fix: preserve vector DDL errors after embedding retries

[willlling]

Summary

• retry transient CURLE_RECV_ERROR failures in embedding tasks with the existing bounded exponential backoff
• refresh the parent vector-index DDL status before health decisions
• while the parent waits for an auxiliary-table child DDL, let the child result be authoritative instead of replacing its original error with a secondary OB_TABLE_NOT_EXIST
• retain the normal base-table health check and all auxiliary-schema checks outside child-wait states

Verification

• release build: make -j80
• normal hybrid vector-index create/rebuild path passed
• added a no-mock mysqltest against a real HTTP 503 endpoint with model_max_retries=2
• the test verifies at least six seconds of retry backoff, the post-retry product error, and complete auxiliary-table cleanup
• old binary: test fails with MySQL 1146 (Table doesn't exist)
• fixed binary: test passes with the original child failure preserved as MySQL 4016, and zero residual index tables

Issue: SEEK-511

[CLAassistant]

All committers have signed the CLA.

[Copilot]

🟡 Changes recommended

Task matching remains overly broad, a completion race can misclassify valid schema, and cleanup coverage is nondeterministic.

Once you've addressed the issues Copilot identified, you can request another Copilot review.

Pull request overview

Corrects vector refresh/rebuild error classification while HNSW auxiliary tables are being created.

Changes:

• Checks active vector DDL tasks when the hidden index-id table is absent.
• Returns transient or schema errors based on task state.
• Adds race and cancellation mysqltests.

File summaries

File	Description
ob_vector_refresh_index_executor.cpp	Adds DDL-task-based error classification.
ob_vector_refresh_index_executor.h	Declares the task-check helper.
vector_index_refresh_while_creating.test	Tests refresh/rebuild during creation.
vector_index_refresh_while_creating.result	Adds expected race-test output.
vector_index_create_failure_cleanup.test	Tests cancellation cleanup and recreation.
vector_index_create_failure_cleanup.result	Adds expected cleanup-test output.

Review details

• Files reviewed: 6/6 changed files
• Comments generated: 3
• Review effort level: Balanced

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[wangyunlai-seekdb]

Reviewed commit 26b5c9d.

I reviewed the force-pushed fixes for the existing Copilot threads. This review only reports an additional issue that is not covered there.

[Major] Register the new regressions in mysqltest CI

Location: tools/deploy/mysqltest_config.yaml:258-279

Neither vector_index.vector_index_create_failure_cleanup nor vector_index.vector_index_refresh_while_creating is listed in runtime_configs.psmall.test-set. discover_cases() executes only configured names and silently ignores unconfigured suite cases. The current successful run 33607668840 ran 68+68+68+67 = 271 configured cases, and neither new name appears in its logs. Add both cases to the vector-index list and rerun the slices so this fix is enforced by PR and future CI.