fix(plan-ceo-review): persist + stop on /absolute-brainstorm branch

Codex cross-review on cc86fe8 surfaced two blocking findings on the
mid-session-detection /absolute-brainstorm branch:

1) state_mutation -- option B told the agent to "note progress and pause"
   with no persisted artifact, so the next user turn could not resume.
2) if_completeness -- no explicit stop condition; agent could fall through
   into the rest of the review in the same turn.

Fix: option B now writes a `*-ceo-handoff-brainstorm.md` artifact (matching
the existing `*-ceo-handoff-*.md` glob already read at the top of the
skill, so the standard handoff-note check picks it up on return), and the
branch ends with an explicit STOP-and-wait instruction. The "Note current
progress / after completion" lines are scoped to option A so option B
does not fall through into them.

Finding 1 (import_resolution -- /absolute-brainstorm not present in this
repo) is left as the documented PR caveat: this PR surfaces the offer
in /plan-ceo-review; the consuming installation supplies the skill.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

plan-ceo-review/SKILL.md

@@ -1029,13 +1029,30 @@ Follow its instructions from top to bottom, **skipping these sections** (already
 
 Execute every other section at full depth. When the loaded skill's instructions are complete, continue with the next step below.
 
-If they choose B: tell the user to run `/absolute-brainstorm` directly in their
-next message — it's a sibling skill, not a sub-invocation. Note current Step 0A
-progress, pause this review, and pick up once they return with the brainstorm's
-output.
-
 Note current Step 0A progress so you don't re-ask questions already answered.
-After completion, re-run the design doc check and resume the review.
+After option A completes, re-run the design doc check and resume the review.
+
+If they choose B:
+
+Write a handoff note to `~/.gstack/projects/$SLUG/$(date -u +%Y%m%d-%H%M%S)-$BRANCH-ceo-handoff-brainstorm.md`
+with:
+- Current Step 0A progress (the questions already answered)
+- The specific proposal the user wanted vetted
+- A note that the review paused for `/absolute-brainstorm`
+
+Then say: "Saved a handoff note. Run `/absolute-brainstorm` in your next
+message. When you come back to `/plan-ceo-review`, I'll read the handoff
+plus the brainstorm output and pick up Step 0A from where we left off."
+
+**STOP here and wait for the user's next message.** Do not continue with
+the rest of `/plan-ceo-review` in this turn — `/absolute-brainstorm` is
+a sibling skill, not a sub-invocation, so control must return to the user
+before any further work in this review happens.
+
+When the user returns to `/plan-ceo-review`, the standard handoff-note
+check at the top of this skill will read `*-ceo-handoff-brainstorm.md` the
+same way it reads other handoff notes, and the review resumes from the
+recorded Step 0A point with the brainstorm's output as additional input.
 
 When reading TODOS.md, specifically:
 * Note any TODOs this plan touches, blocks, or unlocks

plan-ceo-review/SKILL.md.tmpl

@@ -181,13 +181,30 @@ If they choose A:
 
 {{INVOKE_SKILL:office-hours}}
 
-If they choose B: tell the user to run `/absolute-brainstorm` directly in their
-next message — it's a sibling skill, not a sub-invocation. Note current Step 0A
-progress, pause this review, and pick up once they return with the brainstorm's
-output.
-
 Note current Step 0A progress so you don't re-ask questions already answered.
-After completion, re-run the design doc check and resume the review.
+After option A completes, re-run the design doc check and resume the review.
+
+If they choose B:
+
+Write a handoff note to `~/.gstack/projects/$SLUG/$(date -u +%Y%m%d-%H%M%S)-$BRANCH-ceo-handoff-brainstorm.md`
+with:
+- Current Step 0A progress (the questions already answered)
+- The specific proposal the user wanted vetted
+- A note that the review paused for `/absolute-brainstorm`
+
+Then say: "Saved a handoff note. Run `/absolute-brainstorm` in your next
+message. When you come back to `/plan-ceo-review`, I'll read the handoff
+plus the brainstorm output and pick up Step 0A from where we left off."
+
+**STOP here and wait for the user's next message.** Do not continue with
+the rest of `/plan-ceo-review` in this turn — `/absolute-brainstorm` is
+a sibling skill, not a sub-invocation, so control must return to the user
+before any further work in this review happens.
+
+When the user returns to `/plan-ceo-review`, the standard handoff-note
+check at the top of this skill will read `*-ceo-handoff-brainstorm.md` the
+same way it reads other handoff notes, and the review resumes from the
+recorded Step 0A point with the brainstorm's output as additional input.
 
 When reading TODOS.md, specifically:
 * Note any TODOs this plan touches, blocks, or unlocks