HowlFrame #90 Phase 2d: mediate fetch on Go and JavaScript

[howlcipher]

Summary

Phase 2d of #90 mediates (fetch url method [body]) on generated Go and JavaScript under the existing network grant. This follows the Phase 2a–2c HOWLFRAME_ALLOW_CAPS / CAPABILITY_DENIED pattern. #90 stays Partial. Production -compile-bc is unchanged.

• howlFrameFetch checks network before http.NewRequest / http.DefaultClient.Do (Go) or fetch (JavaScript). An empty, missing, or non-network grant panics or throws CAPABILITY_DENIED: capability denied: network and does not open a connection. The denial text does not include the URL.
• A network grant performs the request. Go try_let still binds (bytes, error). let and bytes_to_string use howlFrameFetchBytes. JavaScript returns the response text.
• The interpreter sends the request only after its existing network check. The bytecode VM is unchanged: OpFetch is already network, and the gate runs before the request.
• Conformance adds fetch_denied and fetch_granted on the interpreter, the bytecode VM, Go, and JavaScript. The fixture is (fetch "http://127.0.0.1:47653/howlframe-abi-v1-phase2d" "GET"). Denial records zero requests to that server.
• write_file, mkdir, and other host effects are not mediated. No new capability, no new opcode, and no Wasm change.

Journal: docs/journals/2026-09-30_lowered_hfir_abi_phase2d_fetch.md.

How to test

gofmt -l .
go vet ./...
go test ./internal/backend/gogen/ ./internal/backend/javascript/ ./internal/vm/ ./tools/difftest/ -count=1

TestLoweredHFIRABIConformance serves phase2d-fetch-marker on 127.0.0.1:47653 and checks that fetch_denied makes no HTTP request while fetch_granted prints the marker on all four hosts.

Local evidence: gofmt -l . was clean, go vet ./... passed, and go test ./... passed.

  

[howlcipher]

COMMENT OK on head 32cd2e40 (CI build green).

Phase 2d scope check: Go+JS mediate (fetch) under existing network via HOWLFRAME_ALLOW_CAPS / howlFrameGrantHas; CAPABILITY_DENIED before http.NewRequest / fetch; denial text has no URL; denied cases record zero HTTP hits. Interpreter sends only after its existing network gate. Conformance fetch_denied / fetch_granted on interpreter / bytecode VM / Go / JS. write_file / mkdir untouched. -compile-bc still AST path. #90 stays Partial.

Hard nos clean: no half bytecode linker / HFIR module smuggle / VM module opcodes; no new caps or opcodes; don’t reopen #102–#105/#108; no path flip / Wasm as this item; no batch of remaining host effects.

Okabe: undraft + squash-merge when ready.