…engine#3541)

* fix(agent): keep executor from answering as planner

* fix(agent): scope handoff-confusion match to role-identity phrases

Bare permission claims (no write access / 没有写入权限) are the exact
vocabulary a correctly-executing model uses to report a real blocker;
matching them mis-fired the planner-confusion guard and could hard-error
a legitimately-blocked task. Drop those phrases, keep role-identity ones,
and lock it with a regression test.

* fix(agent): detect executor punt by behavior, not keywords

The keyword list matched on vocabulary, so it both missed paraphrases
and false-flagged legitimate blocker reports ("no write access" is the
exact phrasing the handoff prompt asks the executor to use). Replace it
with a structural signal: if the executor reaches a final answer in
handoff mode having called zero tools, nudge once with the executor
instructions, then trust it — no keyword table, no hard error. Any tool
use (including read-only) exempts it, so only a true punt triggers the
nudge. Language-independent.

Tests cover both the nudge and the no-nudge-when-acting path; verified
end-to-end with a live deepseek-pro planner / deepseek-flash executor
run that wrote and ran the file without tripping the guard.

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Co-authored-by: reasonix <reasonix@deepseek.com>