[Mikola Lysenko (mikolalysenko)]

LLM Description written by Claude Code:claude-opus-5-5

Fixes #1862

Stacked on #1843. This branch starts from agent/fix-go-unpruned-replace-target (plus a merge of main), because the fix reuses the module-mode ModuleGraph reader #1843 adds. Until #1843 merges, the diff includes its commits; review the commits after Start fix for #1862.

Problem

In a go 1.16-or-older module, go get M@<lower> lowers go.mod's require but keeps the old version's go.sum lines until go mod tidy. go_build_list::select took the highest go.sum zip line as the version the build selects, so after a downgrade:

1. Below the patched version: apply wrote an unused replace and reported applied, apply --check passed, and vex attested not_affected, while the build linked the unpatched module.
2. To the patched version: apply refused a patch for the version the build really uses.

Root cause

A go.sum zip line above go.mod's own require is either a dependency's raise or a line a downgrade left behind. go.mod and go.sum alone can't tell those apart, and the unpruned branch of select treated every such line as a raise.

Fix

• go_build_list: when go.mod requires a module below one of its go.sum zip lines, ask the module graph read from the module cache (Fix Go replace target missed in go 1.16 graphs (#1840) #1843's ModuleGraph, i.e. MVS over every go.mod the build reads). needs_module_graph / may_need_module_graph now take go.sum and also trigger on this shape.
• No complete graph (the cache lacks a needed go.mod): new Selection::Unproven, which fails closed.
  • apply refuses and writes nothing.
  • apply --check reports a new UnprovenStaleSum drift.
  • vex leaves the patch out.
  • The hosted rewriter writes no pin.
  • VEX discovery won't attest a hosted ref.
  • All of them share one explanation (UNPROVEN_REASON) that names go mod download.
• VEX discovery: a Socket module's own go.sum zip line no longer outranks a complete module graph that shows the build picks another version, because that line can be just as stale.
• Patch below require: when the patched version is below go.mod's require (so it is never selected), the reported version is the require, or the graph's answer, instead of a possibly stale go.sum line.

Trade-off (deliberate)

Without a module cache, a go 1.16 module that a dependency legitimately raises past go.mod's require is now Unproven, not Selected/Other:

• On a fresh clone that never ran go mod download, apply --check flags it.
• The in-memory hosted engine, which has no cache, won't pin it.

Before this change the same files were read as proof, and that is exactly what produced the false not_affected attestation in #1862. Any machine that has built the project has the cache and gets the exact MVS answer.

Tests (red → green)

Issue case	Test	Without fix	With fix
#1862 case 1 (unit)	go_build_list::tests::stale_zip_line_above_require_does_not_prove_the_patched_version	FAILED	ok
#1862 case 2 (unit)	go_build_list::tests::stale_zip_line_above_require_does_not_refuse_the_required_version	FAILED	ok
#1862 case 1 (real go 1.24.7)	e2e_golang_build::downgrade_below_the_patch_leaves_its_replace_unattested: apply refuses; an earlier replace fails apply --check with and without the cache; vex omits it	FAILED	ok
#1862 case 2 (real go)	e2e_golang_build::downgrade_to_the_patch_applies_and_checks_in_sync: apply patches, build prints PATCHED, check passes	FAILED	ok
hosted VEX stale socket line	vex::discover::golang::tests::module_graph_outranks_a_stale_socket_zip_line	FAILED	ok

Also added module_graph_confirms_a_dependency_raise (the graph tells a raise from a stale line). unpruned_require_is_a_lower_bound now expects Unproven for the no-graph raise (the trade-off above).

Commands run locally:

• cargo fmt --all -- --check: clean.
• cargo clippy --workspace --all-features -- -D warnings: clean.
• SOCKET_PATCH_GO_E2E_REQUIRED=1 cargo test -p socket-patch-cli --all-features --test e2e_golang_build: 35/35 pass.
• cargo test --workspace --all-features: 8043 pass. 11 fail, all permission-denial tests that can't fail when run as root, which this container runs as (copy_tree::relax_loop_must_not_traverse_symlinked_root, vlt_heal/pypi_* write-failure tests, in_process_redirect write failures, repair unremovable lock, e2e_bun_lockb x2). None touch Go code; CI runs non-root.

No npm/pypi/gem wrapper changes: this is all in the Rust core.

/code-review high

Fixed: the discovery stale socket zip line, the stale version reported for a patch below require, the "go.sum shows" wording when the graph answered, the duplicated message, and the double go.sum parse.

Not fixed:

• No-cache Unproven for legitimate raises: deliberate (see Trade-off).
• One graph read per patched purl in project_selection, and may_need_module_graph triggering on any raised module: both are offline go.mod reads from the cache, and the per-call read is Fix Go replace target missed in go 1.16 graphs (#1840) #1843's design. A per-project memo is a follow-up if it shows up in benches.

Follow-up (not in this PR)

Hosted-mode VEX discovery when the downgrade leaves no zip line above require but a stale Socket module zip line, and there is no graph: proven still trusts that socket line.

Taken ahead of the open p1 issues because those are all refactors that change no behavior, while this one is a false VEX not_affected attestation.

https://claude.ai/code/session_011f9aeSFJwUPaqWXN5AA5kk

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[Mikola Lysenko (mikolalysenko)]

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