DA-03 · LESSON 04

Two-transaction actions

KEY DEFINITIONS

Terms used in this lesson

Vault: A set of Bitcoin outputs and spending rules that holds collateral and represents the current loan state.
UNIT: Ducat’s dollar-pegged stablecoin, the asset a borrower can create against bitcoin collateral.

Open, borrow, and repay use an issue-or-burn transaction plus a vault transaction connected so package structure and fees matter.

65 min Difficulty 4/5 Not started

VISUAL MODEL

See the whole mechanism before going step by step

Use the diagrams to orient yourself. Then the guided explanation below teaches every part in depth.

4 explanatory views

CONCEPT-SPECIFIC MAP · ducat vaultA Ducat action moves one Bitcoin-anchored vault state to a successorSelect any state to inspect its exact role.

RELATIONSHIP MAPInputs, rule, and outputs

01
PREDECESSORCurrent vault outpoint
The current Bitcoin output anchors collateral and identifies the state being spent.
02
REQUESTTwo-transaction actions
The Two-transaction actions workflow proposes one exact action and successor state.
03
POLICYProfile, oracle, signatures
Applicable policy, price evidence, authorization, and transaction shape are checked.
04
BITCOIN SPENDScript-valid transaction
Bitcoin miners and nodes can include only a transaction that satisfies Bitcoin rules.
05
SUCCESSORNew outpoint and state
Ducat validators reconstruct debt, collateral, token, and account changes from the confirmed transaction.

Rule shown: Bitcoin checks the spend; Ducat components independently reconstruct and validate the additional protocol state.

STAGE 1 OF 5PREDECESSOR: Current vault outpoint

The current Bitcoin output anchors collateral and identifies the state being spent.

Governing relationship: Bitcoin checks the spend; Ducat components independently reconstruct and validate the additional protocol state. Complete path: 1. PREDECESSOR, Current vault outpoint. The current Bitcoin output anchors collateral and identifies the state being spent. 2. REQUEST, Two-transaction actions. The Two-transaction actions workflow proposes one exact action and successor state. 3. POLICY, Profile, oracle, signatures. Applicable policy, price evidence, authorization, and transaction shape are checked. 4. BITCOIN SPEND, Script-valid transaction. Bitcoin miners and nodes can include only a transaction that satisfies Bitcoin rules. 5. SUCCESSOR, New outpoint and state. Ducat validators reconstruct debt, collateral, token, and account changes from the confirmed transaction.

1. State transitionWhat exists, what changes, and what results

BEFORE

Use a 180-vB parent paying 180 sats and a 270-vB child paying 4,320 sats. Required practice uses another package.

MECHANISM

The issue or burn transaction establishes the UNIT-side change and a child-spendable output or relationship.

AFTER

Relay still applies the displayed minimum and ancestor limit separately from dependency and Ducat reconciliation. Required practice uses a separate server-executed vector.

Text equivalent: Starting from Use a 180-vB parent paying 180 sats and a 270-vB child paying 4,320 sats. Required practice uses another package. The mechanism begins when The issue or burn transaction establishes the UNIT-side change and a child-spendable output or relationship. The resulting lesson is Relay still applies the displayed minimum and ancestor limit separately from dependency and Ducat reconciliation. Required practice uses a separate server-executed vector.

2. Mechanism pathSelect a stage to inspect its job

STAGE 1 OF 4

Construct the parent

The issue or burn transaction establishes the UNIT-side change and a child-spendable output or relationship.

Complete path: 1. Construct the parent: The issue or burn transaction establishes the UNIT-side change and a child-spendable output or relationship. 2. Construct the child: The vault transaction consumes the required parent output and the current vault where applicable. 3. Validate as a package: Ducat checks token and debt relationships while mempool and miners consider transaction dependencies and fee policy. 4. Broadcast in order: The parent must be known before the child can be accepted, although package submission may communicate them together.

3. Rule and failure boundaryWhat accepts the result and where it can stop

ACCEPTED PATH

The worked case executes the named inputs and checks in the displayed order. The parent must be known before the child can be accepted, although package submission may communicate them together.

CHANGED CONDITION

A missing, malformed, stale, unauthorized, or inconsistent required input stops at its first named boundary. A child cannot precede the parent output it spends. Its fee can make mining both attractive, but dependency order remains fixed.

Important distinction: The child can confirm first because it pays the package fee. A child cannot precede the parent output it spends. Its fee can make mining both attractive, but dependency order remains fixed.

Text equivalent: The accepted path is enforced by The worked case executes the named inputs and checks in the displayed order. The parent must be known before the child can be accepted, although package submission may communicate them together. If the required condition changes, A missing, malformed, stale, unauthorized, or inconsistent required input stops at its first named boundary. A child cannot precede the parent output it spends. Its fee can make mining both attractive, but dependency order remains fixed.

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Learn the idea

A two-transaction action has a parent that creates an output the child spends. In the captured Ducat client, open, borrow, and repay use issue-or-burn parents plus vault children, so dependency order and combined fees matter.

GUIDED EXPLANATION1/4 ideas inspected

Construct the parent

The issue or burn transaction establishes the UNIT-side change and a child-spendable output or relationship.

The worked example follows the explanation

Inspect every idea above to open it.

Important distinction“The child can confirm first because it pays the package fee.”

A child cannot precede the parent output it spends. Its fee can make mining both attractive, but dependency order remains fixed.

FINISH LEARNING FIRST

The questions unlock after every required learning activity

Inspect every guided idea, open the worked example, rebuild its mechanism, and complete the deterministic lesson tool. Your progress is saved automatically.