Background-stream error notice never shown — checkBackgroundStream purges the entry before its own error branch runs

[jdmanring]

Summary

When a background stream errors while the user is on a different session, the failure is never shown. Returning to that session displays a chat that simply stopped, with no indication the background response failed.

Root cause

checkBackgroundStream(sessionId) (static/js/chat.js) begins by calling _purgeStaleBackgroundStreams(), which deletes every completed/error entry from _backgroundStreams — including the current session's. The has(sessionId) guard on the next line then early-returns, so the error branch that appends "[Background stream encountered an error]" to #chat-history is now unreachable dead code.

The error branch is original behavior (commit e5c99a5e, "Odysseus v1.0"). It was killed by fork commits: 67268d2b added the _purgeStaleBackgroundStreams primitive, and 1e8a217a placed a call to it at the top of checkBackgroundStream. Upstream has no purge, so this is a fork-introduced regression.

The error entry is intentionally left in the map by the catch handler (bgErr.status = 'error', not deleted) precisely so checkBackgroundStream can surface it later — the top-of-function purge defeats that.

Fix

Exclude the current sessionId from the purge: _purgeStaleBackgroundStreams(exceptSid) skips that entry, so other sessions' finished streams are still cleaned up while the current session's error/completed entry survives for its own branch to handle.

Classification

Fork-only regression (the purge exists only on the fork). Fix on develop.

[github-actions]

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[jdmanring]

Fixed on develop (a498776a): checkBackgroundStream now purges with the current sessionId excluded, so its error/completed branch runs. Fork-only regression (the purge exists only on the fork). Source-assertion guard tests/test_background_stream_error_notice_js.py.