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Thanks for the contribution. I reviewed the full current diff on the latest head (d5337cca70) and this looks like a focused fix that correctly restores the intended ignoreIfNotExists semantics in the Paimon catalog wrapper.

What this PR solves

• User pain: callers can pass ignoreIfNotExists = false into PaimonCatalog.alterTable(...), but the current wrapper always forwards true to the underlying Paimon catalog, so a missing table can be silently ignored instead of failing fast.
• Fix approach: pass the flag through as-is in both alterTable overloads, and translate the underlying Paimon TableNotExistException into SeaTunnel's own TableNotExistException.
• One-line summary: this PR makes the alter-table wrapper behave consistently with its own method contract.

Simple example

If schema evolution tries to add a column to a Paimon table that has already been deleted, ignoreIfNotExists = false should surface an error immediately. Before this patch it could still be ignored; after this patch it fails fast as expected, while the ignoreIfNotExists = true path still keeps the best-effort behavior.

Actual runtime path I re-checked

schema change event
  -> AlterPaimonTableSchemaEventHandler.apply() [80-92]
      -> applySingleSchemaChangeEvent(...) [94-134]
          -> add/modify/change paths call paimonCatalog.alterTable(..., false)
          -> drop-column path calls paimonCatalog.alterTable(..., true)

catalog wrapper
  -> PaimonCatalog.alterTable(...) [358-387]
      -> old behavior: always delegated with `true`
      -> new behavior: delegates with the caller's actual ignore flag
      -> missing table:
           - ignore=false => throw TableNotExistException
           - ignore=true  => keep ignore semantics

Findings

• The bug is real and it is on the normal schema-evolution path, not an unreachable edge branch.
• The fix is complete for both overloads (SchemaChange and List<SchemaChange>).
• The new regression test covers both forms and directly checks the intended semantic split between false and true.
• I did not find a blocking correctness issue in the current implementation.

Test stability

The new test in PaimonCatalogTest looks stable to me:

• no sleeps
• no timing-based assertions
• no fixed-port or external-service dependency
• direct assertThrows / assertDoesNotThrow coverage for the exact bug

Stability rating for the new test change: stable.

CI readout

I checked the failing Build job as well.

• Dead links fails on two external Airtable links in docs/zh/connectors/source/Airtable.md returning 406.
• unit-test (8, ubuntu-latest) fails in seatunnel-engine-client, specifically SeaTunnelEngineClusterRoleTest.testWorkerIsFirstMemberThenGetJobDetailStatus, which times out waiting for CANCELED and still sees CANCELING.

I do not see evidence that either failure is caused by this PR:

• the PR diff only touches the two Paimon files
• the failing unit test is in seatunnel-engine-client, outside this diff
• there is no newer upstream/dev fix on that failing test path after this PR's merge-base

So from my side this looks like unrelated CI noise / flakiness rather than a blocker caused by the current Paimon change.

Conclusion

Conclusion: can merge

1. Blocking items

• None from my side on the current code.

2. Suggested follow-up

• Please rerun or recheck the current CI failures, but I would treat them as unrelated to this PR's source change unless new evidence shows otherwise.

Overall, this is a clean and appropriately scoped fix. The wrapper behavior now matches the caller contract, and the regression test covers the exact scenario that was previously wrong.

LGTM