) -> index into recentPackets[]. Uses linear probing with a load factor <= 0.5.
+    // The load factor invariant holds permanently: hashCapacity = 2 * nextPowerOf2(recentPacketsCapacity),
+    // and at most recentPacketsCapacity entries can ever be live (one per recentPackets[] slot).
+    static constexpr uint16_t HASH_EMPTY = 0xFFFF;
+    uint16_t *hashIndex = NULL;
+    uint32_t hashCapacity = 0; // Always a power of 2
+    uint32_t hashMask = 0;     // hashCapacity - 1, for fast modular indexing
+
+    uint32_t hashSlot(NodeNum sender, PacketId id) const;
+    void hashInsert(NodeNum sender, PacketId id, uint16_t slotIdx);
+    void hashRemove(NodeNum sender, PacketId id);
+    void hashRebuild();
+#endif
+
     /** Find a packet record in history.
      * @param sender NodeNum
      * @param id PacketId
@@ -70,6 +86,16 @@ class PacketHistory
      * @return true if node was indeed a relayer, false if not */
     bool wasRelayer(const uint8_t relayer, const uint32_t id, const NodeNum sender, bool *wasSole = nullptr);
 
+    /**
+     * Check two relayers against the same packet record with a single lookup.
+     * Avoids redundant find() calls when checking multiple relayers for the same (id, sender) pair.
+     * @param r1Result set to true if relayer1 was a relayer
+     * @param r2Result set to true if relayer2 was a relayer
+     * @param r2WasSole if not nullptr, set to true if relayer2 was the sole relayer
+     */
+    void checkRelayers(uint8_t relayer1, uint8_t relayer2, uint32_t id, NodeNum sender, bool *r1Result, bool *r2Result,
+                       bool *r2WasSole = nullptr);
+
     // Remove a relayer from the list of relayers of a packet in the history given an ID and sender
     void removeRelayer(const uint8_t relayer, const uint32_t id, const NodeNum sender);
 
diff --git a/src/meshUtils.h b/src/meshUtils.h
index da3a4593b..fe94ead2f 100644
--- a/src/meshUtils.h
+++ b/src/meshUtils.h
@@ -11,6 +11,24 @@ template <class T> constexpr const T &clamp(const T &v, const T &lo, const T &hi
     return (v < lo) ? lo : (hi < v) ? hi : v;
 }
 
+/// Return the smallest power of 2 >= n (undefined for n > 2^31)
+static inline uint32_t nextPowerOf2(uint32_t n)
+{
+    if (n <= 1)
+        return 1;
+#if defined(__GNUC__)
+    return 1U << (32 - __builtin_clz(n - 1));
+#else
+    n--;
+    n |= n >> 1;
+    n |= n >> 2;
+    n |= n >> 4;
+    n |= n >> 8;
+    n |= n >> 16;
+    return n + 1;
+#endif
+}
+
 #if HAS_SCREEN
 #define IF_SCREEN(X)                                                                                                             \
     if (screen) {                                                                                                                \
diff --git a/test/test_packet_history/test_main.cpp b/test/test_packet_history/test_main.cpp
new file mode 100644
index 000000000..2453956c5
--- /dev/null
+++ b/test/test_packet_history/test_main.cpp
@@ -0,0 +1,834 @@
+/*
+ * Unit tests for PacketHistory — the packet deduplication engine
+ * used by the mesh routing stack.
+ *
+ * PacketHistory maintains a fixed-size array of PacketRecords with an
+ * optional hash table for O(1) lookup. It tracks which nodes relayed
+ * each packet, supports LRU-style eviction, and detects fallback-to-
+ * flooding and hop-limit upgrades.
