Design stable public module boundaries — Boundary detective

PART I

Warm-up

Reconnect with a useful idea before starting design stable public module boundaries. In one or two sentences, describe the input, output or host boundary from the previous exercise that this lesson builds on. If you are arriving directly, skim the worked example first; there is no locked prerequisite.

A rough note is enough. You can revise it after the example.

PART II

Instruction & guided example

Test a missing required result

An extension platform separates the script’s intent from native-service implementation, public compatibility promises, caller-scoped authorization and owner lifetimes. Those boundaries require explicit host contracts; import visibility does not establish resource permission or execution.

Supplied fixture: Provider returns title but omits promised status. Old client must choose a completion screen.

The client lacks the contract’s decision value. Inventing ready as a default could show incomplete work as complete. Treat it as an invalid provider response and preserve the last verified state under an explicit host policy.

The source anchor below is illustrative. WillowScript, its object/anonymous-function extensions and native libraries remain proposed/unimplemented here. Application and data symbols are exercise-host inputs. State missing signatures or recovery guarantees as requirements; do not invent transaction, cancellation or restore methods and do not claim these paper traces executed.

Worked reasoning and supplied artifact

// PAPER FIXTURE — Test a missing required result
// Manual worked artifact; comments below are not executable source.
// INPUT / CONTRACT: Supplied fixture: Provider returns title but omits promised status. Old client must
// choose a completion screen.
// DERIVATION / EXPECTED ARTIFACT: The client lacks the contract’s decision value. Inventing ready as a
// default could show incomplete work as complete. Treat it as an invalid provider response and preserve the
// last verified state under an explicit host policy.

Illustrative example from the proposed WillowScript design. The language and WUIX/WMATH/WDB/WAUDIO/WTMP services are not implemented in the supplied source. This site has no interpreter, VM or native host and does not execute or certify the snippet.

Try the guided change

Guided work: reproduce the fixture as a state/operation ledger and identify the exact evidence boundary supporting its conclusion.

• Write the supplied inputs and initial state before following the example.
• Reconstruct each intermediate calculation or host decision, then compare with the worked artifact.
• Explain why the contrasting alternative fails before attempting the changed inputs in Part IV.

PART III

Take a breather

Step back after the guided example. Look away from the screen, stretch, or reread your prediction. This is an optional learning pause, not a timer or an assessment gate.

When you return, try to name the lesson’s key idea without copying its wording. If that feels difficult, return to Part II and trace one line rather than restarting the entire lesson.

PART IV

Independent practice

Project context: Versioned extension architecture. Build a small, understandable change around design stable public module boundaries.

Create valid/missing/unknown status fixtures and expected client outcomes. Use different disposable record/resource identities from the worked fixture. Supply intended invariant, step-by-step normal trace, contrasting failed trace, final state and unresolved host requirements.

What to produce

Create valid/missing/unknown status fixtures and expected client outcomes. Include explicit inputs, intermediate states, correct final artifacts and acceptance criteria.

• State the intended behavior in a sentence before editing.
• Use only source-backed syntax and the host services whose contract you have been given.
• Record a normal case and a boundary or unavailable-resource case.
• Label hand predictions separately from anything actually measured in a supplied toolchain.

Syntax colors are a reading aid, not a compiler. The line you are editing stays uncolored until you move to a different line; capitalization is never changed. Drafts stay on this browser and code is not executed.

import wuix.widget;
import app;
domain Workspace {
    const application = Application({
        name: "Workspace",
        window: { title: "Dashboard", size: [1280, 800] },
        events: {
            "app.ready": fnc() -> void { console.log("Ready"); }
        }
    });
}

PART V

Self-check

Use this check to notice what to revisit. It does not award a private course grade, block another page or claim to verify compiled code. Every answer has a learning explanation.

You may keep exploring even if you are unsure. Use the hint, compare the trace, and revise your explanation.

PART VI

Recap & small task

Bring the idea back to the mod feature you are building. A useful recap connects the mechanism to a decision you can make in your own code.

• Test a missing required result
• Provider returns title but omits promised status. Old client must choose a completion screen.
• Separate source-backed behavior, host requirements and untested predictions.

One small recap task

Change one timing, permission, version or ownership condition in the supplied fixture. State which final artifact changes and which invariant must remain preserved.

This marks your personal practice record only. It is not a certification or an official workspace assessment.