did2.build: key_id / positions_from (did-schema 2026-10-05)

[jesshaley]

did-schema renamed the edge a key takes its positions through: key_labels_id → key_id and the key field labels_from → positions_from, and the edge now points only at a data_type document. This was signed 2026-10-05 in V_eta_study_plan.md, did-schema PR #87. This PR follows the rename in the builders:

• did2.build.key: 'LabelsFrom' → 'PositionsFrom' (emits positions_from).
• did2.build.sampledBody / opaqueBody: 'KeyLabelsIds' → 'KeyIds' (emits key_id).
• did2.build.statement gains 'KeyIds', so a statement can key by another statement's entries. The Haley import's encounters are the first use: per-encounter values keyed by a worm's encounter-onset list.
• The key rule check (private/checkRules.m) names positions_from.
• New testKeyPositionsFromAnotherDocument.

No import or migrator wrote the old names, and empty edges are still dropped (forward.m). Callers that never set them are unaffected by either schema.

Merge order: did-schema #87 first. test-builder.yml runs against did-schema main, and the new test filters itself until main declares key_id.

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[jesshaley]

"Quick migrator tests / Migrator transform tests (no corpora)" is red: 78 tests fail. The failures are not from this PR.

• The same 78 fail on testBuild: counts take a tolerance (CHANGE 7 amendment 1) #214 and did2 sqlitedb: a file store (ingestion) #215.
• They are migrator and batch-pass tests, such as testResponseParametersFold, testTuningCurveLevels and testValidIntervalDecompose. Those migrators were written for the schema from before Bug: did.database.findfilematch fails if input "expectedName" ends with # symbol #73, and the tests fail against the current schema.
• This PR only touches +did2/+build and testBuild.m.
• No fix exists yet. The fix is the Bug: did.database.findfilematch fails if input "expectedName" ends with # symbol #73 migrator catch-up.

The builder tests do cover this change, but they did not trigger on their own. The test-builder.yml path filters are written as +did2/.... In GitHub's path filters, + is a pattern character, so the filters probably never match the +package folders. I've started the workflow manually with workflow_dispatch on this branch.

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