cleanup: drop redundant nil-handler guards; tighten WithLogHandler doc

[robbyt]

Summary

Drops the six cfg.handler != nil guards that wrapped WithLogHandler calls in polyscript.go and engines/{risor,starlark,extism}/new.go. They existed solely to work around the pre-#111 nil-rejection — now that WithLogHandler(nil) is a true no-op across all three engines (PR #113), each guard produces identical behavior to an unconditional append.

Also tightens the top-level polyscript.WithLogHandler godoc to match the per-engine wording. The previous "If unset, the underlying engine picks a default" was vague about the nil case; the new wording matches engines/{risor,starlark,extism}/options.go:19-21.

Diff shape

// before
func newRisor(ldr loader.Loader, cfg *config) (platform.Evaluator, error) {
    var opts []risorMachine.Option
    if cfg.handler != nil {
        opts = append(opts, risorMachine.WithLogHandler(cfg.handler))
    }
    if cfg.staticData != nil {
        opts = append(opts, risorMachine.WithStaticData(cfg.staticData))
    }
    return risorMachine.FromRisorLoader(ldr, opts...)
}

// after
func newRisor(ldr loader.Loader, cfg *config) (platform.Evaluator, error) {
    opts := []risorMachine.Option{risorMachine.WithLogHandler(cfg.handler)}
    if cfg.staticData != nil {
        opts = append(opts, risorMachine.WithStaticData(cfg.staticData))
    }
    return risorMachine.FromRisorLoader(ldr, opts...)
}

Out of scope (audited, no action)

• helpers.SetupLogger callers — 10 sites, all consistent (engine, struct) naming.
• Logger struct fields — logHandler slog.Handler + logger *slog.Logger everywhere.
• slog.Default().Debug cleanup-error logs in platform/script/loader/{fromHTTP,fromDisk}.go — these structs have no logger field; routing them through SetupLogger is a separate design call.
• No remaining logging-related TODOs in production code.

Test plan

• git grep -n 'cfg.handler != nil' polyscript.go engines/{risor,starlark,extism}/new.go returns zero hits
• go test -race -count=1 ./... — green
• go vet ./... — clean
• Existing polyscript_options_test.go:198-205 "WithLogHandler accepts nil" subtest stays green
• CI on the PR

Closes #112

https://claude.ai/code/session_01C61VEAmjxSnX5Xhbab8NvL

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Generated by Claude Code

[github-actions]

Dependency Review

✅ No vulnerabilities or license issues or OpenSSF Scorecard issues found.

Scanned Files

None

[sonarqubecloud]

Quality Gate passed

Issues
0 New issues
0 Accepted issues

Measures
0 Security Hotspots
100.0% Coverage on New Code
0.0% Duplication on New Code

See analysis details on SonarQube Cloud

[Copilot]

Pull request overview

This PR removes redundant cfg.handler != nil guards around WithLogHandler option application in the top-level polyscript.New façade and the per-engine From*Loader constructors, relying on the now-defined “nil handler is a no-op” behavior in the underlying compiler functional options. It also updates the polyscript.WithLogHandler godoc to explicitly describe the nil behavior.

Changes:

• Remove conditional nil-guards and always include WithLogHandler(cfg.handler) when building engine/compiler option slices.
• Reword polyscript.WithLogHandler documentation to explicitly define nil semantics (“inherit from slog.Default()”).

Reviewed changes

Copilot reviewed 4 out of 4 changed files in this pull request and generated no comments.

File	Description
polyscript.go	Updates WithLogHandler godoc and simplifies engine option construction by removing redundant nil-guards.
engines/risor/new.go	Always passes compiler.WithLogHandler(cfg.handler) in compiler options (removes guard).
engines/starlark/new.go	Always passes compiler.WithLogHandler(cfg.handler) in compiler options (removes guard).
engines/extism/new.go	Always passes compiler.WithLogHandler(cfg.handler) in compiler options (removes guard).

Comments suppressed due to low confidence (1)

polyscript.go:193

• The updated doc says a nil handler is equivalent to omitting the option, but the implementation still unconditionally assigns c.handler = h. This means WithLogHandler(nonNil) followed by WithLogHandler(nil) will clear the previously configured handler, which is not equivalent to omitting and is inconsistent with the engine-level functional options’ “nil is a no-op and preserves prior state” behavior. Consider making WithLogHandler(nil) a true no-op (e.g., return a nil Option or skip assignment when h == nil).

// slog.Default()" — equivalent to omitting the option.
//
// The type parameter is normally inferred from the surrounding [New] call.
func WithLogHandler[E Engine](h slog.Handler) Option[E] {
	return func(c *config) { c.handler = h }

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