[codex] Fix Pydantic model_fields access

[den-sq]

Fixes #98

Summary

• switch copy_values_from_other to class-level Pydantic model_fields access through type(self)
• mark the existing copy-values coverage so PydanticDeprecatedSince211 warnings fail that test path

Root Cause

Pydantic 2.11 deprecated accessing model_fields on a model instance. The helper copied fields with self.model_fields, which still works today but warns and is scheduled for removal in Pydantic 3.0.

Validation

• poetry run pytest test/helpers/test_models.py -W error::pydantic.PydanticDeprecatedSince211
  • 7 passed in 0.08s
• rg "self\\.model_fields|self\\.model_fields_set|self\\.model_computed_fields" python/ouroboros
  • no matches
• poetry run pytest
  • 168 passed, 1 warning in 7.75s
  • the remaining warning is the separate SharedNPArray.__del__ unraisable warning tracked by SharedNPArray.__del__ AttributeError on partially-constructed instance (mem.py:76) #97 / PR [codex] Fix SharedNPArray partial init cleanup #99

[tavateva]

Draft Promotion Criteria — FAIL on criterion 4 (fixable documentation gap)

Fix is correct and minimal. Blocking promotion on the same missing-pass-count issue we hit on den-sq/mctutil#78 and, in parallel, on #99.

Passes:

1. CI & mergeability — all 3 checks green (`coverage`, `server-image`, `test-coverage`); `mergeable: MERGEABLE`, `mergeStateStatus: CLEAN`. ✓

2. Issue Acceptance Criteria — issue #98's 3-item checklist:

   • `models.py:117` uses class-level `model_fields` access → `type(self).model_fields.keys()` at models.py:117. ✓
   • Coverage workflow no longer emits the `PydanticDeprecatedSince211` warning → `@pytest.mark.filterwarnings("error::pydantic.PydanticDeprecatedSince211")` on `test_model_with_json` enforces this at the unit level; CI coverage run passed. ✓
   • Ripgrep confirms no other instance-level `model_fields` remains → PR body explicitly reports `rg "self\.model_fields|self\.model_fields_set|self\.model_computed_fields" python/ouroboros` returned no matches. ✓

3. Test Plan checkboxes — no checkbox section. N/A.

4. Tests run, not just present — Validation section reads:

   `poetry run pytest test/helpers/test_models.py -W error::pydantic.PydanticDeprecatedSince211`
   `rg "self\.model_fields|..." python/ouroboros` returned no matches

   Issue #98's AC includes both a test requirement and a verification command that names a specific pytest invocation. Criterion 4 requires concrete pass/fail counts ("X passed / Y skipped") in the PR body. `rg` result is reported concretely; pytest result is not. Failure.

5. Scope — models.py -1/+1 (single-line fix); test_models.py +2 (`pytest` import + filterwarnings marker). Trivially tight to #98. ✓

6. Regressions & patterns — `type(self).model_fields` preserves subclass polymorphism (Pydantic resolves `model_fields` on the leaf class, so subclass fields are still iterated); no behavior change for callers. Existing `test_model_with_json` still passes on the coverage run, so the marker doesn't spuriously fire on unrelated warnings. ✓

7. Judgement calls — used `type(self).model_fields` rather than `self.class.model_fields` (both work, both were listed as acceptable in #98). No explicit reasoning in PR body, but this is a stylistic call within the sanctioned set. ✓

Fix to promote: append pass counts to the Validation section, e.g.:

```
poetry run pytest test/helpers/test_models.py -W error::pydantic.PydanticDeprecatedSince211
→ N passed, M skipped
```

Also worth including a full-suite `pytest` run with its count. Then all 7 criteria hold.

[tavateva]

Re-review — Draft Promotion Criteria PASS ✅

Validation section updated with concrete pass counts. All 7 criteria hold.

1. CI & mergeability — 3 checks green (`coverage`, `server-image`, `test-coverage`); MERGEABLE / CLEAN. ✓
2. Issue #98 AC — `type(self).model_fields.keys()` at models.py:117; `filterwarnings("error::pydantic.PydanticDeprecatedSince211")` marker on `test_model_with_json`; `rg` reported no other instance-level `model_fields` access. ✓
3. Test Plan checkboxes — N/A.
4. Tests run with counts — targeted `pytest test/helpers/test_models.py -W error::pydantic.PydanticDeprecatedSince211` → 7 passed in 0.08s; `rg` → no matches; full `pytest` → **168 passed, 1 warning in 7.75s`. The remaining warning is explicitly identified as the sibling `SharedNPArray.del` unraisable warning tracked in #97 / PR #99 — no hidden regressions. ✓
5. Scope — models.py -1/+1; test_models.py +2. ✓
6. Regressions & patterns — 168 matches the baseline from PR #96; no test count delta expected (no new tests, just a stricter marker on an existing one). ✓
7. Judgement calls — reasoned inline. ✓

Approving. Safe to promote and merge.