acp_command / acp_args descriptions previously primed the model to
populate them — "Per-task ACP command override (e.g. 'copilot')" —
even when no ACP CLI was installed. Models with weaker schema-following
discipline would set them and the spawn would fail.
Add explicit "Do NOT set unless the user has explicitly told you"
guidance at both the top-level acp_command and the per-task override.
Strengthen acp_args to mention it's empty unless acp_command is set.
Adds 2 tests pinning the descriptions.
Note: this is a cosmetic prompt-engineering fix — the params remain
exposed in the schema. The fully-correct fix is to gate them behind
a config flag or runtime ACP-CLI detection so the schema only emits
them when an ACP harness is available. Tracked as a follow-up; this
PR ships the low-cost stopgap.
Salvage of #22680 (delegate schema only). The original PR also
bundled unrelated fixes for #22548, #21944, #22150 — those
need separate PRs since #22548 and #21944 are already addressed
on main (#22780 + #22798 in flight) and #22150 deserves its own
review.
Closes#22013.
ca13993217