DA-07 · LESSON 03

Client workflow

KEY DEFINITIONS

Terms used in this lesson

SDK: Software development kit: reusable code and tools for building applications against a system.
Validator: Software or a participant that independently checks state transitions under a system's rules. The exact role depends on the protocol being discussed.
Oracle: A system that reports outside information, such as a market price, for use by a protocol.
PSBT: Partially Signed Bitcoin Transaction: a format for passing an unsigned or partly signed transaction between constructors and signers.
Guardian: A Ducat policy-checking signer that can authorize or reject defined protocol transactions.
Outpoint: A transaction ID plus output number that identifies one exact prior output.
BTC: The common market ticker for bitcoin.
UNIT: Ducat’s dollar-pegged stablecoin, the asset a borrower can create against bitcoin collateral.
Vault: A set of Bitcoin outputs and spending rules that holds collateral and represents the current loan state.
Collateral: An asset pledged against a debt; it can be used to cover the debt if agreed conditions are breached.

The SDK coordinates validator reads, oracle data, funding selection, PSBT construction, wallet signatures, Guardian requests, and broadcasts.

55 min Difficulty 5/5 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
REQUESTClient workflow
The Client workflow 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, Client workflow. The Client workflow 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

The client reads issuance account A, profile seven, oracle snapshot S, and wallet funding F. It builds issue parent P and vault child C. A stale-response case spends A elsewh…

MECHANISM

Fetch live outpoints, profile, oracle snapshot, accounts, fee information, and confirmation state.

AFTER

A client draft is recoverable user intent, not authoritative state. On stale input, reread current objects and rebuild new transaction bytes before requesting fresh signature…

Text equivalent: Starting from The client reads issuance account A, profile seven, oracle snapshot S, and wallet funding F. It builds issue parent P and vault child C. A stale-response case spends A elsewhere before broadcast. The mechanism begins when Fetch live outpoints, profile, oracle snapshot, accounts, fee information, and confirmation state. The resulting lesson is A client draft is recoverable user intent, not authoritative state. On stale input, reread current objects and rebuild new transaction bytes before requesting fresh signatures.

2. Mechanism pathSelect a stage to inspect its job

STAGE 1 OF 4

Resolve current state

Fetch live outpoints, profile, oracle snapshot, accounts, fee information, and confirmation state.

Complete path: 1. Resolve current state: Fetch live outpoints, profile, oracle snapshot, accounts, fee information, and confirmation state. 2. Build deterministically: Choose the action-specific one- or two-transaction builder and produce PSBTs plus a bound request manifest. 3. Collect authorizations: The wallet signs owner or funding inputs and the Guardian independently validates and signs its required inputs. 4. Broadcast and reconcile: Send transactions in dependency order, monitor mempool and blocks, and compare validator reconstruction with the intended result.

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. Send transactions in dependency order, monitor mempool and blocks, and compare validator reconstruction with the intended result.

CHANGED CONDITION

A missing, malformed, stale, unauthorized, or inconsistent required input stops at its first named boundary. Only confirmed Bitcoin transactions plus compatible reconstruction establish the new state. Client optimism can be stale or wrong.

Important distinction: If the client displays success, the vault state has changed. Only confirmed Bitcoin transactions plus compatible reconstruction establish the new state. Client optimism can be stale or wrong.

Text equivalent: The accepted path is enforced by The worked case executes the named inputs and checks in the displayed order. Send transactions in dependency order, monitor mempool and blocks, and compare validator reconstruction with the intended result. If the required condition changes, A missing, malformed, stale, unauthorized, or inconsistent required input stops at its first named boundary. Only confirmed Bitcoin transactions plus compatible reconstruction establish the new state. Client optimism can be stale or wrong.

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Learn the idea

The client software development kit, or client SDK, coordinates a user action but is not an authority. A Partially Signed Bitcoin Transaction, or PSBT, carries an unsigned transaction plus the previous-output data and scripts needed by signers. The client reads current state, builds PSBTs, collects wallet and Guardian signatures, broadcasts transactions, and waits for confirmed validator reconstruction before reporting completion.

GUIDED EXPLANATION1/4 ideas inspected

Resolve current state

Fetch live outpoints, profile, oracle snapshot, accounts, fee information, and confirmation state.

The worked example follows the explanation

Inspect every idea above to open it.

Important distinction“If the client displays success, the vault state has changed.”

Only confirmed Bitcoin transactions plus compatible reconstruction establish the new state. Client optimism can be stale or wrong.

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.