Complete the SQL entity source-anchor protocol #12

Problem

FmxSQLEntitySourceAnchor inherits explicit requirements for knowsStart, knowsEnd and hasSource. The duplication detector fails while filtering otherwise valid anchored queries.

Found during the 2026-09-20 FAMIXNGSQL/Moose 13 compatibility audit.

Implementation scope

Implement valid/missing/bounded interval semantics against owner source without inventing file paths; keep generated methods and handwritten behavior separate.

Implementation PR target: deem0n/FAMIXNGSQL, in the deem0n fork first. Keep this issue separate from the other v3.0.0 fixes. The PR must explain the previous failure, resulting behavior, compatibility implications, and actual validation.

Acceptance criteria and tests

Valid anchors, nil owner/source, partial/reversed/out-of-range offsets, empty source, extraction, and MSE round trips. Check all three required selectors.

• Regression tests demonstrate the reported problem and pass with the fix.
• Relevant existing tests pass; validation environment and limitations are recorded in the PR.
• A separate implementation PR is linked here and reviewed.
• Integrated v3.0.0 acceptance is verified before this release blocker is closed.

Release

Part of the v3.0.0 milestone. An open PR is not a completed fix; release qualification is tracked separately.

Implementation

#25

Combined qualification: #32. The implementation is available for review; this issue remains open until its integrated release acceptance is verified.