[fix] apply the Machine step budget and print func to load()ed modules

[vt128]

What

A module executed by load() ran in a bare starlark.Thread that inherited none of the Machine's execution context, so the step budget did not apply (a top-level loop in a loaded source module escaped the DoS guard — the budget only armed the main thread) and print() in a loaded module went to stdout via a hardcoded fmt.Println, bypassing the Machine's print func.

The load cache now builds its child thread from the Machine (newLoadThread): the same print func, an independent copy of the step budget (with the MaxStepsExceeded panic), and the current run's context local. The budget is per-thread — enough to stop one runaway loaded module — not a shared aggregate counter.

Because a loaded module can now panic (OnMaxSteps), the cache's get() recovers around doLoad: a loaded completion sentinel (not recover() != nil, which is nil for panic(nil) under go 1.19) decides whether it panicked; on the panic path it readies the entry with the error, drops it so a retry re-executes, and re-raises so runInternal maps it to a typed error. Without this a second Run after a budget hit blocked forever on the load cache's ready channel.

Not covered here (documented follow-ups)

Lazy loaders built with MakeModuleLoaderFromString/Reader/File still run on their own bare thread and inherit no budget/print (needs an API change); a context timeout cancels only the main thread, so a loaded module's pure-Starlark loop is bounded by the step budget, not the deadline.

Tests

A loaded module hits the step budget; its print() reaches the Machine print func; a second run after a budget panic (and after a panic(nil) loader) returns promptly instead of deadlocking. Full -race/vet/gofmt/Docker go1.19 clean.

[codacy-production]

Up to standards ✅

🟢 Issues 0 issues

Results:
0 new issues

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🟢 Metrics 40 complexity · 2 duplication

Metric	Results
Complexity	40
Duplication	2

View in Codacy

🟢 Coverage 96.55% diff coverage · +0.09% coverage variation

Metric	Results
Coverage variation	✅ +0.09% coverage variation (-1.00%)
Diff coverage	✅ 96.55% diff coverage

View coverage diff in Codacy

Coverage variation details

	Coverable lines	Covered lines	Coverage
Common ancestor commit (5d4c419)	Report Missing	Report Missing	Report Missing
Head commit (9de3b4e)	7824 (+51)	7411 (+55)	94.72% (+0.09%)

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 (#171)	58	56	96.55%

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%

¹ Codacy didn't receive coverage data for the commit, or there was an error processing the received data. Check your integration for errors and validate that your coverage setup is correct.

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[codecov]

Codecov Report

❌ Patch coverage is 92.30769% with 3 lines in your changes missing coverage. Please review.
✅ Project coverage is 93.51%. Comparing base (5d4c419) to head (9de3b4e).

Files with missing lines	Patch %	Lines
cache.go	86.95%	2 Missing and 1 partial ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #171      +/-   ##
==========================================
+ Coverage   93.42%   93.51%   +0.08%     
==========================================
  Files          50       50              
  Lines        6222     6256      +34     
==========================================
+ Hits         5813     5850      +37     
+ Misses        261      257       -4     
- Partials      148      149       +1     

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