[thekevinbot]

Fixes #1562

Root cause

On a watched change, a per-table on-file command's rows were applied only after wait() reaped the child. cat closes stdout before exit_group, so its exit teardown (about 21us) sat on the critical path between the last row and the event.

Change

• command::drain_then_reap drains stdout in whole-line blocks, calls on_eof once stdout closes, and only then reaps the child.
• refresh_table stages the rows at EOF inside a dirsql_unit SQLite savepoint (foreign_key::stage), while the child is still exiting. It keeps them (RELEASE) on a zero exit and discards them (ROLLBACK TO) on a nonzero exit or failure. The hook error event outranks everything else, as before.
• A multi-invocation (pooled) run never ends early; it stages after the hook returns, as before.
• Semantics are unchanged: a failed command leaves no rows, and the events emitted are the same. Hand-checked with dirsql server: cat produces one update event and the new row; a command that prints rows then exits 3 produces one error event and leaves the old row.

Measurements

	main (05880bb)	this branch
in-process apply_file_events per change, cat hook (median of 3000 iterations, 5 interleaved runs)	230-246us (about 238)	209-227us (about 216)
watch_speed_test passes (1.1x bar), 40 interleaved rounds	27/40 (68%)	39/40 (98%)
watch_speed_test median ratio, second batch of 25 rounds	about 1.07	about 0.99

The host load average was about 15 on 32 cores. The rounds ran interleaved (main, then branch), with the two release CLIs on PATH.

Changelog / Migrations

• Changelog fragment added under packages/rust/changelog.d/ (2026-11-02-stage-per-table-rows-at-eof.md)
• Migration fragment with the same slug added under packages/rust/migrations.d/ (every subsection but Summary _None._)

E2E Verification

• Ran e2e suites locally for every affected SDK
• Python SDK e2e: pass
• TypeScript SDK e2e: pass
• Rust core e2e: pass (cargo test -p dirsql --features cli)
• packages/python/e2e-attestations/<branch>.json receipt written
• packages/ts/e2e-attestations/<branch>.json receipt written
• Command(s) run: testing-conventions e2e attest 'uv run python -m pytest tests/e2e/{on_file_query,query_contract,declared_table_name,fanout,use_case_dossier,use_case_join,use_case_notebook,use_case_transcripts,watch_speed}_test.py -q' in packages/python (after maturin develop --release); just e2e-attest-ts
• Result summary: Python 22 passed; TypeScript 18 passed.