diff --git a/.github/workflows/ci.yml b/.github/workflows/ci.yml
index 144b044..eb56723 100644
--- a/.github/workflows/ci.yml
+++ b/.github/workflows/ci.yml
@@ -110,9 +110,9 @@ jobs:
           & $env:GODOT --headless --path . --script res://tests/site_commands.gd
           if ($LASTEXITCODE -ne 0) { throw 'The page and the Connect dialog differ.' }
       - name: Package
-        run: ./tools/package.ps1 -Godot $env:GODOT
+        run: ./tools/package.ps1 -Godot $env:GODOT -Release ${{ github.run_number }}
       - name: Run the packaged app
-        run: ./tests/package_smoke.ps1 -Zip build/AgentGuildStudio-windows.zip -Dir .smoke
+        run: ./tests/package_smoke.ps1 -Zip build/AgentGuildStudio-windows.zip -Dir .smoke -Release ${{ github.run_number }}
       - id: zip
         if: github.event_name == 'push'
         run: Add-Content $env:GITHUB_OUTPUT "sha256=$((Get-FileHash build/AgentGuildStudio-windows.zip).Hash.ToLower())"
@@ -184,7 +184,7 @@ jobs:
           Compress-Archive -LiteralPath "$env:RUNNER_TEMP/stage/AgentGuildStudio" -DestinationPath $zip
           Add-Content $env:GITHUB_OUTPUT "sha256=$((Get-FileHash $zip).Hash.ToLower())"
       - name: Run the signed app
-        run: ./tests/package_smoke.ps1 -Zip "$env:RUNNER_TEMP/signed/AgentGuildStudio-windows.zip" -Dir "$env:RUNNER_TEMP/smoke"
+        run: ./tests/package_smoke.ps1 -Zip "$env:RUNNER_TEMP/signed/AgentGuildStudio-windows.zip" -Dir "$env:RUNNER_TEMP/smoke" -Release ${{ github.run_number }}
       - name: Check the signature
         env:
           PUBLISHER: ${{ vars.WINDOWS_PUBLISHER }}
@@ -274,7 +274,7 @@ jobs:
           & $env:GODOT --headless --path . --script res://tests/site_commands.gd
           if ($LASTEXITCODE -ne 0) { throw 'The page and the Connect dialog differ.' }
       - name: Package
-        run: ./tools/package.ps1 -Godot $env:GODOT -Platform macOS
+        run: ./tools/package.ps1 -Godot $env:GODOT -Platform macOS -Release ${{ github.run_number }}
       - name: Run the packaged app
         run: |
           ditto -x -k build/AgentGuildStudio-macos.zip .smoke
@@ -284,8 +284,10 @@ jobs:
           if (-not [IO.Path]::GetExtension($iconFile)) { $iconFile += '.icns' }
           if ((Get-FileHash ".smoke/AgentGuildStudio.app/Contents/Resources/$iconFile").Hash -ne (Get-FileHash brand/icon.icns).Hash) { throw 'The packaged app does not use brand/icon.icns.' }
           $exe = '.smoke/AgentGuildStudio.app/Contents/MacOS/Agent Guild Studio'
-          $version = & $exe --headless --no-header -- --version
-          if ($LASTEXITCODE -ne 0 -or -not $version) { throw 'The packaged app did not start.' }
+          $version = '0.1.${{ github.run_number }}'
+          $said = & $exe --headless --no-header -- --version
+          $short = & /usr/libexec/PlistBuddy -c 'Print :CFBundleShortVersionString' .smoke/AgentGuildStudio.app/Contents/Info.plist
+          if ($LASTEXITCODE -ne 0 -or "$said" -ne $version -or $short -ne $version) { throw "The packaged app says it is $said ($short), not $version." }
           node tests/mcp_smoke.mjs $exe
           if ($LASTEXITCODE -ne 0) { throw 'The packaged app did not serve MCP.' }
       - name: Signing checks
@@ -347,8 +349,11 @@ jobs:
         run: |
           ditto -x -k "$RUNNER_TEMP/signed/AgentGuildStudio-macos.zip" "$RUNNER_TEMP/smoke"
           exe="$RUNNER_TEMP/smoke/AgentGuildStudio.app/Contents/MacOS/Agent Guild Studio"
-          if [ -z "$("$exe" --headless --no-header -- --version)" ]; then
-            echo "::error::The signed app did not start."
+          version="0.1.${{ github.run_number }}"
+          said="$("$exe" --headless --no-header -- --version)"
+          short="$(/usr/libexec/PlistBuddy -c 'Print :CFBundleShortVersionString' "$RUNNER_TEMP/smoke/AgentGuildStudio.app/Contents/Info.plist")"
+          if [ "$said" != "$version" ] || [ "$short" != "$version" ]; then
+            echo "::error::The signed app says it is $said ($short), not $version."
             exit 1
           fi
           node tests/mcp_smoke.mjs "$exe"
diff --git a/project.godot b/project.godot
index a6d15d5..46c56e8 100644
--- a/project.godot
+++ b/project.godot
@@ -7,7 +7,6 @@ config/name="Agent Guild Studio"
 config/use_custom_user_dir=true
 config/custom_user_dir_name="AgentGuildStudio"
 config/description="Make characters and companions for Agent Guild."
-config/version="0.0.0"
 run/main_scene="res://main.tscn"
 config/features=PackedStringArray("4.7", "Forward Plus")
 boot_splash/bg_color=Color(0.043, 0.039, 0.059, 1)
diff --git a/src/app/main.gd b/src/app/main.gd
index dc6ddbb..e48ca2c 100644
--- a/src/app/main.gd
+++ b/src/app/main.gd
@@ -43,7 +43,7 @@ func _ready() -> void:
 		var parts := arg.trim_prefix("--").split("=", true, 1)
 		options[parts[0]] = parts[1] if parts.size() > 1 else "1"
 	if options.has("version"):
-		print(ProjectSettings.get_setting("application/config/version"))
+		print(Studio.version())
 		get_tree().quit()
 		return
 	if options.has("check-piece") or options.has("check-source"):
diff --git a/src/mcp/server.gd b/src/mcp/server.gd
index 9609e56..8307ddf 100644
--- a/src/mcp/server.gd
+++ b/src/mcp/server.gd
@@ -7,7 +7,6 @@ const SUPPORTED := ["2026-07-28", "2025-11-25", "2025-06-18", "2025-03-26", "202
 const META_VERSION := "io.modelcontextprotocol/protocolVersion"
 const META_CAPABILITIES := "io.modelcontextprotocol/clientCapabilities"
 const META_SERVER := "io.modelcontextprotocol/serverInfo"
-const SERVER_INFO := {"name": "agent-guild-studio", "title": "Agent Guild: Studio", "version": "1"}
 const PARSE_ERROR := -32700
 const INVALID_REQUEST := -32600
 const METHOD_NOT_FOUND := -32601
@@ -30,6 +29,9 @@ var _active: Dictionary = {}
 var _closed := false
 var _left := false
 
