prediction: typed list-response envelopes for candlesticks + bulk endpoints (closes #404)

[TexasCoding]

Completes #404 — the prediction-API parity (the perps half shipped in #418). Closes #404.

The prediction list endpoints extracted their REQUIRED array with data.get(key, []), which silently returned [] on a missing key (masking spec drift) and TypeError'd on a null array. Each now validates a typed envelope:

Endpoint	Envelope
markets.candlesticks	GetMarketCandlesticksResponse{ticker, candlesticks}
markets.bulk_candlesticks	BatchGetMarketCandlesticksResponse{markets}
markets.bulk_orderbooks	GetMarketOrderbooksResponse{orderbooks}

Why NullableList (and not a bare list)

This is released code, so the model is chosen for safety: the array field is NullableList (required key, BeforeValidator coerces null→[]). That gives:

• missing key → ValidationError — surfaces drift (the resources: validate typed list-response envelopes for REQUIRED-array endpoints (perps + prediction) #404 goal), where the old code silently returned [];
• null array → [] — Kalshi's documented "empty-as-null" convention (MarketCandlesticks already notes this), and a strict improvement over the old code which TypeError'd on a null array;
• the candlesticks envelope also validates the previously-discarded required ticker.

Verification

• All 3 envelopes registered in CONTRACT_MAP and pass the drift harness.
• Regression tests (sync and async): each endpoint raises on a missing array key and returns [] on a null array; candlesticks rejects a missing ticker. Existing candlesticks mocks updated to include the spec-required ticker.
• CHANGELOG "Changed" note added (released-behavior change).
• mypy --strict + ruff clean; full suite 3660 passed.

Follow-up note

The perps envelopes in #418 used a non-nullable list (hard-fail on null) per #404's strict "absent or null → raise" wording. Aligning them to NullableList — restoring the pre-#418 or [] null tolerance and matching this PR — is a reasonable small follow-up if you want perps/prediction null-handling identical.

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[claude]

Code Review — PR #419: Typed list-response envelopes (prediction)

Overview

This PR replaces silent data.get(key, []) extraction on three prediction-API list endpoints with typed Pydantic envelope validation, completing the #404 spec-drift hardening for the prediction surface. The approach is clean and consistent with NullableList usage already present in MarketCandlesticks.

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Issues

1. Missing async regression tests (actionable)

test_markets.py adds three new regression tests:

• test_missing_key_raises_but_null_tolerated (candlesticks)
• test_missing_markets_raises_but_null_tolerated (bulk_candlesticks)
• test_missing_orderbooks_raises_but_null_tolerated (bulk_orderbooks)

None of these appear in test_async_markets.py. Sync and async are separate code paths (per the repo convention: "Sync and async share logic via dual transport abstraction — not sync-wrapping-async"), so both paths need coverage. The async resource code makes the same model_validate calls and the null/missing-key regression applies equally to it.

These three tests should be mirrored in test_async_markets.py.

2. Null-handling inconsistency with perps (design concern)

The PR description notes this directly, but it's worth flagging for the review record: perps endpoints (shipped in #418) use non-nullable list (null → hard fail), while these prediction endpoints use NullableList (null → []). The divergence means the two surfaces behave differently on an identical server response pattern. The PR recommends a follow-up to align perps to NullableList — that follow-up should probably be tracked as an issue if it isn't already.

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Minor Notes

• GetMarketOrderbooksResponse.orderbooks: NullableList[dict[str, Any]] — using dict[str, Any] is intentional (documented in the docstring: _orderbook_from_item owns the FixedPoint parsing), but it means Pydantic validates structure/presence of the array while individual item shape is checked only at transform time. This is the same trade-off the pre-existing code made; fine to keep.

• Docstring length — the three new model classes carry multi-paragraph docstrings. The CLAUDE.md style guide says to avoid multi-line docstrings. The NullableList semantics here are genuinely non-obvious (the why is the BeforeValidator coercion behavior), so some comment is justified. Trimming to a single sentence each would be more consistent with project style:

  """Single-market candlesticks envelope — ticker required, null candlesticks coerces to []."""

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What's Working Well

• The model_validate one-liners replacing the two-line get/comprehension pattern are cleaner and correctly surface drift.
• All three envelope models registered in _contract_map.py — drift harness will catch schema changes.
• Existing mocks correctly updated to include "ticker" in the response fixture.
• Sync resource changes are symmetric between MarketsResource and AsyncMarketsResource.
• CHANGELOG entry is accurate and appropriately categorized under "Changed".

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Summary

Solid PR with one actionable gap: mirror the three new regression tests in test_async_markets.py. The null/perps inconsistency should be tracked as a follow-up issue if not already filed.

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