[gustavodemorais]

What is the purpose of the change

Make the ON CONFLICT clause optional by default. A query whose upsert key differs from the sink's primary key no longer fails at planning time without the clause and behaves like ON CONFLICT DO DEDUPLICATE, as before 2.3. Discussed in https://lists.apache.org/thread/46vofq8qp1lshr3j6lnlycb0fdxfm7t4.

Brief change log

• Change the default of table.exec.sink.require-on-conflict to false and update its description.
• Update the ON CONFLICT section of insert.md (English and Chinese) and the generated config docs.
• Enable the option explicitly in tests that expect the planning error and drop it from tests that relied on false.

Verifying this change

• TableSinkTest
• SinkSemanticTests

Does this pull request potentially affect one of the following parts:

• Dependencies (does it add or upgrade a dependency): no
• The public API, i.e., is any changed class annotated with @Public(Evolving): yes - changes the default of table.exec.sink.require-on-conflict in ExecutionConfigOptions
• The serializers: no
• The runtime per-record code paths (performance sensitive): no
• Anything that affects deployment or recovery: JobManager (and its components), Checkpointing, Kubernetes/Yarn, ZooKeeper: no
• The S3 file system connector: no

Documentation

• Does this pull request introduce a new feature? no
• If yes, how is the feature documented? not applicable

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Was generative AI tooling used to co-author this PR?

• Yes (please specify the tool below)

2.1.304 (Claude Code) with Opus 5.5

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CI report:

• 24a80d8 Azure: SUCCESS

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