diff --git a/projects/keepkey-vault/src/bun/txbuilder/hive-ops.test.ts b/projects/keepkey-vault/src/bun/txbuilder/hive-ops.test.ts
index 0fa49323..df1b6594 100644
--- a/projects/keepkey-vault/src/bun/txbuilder/hive-ops.test.ts
+++ b/projects/keepkey-vault/src/bun/txbuilder/hive-ops.test.ts
@@ -290,3 +290,64 @@ describe('comment_options beneficiary rules (finding #6)', () => {
       .not.toThrow()
   })
 })
+
+describe('phase-3: internal market (limit orders)', () => {
+  // Same vector as the firmware unit test Hive.LimitOrderCreateRetainsEveryDisplayedField
+  const CREATE = {
+    owner: 'alice', orderid: 42,
+    amount_to_sell: '1.500 HIVE', min_to_receive: '0.400 HBD',
+    fill_or_kill: true, expiration: 1700003600,
+  }
+  const u32le = (n: number) => { const b = Buffer.alloc(4); b.writeUInt32LE(n); return b }
+
+  test('limit_order_create byte layout', () => {
+    const { serializedTx, tier } = sign(['limit_order_create', CREATE])
+    expect(tier).toBe('active')
+    expect(serializedTx.equals(txBytes(1,
+      Buffer.from([5]), vstr('alice'), u32le(42),
+      vasset(1500n, 3, 'HIVE'), vasset(400n, 3, 'HBD'),
+      Buffer.from([1]), u32le(1700003600),
+    ))).toBe(true)
+  })
+
+  test('limit_order_cancel byte layout', () => {
+    const { serializedTx, tier } = sign(['limit_order_cancel', { owner: 'alice', orderid: 42 }])
+    expect(tier).toBe('active')
+    expect(serializedTx.equals(txBytes(1,
+      Buffer.from([6]), vstr('alice'), u32le(42),
+    ))).toBe(true)
+  })
+
+  test('fill_or_kill false serializes as 0', () => {
+    const { serializedTx } = sign(['limit_order_create', { ...CREATE, fill_or_kill: false }])
+    expect(serializedTx[serializedTx.length - 6]).toBe(0)
+  })
+
+  // Degenerate orders the firmware rejects — mirrored host-side for a clearer error
+  test('same symbol on both sides is rejected', () => {
+    expect(() => sign(['limit_order_create', { ...CREATE, min_to_receive: '0.400 HIVE' }]))
+      .toThrow(/symbols must differ/)
+  })
+  test('zero amount_to_sell is rejected', () => {
+    expect(() => sign(['limit_order_create', { ...CREATE, amount_to_sell: '0.000 HIVE' }]))
+      .toThrow(/greater than zero/)
+  })
+  test('zero min_to_receive is rejected', () => {
+    expect(() => sign(['limit_order_create', { ...CREATE, min_to_receive: '0.000 HBD' }]))
+      .toThrow(/greater than zero/)
+  })
+  test('VESTS never trades on the internal market', () => {
+    expect(() => sign(['limit_order_create', { ...CREATE, amount_to_sell: '1.500000 VESTS' }]))
+      .toThrow(/must be HIVE or HBD/)
+  })
+  test('non-boolean fill_or_kill is rejected', () => {
+    expect(() => sign(['limit_order_create', { ...CREATE, fill_or_kill: 1 }]))
+      .toThrow(/must be a boolean/)
+  })
+  test('cannot share a tx with posting-tier ops', () => {
+    expect(() => sign(
+      ['limit_order_cancel', { owner: 'alice', orderid: 1 }],
+      ['vote', { voter: 'alice', author: 'bob', permlink: 'p', weight: 10000 }],
+    )).toThrow(/Cannot mix posting-tier and active-tier/)
+  })
+})
diff --git a/projects/keepkey-vault/src/bun/txbuilder/hive-ops.ts b/projects/keepkey-vault/src/bun/txbuilder/hive-ops.ts
index f307ea20..a9c765e4 100644
--- a/projects/keepkey-vault/src/bun/txbuilder/hive-ops.ts
+++ b/projects/keepkey-vault/src/bun/txbuilder/hive-ops.ts
@@ -6,6 +6,8 @@
  * (3), withdraw_vesting (4), convert (8), comment_options (19),
  * transfer_to/from_savings (32/33), claim_reward_balance (39),
  * delegate_vesting_shares (40), account_update2 (43, metadata-only).
+ * Phase-3 ops: limit_order_create (5), limit_order_cancel (6) — the internal
+ * market, required for in-wallet HIVE/HBD swaps.
  *
  * Byte-exact mirror of hived's condenser serialization and the independent
  * python-keepkey test serializer (test_msg_hive.py _op_* helpers). The
@@ -21,6 +23,8 @@ const OP_VOTE = 0
 const OP_COMMENT = 1
 const OP_TRANSFER_TO_VESTING = 3
 const OP_WITHDRAW_VESTING = 4
+const OP_LIMIT_ORDER_CREATE = 5
+const OP_LIMIT_ORDER_CANCEL = 6
 const OP_CONVERT = 8
 const OP_CUSTOM_JSON = 18
 const OP_COMMENT_OPTIONS = 19
@@ -174,6 +178,37 @@ function serializeOp([name, p]: HiveOpTuple): { bytes: Buffer; tier: 'posting' |
         ]),
         tier: 'active',
       }
+    case 'limit_order_create': {
+      const sell = positiveAsset(p.amount_to_sell, ['HIVE', 'HBD'], 'limit_order_create amount_to_sell')
+      const recv = positiveAsset(p.min_to_receive, ['HIVE', 'HBD'], 'limit_order_create min_to_receive')
+      // A same-symbol order is a no-op trade on screen but still burns the
+      // fill; firmware refuses it, reject here for a clearer message.
+      if (sell.subarray(9, 16).equals(recv.subarray(9, 16))) {
+        throw new Error('limit_order_create: amount_to_sell and min_to_receive symbols must differ')
+      }
+      // expiration is unbounded here: the device has no RTC and the only cost
+      // of a stale/far-future value is an on-chain rejection, not a bad sign.
+      return {
+        bytes: Buffer.concat([
+          varint(OP_LIMIT_ORDER_CREATE),
+          str(p.owner),
+          u32(Number(p.orderid), 'limit_order_create orderid'),
+          sell, recv,
+          boolByte(p.fill_or_kill, 'limit_order_create fill_or_kill'),
+          u32(Number(p.expiration), 'limit_order_create expiration'),
+        ]),
+        tier: 'active',
+      }
+    }
+    case 'limit_order_cancel':
+      return {
+        bytes: Buffer.concat([
+          varint(OP_LIMIT_ORDER_CANCEL),
+          str(p.owner),
+          u32(Number(p.orderid), 'limit_order_cancel orderid'),
+        ]),
+        tier: 'active',
+      }
     case 'convert':
       return {
         bytes: Buffer.concat([