+ */
+
+#include "PacketHistory.h"
+
+#include "TestUtil.h"
+#include <unity.h>
+
+// ---------------------------------------------------------------------------
+// Constants
+// ---------------------------------------------------------------------------
+static constexpr uint32_t OUR_NODE_NUM = 0xDEAD1234;
+static constexpr uint8_t OUR_RELAY_ID = 0x34; // getLastByteOfNodeNum(OUR_NODE_NUM)
+static constexpr uint32_t SMALL_CAPACITY = 8;
+
+// ---------------------------------------------------------------------------
+// Per-test state
+// ---------------------------------------------------------------------------
+static PacketHistory *ph = nullptr;
+
+// ---------------------------------------------------------------------------
+// Helpers
+// ---------------------------------------------------------------------------
+static meshtastic_MeshPacket makePacket(uint32_t from, uint32_t id, uint8_t hop_limit = 3,
+                                        uint8_t next_hop = NO_NEXT_HOP_PREFERENCE, uint8_t relay_node = 0)
+{
+    meshtastic_MeshPacket p = meshtastic_MeshPacket_init_zero;
+    p.from = from;
+    p.id = id;
+    p.hop_limit = hop_limit;
+    p.next_hop = next_hop;
+    p.relay_node = relay_node;
+    return p;
+}
+
+// ---------------------------------------------------------------------------
+// setUp / tearDown — called before and after every test
+// ---------------------------------------------------------------------------
+void setUp(void)
+{
+    myNodeInfo.my_node_num = OUR_NODE_NUM;
+    ph = new PacketHistory(SMALL_CAPACITY);
+}
+
+void tearDown(void)
+{
+    delete ph;
+    ph = nullptr;
+}
+
+// ===========================================================================
+// Group 1 — Initialization
+// ===========================================================================
+
+void test_init_valid_size(void)
+{
+    PacketHistory h(8);
+    TEST_ASSERT_TRUE(h.initOk());
+}
+
+void test_init_minimum_size(void)
+{
+    PacketHistory h(4);
+    TEST_ASSERT_TRUE(h.initOk());
+}
+
+void test_init_too_small_falls_back(void)
+{
+    // Sizes < 4 or > PACKETHISTORY_MAX are clamped to PACKETHISTORY_MAX inside the constructor
+    PacketHistory h(2);
+    TEST_ASSERT_TRUE(h.initOk());
+}
+
+// ===========================================================================
+// Group 2 — Basic Deduplication
+// ===========================================================================
+
+void test_first_packet_not_seen(void)
+{
+    auto p = makePacket(0x1111, 100);
+    TEST_ASSERT_FALSE(ph->wasSeenRecently(&p));
+}
+
+void test_same_packet_seen_twice(void)
+{
+    auto p = makePacket(0x1111, 100);
+    TEST_ASSERT_FALSE(ph->wasSeenRecently(&p)); // first time
+    TEST_ASSERT_TRUE(ph->wasSeenRecently(&p));  // duplicate
+}
+
+void test_different_id_not_confused(void)
+{
+    auto p1 = makePacket(0x1111, 100);
+    auto p2 = makePacket(0x1111, 200);
+    ph->wasSeenRecently(&p1);
+    TEST_ASSERT_FALSE(ph->wasSeenRecently(&p2));
+}
+
+void test_different_sender_not_confused(void)
+{
+    auto p1 = makePacket(0x1111, 100);
+    auto p2 = makePacket(0x2222, 100);
+    ph->wasSeenRecently(&p1);
+    TEST_ASSERT_FALSE(ph->wasSeenRecently(&p2));
+}
+
+void test_withUpdate_false_no_insert(void)
+{
+    auto p = makePacket(0x1111, 100);
+    // First call with withUpdate=false: should not store
+    TEST_ASSERT_FALSE(ph->wasSeenRecently(&p, /*withUpdate=*/false));
+    // Second call with withUpdate=true: still not found because first didn't store
+    TEST_ASSERT_FALSE(ph->wasSeenRecently(&p, /*withUpdate=*/true));
+}
+
+void test_withUpdate_true_inserts(void)
+{
+    auto p = makePacket(0x1111, 100);
+    TEST_ASSERT_FALSE(ph->wasSeenRecently(&p, /*withUpdate=*/true));
+    TEST_ASSERT_TRUE(ph->wasSeenRecently(&p, /*withUpdate=*/false)); // found without inserting again
+}
+
+// ===========================================================================
+// Group 3 — LRU Eviction
+// ===========================================================================
+
+void test_fill_capacity_all_found(void)
+{
+    for (uint32_t i = 1; i <= SMALL_CAPACITY; i++) {
+        auto p = makePacket(0xAAAA, i);
+        ph->wasSeenRecently(&p);
+    }
+    // All 8 should be found
+    for (uint32_t i = 1; i <= SMALL_CAPACITY; i++) {
+        auto p = makePacket(0xAAAA, i);
+        TEST_ASSERT_TRUE(ph->wasSeenRecently(&p, false));
+    }
+}
+
+void test_eviction_oldest_replaced(void)
+{
+    // Fill all 8 slots
+    for (uint32_t i = 1; i <= SMALL_CAPACITY; i++) {
+        auto p = makePacket(0xAAAA, i);
+        ph->wasSeenRecently(&p);
+    }
+
+    // Advance time so the eviction logic can distinguish "oldest" from "newest".
+    // insert() uses (now_millis - rxTimeMsec) > OldtrxTimeMsec with strict >, so
+    // entries with identical timestamps all have age 0 and none gets selected.
