Compose playback controls, device recovery contracts, and event cleanup — Boundary detective

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

Handle an unknown playback-start outcome

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.

A host start request times out before acknowledgement. Contract says the timeout does not reveal whether the native voice started. A host status query is available conceptually, but its concrete API signature is unspecified.

Worked reasoning: Classify outcome Unknown and avoid an immediate duplicate start. Obtain operation-scoped status evidence first. If confirmed absent, a retry may be allowed; confirmed active should reuse the active voice state.

Failed alternative: Treating timeout as confirmed failure can start a second voice when the first actually began.

Worked reasoning and supplied artifact

Start R1 ->timeout
Known:ack missing
Unknown:native voice existence
Next:operation-scoped status evidence
Confirmed active ->do not start duplicate
Confirmed absent ->retry per 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

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.

Analyze a play request whose acknowledgement is lost after native start. Supply unknown-state status and a check-before-retry plan.

What to produce

An outcome-knowledge table and duplicate-safe recovery decision tree.

• 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.

• Handle an unknown playback-start outcome
• Analyze a play request whose acknowledgement is lost after native start. Supply unknown-state status and a check-before-retry plan.
• Separate source-backed behavior, host requirements and untested predictions.

One small recap task

Use an unknown state until authoritative operation evidence resolves it.

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