+static func server_info() -> Dictionary:
+	return {"name": "agent-guild-studio", "title": "Agent Guild: Studio", "version": Studio.version()}
+
 func _ready() -> void:
 	tools = McpTools.new(self)
 	if read_stdin:
@@ -168,7 +170,7 @@ func _dispatch(msg: Dictionary) -> void:
 				return
 			var asked = params.get("protocolVersion")
 			_legacy_version = asked if asked in LEGACY else LEGACY[0]
-			respond(ctx, {"protocolVersion": _legacy_version, "capabilities": {"tools": {}}, "serverInfo": SERVER_INFO, "instructions": INSTRUCTIONS})
+			respond(ctx, {"protocolVersion": _legacy_version, "capabilities": {"tools": {}}, "serverInfo": server_info(), "instructions": INSTRUCTIONS})
 		"server/discover":
 			if not ctx.modern:
 				_send_error(ctx.id, INVALID_PARAMS, "server/discover needs %s and %s in _meta." % [META_VERSION, META_CAPABILITIES])
@@ -210,7 +212,7 @@ func respond(ctx: Dictionary, result: Dictionary) -> void:
 	if ctx.modern:
 		result["resultType"] = "complete"
 		var meta: Dictionary = result.get("_meta", {})
-		meta[META_SERVER] = SERVER_INFO
+		meta[META_SERVER] = server_info()
 		result["_meta"] = meta
 	_send({"jsonrpc": "2.0", "id": ctx.id, "result": result})
 