+    delay(1);
+
+    // Insert a 9th packet — should evict the oldest
+    auto p9 = makePacket(0xAAAA, 9);
+    ph->wasSeenRecently(&p9);
+
+    // The 9th should be found
+    TEST_ASSERT_TRUE(ph->wasSeenRecently(&p9, false));
+
+    // At least one of the originals should have been evicted
+    int evicted = 0;
+    for (uint32_t i = 1; i <= SMALL_CAPACITY; i++) {
+        auto p = makePacket(0xAAAA, i);
+        if (!ph->wasSeenRecently(&p, false))
+            evicted++;
+    }
+    TEST_ASSERT_TRUE(evicted > 0);
+}
+
+void test_matching_slot_reused(void)
+{
+    // Insert packet, then re-insert same (sender, id) — should reuse slot, not evict others
+    auto p1 = makePacket(0xAAAA, 1);
+    auto p2 = makePacket(0xBBBB, 2);
+    ph->wasSeenRecently(&p1);
+    ph->wasSeenRecently(&p2);
+
+    // Re-observe p1 (triggers merge path)
+    ph->wasSeenRecently(&p1);
+
+    // Both should still be present
+    TEST_ASSERT_TRUE(ph->wasSeenRecently(&p1, false));
+    TEST_ASSERT_TRUE(ph->wasSeenRecently(&p2, false));
+}
+
+void test_free_slot_preferred(void)
+{
+    // Insert 4 packets into capacity-8 history — next insert should use a free slot, not evict
+    for (uint32_t i = 1; i <= 4; i++) {
+        auto p = makePacket(0xAAAA, i);
+        ph->wasSeenRecently(&p);
+    }
+    auto p5 = makePacket(0xAAAA, 5);
+    ph->wasSeenRecently(&p5);
+
+    // All 5 should be present (no eviction needed)
+    for (uint32_t i = 1; i <= 5; i++) {
+        auto p = makePacket(0xAAAA, i);
+        TEST_ASSERT_TRUE(ph->wasSeenRecently(&p, false));
+    }
+}
+
+void test_evict_all_old_packets(void)
+{
+    // Fill with packets 1..8
+    for (uint32_t i = 1; i <= SMALL_CAPACITY; i++) {
+        auto p = makePacket(0xAAAA, i);
+        ph->wasSeenRecently(&p);
+    }
+
+    // Advance time so the replacement batch can evict the originals
+    delay(1);
+
+    // Replace all with packets 101..108
+    for (uint32_t i = 101; i <= 100 + SMALL_CAPACITY; i++) {
+        auto p = makePacket(0xBBBB, i);
+        ph->wasSeenRecently(&p);
+    }
+    // None of the originals should be found
+    for (uint32_t i = 1; i <= SMALL_CAPACITY; i++) {
+        auto p = makePacket(0xAAAA, i);
+        TEST_ASSERT_FALSE(ph->wasSeenRecently(&p, false));
+    }
+    // All new ones should be found
+    for (uint32_t i = 101; i <= 100 + SMALL_CAPACITY; i++) {
+        auto p = makePacket(0xBBBB, i);
+        TEST_ASSERT_TRUE(ph->wasSeenRecently(&p, false));
+    }
+}
+
+// ===========================================================================
+// Group 4 — Relayer Tracking
+// ===========================================================================
+
+void test_wasRelayer_true(void)
+{
+    // Non-us relay_nodes only enter relayed_by[] through the "heard-back" merge path:
+    // we must have relayed first, then observe the packet return at hop_limit-1.
+    auto p1 = makePacket(0x1111, 100, 3, NO_NEXT_HOP_PREFERENCE, OUR_RELAY_ID);
+    ph->wasSeenRecently(&p1);
+
+    // Heard-back from 0xCC at hop_limit=2 (ourTxHopLimit-1) triggers the merge
+    auto p2 = makePacket(0x1111, 100, 2, NO_NEXT_HOP_PREFERENCE, 0xCC);
+    ph->wasSeenRecently(&p2);
+
+    TEST_ASSERT_TRUE(ph->wasRelayer(0xCC, 100, 0x1111));
+}
+
+void test_wasRelayer_false(void)
+{
+    auto p = makePacket(0x1111, 100, 3, NO_NEXT_HOP_PREFERENCE, 0xAA);
+    ph->wasSeenRecently(&p);
+    // 0xCC was never a relayer
+    TEST_ASSERT_FALSE(ph->wasRelayer(0xCC, 100, 0x1111));
+}
+
+void test_wasRelayer_zero_returns_false(void)
+{
+    auto p = makePacket(0x1111, 100);
+    ph->wasSeenRecently(&p);
+    TEST_ASSERT_FALSE(ph->wasRelayer(0, 100, 0x1111));
+}
+
+void test_wasRelayer_not_found(void)
+{
+    // Packet not in history at all
+    TEST_ASSERT_FALSE(ph->wasRelayer(0xAA, 999, 0x9999));
+}
+
+void test_wasRelayer_wasSole_true(void)
+{
+    // relay_node = ourRelayID → relayed_by[0] = ourRelayID
+    auto p = makePacket(0x1111, 100, 3, NO_NEXT_HOP_PREFERENCE, OUR_RELAY_ID);
+    ph->wasSeenRecently(&p);
+
+    bool wasSole = false;
+    bool result = ph->wasRelayer(OUR_RELAY_ID, 100, 0x1111, &wasSole);
+    TEST_ASSERT_TRUE(result);
+    TEST_ASSERT_TRUE(wasSole);
+}
+
+void test_wasRelayer_wasSole_false(void)
+{
+    // First observation: we relay
+    auto p1 = makePacket(0x1111, 100, 3, NO_NEXT_HOP_PREFERENCE, OUR_RELAY_ID);
+    ph->wasSeenRecently(&p1);
+
+    // Second observation: different relayer adds to record
+    auto p2 = makePacket(0x1111, 100, 2, NO_NEXT_HOP_PREFERENCE, 0xBB);
+    ph->wasSeenRecently(&p2);
+
+    bool wasSole = true;
+    bool result = ph->wasRelayer(OUR_RELAY_ID, 100, 0x1111, &wasSole);
+    TEST_ASSERT_TRUE(result);
+    TEST_ASSERT_FALSE(wasSole);
+}
+
+void test_wasRelayer_all_six_slots(void)
+{
+    // First observation: we relay with hop_limit=3 (fills slot 0, ourTxHopLimit=3)
+    auto p = makePacket(0x1111, 100, 3, NO_NEXT_HOP_PREFERENCE, OUR_RELAY_ID);
+    ph->wasSeenRecently(&p);
+
+    // Each heard-back must satisfy: hop_limit == ourTxHopLimit OR ourTxHopLimit-1.
