{"name":"tengu_bg_attach_outcome","slug":"tengu-bg-attach-outcome","family":"flag","title":"Feature flags","noun":"feature flag","description":"Background attach events now record cold starts, surface and first frame details.","description_source":"entry","described_by":{"version":"2.1.221","anchor":"background-attach-telemetry-gets-cold-start-and-surface-dime"},"presence":{"first_seen":null,"removed_in":null,"in_current_build":false,"newest_mined":"2.1.309","builds":0,"mined_builds":150,"first_cited":{"version":"2.1.227","released_at":"2026-08-10 20:56:57","spans":1}},"aliases":[],"entries":[{"version":"2.1.227","anchor":"recovered-background-attaches-report-the-same-way-on-both-co","heading":"Recovered background attaches report the same way on both code paths","line":"Recovered background attaches report identically whether found by the old or new sweep.","released_at":"2026-08-10 20:56:57","reason":"gate cited by this entry, found in this entry's text"},{"version":"2.1.221","anchor":"background-attach-telemetry-gets-cold-start-and-surface-dime","heading":"Background attach telemetry gets cold-start and surface dimensions","line":"Background attach events now record cold starts, surface and first frame details.","released_at":"2026-08-03 22:16:25","reason":"gate cited by this entry, found in this entry's text"},{"version":"2.1.221","anchor":"background-attach-outcomes-are-journaled-to-disk-and-recover","heading":"Background-attach outcomes are journaled to disk and recovered later","line":"Background session attaches now write a small journal file so crashed attaches still report what happened later.","released_at":"2026-08-03 22:16:25","reason":"gate cited by this entry, found in this entry's text"},{"version":"2.1.221","anchor":"much-richer-background-attach-timing-telemetry","heading":"Much richer background-attach timing telemetry","line":"Attaching to a background session now records detailed timing, including a 30-second timeout flag.","released_at":"2026-08-03 22:16:25","reason":"gate cited by this entry, found in this entry's text"},{"version":"2.1.221","anchor":"claude-attach-now-measures-time-to-interactive","heading":"claude attach now measures time-to-interactive","line":"Attaching to a background session now times how long it takes to paint and reach an idle prompt.","released_at":"2026-08-03 22:16:25","reason":"gate cited by this entry, found in this entry's text"}],"entries_total":5,"docs":[],"docs_total":0,"gates":[],"related":[{"name":"tengu_bg_attach_stall_ms","slug":"tengu-bg-attach-stall-ms","description":"Default `5000` (milliseconds). How long attaching to a background session may wait for it to redraw before Claude Code restarts the session with `Session not responding`; after two such restarts it gives up, prints `Session keeps stalling at startup.` and kills the session. `0` turns the restart off; any other value is raised to at least 2000, or 12000 when a background-session launcher is configured."},{"name":"tengu_bg_attach_upgrade","slug":"tengu-bg-attach-upgrade","description":"Default `true`. Gates the background-session supervisor's prewarming: restarting idle background sessions whose recorded Claude Code version is stale onto the running version, in one delayed burst once the supervisor is ready and up to `tengu_bg_prewarm_per_sweep` (default `3`) per periodic sweep while memory is not low. Sessions launched in `exec` mode are skipped and a session on a newer version is not downgraded. Turning it off stops prewarming; the sweep still restarts sessions in its pinned set."}],"url":"https:\/\/changelogs.core-directive.com\/reference\/flag\/tengu-bg-attach-outcome","family_url":"https:\/\/changelogs.core-directive.com\/reference\/flag.json"}