docs(codex): wire the compaction hook into README and codex-tools, add drift-cure footer

README gains the hook install step for Codex users (hooks.json merge,
one-time trust prompt, --dangerously-bypass-hook-trust for headless
automation). codex-tools.md aligns its claims with the mechanism — the
dispatch rules bind every spawn, the printed hints appear at scripted
boundaries, and the hook covers post-compaction re-grounding — and adds
a section telling controllers compaction sheds these instructions and
to treat every printed hint as authoritative.

The hints file gains a drift-cure footer both scripts print after the
role line: in the instrumented run that broke post-compaction,
reprinted hints alone did not heal the already-broken dispatch pattern
across three subsequent boundaries — recovery text must name the drift
and prescribe the re-read.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

tests/claude-code/test-sdd-workspace.sh

@@ -175,9 +175,16 @@ PLAN
         echo "    got: $brief_hint"
     fi
 
+    if [[ "$brief_hint" == *"you have drifted"* ]]; then
+        pass "task-brief prints the drift-cure footer after the hint"
+    else
+        fail "task-brief prints the drift-cure footer after the hint"
+        echo "    got: $brief_hint"
+    fi
+
     local rp_hint
     rp_hint="$(cd "$repo" && env -u CLAUDECODE "$SDD_SCRIPTS/review-package" plan-a.md HEAD~1 HEAD)"
-    if [[ "$rp_hint" == *"dispatch (spawn_agent): fork_turns=none model=gpt-5.6-terra reasoning_effort=high"* ]]; then
+    if [[ "$rp_hint" == *"dispatch (spawn_agent): fork_turns=none model=gpt-5.6-terra reasoning_effort=high"* && "$rp_hint" == *"you have drifted"* ]]; then
         pass "review-package relays the default-role hint off Claude Code"
     else
         fail "review-package relays the default-role hint off Claude Code"