Plan try, recover, and raise boundaries — Connect the previous skills

PART I

Warm-up

Reconnect with a useful idea before starting plan try, recover, and raise 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

Connect recovery to ownership and late responses

Recover only when the workflow can preserve its promise. try, recover and raise describe error handling in the shared vocabulary, but host operation signatures and error payloads must be supplied. Recovery is a decision about state and responsibility: which failure can be handled locally, which must be reported upward, and which effects have already happened?

Window W19 starts save S19 and closes while outcome is unknown. A host reconciliation service owns S19 after initiation. At t=10 it confirms the save. The closed window cannot receive updates.

Use a before-operation-after ledger. Mark the last durable change before a failure and identify the evidence available to the handler. Retrying without knowing whether an operation committed can duplicate effects; swallowing an error cannot turn incomplete work into success. Worked case: Reconciliation records S19 as saved in the service’s request record. It does not reopen W19. A later user view may query the recorded outcome through its own authorized contract. Handling failure must preserve operation identity across owner closure.

Compare the tempting alternative: Dropping S19’s identity on close makes the outcome untraceable; sending the result to whichever window is visible violates owner identity.

Worked reasoning and supplied artifact

// Paper trace / supplied exercise-host contract; no execution claimed.
// Window W19 starts save S19 and closes while outcome is unknown. A host reconciliation service owns S19 after initiation. At t=10 it confirms the save. The closed window cannot receive updates.
// Reconciliation records S19 as saved in the service’s request record. It does not reopen W19. A later user view may query the recorded outcome through its own authorized contract. Handling failure must preserve operation identity across owner closure.

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: Safe extension design. Build a small, understandable change around plan try, recover, and raise boundaries.

Draw the owner/operation timeline and contrast confirmed save with confirmed no-write. State how a later view can request the outcome safely.

What to produce

A lifecycle-aware outcome ledger and a later-view access contract.

• 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;
const button = widget.Button({
    text: "Continue",
    events: {
        click: fnc() -> void {
            navigator.open("dashboard");
        }
    }
});

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.

• Connect recovery to ownership and late responses
• Draw the owner/operation timeline and contrast confirmed save with confirmed no-write. State how a later view can request the outcome safely.
• Separate source-backed behavior, host requirements and untested predictions.

One small recap task

Name the identity retained until reconciliation finishes.

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