Several worlds: a Worlds list with load, rename and delete; old save migrates to World 1

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

docs/DESIGN.md

@@ -196,6 +196,9 @@ above, including:
 - **Screw tubes carry bars**, one whole bar at a time, in line with the grains: a belt pushes a
   bar into a tube's side, it rides through corners and leaves the mouth. The owner asked how bars
   should be moved and chose tubes over a separate bar lift.
+- **Several worlds are kept.** Each world has its own save and autosave; the title screen's Worlds
+  list loads, renames and deletes them, and a new or imported world never overwrites another. An
+  old single save becomes 'World 1'. The owner asked for multiple saves.
 
 ## Ideas not built yet
 

docs/PROJECT_MAP.md

@@ -369,16 +369,16 @@ The title screen art.
 - functions: buildTitleCells, drawTitle
 - variables: FONT5, TITLE
 
-### src/ui/saves.js (106 lines)
+### src/ui/saves.js (177 lines)
 Saves in IndexedDB, world files (export / import) and the blueprint library.
-- functions: saveWorld, newestSave, b64FromBytes, bytesFromB64, gz, exportWorld, importWorldFile, libLoad, libSave, bpEncode, bpValid, bpDecode
-- variables: DB
+- functions: newWorldId, worldWrite, listWorlds, putWorldEntry, worldNewest, deleteWorld, renameWorld, migrateWorlds, saveWorld, newestSave, b64FromBytes, bytesFromB64, gz, exportWorld, importWorldFile, libLoad, libSave, bpEncode, bpValid, bpDecode
+- variables: DB, worldIdTime, worldIdCounter, worldWrites
 
-### src/ui/session.js (87 lines)
+### src/ui/session.js (122 lines)
 Starting, loading and quitting a game; modal dialogs; the pause menu.
-- functions: showLoading, enterGame, startNewWorld, startFromSave, quitToTitle, refreshContinue, anyModal, openModal, closeModal, closeAllModals, topModal, dialog, openPause
+- functions: showLoading, enterGame, startNewWorld, startFromSave, quitToTitle, refreshContinue, anyModal, openModal, closeModal, closeAllModals, topModal, dialog, openPause, renderWorlds
 
-### src/ui/settings.js (116 lines)
+### src/ui/settings.js (122 lines)
 The settings screen.
 - functions: openSettings, renderSettings, applySettings, toggleFullscreen, confirmWipe
 - variables: SET_TABS, setTab
@@ -430,7 +430,7 @@ Previews drawn under the cursor: build ghosts, drill aim and pulses, selections,
 Events from the simulation (emit) turned into sounds, toasts and cards.
 - functions: drainEvents
 
-### src/ui/loop.js (117 lines)
+### src/ui/loop.js (119 lines)
 The frame loop and boot.
 - functions: scanVisible, frame, boot
 - variables: lastT, acc, lastRender, frameMs, simMs, fpsSm, ambientT

docs/agent-log.md

@@ -4,6 +4,30 @@ What agents have done, newest first. Add an entry for every piece of work: the d
 note or request it was for, what changed, the files touched, the tests run, and anything left
 open or not verified. Keep each entry short; the git history has the details.
 
+## 2026-10-24: several worlds, with a Worlds list (Claude Code, with Codex)
+
+Note: "support multiple saves". The owner chose a world list.
+
+- `src/ui/saves.js`: each world has an id and its own `<id>:main` / `<id>:auto` saves, plus an
+  index record `worlds` (name, seed, size, created, saved, playtime). A save writes the world
+  and its index entry in one transaction. `GAME.worldId` is the open world.
+- Migration: an old single `main` / `auto` save is copied to "World 1", every byte compared,
+  and only then are the old keys deleted (in the same transaction that writes the index). If
+  anything fails the old save is kept and a toast says so.
+- Title screen: Continue loads the most recently saved world; a Worlds button opens a list
+  with Load, Rename (trimmed, at most 40 characters, escaped when shown) and Delete (with a
+  confirmation). New and imported worlds get new ids. Settings' "Delete saves" became "Delete
+  all worlds" with a confirmation. `shell.html`, `session.js`, `loop.js`, `settings.js`,
+  `state.js`, `style.css`, `docs/DESIGN.md`, `docs/PROJECT_MAP.md`.
+- `test/play.py` (149 checks): migration of an old save, two worlds listed, load switches,
+  rename survives a reload, HTML in a name shows as text, long names cut to 40, delete and
+  cancel, Continue picks the newest, import adds a world. All 11 headless suites pass;
+  `t_smooth.py` passed in Codex's run and failed its known flaky check in mine.
+- Shots: `shots/worlds-{pixel,smooth}.png` and `-900` versions.
+- Not committed: a line in `AGENTS.md` about running `kandown work` appeared in the working
+  tree during this task; it was not part of the task and is left for the owner.
+- Open: nothing.
+
 ## 2026-10-24: screw tubes carry bars (Claude Code, with Codex)
 
 Note: "how do you transport bars? belts work but tubes do not, should they?" The owner chose