@@ -225,4 +227,4 @@ func _send_error(id: Variant, code: int, message: String) -> void:
 	_send({"jsonrpc": "2.0", "id": id, "error": {"code": code, "message": message}})
 
 func _send(msg: Dictionary) -> void:
-	write_line.call(JSON.stringify(msg))
+	write_line.call(StrictJson.stringify(msg))
diff --git a/src/mcp/tools.gd b/src/mcp/tools.gd
index 4560193..0843720 100644
--- a/src/mcp/tools.gd
+++ b/src/mcp/tools.gd
@@ -35,7 +35,7 @@ func failure(text: String, data: Variant = null) -> Dictionary:
 	return out
 
 func _done(text: String, data: Variant = null) -> Dictionary:
-	var out := {"content": [{"type": "text", "text": text if data == null else text + "\n" + JSON.stringify(data)}], "isError": false}
+	var out := {"content": [{"type": "text", "text": text if data == null else text + "\n" + StrictJson.stringify(data)}], "isError": false}
 	if data != null:
 		out["structuredContent"] = data
 	return out
@@ -148,7 +148,7 @@ func _definitions() -> Array:
 				"hue": hue, "tint": tint, "change_color": change_color, "spread": spread,
 				"replace": replace}, ["slot", "look", "to"]), "annotations": writes},
 		{"name": "check_piece", "title": "Check a piece", "description": "Checks a piece folder (piece.json and its models) as Studio checks the ones it makes, for the world and slot its piece.json names.",
-			"inputSchema": _object({"folder": _path("The piece's folder, as a full path.")}, ["folder"]), "annotations": read},
+			"inputSchema": _object({"folder": _path("The piece's folder, as a full path.")}, ["folder"]), "annotations": {"readOnlyHint": true, "openWorldHint": true}},
 		{"name": "list_pieces", "title": "List pieces", "description": "The pieces made with Studio on this computer, by the person in its window or by an agent: each one's `piece` value, title, slot and the folder it was saved to.",
 			"inputSchema": _object({}, []), "annotations": read},
 		{"name": "remove_piece", "title": "Remove a piece", "description": "Takes a piece off Studio's list. The folder it was saved to is left as it is.",
@@ -225,6 +225,9 @@ func _make(ctx: Dictionary, args: Dictionary, options: Dictionary, recipe: Dicti
 		return failure("%s is a file, not a folder." % to)
 	if DirAccess.dir_exists_absolute(to) and not args.get("replace", false) and not (DirAccess.get_files_at(to).is_empty() and DirAccess.get_directories_at(to).is_empty()):
 		return failure("%s already holds files. Choose another folder, or set `replace`." % to)
+	var other := StudioExport.other(to)
+	if other != "":
+		return failure("%s holds %s, which a piece folder may not. Choose another folder." % [to, other])
 	if args.has("title"):
 		options.title = args.title
 	var where := Studio.slot(options.slot)
@@ -243,11 +246,12 @@ func _make(ctx: Dictionary, args: Dictionary, options: Dictionary, recipe: Dicti
 	var library: PieceLibrary = server.host.pieces
 	library.refresh()
 	var id := await library.add_local(folder, "", recipe)
-	var listed: bool = library.pieces.get(id, {}).get("error", "x") == ""
-	if listed:
-		library.pieces[id].saved = folder
-		library.keep()
-	return _done("Made and checked. The piece is in %s." % folder, {"folder": folder, "files": files, "slot": options.slot, "notes": notes, "piece": id if listed else ""})
+	var problem: String = library.pieces.get(id, {}).get("error", "it was not listed")
+	if problem != "":
+		return failure("The piece in %s was made, but Studio couldn't list it: %s." % [folder, problem], {"folder": folder, "files": files, "slot": options.slot, "notes": notes, "problem": problem})
+	library.pieces[id].saved = folder
+	library.keep()
+	return _done("Made and checked. The piece is in %s." % folder, {"folder": folder, "files": files, "slot": options.slot, "notes": notes, "piece": id})
 
