[pasmud]

Summary

Assigning a non-table value to an array of tables currently succeeds, but dumping the document then raises an AttributeError. For example, doc['a'][0] = 42 leaves a scalar where the renderer expects a table.

Validate converted integer and slice replacements before updating either storage representation. Reject non-table values with ValueError, matching the validation already used by AoT.insert. Failed assignments leave the document unchanged.

Validation: all 20 regression cases fail against unchanged source. With the fix, all 1,455 tests pass on Windows / Python 3.13.1 with python -m pytest -q --override-ini addopts='', including the pinned toml-test compliance cases. Ruff 0.17.4 lint and formatting checks pass for both changed files, as does git diff --check. Before the final test expansion, Mypy 1.19.1 reported the same 33 diagnostics in eight files on the patch and unchanged source checked using shadow files, allowing for shifted line numbers. No successful type check, other operating systems or upstream CI results are claimed.

Duplicate Check

• I searched the open PRs and found none that already fixes this issue.
• Related: merged PR Fix array-of-tables assignment serialization and list storage #631 fixed conversion and storage synchronization for valid assignments. Open PR Preserve line boundaries when moving array-of-tables elements #679 concerns line boundaries when moving tables. This change validates replacement types before mutation.

Agent Drafting Metadata

• Agent: OpenAI Codex
• Model: GPT-6 (session identity; exact variant not independently verified)
• Notes: Agent investigated the bug, prepared the code and regression tests, executed the reported checks, and drafted this text. The submitting contributor supplied the personal attestation below and explicitly authorized publication.

Human Attestation

Attestation supplied by the submitting contributor:

I reviewed the full patch, understand the changes, confirm they are correct and intended, and take responsibility for this contribution. Please open the PR

[human-attestation]

✅ Human Attestation: @pasmud attested this PR at commit 622d516 (2026-11-12T13:22:10.954Z).

I have read and understood all agent-written code in this PR. / 我已阅读并理解此 PR 中 Agent 编写的全部代码。

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