+    // Using hop_limit=2 (ourTxHopLimit-1) for all, which triggers the heard-back
+    // merge path each time. Each new relay_node pushes to slot 0 and shifts existing
+    // relayers right, eventually filling all NUM_RELAYERS(6) slots.
+    uint8_t relayers[] = {0x11, 0x22, 0x33, 0x44, 0x55};
+    for (int i = 0; i < 5; i++) {
+        auto pn = makePacket(0x1111, 100, 2, NO_NEXT_HOP_PREFERENCE, relayers[i]);
+        ph->wasSeenRecently(&pn);
+    }
+
+    // All 6 should be detected
+    TEST_ASSERT_TRUE(ph->wasRelayer(OUR_RELAY_ID, 100, 0x1111));
+    for (int i = 0; i < 5; i++) {
+        TEST_ASSERT_TRUE(ph->wasRelayer(relayers[i], 100, 0x1111));
+    }
+}
+
+// ===========================================================================
+// Group 5 — removeRelayer
+// ===========================================================================
+
+void test_removeRelayer_removes(void)
+{
+    auto p1 = makePacket(0x1111, 100, 3, NO_NEXT_HOP_PREFERENCE, OUR_RELAY_ID);
+    ph->wasSeenRecently(&p1);
+    TEST_ASSERT_TRUE(ph->wasRelayer(OUR_RELAY_ID, 100, 0x1111));
+
+    ph->removeRelayer(OUR_RELAY_ID, 100, 0x1111);
+    TEST_ASSERT_FALSE(ph->wasRelayer(OUR_RELAY_ID, 100, 0x1111));
+}
+
+void test_removeRelayer_compacts(void)
+{
+    // We relay first
+    auto p1 = makePacket(0x1111, 100, 3, NO_NEXT_HOP_PREFERENCE, OUR_RELAY_ID);
+    ph->wasSeenRecently(&p1);
+    // Second relayer
+    auto p2 = makePacket(0x1111, 100, 2, NO_NEXT_HOP_PREFERENCE, 0xBB);
+    ph->wasSeenRecently(&p2);
+
+    // Remove us, 0xBB should still be found
+    ph->removeRelayer(OUR_RELAY_ID, 100, 0x1111);
+    TEST_ASSERT_FALSE(ph->wasRelayer(OUR_RELAY_ID, 100, 0x1111));
+    TEST_ASSERT_TRUE(ph->wasRelayer(0xBB, 100, 0x1111));
+}
+
+void test_removeRelayer_nonexistent_safe(void)
+{
+    auto p = makePacket(0x1111, 100, 3, NO_NEXT_HOP_PREFERENCE, OUR_RELAY_ID);
+    ph->wasSeenRecently(&p);
+    // Removing a relayer that doesn't exist should not crash
+    ph->removeRelayer(0xFF, 100, 0x1111);
+    // Original should still be there
+    TEST_ASSERT_TRUE(ph->wasRelayer(OUR_RELAY_ID, 100, 0x1111));
+}
+
+void test_removeRelayer_packet_not_found_safe(void)
+{
+    // Packet not in history — should not crash
+    ph->removeRelayer(0xAA, 999, 0x9999);
+}
+
+// ===========================================================================
+// Group 6 — checkRelayers
+// ===========================================================================
+
+void test_checkRelayers_both_found(void)
+{
+    // We relay first
+    auto p1 = makePacket(0x1111, 100, 3, NO_NEXT_HOP_PREFERENCE, OUR_RELAY_ID);
+    ph->wasSeenRecently(&p1);
+    // Second relayer
+    auto p2 = makePacket(0x1111, 100, 2, NO_NEXT_HOP_PREFERENCE, 0xBB);
+    ph->wasSeenRecently(&p2);
+
+    bool r1 = false, r2 = false;
+    ph->checkRelayers(OUR_RELAY_ID, 0xBB, 100, 0x1111, &r1, &r2);
+    TEST_ASSERT_TRUE(r1);
+    TEST_ASSERT_TRUE(r2);
+}
+
+void test_checkRelayers_one_found(void)
+{
+    auto p = makePacket(0x1111, 100, 3, NO_NEXT_HOP_PREFERENCE, OUR_RELAY_ID);
+    ph->wasSeenRecently(&p);
+
+    bool r1 = false, r2 = false;
+    ph->checkRelayers(OUR_RELAY_ID, 0xCC, 100, 0x1111, &r1, &r2);
+    TEST_ASSERT_TRUE(r1);
+    TEST_ASSERT_FALSE(r2);
+}
+
+void test_checkRelayers_r2WasSole(void)
+{
+    auto p = makePacket(0x1111, 100, 3, NO_NEXT_HOP_PREFERENCE, OUR_RELAY_ID);
+    ph->wasSeenRecently(&p);
+
+    bool r1 = false, r2 = false, r2Sole = false;
+    // relayer1=0xCC (not found), relayer2=OUR_RELAY_ID (sole relayer)
+    ph->checkRelayers(0xCC, OUR_RELAY_ID, 100, 0x1111, &r1, &r2, &r2Sole);
+    TEST_ASSERT_FALSE(r1);
+    TEST_ASSERT_TRUE(r2);
+    TEST_ASSERT_TRUE(r2Sole);
+}
+
+// ===========================================================================
+// Group 7 — wasSeenRecently Merge Logic