 ## The world's art, downloaded if it isn't here, then loaded; "" or why not.
 func _art(ctx: Dictionary, world: String) -> String:
diff --git a/src/pieces/piece_check.gd b/src/pieces/piece_check.gd
index 180a5b8..8d26430 100644
--- a/src/pieces/piece_check.gd
+++ b/src/pieces/piece_check.gd
@@ -347,7 +347,7 @@ static func run(options: Dictionary) -> int:
 	var watchdog := Thread.new()
 	watchdog.start(_watch.bind(Time.get_ticks_msec() + int(float(options.get("check-timeout", TIMEOUT)) * 1000) + 5000))
 	if options.get("check-fault", "") == "crash":
-		OS.crash("A check fault, for the tests.")
+		OS.kill(OS.get_process_id())
 	var verdict: Dictionary
 	if options.has("check-source"):
 		verdict = StudioSource.check(options["check-source"], options.get("check-dir", ""))
diff --git a/src/pieces/piece_validator.gd b/src/pieces/piece_validator.gd
index 15a6344..a265ace 100644
--- a/src/pieces/piece_validator.gd
+++ b/src/pieces/piece_validator.gd
@@ -9,7 +9,6 @@ var pid := -1
 var _count := 0
 var _out := ""
 
-# stage "load" (no header checks) and fault "crash" are for tests/pieces_test.gd only.
 func check(path: String, kind: String, clips: Dictionary, stage := "", fault := "") -> Dictionary:
 	var args := ["--check-piece=" + ProjectSettings.globalize_path(path), "--check-kind=" + kind,
 		"--check-clips=" + PieceCheck.clips_arg(clips)]
diff --git a/src/studio/studio.gd b/src/studio/studio.gd
index 5b1a194..54bfd64 100644
--- a/src/studio/studio.gd
+++ b/src/studio/studio.gd
@@ -11,10 +11,14 @@ class_name Studio
 ##   AgentGuildStudio -- --build=ghost.glb[,b.glb,c.glb,d.glb] --slot=grove/companion --out=DIR [--move=rigid|soft] [--variants=tint|turn] [--turn=DEGREES]
 ##   AgentGuildStudio -- --recolour=look0|look1|look2|agent|shell --slot=... --out=DIR [--pick=#RRGGBB|U,V] [--spread=0.15] [--hue=DEGREES] [--tint=#RRGGBB]
 
-## Each world's Studio clip set (tools/premium.py studio): its motions with
+## Each world's Studio clip set: its motions with
 ## both arms free, on a skeleton of its own, for character pieces.
 const CLIP_SETS := "res://assets/premium/studio/%s.glb"
 
+static func version() -> String:
+	var stamped := String(ProjectSettings.get_setting("application/config/version", ""))
+	return stamped if stamped != "" else "dev"
+
 ## { world, kind, crew } for "world/crew" or "world/companion", or { reason }.
 static func slot(text: String) -> Dictionary:
 	var parts := text.split("/")
@@ -323,29 +327,42 @@ static func run(host: Node, options: Dictionary) -> int:
 	if made.has("reason"):
 		return _fail(made.reason)
 	var models: Array = made.pieces.map(func(p): return StudioExport.scene(p, where.kind))
-	return await _save(host, where, models, clips, options.get("title", options.build.get_file().get_basename()), made.notes, options)
+	return await _save(host, where, models, clips, options.get("title", options.build.get_slice(",", 0).get_file().get_basename()), made.notes, options)
 
