fix: review the saved plan before execution

Present the saved, self-reviewed plan for human review before implementation.
Request an execution method when none was supplied; preserve an existing
choice and ask only for plan review when the human already chose a method.

This completes the shared-intent repair without interpreting approval of an
earlier idea or scope as approval of an unseen implementation plan. Four
saved-plan smoke cases covered old/new wording with/without a prior choice;
all passed the narrower handoff checks, including old controls, so this is
not evidence of measured improvement.

Jesse requested consolidation into two commits and removal of the supporting
spec/plan research content from the PR. The skill bytes remain identical to
the reviewed branch; the complete research and original history are retained
in local archives.

skills/writing-plans/SKILL.md

@@ -152,15 +152,25 @@ If you find issues, fix them inline. No need to re-review — just fix and move
 
 ## Execution Handoff
 
-After saving the plan, offer execution choice:
+After saving and self-reviewing the plan, link it for your human partner
+to read. If they have already explicitly supplied an execution method, ask
+them to review the plan and confirm it captures what they want; wait for that
+review before implementation, then use the preserved method. Otherwise, ask
+them to review the plan and choose an execution method before implementation.
 
-**"Plan complete and saved to `docs/superpowers/plans/<filename>.md`. Two execution options:**
+**When no execution method has already been supplied:**
+
+**"Plan complete and saved to `docs/superpowers/plans/<filename>.md`. Please review the plan. Two execution options:**
 
 **1. Subagent-Driven (recommended)** - I dispatch a fresh subagent per task, review between tasks, fast iteration
 
 **2. Inline Execution** - Execute tasks in this session using executing-plans, batch execution with checkpoints
 
-**Which approach?"**
+**Does the plan capture what you want, and which approach should we use?"**
+
+**When an execution method has already been supplied:**
+
+**"Plan complete and saved to `docs/superpowers/plans/<filename>.md`. Please review the plan. Does it capture what you want?"**
 
 **If Subagent-Driven chosen:**
 - **REQUIRED SUB-SKILL:** Use superpowers:subagent-driven-development