docs: close core ty override debt

[lbliii]

Summary

• mark the parser/compiler/analysis ty override cleanup as implemented
• remove Pay down parser/compiler/analysis ty override debt from mixin dispatch #142 from the active planning index
• update parser and compiler steward contracts to protect default ty severity
• add a regression test that rejects unresolved-attribute overrides

Why

PR #176 removed all three core unresolved-attribute = "warn" override blocks, but the planning RFCs and scoped steward guidance still described that debt as active. That stale guidance could route future work toward an already-completed migration or allow the broad overrides to return unnoticed.

Impact

No runtime, syntax, public API, or generated-output behavior changes. This closes the documentation and maintenance-contract collateral for the shipped type-check cleanup.

Verification

• make lint
• make format-check
• make ty
• uv run pytest tests/test_type_config_contract.py -q (1 passed)
• make test (4,451 passed, 5 skipped)
• git diff --check

Steward Notes

• Consulted: planning, parser/syntax, compiler/codegen, static-analysis, test-corpus, internal-docs, and root runtime guidance as part of the backlog-wide steward pass.
• Accepted: record refactor: remove obsolete core ty overrides #176 as the completed core override cleanup and make the no-override state executable in a focused test.
• Required proof: default-severity ty, focused configuration contract, and full suite.
• No collateral: no changelog, public docs, examples, schemas, or benchmarks because this preserves already-shipped type-check configuration without changing user-visible behavior.
• Steward feedback loop: the scoped parser/compiler checklists now explicitly prohibit restoring core unresolved-attribute overrides without contract review.

Closes #142.

[Copilot]

Pull request overview

Closes the remaining documentation/contract collateral for the already-shipped ty override cleanup by updating planning/steward guidance to reflect the default-severity policy, and making that policy executable via a regression test.

Changes:

• Add a focused contract test that fails if pyproject.toml reintroduces unresolved-attribute overrides under tool.ty.overrides.
• Update parser/compiler steward contracts to explicitly protect “default ty severity” (no core unresolved-attribute overrides without contract review).
• Mark historical planning RFCs as completed and remove issue #142 from the active planning index.

Reviewed changes

Copilot reviewed 7 out of 7 changed files in this pull request and generated no comments.

Show a summary per file

File	Description
tests/test_type_config_contract.py	Adds a regression test enforcing that unresolved-attribute is not overridden in tool.ty.overrides.
src/kida/parser/AGENTS.md	Updates parser steward invariants/checklist to prohibit restoring core unresolved-attribute overrides.
src/kida/compiler/AGENTS.md	Updates compiler steward invariants/checklist to prohibit restoring core unresolved-attribute overrides.
plan/rfc-type-suppression-reduction.md	Updates historical RFC status/note to reflect completion of core ty override cleanup and link to #142/#176.
plan/rfc-type-checking-strategy.md	Updates the NOTE to reflect override debt completion and link to #142/#176.
plan/rfc-mixin-protocol-typing.md	Marks the RFC as implemented and updates the NOTE to reflect override removal and link to #142/#176.
plan/README.md	Removes #142 from the “Active issue” planning index row now that it is closed.