Source-read licence: enforced at the one consumer, not repo-wide (2026-09-12)

Index: Known gaps

Status (re-verified 2026-10-09 at 456989f): OPEN. Both deliberate residuals are still open: scripts/check_ai_readiness.py has no source-read licence gate (grep 'licen' finds only license-header checks), and there are no per-input content digests. The third residual is recorded as closed.

The contract — a path recorded in a snapshot is provenance, not a licence to re-read the current filesystem for historical facts — is stated in abicheck/buildsource/source_inputs.py and enforced in the one place that had violated it: workflows/pattern_preprocessor_scan.py, plus the two primitives beneath it (buildsource/pattern_facts.py's find_pattern_facts, which now refuses to stat an unlicensed root, and buildsource/preprocessor_facts.py, which is simply not invoked for an unlicensed side since clang -E resolves #includes against the filesystem it runs on).

Two residuals are deliberately open, both recorded on the evidence.stored_snapshot_rederivation bug class in tests/regressions/manifest.py:

1. No mechanical gate against a future violator. Nothing stops a new consumer from reading AbiSnapshot.source_header (or a compile unit's source) and opening it without resolving a licence first — nor a new front end from calling dumper.dump directly and forgetting to grant one. Both halves of that already bit once: the ABICC-compatible CLI was found doing exactly the second (PR #1236's review round), after service.run_dump had already been fixed for the first. The shape of the fix is known — an AST scan in scripts/check_ai_readiness.py, the way fact-field-readers guards Fact[T] reads, with an allowlist of the reader sites that legitimately hold a licence — but it is a gate of its own, not part of this fix, and today there is exactly one such consumer to guard.

2. The licence is object-level, not content-verified. A header-derived live extraction grants it for the whole run; it does not digest each source input and re-check that digest at read time. The consequence is the conservative direction (a stored snapshot declines to re-derive even when the tree on disk genuinely is the one it was dumped from), which is why it is a gap rather than a defect. Closing it properly means persisting per-input content digests, i.e. an AbiSnapshot schema bump inside the ADR-050 comparability contract plus a codec and migration — the "persist the facts at dump time" half of the original two-option brief. That is the route to take if stored-versus-stored pattern/preprocessor evolution ever needs to be answerable rather than honestly declined; do not instead widen the licence, which would reintroduce exactly the defect above.

Closed, and how (one licence per evidence source). A third residual used to sit here: the licence required header-derived provenance (extraction_read_source_inputs), so a dump that collected only L3 build evidence (--sources with no -H) reported its source-derived facts as not evaluated even though it genuinely had read its compile units, because nothing at the grant point separated that from a loaded pack whose paths are as historical as a stored snapshot's. The same coarseness had a worse, opposite failure the same review round found: a live header dump merged with a pre-captured --build-info pack was granted one snapshot-wide licence off the header AST, and the pattern/preprocessor scans then read the pack's recorded compile-unit paths from whatever occupies them on this runner — the original fabrication, reached through the other evidence source (PR #1236, Codex P2).

Both directions are one defect: a side holds up to two source-evidence sources with independent provenance, and one licence cannot be correct for both. So the licence is now resolved per source — declared headers via snapshot_source_licence, an embedded build pack via build_evidence_licence, which asks the pack itself (BuildSourcePack.live_source_evidence, stamped by buildsource/embed.py only for an inline collection performed in this run and, like the snapshot flag, never serialized). A partially-licensed side reports what it read and keeps the unlicensed roots in the expected-input account as not_licensed gaps, so no absence is established from the half that was read. What remains true is that the grant is conditional, which is the point for a DWARF-only dump whose DW_AT_decl_file paths name the build machine's tree: that side never opened them, so it gets no header licence.

Note also the shape of the accepted trade-off in the third fix: the evolution fold now decides each identity from what is established for that identity, which means persistent is reported from two observations even when both sides had coverage gaps elsewhere. An earlier revision withheld it globally. That is not a regression of the earlier fix: an incomplete scan cannot un-see a hit, so two observations are the strongest premise the fold has, while introduced/resolved each assert an absence and still require the relevant side's sufficiency. The lexical scan cannot, however, attribute an unread file to a particular PatternKind, so a gap in any declared root leaves every kind's absence unestablished on that side — a per-kind answer would need per-kind input attribution the scanner does not have, and is recorded as a gap on coverage.discovery_derived_completeness.