Compose playback controls, device recovery contracts, and event cleanup — Change one requirement

PART I

Warm-up

Reconnect with a useful idea before starting compose playback controls, device recovery contracts, and event cleanup. 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

Adapt recovery to a restart-only device

A device transition changes what an audio host can currently do, but does not define a universal recovery policy. Track device identity, user intent, position and owner. Resume, reload, restart and remain-paused are distinct decisions that must come from an explicit contract.

Device A supported retained-position resume. Device D supports restart only; it cannot seek. The voice was paused at18s, and the user chooses Continue. Policy must disclose that D would restart from0.

Worked reasoning: Do not promise resume at 18s on D. Offer Restart from beginning or remain paused; an explicit choice can then authorize the supported action. Internal compatibility does not arise from identical Play labels.

Failed alternative: Issuing an invented seek(18) call conceals the missing capability and cannot be verified from the source.

Worked reasoning and supplied artifact

Requested continuity:18s
Device D capability:restart at 0s only
Available choices:Restart from beginning /remain paused
Unsupported claim:resume at 18s without seek support

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

Reconstruct the supplied worked case first: list its inputs, intermediate decisions and final artifact. Compare each row with the explanation and identify exactly where the rejected alternative fails. Then use the changed inputs in Part IV for independent work.

• 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: Media operations console. Build a small, understandable change around compose playback controls, device recovery contracts, and event cleanup.

Compare a retained-position device at9s with a restart-only fallback. Write distinct user messages and actions.

What to produce

A desired-operation/device-capability/allowed-response table.

• 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 wdb;
domain Inventory {
    const lowStock = wdb.query({
        from: products,
        select: [id, name, stock],
        where: [[ stock < 10 ]],
        order: { by: stock, direction: ascending }
    });
}

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.

• Adapt recovery to a restart-only device
• Compare a retained-position device at9s with a restart-only fallback. Write distinct user messages and actions.
• Separate source-backed behavior, host requirements and untested predictions.

One small recap task

Match recovery wording to the devices documented operation, not the old devices behavior.

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