 ## Writes the models as a piece folder, frees them, and checks each as Looks
 ## would.
 static func _save(host: Node, where: Dictionary, models: Array, clips: Dictionary, title: String, notes: Array, options: Dictionary) -> int:
-	var folder := ProjectSettings.globalize_path(options.get("out", "user://studio/build"))
+	var folder := ProjectSettings.globalize_path(options.get("out", "user://studio/build")).rstrip("/\\")
 	var manifest := { "format": 1, "kind": where.kind, "world": where.world, "title": title }
 	if where.kind == "character":
 		manifest.crew = where.crew
-	var reason := StudioExport.save(models, folder, manifest)
+	var other := StudioExport.other(folder)
+	if other != "":
+		for model in models:
+			model.free()
+		return _fail("%s holds %s, which a piece may not" % [folder, other])
+	var part := StudioFiles.make_beside(folder, "part")
+	var reason := StudioExport.save(models, part, manifest) if part != "" else "a folder to work in could not be made in %s" % folder.get_base_dir()
 	for model in models:
 		model.free()
+	if reason == "":
+		var validator := PieceValidator.new()
+		host.add_child(validator)
+		for k in models.size():
+			var file: String = PieceLibrary.FILES[where.kind][k]
+			var verdict: Dictionary = await validator.check(part.path_join(file), where.kind, clips)
+			if verdict.reason != "":
+				reason = "%s did not pass its check: %s" % [file, verdict.reason]
+				break
+		validator.queue_free()
+	if reason == "":
+		reason = PieceLibrary.check_folder(part).get("reason", "")
+	if reason == "":
+		reason = StudioFiles.move_in(part, folder, StudioExport.names())
+	if part != "":
+		StudioFiles.remove_tree(part)
 	if reason != "":
 		return _fail(reason)
-	var validator := PieceValidator.new()
-	host.add_child(validator)
-	for k in models.size():
-		var file: String = PieceLibrary.FILES[where.kind][k]
-		var verdict: Dictionary = await validator.check(folder.path_join(file), where.kind, clips)
-		if verdict.reason != "":
-			validator.queue_free()
-			return _fail("%s did not pass its check: %s" % [file, verdict.reason])
-	validator.queue_free()
 	said = { "folder": folder, "notes": notes }
 	if not quiet:
 		for note in notes:
diff --git a/src/studio/studio_export.gd b/src/studio/studio_export.gd
index ae68340..46575cc 100644
--- a/src/studio/studio_export.gd
+++ b/src/studio/studio_export.gd
@@ -78,6 +78,23 @@ static func write_glb(root: Node, path: String) -> Error:
 	var err := doc.append_from_scene(root, state)
 	return doc.write_to_filesystem(state, path) if err == OK else err
 
+static func names() -> Array:
+	var out: Array = ["piece.json"] + PieceLibrary.PREVIEWS
+	for kind in PieceLibrary.FILES:
+		out += PieceLibrary.FILES[kind]
+	return out
+
+static func other(folder: String) -> String:
+	if not DirAccess.dir_exists_absolute(folder):
+		return ""
+	var dirs := DirAccess.get_directories_at(folder)
+	if not dirs.is_empty():
+		return dirs[0]
+	for file in DirAccess.get_files_at(folder):
+		if not file in names():
+			return file
+	return ""
+
 ## A piece folder Looks takes in: its model (a character's one, or a
 ## companion's four, in order) and piece.json.
 static func save(models: Array, folder: String, manifest: Dictionary) -> String:
diff --git a/src/studio/studio_files.gd b/src/studio/studio_files.gd
index 09df14e..59b94b2 100644
--- a/src/studio/studio_files.gd
+++ b/src/studio/studio_files.gd
@@ -14,3 +14,53 @@ static func remove_tree(path: String) -> void:
 	for name in dir.get_files():
 		dir.remove(name)
 	DirAccess.remove_absolute(path)
+
+## A new, empty folder beside `folder` that only the caller holds, or "".
