[P3] Differential testing infrastructure: st8 vs d8

[Copilot]

• Explore repository structure and understand existing codebase
• Add NativeFn wrapper and JsValue::NativeFunction variant to stator_core
• Add thread-local globals (set_global, get_global, clear_globals) to interpreter
• Handle LdaGlobal/LdaGlobalInsideTypeof/StaGlobal opcodes in interpreter
• Handle NativeFunction in all Call* and Construct* opcode handlers
• Implement st8 binary with file/inline execution, print() global, proper exit codes
• Create tests/diff/ corpus (arithmetic, comparisons, control_flow, functions, closures, exceptions)
• Create scripts/diff_test.sh (PASS/KNOWN_DIFF/BUG categorisation, corpus mode, single-file mode)
• Create scripts/known_diffs.txt documenting string literal quote divergence
• Create .github/workflows/diff_test.yml (PR + nightly CI jobs)
• Fix CI: replace env: PATH: ... with echo ... >> $GITHUB_PATH step to avoid overriding system PATH (was causing chmod: command not found)
• All 191 tests pass, clippy clean, cargo fmt applied

Original prompt

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This section details on the original issue you should resolve

<issue_title>[P3] Set up differential testing: st8 vs V8 d8</issue_title>
<issue_description>Implement automated differential testing comparing Stator (st8) output against V8 (d8):

Setup:

• Script runner that executes the same .js file in both st8 and d8
• Compare: stdout output, return value, thrown exceptions
• Corpus: Test262 tests + hand-written regression tests + fuzzer-generated inputs

CI integration:

• Run differential testing on every PR (subset of corpus)
• Nightly: full corpus run
• Dashboard showing pass/fail/divergence rates

Divergence categories:

1. PASS: identical output
2. KNOWN_DIFF: documented intentional difference (e.g., error message wording)
3. BUG: unexpected divergence (auto-files issue)

Acceptance criteria:

• scripts/diff_test.sh <file.js> runs in both engines, reports comparison
• CI runs subset on every PR
• No BUG-category divergences in the existing passing tests</issue_description>

Comments on the Issue (you are @copilot in this section)

• Fixes [P3] Set up differential testing: st8 vs V8 d8 #111

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[codecov]

Codecov Report

❌ Patch coverage is 35.96838% with 162 lines in your changes missing coverage. Please review.

Files with missing lines	Patch %	Lines
crates/stator_core/src/interpreter/mod.rs	24.85%	130 Missing ⚠️
crates/st8/src/main.rs	61.76%	26 Missing ⚠️
crates/stator_core/src/objects/value.rs	50.00%	6 Missing ⚠️

📢 Thoughts on this report? Let us know!

[telecos]

@copilot fix failing ci

[Copilot]

@copilot fix failing ci

Fixed in 7b1aa36. The Differential Tests workflow was failing with chmod: command not found because env: PATH: ${{ github.workspace }}/target/release:$PATH replaced the entire system PATH (the $PATH part is a literal string in the env: block, not a shell variable expansion). Replaced it with a dedicated echo ... >> $GITHUB_PATH step, which is the correct GitHub Actions way to prepend a directory to PATH.

[telecos]

@copilot the codecov ci is failing can you fix it?