Enable strict tool use on the Anthropic structured-output call

[exactml]

Summary

• AnthropicProvider.generate_structured now sets "strict": true on its tool definition
• Anthropic's strict tool use compiles input_schema into a grammar and constrains token sampling at generation time, so the response is guaranteed schema-conformant -- not just requested to be. This is the server-side fix for the failure class ISSUE-96's retry was mitigating client-side: an extra wrapper key, a double-encoded string, a stringified array -- all observed live on _FindingsResponse, all a symptom of the model's free-form generation drifting from the schema
• Verified both _FindingsResponse and its nested Finding already emit "additionalProperties": false at every level (a strict mode expectation, per Anthropic's docs examples) via pydantic's existing ConfigDict(extra="forbid") -- no schema changes needed, only the flag
• The two-attempt retry from Retry once on a structured-output schema mismatch instead of failing outright #96/Retry once on a structured-output schema mismatch #97 stays in place, unchanged, as a dormant safety net -- kept per instruction, not removed. If _FindingsResponse ever grows complex enough to hit strict mode's documented compilation-time limits, that fails at the request level (anthropic.APIError, already handled, not retried) rather than reintroducing a validation mismatch, so the retry branch should simply go unused rather than get in the way

Relates to #96 -- not a new issue, this is the follow-up fix for the same root problem.

Test plan

• make lint -- clean
• make test -- 160 passed (1 new), asserting strict: True is actually present in the request sent to messages.create
• Real-world verification: once released, re-run the review check on Resolve a diff's changed functions to their out-of-diff callers #94 (which has repeatedly hit this exact failure) to confirm it now comes back clean

[github-actions]

🤖 marginal review

PR #99: Enable strict tool use on the Anthropic structured-output call · open · 5144f395166e65483d632dc93bfe8fed207eb597 → 341e1765212417684125dd2f0298255680e2a54b · 3 files changed

Changed files (3)

• CHANGELOG.md
• marginal/providers/anthropic.py
• tests/test_providers.py