+static func make_beside(folder: String, kind: String) -> String:
+	var parent := folder.get_base_dir()
+	DirAccess.make_dir_recursive_absolute(parent)
+	for n in range(1, 1000):
+		var path := parent.path_join(".%s.%s%s" % [folder.get_file(), "" if n == 1 else "%d." % n, kind])
+		var err := DirAccess.make_dir_absolute(path)
+		if err == OK:
+			return path
+		if err != ERR_ALREADY_EXISTS:
+			break
+	return ""
+
+## Moves the files in `part` into `folder`, first setting aside the files
+## `folder` holds of `names`, which go back if any move fails; "" or why not.
+static func move_in(part: String, folder: String, names: Array) -> String:
+	var previous := make_beside(folder, "previous")
+	if previous == "":
+		return "a folder to work in could not be made in %s" % folder.get_base_dir()
+	var made := not DirAccess.dir_exists_absolute(folder)
+	DirAccess.make_dir_recursive_absolute(folder)
+	var aside := []
+	var placed := []
+	var reason := ""
+	for name in names:
+		if FileAccess.file_exists(folder.path_join(name)):
+			if DirAccess.rename_absolute(folder.path_join(name), previous.path_join(name)) != OK:
+				reason = "%s could not be set aside" % folder.path_join(name)
+				break
+			aside.append(name)
+	if reason == "":
+		for name in DirAccess.get_files_at(part):
+			if DirAccess.rename_absolute(part.path_join(name), folder.path_join(name)) != OK:
+				reason = "it could not be moved into %s" % folder
+				break
+			placed.append(name)
+	if reason == "":
+		remove_tree(previous)
+		return ""
+	for name in placed:
+		DirAccess.remove_absolute(folder.path_join(name))
+	var kept := true
+	for name in aside:
+		kept = DirAccess.rename_absolute(previous.path_join(name), folder.path_join(name)) == OK and kept
+	if kept:
+		remove_tree(previous)
+	if made:
+		DirAccess.remove_absolute(folder)
+	return reason if kept else "%s; the files it held are in %s" % [reason, previous]
diff --git a/src/studio/studio_flow.gd b/src/studio/studio_flow.gd
index 96aa9e8..953ac4e 100644
--- a/src/studio/studio_flow.gd
+++ b/src/studio/studio_flow.gd
@@ -385,12 +385,12 @@ func _save(parent: String, title: String) -> void:
 	panel.working("Saving it in %s…" % parent)
 	await _shown()
 	var reason := await _exact()
-	var part := parent.path_join(".%s.part" % name)
+	var part := ""
 	var folder := ""
 	if reason == "":
 		_working("Saving it in %s…" % parent)
-		StudioFiles.remove_tree(part)
-		reason = _write(part, title)
+		part = StudioFiles.make_beside(parent.path_join(name), "part")
+		reason = _write(part, title) if part != "" else "a folder to work in could not be made"
 	var n := 1
 	while reason == "" and folder == "":
 		var free := parent.path_join(name if n == 1 else "%s (%d)" % [name, n])
@@ -402,7 +402,8 @@ func _save(parent: String, title: String) -> void:
 		elif not DirAccess.dir_exists_absolute(free):
 			reason = "it could not be moved into %s" % free
 	if reason != "":
-		StudioFiles.remove_tree(part)
+		if part != "":
+			StudioFiles.remove_tree(part)
 		_kept("It could not be saved: %s. Nothing was left in %s." % [reason, parent], true)
 		return
 	var id := editing if editing != "" else PieceLibrary.local_id()
diff --git a/src/ui/home_panel.gd b/src/ui/home_panel.gd
index cea6d96..5fd001f 100644
--- a/src/ui/home_panel.gd
+++ b/src/ui/home_panel.gd
@@ -112,6 +112,8 @@ func _build() -> void:
 	_heading("Agents", false)
 	_note("An agent can make pieces with Studio for you.")
 	_button("Connect an agent…", func(): connect_requested.emit())
+	var version := Studio.version()
+	_note("Development build" if version == "dev" else "Build " + version.get_slice(".", 2))
 
