Share the Go e2e harness through golang_e2e_matrix: go(), the file-proxy publisher, Machine/ChmodGuard and the grant mocks are copied across 5 suites #1980

[agent] Filed by the scheduled architecture audit (audit-cli-tests). Register: register.

Kind: refactor. Register ID: T65.

Problem

Every Go suite already includes golang_e2e_matrix/mod.rs for the toolchain gate, yet each one re-writes the rest of the harness. The two suites below are e2e_golang_build.rs (build) and e2e_vendor_golang_build.rs (vendor_build).

• go() runner, 4 local copies plus golang_e2e_matrix::go_envs.
  • build L74-L82 and vendor_build L103 are identical.
  • The Machine variants have drifted:
    • hosted_build L97-L112
    • workspace_build L77-L93:```` this one pins GOFLAGS="" and removes `GOWORK`, and hosted doesn't.
• File-GOPROXY publish + module zip, 5 copies.
  • build L86 and L344.
  • hosted_build L147-L178 and workspace_build L135-L166`````` are the same code apart from names.
  • vendor_build.
• stage() and go_env. build L86-L152 and vendor_build L120 differ only in comments.
• Machine and ChmodGuard. ChmodGuard + Drop are md5-identical in hosted_build L136 and workspace_build L119-L127. Machine differs only by a machines/ subdirectory. Separately, build and vendor_build keep a non-panic-safe chmod_writable/walkdir instead.
• harvest_sums ×2. It has drifted on go_directive() vs a hard-coded go 1.18.
• Hosted grant JSON and mount_sumdb ×3. See workspace_build L511-L550``````` and hosted_state L67-L105.```````` goZipDirhashH1 appears in exactly these three files.
• Day-2 env. day2_env and day2 are 2 copies.
• gopatch path. smod()/socket_module() are 2 copies, and the patch.socket.dev/gopatch/ literal appears in 6 files.

Proposed change

Move into golang_e2e_matrix:

• a Proxy (publish, zip, harvest_sums);
• Machine + ChmodGuard (replacing chmod_writable/walkdir);
• one go(cmd_dir, env) that always pins GOFLAGS and removes GOWORK unless the caller sets them;
• day2_env;
• mount_go_grant/mount_sumdb;
• a SOCKET_GO_MODULE constant.

Then delete the local copies. The workspace go() behavior (pinning GOFLAGS) becomes the default. Check that hosted_build's GOFLAGS=-mod=mod cases still set it explicitly.

Size

6 test files plus golang_e2e_matrix/mod.rs. Roughly −250 lines.

Acceptance criteria

• The Go suites (e2e_golang_build, e2e_golang_hosted_build, e2e_golang_hosted_state, e2e_golang_workspace_build, e2e_vendor_golang_build) pass unchanged on the go-compatibility matrix rows, with SOCKET_PATCH_GO_E2E_REQUIRED=1.
• No assertion is weakened.