Summary

• Fixes [Bug] Plan Execute dual-model: executor handoff nudge forces task invention on guidance-only turns #4867 by allowing PE executor handoffs to finish with a text-only answer when the original turn or planner output is clearly user-facing guidance, a summary, or a follow-up question.
• Keeps the existing handoff nudge for real work tasks and deferral-style answers, so code/file changes still require executor tool calls.
• Updates the executor handoff instructions to avoid invented local tool calls for pure guidance-only turns.

Verification

• go test ./internal/agent -run 'TestCoordinator(AllowsGuidanceOnlyExecutorHandoff|NudgesExecutorThatAnswersWithoutActing|NudgesWorkTaskEvenIfPlannerMentionsUserGuidance|DoesNotNudgeExecutorThatActs)' -count=1
• go test ./internal/agent -count=1
• go test ./...
• (cd desktop && go test ./...) (passes; local linker prints the existing duplicate -lobjc warning)
• go vet ./...
• (cd desktop && go vet ./...)
• git diff --check
• gofmt -l .

Cache impact

Cache-impact: low - touches the executor handoff gate and one handoff user-turn instruction; system prompt and tool schemas are unchanged.
Cache-guard: Added focused coordinator regressions for guidance-only handoffs and for preserving the work-task nudge; also ran go test ./internal/agent -count=1 and go test ./....
System-prompt-review: N/A