+// ===========================================================================
+
+void test_merge_preserves_original_next_hop(void)
+{
+    // First observation with next_hop=0x55
+    auto p1 = makePacket(0x1111, 100, 3, 0x55, 0xAA);
+    ph->wasSeenRecently(&p1);
+
+    // Re-observation with different next_hop
+    auto p2 = makePacket(0x1111, 100, 2, 0x77, 0xBB);
+    ph->wasSeenRecently(&p2);
+
+    // The stored next_hop should still be 0x55 (the original)
+    // We verify via weWereNextHop: if we set original next_hop to ourRelayID, it should detect it
+    auto p3 = makePacket(0x1111, 200, 3, OUR_RELAY_ID, 0xAA);
+    ph->wasSeenRecently(&p3);
+    auto p4 = makePacket(0x1111, 200, 2, 0x99, 0xBB);
+    bool weWereNextHop = false;
+    ph->wasSeenRecently(&p4, true, nullptr, &weWereNextHop);
+    TEST_ASSERT_TRUE(weWereNextHop);
+}
+
+void test_merge_preserves_highest_hop_limit(void)
+{
+    // First observation with hop_limit=5
+    auto p1 = makePacket(0x1111, 100, 5);
+    ph->wasSeenRecently(&p1);
+
+    // Re-observation with hop_limit=2 (lower)
+    auto p2 = makePacket(0x1111, 100, 2);
+    ph->wasSeenRecently(&p2);
+
+    // Third observation with hop_limit=3 should not trigger upgrade (highest was 5)
+    bool wasUpgraded = true;
+    auto p3 = makePacket(0x1111, 100, 3);
+    ph->wasSeenRecently(&p3, true, nullptr, nullptr, &wasUpgraded);
+    TEST_ASSERT_FALSE(wasUpgraded);
+}
+
+void test_merge_no_duplicate_relayers(void)
+{
+    // Observe with relayer 0xAA (stored via relay_node, but only slot 0 for ourRelayID)
+    // We need to use ourRelayID for the first observation to get it into slot 0
+    auto p1 = makePacket(0x1111, 100, 3, NO_NEXT_HOP_PREFERENCE, OUR_RELAY_ID);
+    ph->wasSeenRecently(&p1);
+
+    // Re-observe with same relay_node=ourRelayID — should not create duplicates
+    auto p2 = makePacket(0x1111, 100, 2, NO_NEXT_HOP_PREFERENCE, OUR_RELAY_ID);
+    ph->wasSeenRecently(&p2);
+
+    // ourRelayID should appear exactly once — wasSole should still be true
+    bool wasSole = false;
+    TEST_ASSERT_TRUE(ph->wasRelayer(OUR_RELAY_ID, 100, 0x1111, &wasSole));
+    TEST_ASSERT_TRUE(wasSole);
+}
+
+void test_merge_adds_new_relayer(void)
+{
+    auto p1 = makePacket(0x1111, 100, 3, NO_NEXT_HOP_PREFERENCE, OUR_RELAY_ID);
+    ph->wasSeenRecently(&p1);
+
+    auto p2 = makePacket(0x1111, 100, 2, NO_NEXT_HOP_PREFERENCE, 0xBB);
+    ph->wasSeenRecently(&p2);
+
+    TEST_ASSERT_TRUE(ph->wasRelayer(OUR_RELAY_ID, 100, 0x1111));
+    TEST_ASSERT_TRUE(ph->wasRelayer(0xBB, 100, 0x1111));
+}
+
+void test_merge_we_relay_sets_slot_zero(void)
+{
+    // When relay_node == ourRelayID, relayed_by[0] should be set to ourRelayID
+    auto p = makePacket(0x1111, 100, 3, NO_NEXT_HOP_PREFERENCE, OUR_RELAY_ID);
+    ph->wasSeenRecently(&p);
+
+    TEST_ASSERT_TRUE(ph->wasRelayer(OUR_RELAY_ID, 100, 0x1111));
+}
+
+void test_merge_heard_back_stores_relay_node(void)
+{
+    // First: we relay (hop_limit=3)
+    auto p1 = makePacket(0x1111, 100, 3, NO_NEXT_HOP_PREFERENCE, OUR_RELAY_ID);
+    ph->wasSeenRecently(&p1);
+
+    // Second: we hear the packet back with hop_limit=2 (one less), from relay_node=0xCC
+    // This triggers the "heard back" logic: weWereRelayer && hop_limit == ourTxHopLimit-1
+    auto p2 = makePacket(0x1111, 100, 2, NO_NEXT_HOP_PREFERENCE, 0xCC);
+    ph->wasSeenRecently(&p2);
+
+    TEST_ASSERT_TRUE(ph->wasRelayer(OUR_RELAY_ID, 100, 0x1111));
+    TEST_ASSERT_TRUE(ph->wasRelayer(0xCC, 100, 0x1111));
+}
+
+// ===========================================================================
+// Group 8 — Fallback-to-Flooding Detection
+// ===========================================================================
+
+void test_fallback_detected(void)
+{
+    // The fallback condition requires wasRelayer(relay_node) && !wasRelayer(ourRelayID).
