[calebl]

Stage 3 of the dungeon plan, server half: who stands on a floor. This PR pins renderedstep/engine#95 at its head (6247b4b9df29d202046bba845cdfee529033fc3b) and does every item in that PR's "What the server pin PR must change" list.

• A guard the world posts to a floor is stood by the engine in the floor's way-down room when it lays the floor out. This happens once, for the world (VISION principle 7).
• Everybody born on a floor that names a monster_level is born at that level.

A world with neither key plays exactly as before, and no checked-in story world turns either one on. No prompt changed and no model was called.

What changed

1. Migration 20261030230000_add_guards_and_monster_level_to_floors.rb uses the engine's version and declaration. db/schema.rb moves to 2026_10_30_230000; I hand-placed the lines so the existing column order stays as it was. No later migration is on origin/main (7d6324c).
2. Models
   • Character belongs_to :posted_to (a Location, optional).
   • Location has_many :posted_guards, nullified when the place is deleted.
   • Floor validates monster_level in Character::LEVELS, nil allowed.
   • Factories gain the :posted character trait and the :deep floor trait. Neither rolls dice.
   • Model tests added.
3. WorldSeed::Loader reads floor: { monster_level, guards }.
   • Refuses every case the engine PR lists, each with a test:
     • a non-Integer or out-of-range level;
     • guards that is not a list of names;
     • an unknown name;
     • a guard who is not absent: true or who has a location;
     • a guard with no stats;
     • the protagonist or a companion as a guard;
     • one character posted to two floors.
   • Writes monster_level and posted_to in both directions on every load.
   • Re-seed rule: once the guard's floor has rooms, the loader leaves the guard's location_id, deliberately_absent, x and y as they are. Before layout, absent: true is written as for anybody else.
4. WorldSeed::Exporter writes monster_level and guards (full names, in id order). Each guard is written as absent: true, with no location or spot and with their stats, wherever the layout stood them. The round-trip test lays the floor out first. The floor-rooms warning no longer counts posted guards.
5. Character::Registry gives a person born on a floor, or in a room of one, that floor's monster_level when it names one. Otherwise they get StatBlock::STARTING_LEVEL. The hit die and abilities are rolled as before (realize.rs admit_new).
6. Story::Doctor has two new findings. Both are warning/manual and are reported, never repaired:
   • guard_posted_to_no_floor;
   • guard_nowhere_on_a_laid_out_floor.
7. EngineSweep::Invariants#cast_unmoved now accepts a guard the file keeps nowhere when they stand in a room of the floor they are posted to, at Location::Placement.in_the_world's spot.
   • I used that check rather than rolled_in_the_world?, because rolled_in_the_world? also requires laid_out_alone?, which a room of a floor never is.
   • Removing the exception makes a-guard-waits-at-the-stairs fail with "Brask the Stairwarden is in The Upper Floor room 2 at 9,3 and the file says nowhere", so the check is exercised.
   • stat_blocks_unmoved is unchanged.
8. Copies of a world
   • Playthrough::SqlitePackage copies SELECT * with ids kept, so posted_to_id already comes along; there is now a test for it.
   • Story::Fork and Story::Snapshot go through the exporter and loader, so a fork's guard is posted to the fork's own floor (test).
   • Location::OneRoomFold::REFERENCES gains characters.posted_to_id. Its schema-walking test requires that.
9. Sweep
   • Worlds a-guarded-stair and a-deeper-floor, and scripts a-guard-waits-at-the-stairs and a-deeper-floor-births-stronger-people, copied from the engine PR body with their comments and why: notes.
   • Goldens vendored, and test/engine_parity/<script>.checks.json written for both.
   • The engine's parity/records/ files are not vendored in this repository, so there was nothing to copy for the four records files.
   • test/ruby_loop_coverage.yml does not list scripts, so it is unchanged.
   • test/engine_vectors/{plan,kept_requests}.json were re-exported. The only change is that the recorded character rows gain "posted_to_id": null.
10. Pin: ext/renderedstep/Cargo.toml and Cargo.lock now point at 6247b4b.

Gates (both provider keys unset)

• bin/rails test: 5447 runs, 0 failures, 0 errors. This includes the game sweep and the engine-vectors test.
• bin/rails engine:rust_gates: PASSED, 108 scripts: goldens, invariants, doctor and audit.
• bin/rails engine:vendored: VENDORED, byte for byte against 6247b4b.
• bin/rails engine:kept_requests: the engine reproduces every golden vector and kept request.
• bundle exec rubocop: no offenses. bin/rails zeitwerk:check: all good. bin/brakeman: no warnings.

Follow-up on the engine side

The engine PR asks for parity/worlds/a-guarded-stair.sql and a-deeper-floor.sql to be rebuilt from this branch's loader, now that it reads guards: and monster_level:. That happens in the engine repository and is not done here. After engine#95 merges, this PR re-pins to the merge commit.