formatter: linter-guided retry to suppress GPT-5 reasoning drift

GPT-5 is a reasoning model and is not bit-deterministic even at the API
level (no temperature override allowed). Variance testing in iter 7
showed ~1 in 6 loop runs hit a nondeterministic regression: in one run
the magazine_mead exemplar lost its italic markers around "New Yorker"
even though the exact same input had produced a clean output 5 times
prior. The scoring linter caught it (rule_magazine_name_italicized) but
the formatter still emitted the bad output to the user.

This commit adds a runtime guardrail:

- New module src/cmos/runtime_validator.py — type-independent
  structural sanity checks. Operates on a single candidate string
  with no Exemplar context, because at runtime we don't know the
  source type. Checks: ends with period, no Ibid., has at least one
  italic span (almost every CMOS bibliography entry italicizes
  something), balanced * and " markers. Deliberately weaker than the
  scoring linter; it's a fast guardrail, not a full validator.

- format_bibliography_entry now retries up to DEFAULT_MAX_RETRIES (2)
  times when the validator rejects a candidate. Independent re-calls
  are usually enough because the failures are stochastic. If every
  attempt fails, the LAST attempt is returned (no exception) — the
  caller still gets something usable, and the failure surfaces
  through the scoring linter or human review. The retry path costs
  zero on the common case (1 call per entry); ~1-2% extra calls on
  noisy drafts.

Empirical: 3 consecutive loop runs after this change are scalar 1.000
canary 1.000 (vs 5/6 clean in the variance test before). Sample is too
small to claim full suppression but the signal is positive.

Also adds a new exemplar journal_multiauthor_secondary_first_last.toml
captured from the user's HML draft (Hasanah et al., IJIDI 2024). It
exercises the case where a multi-author entry has the first author
inverted and the rest in First Last form — which the iter 7 HML run
got wrong on one entry. Variance testing showed the exemplar passes
6/6 in isolation, so the original HML failure was nondeterminism, not
a missing rule. Keeping the exemplar regardless: it adds canary
coverage of a real-world multi-author pattern, no-DOI / JSTOR-URL
variant, and the year-suffix author-date holdover stripping.

Tests: 85 → 95 (8 new for runtime_validator + 2 new for formatter
retry). All passing.

tests/test_runtime_validator.py

@@ -0,0 +1,70 @@
+"""Tests for src/cmos/runtime_validator.py.
+
+Runtime validator runs at format time on a single candidate string with no
+exemplar context. It checks type-independent structural sanity rules so the
+formatter can self-retry when GPT-5's reasoning drift produces a malformed
+entry. It is deliberately weaker than the scoring linter (which has access
+to canonical fields and source type) but it catches the most common
+nondeterministic failures: missing terminal period, stray Ibid., dropped
+italic markers, unbalanced quotes/asterisks.
+"""
+
+from cmos.runtime_validator import validate
+
+
+def test_clean_book_entry_passes():
+    candidate = "Yu, Charles. *Interior Chinatown*. Pantheon Books, 2020."
+    result = validate(candidate)
+    assert result.passed is True
+    assert result.failures == []
+
+
+def test_clean_journal_entry_passes():
+    candidate = (
+        'Kwon, Hyeyoung. "Inclusion Work: Children of Immigrants Claiming Membership in Everyday Life." '
+        "*American Journal of Sociology* 127, no. 6 (2022): 1818–59. "
+        "https://doi.org/10.1086/720277."
+    )
+    assert validate(candidate).passed
+
+
+def test_missing_terminal_period_fails():
+    result = validate("Yu, Charles. *Interior Chinatown*. Pantheon Books, 2020")
+    assert result.passed is False
+    assert any("period" in f.lower() for f in result.failures)
+
+
+def test_ibid_fails():
+    result = validate("Ibid., 42.")
+    assert result.passed is False
+    assert any("ibid" in f.lower() for f in result.failures)
+
+
+def test_missing_italics_anywhere_fails():
+    # The "New Yorker" magazine regression we saw in iter 7 variance: italic
+    # markers around the magazine name disappeared. This rule should catch
+    # that — almost every CMOS bibliography entry italicizes something.
+    candidate = 'Mead, Rebecca. "Terms of Aggrievement." New Yorker, December 18, 2023.'
+    result = validate(candidate)
+    assert result.passed is False
+    assert any("italic" in f.lower() for f in result.failures)
+
+
+def test_unbalanced_italic_markers_fails():
+    candidate = "Yu, Charles. *Interior Chinatown. Pantheon Books, 2020."
+    result = validate(candidate)
+    assert result.passed is False
+    assert any("italic" in f.lower() or "*" in f for f in result.failures)
+
+
+def test_unbalanced_double_quotes_fails():
+    candidate = 'Mead, Rebecca. "Terms of Aggrievement. *New Yorker*, December 18, 2023.'
+    result = validate(candidate)
+    assert result.passed is False
+    assert any("quote" in f.lower() for f in result.failures)
+
+
+def test_passed_property_is_negation_of_failures():
+    # Sanity: passed should be True iff there are no failures.
+    result = validate("Yu, Charles. *Interior Chinatown*. Pantheon Books, 2020.")
+    assert result.passed == (result.failures == [])