+    // Non-us relayers only enter relayed_by[] via the heard-back merge path, which
+    // also stores ourRelayID. So we must removeRelayer(ourRelayID) to satisfy both.
+    //
+    // Scenario: we relay a directed packet, hear it back from 0xAA, then the router
+    // removes us from the relayer list. Later the sender falls back to flooding.
+
+    // Step 1: We relay (directed to next_hop=0x55)
+    auto p1 = makePacket(0x1111, 100, 3, 0x55, OUR_RELAY_ID);
+    ph->wasSeenRecently(&p1);
+
+    // Step 2: Heard-back from 0xAA at hop_limit-1 → stores 0xAA in relayed_by
+    auto p2 = makePacket(0x1111, 100, 2, 0x55, 0xAA);
+    ph->wasSeenRecently(&p2);
+
+    // Step 3: Router removes us from the relayer list
+    ph->removeRelayer(OUR_RELAY_ID, 100, 0x1111);
+
+    // Step 4: Sender falls back to flooding — same packet, NO_NEXT_HOP_PREFERENCE, from 0xAA
+    auto p3 = makePacket(0x1111, 100, 1, NO_NEXT_HOP_PREFERENCE, 0xAA);
+    bool wasFallback = false;
+    ph->wasSeenRecently(&p3, true, &wasFallback);
+    TEST_ASSERT_TRUE(wasFallback);
+}
+
+void test_fallback_not_when_we_relayed(void)
+{
+    // First observation: directed, we relayed it
+    auto p1 = makePacket(0x1111, 100, 3, 0x55, OUR_RELAY_ID);
+    ph->wasSeenRecently(&p1);
+
+    // Second observation: fallback to flooding from same relayer (us)
+    // But since we already relayed, wasFallback should be false
+    auto p2 = makePacket(0x1111, 100, 2, NO_NEXT_HOP_PREFERENCE, OUR_RELAY_ID);
+    bool wasFallback = false;
+    ph->wasSeenRecently(&p2, true, &wasFallback);
+    TEST_ASSERT_FALSE(wasFallback);
+}
+
+void test_fallback_not_on_first_observation(void)
+{
+    // First time seen — can't be a fallback
+    auto p = makePacket(0x1111, 100, 3, NO_NEXT_HOP_PREFERENCE, 0xAA);
+    bool wasFallback = false;
+    ph->wasSeenRecently(&p, true, &wasFallback);
+    TEST_ASSERT_FALSE(wasFallback);
+}
+
+// ===========================================================================
+// Group 9 — Next-Hop and Upgrade Detection
+// ===========================================================================
+
+void test_weWereNextHop_true(void)
+{
+    // Packet directed to us (next_hop = ourRelayID)
+    auto p1 = makePacket(0x1111, 100, 3, OUR_RELAY_ID, 0xAA);
+    ph->wasSeenRecently(&p1);
+
+    // Re-observe: check if we were the original next_hop
+    auto p2 = makePacket(0x1111, 100, 2, NO_NEXT_HOP_PREFERENCE, 0xBB);
+    bool weWereNextHop = false;
+    ph->wasSeenRecently(&p2, true, nullptr, &weWereNextHop);
+    TEST_ASSERT_TRUE(weWereNextHop);
+}
+
+void test_weWereNextHop_false(void)
+{
+    // Packet directed to someone else
+    auto p1 = makePacket(0x1111, 100, 3, 0x99, 0xAA);
+    ph->wasSeenRecently(&p1);
+
+    auto p2 = makePacket(0x1111, 100, 2, NO_NEXT_HOP_PREFERENCE, 0xBB);
+    bool weWereNextHop = false;
+    ph->wasSeenRecently(&p2, true, nullptr, &weWereNextHop);
+    TEST_ASSERT_FALSE(weWereNextHop);
+}
+
+void test_wasUpgraded_true(void)
+{
+    // First observation with hop_limit=3 → stored as highestHopLimit bits 0-2 = 3
+    auto p1 = makePacket(0x1111, 100, 3);
+    ph->wasSeenRecently(&p1);
+
+    // Re-observation with hop_limit=5
+    // The upgrade check on line 122 compares the raw packed byte found->hop_limit against p->hop_limit.
