[fix] preserve the step budget and script-cache choice across Reset

[vt128]

Problem

SetMaxExecutionSteps pushed the CPU-step budget onto the current starlet.Machine only — the Starbox kept no copy. Reset() swaps in a fresh machine (newStarMachine), which defaults to no step limit and an enabled script cache. So after the first run the guard silently vanished:

New → SetMaxExecutionSteps(1000) → Run → Reset → Run   // 2nd run had NO step guard

This directly contradicts Reset's own doc ("keeping the Box's limits"), and Reset is exactly the sanctioned path for serially reusing one Box across untrusted scripts — so a security-minded host hits the dangerous case. SetScriptCache(nil) (disable) had the symmetric bug: Reset re-enabled the cache.

maxOutputEntries did not have this bug because it is a struct field re-read at run time — the asymmetry confirmed the root cause.

Fix

• Promote maxSteps / scriptCache / scriptCacheSet to Starbox fields; the setters store them.
• Reset() re-applies both to the fresh machine eagerly (right after newStarMachine), not lazily at the next run — so a caller that reaches for the raw machine via GetMachine() immediately after Reset() also sees the guard, closing that bypass.
• applyScriptCache() respects scriptCacheSet: an untouched cache stays default-enabled; an explicit SetScriptCache(nil) stays disabled across every Reset.

Test

TestMaxExecutionStepsSurvivesReset (test-first): set budget → Run (hits MaxStepsExceededError) → Reset() → Run → still hits MaxStepsExceededError.

Verification

gofmt/go vet clean; go test, go test -race -count=2, and docker golang:1.19 go test -race all green.

[codacy-production]

Up to standards ✅

🟢 Issues 0 issues

Results:
0 new issues

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🟢 Metrics 0 complexity · 0 duplication

Metric	Results
Complexity	0
Duplication	0

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🟢 Coverage 100.00% diff coverage · +0.01% coverage variation

Metric	Results
Coverage variation	✅ +0.01% coverage variation (-1.00%)
Diff coverage	✅ 100.00% diff coverage

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Coverage variation details

	Coverable lines	Covered lines	Coverage
Common ancestor commit (fd18a0f)	Report Missing	Report Missing	Report Missing
Head commit (fb4d38b)	1169 (+15)	1160 (+15)	99.23% (+0.01%)

Coverage variation is the difference between the coverage for the head and common ancestor commits of the pull request branch: <coverage of head commit> - <coverage of common ancestor commit>

Diff coverage details

	Coverable lines	Covered lines	Diff coverage
Pull request (#29)	17	17	100.00%

Diff coverage is the percentage of lines that are covered by tests out of the coverable lines that the pull request added or modified: <covered lines added or modified>/<coverable lines added or modified> * 100%

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[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 98.96%. Comparing base (fd18a0f) to head (fb4d38b).

Additional details and impacted files

@@            Coverage Diff             @@
##           master      #29      +/-   ##
==========================================
+ Coverage   98.95%   98.96%   +0.01%     
==========================================
  Files          12       12              
  Lines         862      871       +9     
==========================================
+ Hits          853      862       +9     
  Misses          5        5              
  Partials        4        4              

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