Summary

• add focused pool tests for marshaler initialization behavior in interp/pool.go
• verify interpreters from the same pool share one default marshaler instance
• verify a later WithMarshaler(custom) option still overrides the pool default

Changed paths tested

• interp/pool.go

Added tests

• TestNewPool/shares default marshaler within pool
• TestNewPool/custom marshaler overrides pool default

Validation

• go test ./interp -run 'TestNewPool|TestWithMarshaler|TestInterpreter_Marshal|TestHostObject'
• go test ./interp
• make lint

Skipped targets

• interp/host.go, interp/marshal.go, interp/interp_test.go: already covered by the recent commit's added tests; no additional uncovered changed branch found that stayed narrow and high-confidence.
• docs changes: no executable behavior to regression-test.