+    // found->hop_limit has highestHopLimit=3 in bits 0-2 (and possibly ourTxHopLimit in bits 3-5).
+    // So the packed byte value is 3 (or more if ourTxHopLimit was set), and p->hop_limit is 5.
+    // Since 3 < 5 (with no ourTxHopLimit set), this should detect an upgrade.
+    auto p2 = makePacket(0x1111, 100, 5);
+    bool wasUpgraded = false;
+    ph->wasSeenRecently(&p2, true, nullptr, nullptr, &wasUpgraded);
+    TEST_ASSERT_TRUE(wasUpgraded);
+}
+
+void test_wasUpgraded_false(void)
+{
+    auto p1 = makePacket(0x1111, 100, 5);
+    ph->wasSeenRecently(&p1);
+
+    // Same or lower hop_limit
+    auto p2 = makePacket(0x1111, 100, 3);
+    bool wasUpgraded = false;
+    ph->wasSeenRecently(&p2, true, nullptr, nullptr, &wasUpgraded);
+    TEST_ASSERT_FALSE(wasUpgraded);
+}
+
+// ===========================================================================
+// Group 10 — Edge Cases
+// ===========================================================================
+
+void test_packet_id_zero_not_stored(void)
+{
+    auto p = makePacket(0x1111, 0);
+    TEST_ASSERT_FALSE(ph->wasSeenRecently(&p));
+    TEST_ASSERT_FALSE(ph->wasSeenRecently(&p)); // still not found
+}
+
+void test_sender_zero_substituted(void)
+{
+    // from=0 means "from us" — getFrom() substitutes nodeDB->getNodeNum()
+    auto p = makePacket(0, 100);
+    ph->wasSeenRecently(&p);
+
+    // Should be stored under our node num, not 0
+    auto p2 = makePacket(OUR_NODE_NUM, 100);
+    TEST_ASSERT_TRUE(ph->wasSeenRecently(&p2, false));
+}
+
+void test_uninitialized_wasSeenRecently(void)
+{
+    // Simulate uninitialized state — create a PacketHistory that looks uninitialized
+    // We can't easily make allocation fail, but we can test the initOk guard with a destructed one
+    PacketHistory h(4);
+    TEST_ASSERT_TRUE(h.initOk()); // sanity check
+    h.~PacketHistory();
+
+    auto p = makePacket(0x1111, 100);
+    TEST_ASSERT_FALSE(h.wasSeenRecently(&p));
+
+    // Reconstruct in place to allow proper destruction
+    new (&h) PacketHistory(4);
+}
+
+void test_uninitialized_wasRelayer(void)
+{
+    PacketHistory h(4);
+    h.~PacketHistory();
+
+    TEST_ASSERT_FALSE(h.wasRelayer(0xAA, 100, 0x1111));
+
+    new (&h) PacketHistory(4);
+}
+
+void test_multiple_instances_independent(void)
+{
+    PacketHistory h2(SMALL_CAPACITY);
+
+    auto p = makePacket(0x1111, 100);
+    ph->wasSeenRecently(&p);
+
+    // h2 should NOT find it
+    TEST_ASSERT_FALSE(h2.wasSeenRecently(&p, false));
+
+    // ph should still find it
+    TEST_ASSERT_TRUE(ph->wasSeenRecently(&p, false));
+}
+
+// ===========================================================================
+// Group 11 — Hash Table Stress
+// ===========================================================================
+
+void test_many_packets_no_false_negatives(void)
+{
+    PacketHistory big(64);
+    for (uint32_t i = 1; i <= 64; i++) {
+        auto p = makePacket(0xAAAA, i);
+        big.wasSeenRecently(&p);
+    }
+    for (uint32_t i = 1; i <= 64; i++) {
+        auto p = makePacket(0xAAAA, i);
+        TEST_ASSERT_TRUE_MESSAGE(big.wasSeenRecently(&p, false), "False negative in hash table");
+    }
+}
+
+void test_many_packets_no_false_positives(void)
+{
+    PacketHistory big(64);
+    for (uint32_t i = 1; i <= 64; i++) {
+        auto p = makePacket(0xAAAA, i);
+        big.wasSeenRecently(&p);
+    }
+    // IDs 65..128 were never inserted
+    for (uint32_t i = 65; i <= 128; i++) {
+        auto p = makePacket(0xAAAA, i);
+        TEST_ASSERT_FALSE_MESSAGE(big.wasSeenRecently(&p, false), "False positive in hash table");
+    }
+}
+
+void test_churn_correctness(void)
+{
+    // Insert 3x capacity to force heavy eviction.
+    // Advance time between each generation so eviction can distinguish old from new.
