tip leaf: finish process when descendants hold stdio (#50701)

[kvnloo]

Goal

Fork-only tip leaf for origin anomalyco#50701 — finish process when descendants hold stdio.

Context

Origin tip SHA ea7ffc1007ce2fd5d399d52f6e81690a0130b870. Base: fork dev. github_writes_origin=0. Codex promote parked.

Acceptance

• CLEAN fail→pass on descendant-stdio tip tests (GREEN 3 / NEG 1 fail / RESTORE 3)

Return

Ship fork PR with grok bot + envelope; no origin writes.

[kvnloo]

QA: HOLD / superseded direction.

#50701 interrupts stdout/stderr immediately when exitCode resolves. Node's process exit can precede stdio closure, so that creates a tail-output truncation risk even though the descendant-held-stdio hang disappears.

There is now a stronger origin implementation at anomalyco/opencode#51668: it buffers output before lazy consumption, proves delayed reads after process completion, covers 256 KiB backpressure on both streams, and only cuts descendant-held stdio after a bounded post-exit deadline.

Please stop promoting #50701 as CLEAN and treat the #51668 leaf as the replacement. The old 27/27 suite proves termination, not preservation of all foreground output.

[kvnloo]

Exact head is unchanged. Focused behavioral evidence is already upstream: packages/core process suite 27/27 with the descendant-held-stdio completion invariant covered. No duplicate promotion.