Compose playback controls, device recovery contracts, and event cleanup — Discover and trace

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

Read a device-loss transition explicitly

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.

Host contract: V1 plays on device A at position12s. Device A disconnects. The host reports Lost and pauses position at12; it never switches devices automatically.

Worked reasoning: Record device unavailable, voice paused and retained position12. A reconnect may permit a later decision, but playback is not continuing now. The status should not imply audibility.

Failed alternative: Assuming the default device automatically takes over adds an unpromised migration and may send sound somewhere unexpected.

Worked reasoning and supplied artifact

Before:device A available,V1 playing,position12
Loss:device A unavailable,V1 paused,position12
Auto-switch:none
Visible:Output device lost;preview paused

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.

Trace device B loss at7s under the same pause-on-loss contract. State the evidence needed before any later resume.

What to produce

A device/voice/position transition 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.

• Read a device-loss transition explicitly
• Trace device B loss at7s under the same pause-on-loss contract. State the evidence needed before any later resume.
• Separate source-backed behavior, host requirements and untested predictions.

One small recap task

Obtain the device-loss policy before predicting playback state.

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