fix(USE-003): emit staged mode preview summary in upload_artifact handler

[Copilot]

upload_artifact.cjs silently skipped uploads in staged mode with only a bare core.info log, unlike every other handler which writes a rich 🎭 Staged Mode step summary so users can verify intent before going live.

Changes

• actions/setup/js/upload_artifact.cjs: Replace the silent core.info in the staged-mode else-block with a full step summary via core.summary.addRaw(...).write(), listing artifact name, files, total size, and retention days:

## 🎭 Staged Mode: Upload Artifact Preview

The following artifact upload would be performed if staged mode was disabled:

**Artifact Name:** my-reports
**Files (2):**
- `dist/report.json`
- `dist/summary.html`

**Total Size:** 4096 bytes
**Retention:** 30 days

> ℹ️ Upload skipped (staged mode active)

• actions/setup/js/upload_artifact.test.cjs: Add test asserting the summary is written and contains 🎭 Staged Mode / Upload Artifact Preview when staged mode is active.

[Copilot]

Pull request overview

Adds a rich step summary preview for upload_artifact when staged mode is active, aligning its behavior with other handlers so users can verify what would have been uploaded before enabling live writes.

Changes:

• Replace the staged-mode core.info skip message with a full core.summary preview (artifact name, file list, total size, retention, and “skipped” note).
• Add a unit test asserting the staged-mode step summary is written and contains key preview text.

Show a summary per file

File	Description
actions/setup/js/upload_artifact.cjs	Writes a staged-mode upload preview to the GitHub Actions step summary instead of only logging a skip message.
actions/setup/js/upload_artifact.test.cjs	Adds coverage to ensure the staged-mode preview summary is emitted and written.

Copilot's findings

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• Files reviewed: 2/2 changed files
• Comments generated: 0

[github-actions]

🧪 Test Quality Sentinel Report

Test Quality Score: 100/100

✅ Excellent test quality

Metric	Value
New/modified tests analyzed	1
✅ Design tests (behavioral contracts)	1 (100%)
⚠️ Implementation tests (low value)	0 (0%)
Tests with error/edge cases	1 (100%)
Duplicate test clusters	0
Test inflation detected	No (1:1 ratio — 14 test lines / 14 production lines)
🚨 Coding-guideline violations	None

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Test Classification Details

Test	File	Classification	Issues Detected
"emits a staged mode preview summary when staged mode is active"	actions/setup/js/upload_artifact.test.cjs:402	✅ Design	None

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Flagged Tests — Requires Review

No tests flagged. The single new test is clean.

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Language Support

Tests analyzed:

• 🐹 Go (*_test.go): 0 tests
• 🟨 JavaScript (*.test.cjs, *.test.js): 1 test (vitest)

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Verdict

✅ Check passed. 0% of new tests are implementation tests (threshold: 30%).

The new test directly exercises the behavioral contract introduced by the fix: when staged mode is active, the handler must emit a core.summary preview containing the artifact name, file list, size, and retention information. It verifies the observable output (summary content strings and the write() call), not internal implementation details.

Mocking strategy is appropriate — global.core and the artifact client are external I/O (GitHub Actions runtime), not internal business logic.

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📖 Understanding Test Classifications

Design Tests (High Value) verify what the system does:

• Assert on observable outputs, return values, or state changes
• Cover error paths and boundary conditions
• Would catch a behavioral regression if deleted
• Remain valid even after internal refactoring

Implementation Tests (Low Value) verify how the system does it:

• Assert on internal function calls (mocking internals)
• Only test the happy path with typical inputs
• Break during legitimate refactoring even when behavior is correct
• Give false assurance: they pass even when the system is wrong

Goal: Shift toward tests that describe the system's behavioral contract — the promises it makes to its users and collaborators.

🧪 Test quality analysis by Test Quality Sentinel · ● 1.2M · ◷

[github-actions]

✅ Test Quality Sentinel: 100/100. Test quality is excellent — 0% of new tests are implementation tests (threshold: 30%). The single new test verifies the behavioral contract that staged mode emits a correctly-structured summary preview.