docs(adr): define Rust polytomous period artifact

[seonghobae]

Outcome

Defines the owner-side Rust artifact required to remove active Python GRM/GPCM period-report arithmetic from downstream consumers without preserving an unsupported weighted model-selection score.

The proposed contract keeps authorization/period state downstream, moves matrix construction and measurement summaries into one Rust-owned artifact, requires formal distinguishability before GRM/GPCM preference, returns explicit unavailable/indeterminate states instead of a Python numerical fallback, and requires recovery/parity/fingerprint evidence before acceptance.

Stack / freshness — 2026-09-03

This Draft is intentionally stacked on #1417 because it reuses the residual interaction-map envelope.

• exact parent feat(interaction-map): extend Rust result envelope #1417: feat/interaction-map-rust-summary-1412@3cdc684a94d7cdc0c30c0db773c0e92cfd9492f2;
• predecessor child: 78a54ed032635713d57a803077feb4e92e71a9d1;
• exact current child: feat/polytomous-period-artifact-adr@d7387d7e09e1c7cd45d606ece96dd054d06cb843.

Fresh comparison before repair showed the predecessor child diverged from the current #1417 parent (behind_by=2) while its only effective child-owned delta remained docs/adr/0027-polytomous-period-artifact.md. The child was repaired non-destructively: d7387d7e... records predecessor 78a54ed... as first parent and exact current #1417 parent 3cdc684... as second parent, with a tree constructed from the exact parent tree plus the already-reviewed ADR blob. No force push, destructive rebase, unrelated source copy, or numerical change was used.

#1417 must land first. Any future parent movement invalidates child exact-head/base evidence and requires fresh comparison before another stack action.

Verification

Every predecessor child workflow/review result is historical after d7387d7e.... Keep this PR Draft until the unchanged exact child head has regenerated applicable hosted CI/security/documentation evidence and the live review/protection policy is satisfied.

No numerical implementation, Python numerical fallback, heuristic model-selection score, or psychometric/statistical arithmetic is added.

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[devin-ai-integration]

Devin Review found 1 potential issue.