[codex] add cross-provider analysis showcase

[hudsonaikins]

Problem

Kalshi sports parsing produced incorrect game metadata, Polymarket US public reads required credentials even where the public Retail Market API permits anonymous access, and the examples did not provide a deterministic cross-provider analysis proof.

Outcome

• Correct Kalshi sports date and matchup parsing.
• Support anonymous Polymarket US market and quote reads through public endpoints.
• Normalize Kalshi and Polymarket US sports data into one analysis stream.
• Provide deterministic buy_yes, buy_no, and hold proof without live-provider dependence.
• Remove the UTF-8 BOM that broke documentation and Python 3.10 validation.

Acceptance Criteria

• Kalshi NBA and related sports helpers return correct date and matchup metadata.
• Public Polymarket US reads work without credentials where the upstream API permits them.
• Cross-provider examples parse and pass repository documentation validation.
• Deterministic replay produces buy_yes, buy_no, and hold.
• Full repository lint, type, and test gates pass without live credentials or paid calls.

Validation

Exact candidate: 942d9a8c68e452fa5c926bdf240370f54ad68ce7

• uv run ruff check . — passed
• uv run black --check . — passed
• uv run mypy neural — passed, 67 source files
• uv run pytest -q — passed, 109 passed and 6 skipped
• Python 3.10 deterministic replay regression — passed
• Polymarket Amount-wrapper, market-list quote, and malformed-secret regressions — passed
• uv run python scripts/validate_examples.py — passed with existing advisory warnings
• uv run python scripts/validate_docs.py — passed with existing documentation-coverage warnings
• Focused cross-provider suite — passed, 25 tests
• Deterministic replay — passed; produced buy_yes, buy_no, and hold
• Cost and external effects — $0; deterministic fixtures only, no live orders or authenticated provider calls

Residual Risk

Live public feeds remain unsuitable as deterministic proof because market movement and quote depth vary. This PR uses fixtures for acceptance and does not deploy, publish, merge, or access production.

[github-actions]

📚 Documentation Status

✅ Code changes detected

• Docstring coverage checked
• API documentation validation completed
  ✅ Example changes detected
• Example documentation validated
• Code syntax verified
  ✅ README changes detected

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This comment is automatically generated by the documentation workflow.

[chatgpt-codex-connector]

💡 Codex Review

Here are some automated review suggestions for this pull request.

Reviewed commit: 62edb9e7f2

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[hudsonaikins]

@codex review

Please review exact head 942d9a8c68e452fa5c926bdf240370f54ad68ce7. All prior findings were fixed, answered, and resolved; exact-head CI is green.

[chatgpt-codex-connector]

Codex Review: Didn't find any major issues. Chef's kiss.

Reviewed commit: 942d9a8c68

ℹ️ About Codex in GitHub

Codex has been enabled to automatically review pull requests in this repo. Reviews are triggered when you

• Open a pull request for review
• Mark a draft as ready
• Comment "@codex review".

If Codex has suggestions, it will comment; otherwise it will react with 👍.

When you sign up for Codex through ChatGPT, Codex can also answer questions or update the PR, like "@codex address that feedback".