Restore original 7-field ReadPipe event contract in Boost.Asio implementation

[akleshchev]

Description

The new Boost.Asio-based ReadPipeImpl broke the original APR implementation's event contract in two ways: it posted only 4–5 fields per event instead of 7, and at EOF it split the final data and the eof signal into two separate events rather than one combined event.

Original APR contract — every pump post included all 7 fields:

data, len, slot, name, desc, eof, exhst

What was broken:

• name (e.g. "stdout", "stderr") was never included
• eof boolean was absent from normal data events
• exhst boolean was absent from all events
• data was omitted when mLimit == 0 (original always emitted it, as an empty string)
• At EOF with pending bytes: two events were posted (data event + separate eof event) instead of one combined event

Fix in llprocess.cpp: Both the normal-read and EOF branches now always post all 7 fields. The async read states map to the original APR state machine as follows:

Async event	eof	exhst
Successful read (was EXHAUSTED)	false	true
EOF (was CLOSED)	true	false

Fix in llprocess_test.cpp: Reverted the setLimit() test (test 20) workaround — history.back() is correct again since the last event is the combined eof+data event.

Related Issues

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  • Feature/Enhancement: Link to an issue with a write-up, rationale, and requirements.

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Additional Notes

The exhst field semantics in the async model: Boost.Asio's async_read_some returns whenever any bytes are available, which corresponds to EXHAUSTED (read until no more data, pipe still open). There is no RETRY loop equivalent in the async model, so exhst is always true on non-EOF events and false on the EOF event.