Pipeline vfs raw parsing and DuckDB appends

[fanyang89]

Motivation

• Improve throughput by decoupling JSON parsing from DuckDB writes so parsing can proceed while writes complete, reducing idle IO waiting.

Description

• Introduced a buffered events channel and a writer goroutine that consumes events and calls appender.AppendRow in cmd_vfs_raw.go.
• Added a writeErrCh to propagate writer errors back to the parser and a done channel to coordinate shutdown.
• Changed the jsonParseThenAppend callback to send parsed *vfsEvent into the events channel and handle early writer errors.
• Ensured orderly shutdown by closing events, waiting for the writer to finish, and returning any parse or write errors.

Testing

• No automated tests were executed for this change.

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Codex Task

[chatgpt-codex-connector]

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[chatgpt-codex-connector]

Stop parsing immediately when writer errors

The select can still choose events <- e even when writeErrCh is already readable, because Go selects randomly among ready cases. If the writer goroutine fails, the parser may enqueue up to the remaining buffer capacity (1024) of additional events before it eventually notices the error, and those events will be dropped because the writer has exited. That creates silent data loss in the exact scenario the error reporting is meant to handle. Consider prioritizing the error path (e.g., non-blocking check of writeErrCh before enqueue) so parsing halts as soon as the writer fails.

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[fanyang89]

Wrong