fix(audit-h2,h3): remove bare-name bypass in compose-solution phase-2; backup settings.json in activate_hooks

- phase-2-decompose.md: delete 'or researcher if that agent is present in the user's
  global fleet' clause that silently bypassed the kei-namespace. Replace with an
  explicit prefer-kei note warning that bare 'researcher' matches only the user's
  personal fleet and may have divergent handoffs.
- install.sh activate_hooks(): call backup_file "$target" on the merge path
  (after the 'create new' early-return) so ERR-trap rollback can restore the
  pre-merge settings.json. Previously an ERR in the jq-merge or mv left no
  backup pair to restore.

install.sh

@@ -142,6 +142,10 @@ activate_hooks() {
     say "created $target from snippet (no prior settings.json)"
     return 0
   fi
+  # Merge path: back up the pre-merge settings.json so rollback can restore
+  # it if a later step ERR-traps. The "create new" path above exits before
+  # reaching here, so backup_file is only invoked when $target exists.
+  backup_file "$target"
   # Merge: walk each matcher-group in PostToolUse / PreToolUse, append hooks,
   # unique_by command. jq filter is written for readability, not golf.
   tmp="$(mktemp "$target.XXXXXX")"

skills/compose-solution/phase-2-decompose.md

@@ -8,9 +8,11 @@ independently researched and composed.
 For heavy / deep-domain / unfamiliar-domain tasks, delegate to the
 `research` skill (`skills/research/SKILL.md`, Variant C "Deep decomposition"
 is the pattern — Wave 0 decomposition, then Wave 1 per-component
-exploration). Invoke via the Agent tool with `subagent_type: kei-researcher`
-(or `researcher` if that agent is present in the user's global fleet). Pass
-`DESC` as the research question with the constraint:
+exploration). Invoke via the Agent tool with `subagent_type: kei-researcher`.
+Always prefer `kei-researcher` when it exists in the kit; bare `researcher`
+matches only the user's personal fleet and may have divergent handoffs — do
+not fall back to it silently. Pass `DESC` as the research question with the
+constraint:
 
 > Decompose into 2-5 orthogonal components, each with a 1-line description
 > and 3-5 distinctive keywords suitable for grep prior-art search.