Provide sandbox-writable toolchain caches and classify environment denials #43

Status (issue sync, 2026-10-26)

Already on main: resources/gocache.go, the Lab check TMPDIR and GOTMPDIR (verification/run.go).
Remaining scope of this issue: A sandbox preflight and a blocked-by-environment failure class.

Problem

Sandboxed harness runs repeatedly lost verification because of the toolchain environment, not the code:

• Codex workspace-write runs: go test ./... / go vet ./... exited 1, "sandbox denial accessing ~/Library/Caches/go-build" (Molecules for issues 82 and 84 in the private-history Lab).
• The latest issue Make Formulas own the supported sequential Atom workflow #5 Molecule's full suite failed only on TestIssueQueueCancellationStopsPipeHoldingDescendant because /bin/ps was denied.
• Localhost binding was denied for installer HTTPS lifecycle tests.

Harness reports said "blocked, not retried", which is honest but leaves the operator to rerun everything outside the harness.

Proposal

• Provision Lab-owned, workspace-local toolchain dirs for harness and check runs: GOCACHE, GOMODCACHE, GOTMPDIR, TMPDIR, npm_config_cache (allowlisted per detected component), so caches are writable inside the sandbox and reusable across attempts for the same Molecule.
• Add a sandbox preflight per adapter that runs inside the same sandbox (write the cache dir, run go env GOCACHE, spawn a child, list processes) and classifies capabilities. Record the result in the ledger.
• Classify check failures as blocked-by-environment (with the denied resource) distinctly from failed, and surface them in the gate summary.
• Tests that need process listing or sockets declare it, so they can be skipped with an explicit reason inside restricted sandboxes rather than failing.

Acceptance

• Fake harness tests confirm the env vars are set to workspace-local paths and are recorded.
• A denied cache write is reported as blocked-by-environment with the resource, not as a test failure.
• The ps-dependent test reports an explicit environment skip inside a sandbox fixture and still runs in CI.
• No sandbox is weakened; no automatic retry outside the sandbox.

Execution boundary

Implement through a separately reviewed Forgecell Molecule. Freeze current public repository inputs before execution. Preserve local evidence, exact Formula approval, reviewed ticket scopes, independent review and passing exact-head CI. Deterministic fake-harness tests only; no real credentials, provider APIs or model calls in tests. No release or deployment is authorized.