Defend version compatibility, capability policy, and migration decisions — Discover and trace

PART I

Warm-up

Reconnect with a useful idea before starting defend version compatibility, capability policy, and migration decisions. 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

Trace the new operation for an old grant

Permission migration changes who may perform an operation, not merely which names are visible. Keep the identity, operation, resource and decision together in every example. A new capability should be explicitly granted through the host policy; existing public API exposure cannot silently supply it.

Exercise policy: profile.read permits reading the caller’s own display name; profile.export is a separate grant for exporting the caller’s own profile. Version 1 clients have only profile.read. Version 2 adds export as an optional operation. The source does not define a manifest schema, so the artifacts here are plain policy tables, not executable permission syntax.

Supplied case: Caller Mira owns profile M; grants = profile.read. Request: export M after a version-2 rollout.

Worked reasoning: First identify the requested operation as export, not read. Then compare its required profile.export grant with Mira’s set: absent, so refuse export and preserve the existing read workflow. No export artifact should be reported as produced.

Contrast and diagnosis: Treating export as “just a larger read” quietly widens every old grant and bypasses the new decision boundary.

Worked reasoning and supplied artifact

// Disposable exercise fixture / host-contract notes; not executable API syntax.
// Supplied input: Caller Mira owns profile M; grants = profile.read. Request: export M after a version-2 rollout.
// Worked prediction: First identify the requested operation as export, not read. Then compare its required profile.export grant with Mira’s set: absent, so refuse export and preserve the existing read workflow. No export artifact should be reported as produced.
// Rejected alternative: Treating export as “just a larger read” quietly widens every old grant and bypasses the new decision boundary.

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: Extension compatibility portfolio. Build a small, understandable change around defend version compatibility, capability policy, and migration decisions.

Trace caller Bo with only profile.read requesting display-name read and profile export; record required grant and decision separately.

What to produce

Trace caller Bo with only profile.read requesting display-name read and profile export; record required grant and decision separately. Include input → intermediate decision/state → predicted outcome, with any required host rule stated explicitly.

• 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.

• Trace the new operation for an old grant
• Explain the decision for the supplied case, then independently work the changed fixture.
• Separate source-backed behavior, host requirements and untested predictions.

One small recap task

In one or two sentences, name the decisive rule in “Trace the new operation for an old grant” and predict the outcome of one changed input from your independent fixture. State which host behavior still needs real verification.

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