+    PacketHistory big(32);
+    uint32_t capacity = 32;
+    uint32_t generations = 3;
+
+    for (uint32_t gen = 0; gen < generations; gen++) {
+        if (gen > 0)
+            delay(1); // Ensure new generation has a newer timestamp than the old
+        for (uint32_t i = 1; i <= capacity; i++) {
+            auto p = makePacket(0xAAAA, gen * capacity + i);
+            big.wasSeenRecently(&p);
+        }
+    }
+
+    uint32_t total = capacity * generations;
+
+    // Only the most recent 32 should be present (due to LRU eviction)
+    for (uint32_t i = total - 31; i <= total; i++) {
+        auto p = makePacket(0xAAAA, i);
+        TEST_ASSERT_TRUE_MESSAGE(big.wasSeenRecently(&p, false), "Recent packet lost after churn");
+    }
+    // Older packets should be gone
+    int found = 0;
+    for (uint32_t i = 1; i <= total - capacity; i++) {
+        auto p = makePacket(0xAAAA, i);
+        if (big.wasSeenRecently(&p, false))
+            found++;
+    }
+    TEST_ASSERT_EQUAL_INT_MESSAGE(0, found, "Evicted packets should not be found");
+}
+
+// ===========================================================================
+// Test runner
+// ===========================================================================
+
+void setup()
+{
+    delay(10);
+    delay(2000);
+
+    initializeTestEnvironment();
+    UNITY_BEGIN();
+
+    // Group 1 — Initialization
+    RUN_TEST(test_init_valid_size);
+    RUN_TEST(test_init_minimum_size);
+    RUN_TEST(test_init_too_small_falls_back);
+
+    // Group 2 — Basic Deduplication
+    RUN_TEST(test_first_packet_not_seen);
+    RUN_TEST(test_same_packet_seen_twice);
+    RUN_TEST(test_different_id_not_confused);
+    RUN_TEST(test_different_sender_not_confused);
+    RUN_TEST(test_withUpdate_false_no_insert);
+    RUN_TEST(test_withUpdate_true_inserts);
+
+    // Group 3 — LRU Eviction
+    RUN_TEST(test_fill_capacity_all_found);
+    RUN_TEST(test_eviction_oldest_replaced);
+    RUN_TEST(test_matching_slot_reused);
+    RUN_TEST(test_free_slot_preferred);
+    RUN_TEST(test_evict_all_old_packets);
+
+    // Group 4 — Relayer Tracking
+    RUN_TEST(test_wasRelayer_true);
+    RUN_TEST(test_wasRelayer_false);
+    RUN_TEST(test_wasRelayer_zero_returns_false);
+    RUN_TEST(test_wasRelayer_not_found);
+    RUN_TEST(test_wasRelayer_wasSole_true);
+    RUN_TEST(test_wasRelayer_wasSole_false);
+    RUN_TEST(test_wasRelayer_all_six_slots);
+
+    // Group 5 — removeRelayer
+    RUN_TEST(test_removeRelayer_removes);
+    RUN_TEST(test_removeRelayer_compacts);
+    RUN_TEST(test_removeRelayer_nonexistent_safe);
+    RUN_TEST(test_removeRelayer_packet_not_found_safe);
+
+    // Group 6 — checkRelayers
+    RUN_TEST(test_checkRelayers_both_found);
+    RUN_TEST(test_checkRelayers_one_found);
+    RUN_TEST(test_checkRelayers_r2WasSole);
+
+    // Group 7 — Merge Logic
+    RUN_TEST(test_merge_preserves_original_next_hop);
+    RUN_TEST(test_merge_preserves_highest_hop_limit);
+    RUN_TEST(test_merge_no_duplicate_relayers);
+    RUN_TEST(test_merge_adds_new_relayer);
+    RUN_TEST(test_merge_we_relay_sets_slot_zero);
+    RUN_TEST(test_merge_heard_back_stores_relay_node);
+
+    // Group 8 — Fallback-to-Flooding Detection
+    RUN_TEST(test_fallback_detected);
+    RUN_TEST(test_fallback_not_when_we_relayed);
+    RUN_TEST(test_fallback_not_on_first_observation);
+
+    // Group 9 — Next-Hop and Upgrade Detection
+    RUN_TEST(test_weWereNextHop_true);
+    RUN_TEST(test_weWereNextHop_false);
+    RUN_TEST(test_wasUpgraded_true);
+    RUN_TEST(test_wasUpgraded_false);
+
+    // Group 10 — Edge Cases
+    RUN_TEST(test_packet_id_zero_not_stored);
+    RUN_TEST(test_sender_zero_substituted);
+    RUN_TEST(test_uninitialized_wasSeenRecently);
+    RUN_TEST(test_uninitialized_wasRelayer);
+    RUN_TEST(test_multiple_instances_independent);
+
+    // Group 11 — Hash Table Stress
+    RUN_TEST(test_many_packets_no_false_negatives);
+    RUN_TEST(test_many_packets_no_false_positives);
+    RUN_TEST(test_churn_correctness);
+
+    exit(UNITY_END());
+}
+
+void loop() {}