[tests] Cancellation, composite-provider matrix, HTTP errors, adapter packages

[robbyt]

Summary

A few coverage gaps surfaced during code review. Bundling them so they can be tackled together (or split into separate PRs per package as appropriate).

Cancellation tests for each engine

PR #81 fixed a Starlark goroutine leak by switching to context.AfterFunc, but no test asserts cancellation actually halts execution within a bounded time. Add:

• A "cancel an in-flight Eval" test for Risor.
• The same for Starlark (regression test for fix starlark goroutine leak in exec() with context.AfterFunc #81).
• The same for Extism — it uses instance.CallWithContext and should respect context cancellation; verify it does.

Race test for concurrent AddDataToContext

Tracked also under #93 (ContextProvider thread-safety). Add go test -race goroutines hammering the same parent context.

CompositeProvider edge-case branches

platform/data/compositeProvider.go:138-146 has two subtle branches — "static-only-and-they-all-error" and "non-static-and-all-fail". Add explicit table cases in compositeProvider_test.go.

HTTP loader error-path tests

platform/script/loader/fromHTTP_test.go doesn't cover:

• 4xx / 5xx response codes
• Context cancelled mid-stream
• Oversize body (covered by [security] Add MaxBodySize limit to HTTP loader (DoS via unbounded body) #98)
• Auth failure path

Adapter package coverage

engines/risor/adapters/interfaces.go and engines/starlark/adapters/interfaces.go have zero *_test.go files. They're intentionally tiny interface stubs, but a build-time var _ Adapter = (*sdk.Whatever)(nil) check would catch SDK-side breaking changes early.

Files

• engines/{extism,risor,starlark}/evaluator/evaluator_test.go
• platform/data/contextProvider_test.go
• platform/data/compositeProvider_test.go
• platform/script/loader/fromHTTP_test.go
• engines/risor/adapters/ (new test file)
• engines/starlark/adapters/ (new test file)

[robbyt]

Closing this as outdated. When I went to work on each piece, three of the five had already been addressed by unrelated PRs since this was filed (May 2026), and the remaining two are now tracked under focused issues:

Piece	Status	Note
Cancellation tests for each engine	Partially done	Extism is covered (PR #121). Risor + Starlark gap refiled as #125.
Race test for concurrent AddDataToContext	Open	Refiled as #126 (pairs with #93).
CompositeProvider edge-case branches	Already 100% covered	composite with only static providers (compositeProvider_test.go:517) covers static-only-error; all providers fail (line 479) covers non-static-fail. Both predate this issue.
HTTP loader error-path tests	Mostly covered	401/404/ctx-cancel/auth-fail are all exercised. fromHTTP.go is at 85.3% coverage; remaining uncovered lines are defensive log-on-close-error branches (effectively untestable without elaborate net.Conn mocks) and a TLS nil-config branch. Not worth a dedicated PR.
Adapter package coverage	Misaligned and resolved differently	engines/risor/adapters/ and engines/starlark/adapters/ contained no interfaces to assert against — just dead orphan struct sketches from the init commit. Cleaned up in PR #124 (deleted both directories and the parallel ExtismExecutable struct from the extism adapter).

Net: nothing actionable remains under this issue's body that isn't already done or refiled. Closing as not planned. Pick up under #125 and #126.

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