Defend version compatibility, capability policy, and migration decisions — Build the smallest useful slice

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

Build a least-scope policy row

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: Mira is granted profile.export for her own profile M; she requests export of profile N owned by Noor.

Worked reasoning: The operation grant exists but the resource ownership condition fails. Deny N while allowing M. A permission name without resource scope is an incomplete authorization rule.

Contrast and diagnosis: Checking only whether profile.export is present lets one user export another user’s data.

Worked reasoning and supplied artifact

// Disposable exercise fixture / host-contract notes; not executable API syntax.
// Supplied input: Mira is granted profile.export for her own profile M; she requests export of profile N owned by Noor.
// Worked prediction: The operation grant exists but the resource ownership condition fails. Deny N while allowing M. A permission name without resource scope is an incomplete authorization rule.
// Rejected alternative: Checking only whether profile.export is present lets one user export another user’s data.

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.

Write two policy rows for Mira exporting M and N. Include caller, owner, grant and decision; specify the nonrevealing refusal text.

What to produce

Write two policy rows for Mira exporting M and N. Include caller, owner, grant and decision; specify the nonrevealing refusal text. 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.

• Build a least-scope policy row
• 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 “Build a least-scope policy row” 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.