 func _heading(text: String, first: bool) -> void:
 	var label := Label.new()
diff --git a/tests/mcp_test.gd b/tests/mcp_test.gd
index 0cced2b..9e20cfb 100644
--- a/tests/mcp_test.gd
+++ b/tests/mcp_test.gd
@@ -53,12 +53,17 @@ func run(tree: SceneTree) -> Array:
 	_server.read_stdin = false
 	_server.write_line = func(line: String): _lines.append(JSON.parse_string(line))
 	host.add_child(_server)
-	await _ask(tree, "initialize", { "protocolVersion": "2025-11-25" })
+	var info: Dictionary = (await _ask(tree, "initialize", { "protocolVersion": "2025-11-25" })).get("serverInfo", {})
+	ProjectSettings.set_setting("application/config/version", "0.1.7")
+	var stamped: Dictionary = (await _ask(tree, "initialize", { "protocolVersion": "2025-11-25" })).get("serverInfo", {})
+	ProjectSettings.set_setting("application/config/version", null)
+	check(info.get("version") == "dev" and stamped.get("version") == "0.1.7", "the server does not report its build's version: %s, %s" % [info, stamped])
 
 	var listed: Dictionary = await _ask(tree, "tools/list", {})
 	var names: Array = listed.get("tools", []).map(func(t): return t.name)
 	check(names == ["list_slots", "make_character", "make_companions", "recolor_look", "check_piece", "list_pieces", "remove_piece", "show_window"], "the tools are %s" % [names])
 	check(listed.get("tools", []).all(func(t): return t.inputSchema.type == "object" and t.annotations.has("readOnlyHint") and t.has("description")), "a tool lacks a schema, hints or a description")
+	check(listed.tools.filter(func(t): return t.name == "check_piece")[0].annotations.openWorldHint == true, "check_piece, which can download a world's art, says it stays offline")
 	for name in ["make_character", "make_companions", "recolor_look"]:
 		var props: Dictionary = listed.tools.filter(func(t): return t.name == name)[0].inputSchema.properties
 		check(props.has("hue") and props.has("tint") and props.has("change_color") and props.has("spread"), "%s takes no color choices" % name)
@@ -90,9 +95,24 @@ func run(tree: SceneTree) -> Array:
 	check(color.get("isError") == true and "color" in String(color.content[0].text) and not DirAccess.dir_exists_absolute(to), "a tint that is no color was not refused before any work")
 	var nothing := await _call(tree, "recolor_look", { "slot": "guild/anthropic", "look": "look1", "to": to })
 	check(nothing.get("isError") == true and "hue" in String(nothing.content[0].text), "a recolor with no color choice was not refused")
+	var theirs := ProjectSettings.globalize_path(OUT + "theirs")
+	DirAccess.make_dir_recursive_absolute(theirs)
+	FileAccess.open(theirs.path_join("notes.txt"), FileAccess.WRITE).store_string("mine")
+	var kept := await _call(tree, "make_character", { "model": "C:/x.glb", "slot": "guild/anthropic", "to": theirs, "replace": true })
+	check(kept.get("isError") == true and "notes.txt" in String(kept.content[0].text) and FileAccess.get_file_as_string(theirs.path_join("notes.txt")) == "mine",
+		"a folder holding someone's own file was not refused before any work: %s" % kept)
 	var four := await _call(tree, "make_companions", { "models": ["a.glb", "b.glb"], "slot": "guild/companion", "to": to })
 	check(four.get("isError") == true and "one model or four" in String(four.content[0].text), "two models for companions were not refused")
 	check(host.opened == 1, "a tool other than show_window opened a window")
+
+	# Text from a person's files (a bone, a title) can hold control characters;
+	# the agent's client reads each line with a strict JSON parser.
+	var raw := []
+	_server.write_line = func(line: String): raw.append(line)
+	_server.receive(StrictJson.stringify({ "jsonrpc": "2.0", "id": "odd", "method": "tools/call", "params": { "name": "bone" + String.chr(1) + String.chr(11), "arguments": {} } }))
+	_server.write_line = func(line: String): _lines.append(JSON.parse_string(line))
+	check(raw.size() == 1 and raw[0].contains("bone\\u0001\\u000b") and RegEx.create_from_string("[\\x00-\\x1f]|\\\\v").search(raw[0]) == null,
+		"a reply holds raw control characters or \\v: %s" % [raw])
 	await _lifecycle(tree, host)
 
 	other.free()
diff --git a/tests/package_smoke.ps1 b/tests/package_smoke.ps1
index 98e52fd..422a9c8 100644
--- a/tests/package_smoke.ps1
+++ b/tests/package_smoke.ps1
@@ -1,4 +1,4 @@
-param([Parameter(Mandatory)][string]$Zip, [Parameter(Mandatory)][string]$Dir)
+param([Parameter(Mandatory)][string]$Zip, [Parameter(Mandatory)][string]$Dir, [Parameter(Mandatory)][int]$Release)
 
 $ErrorActionPreference = 'Stop'
 if (Test-Path -LiteralPath $Dir) { throw "$Dir already exists." }
@@ -21,6 +21,12 @@ foreach ($size in 16, 32, 48) {
         throw "The packaged app's $size px icon is not brand/icon.ico."
     }
 }
+$version = "0.1.$Release"
+$info = (Get-Item -LiteralPath $exe).VersionInfo
+if ($info.FileVersion -ne "$version.0" -or $info.ProductVersion -ne "$version.0") { throw "The packaged app's file is version $($info.FileVersion) ($($info.ProductVersion)), not $version.0." }
+$said = Join-Path $Dir 'version.txt'
+$app = Start-Process -FilePath $exe -ArgumentList '--headless', '--no-header', '--', '--version' -RedirectStandardOutput $said -Wait -PassThru
+if ($app.ExitCode -ne 0 -or (Get-Content -LiteralPath $said -Raw).Trim() -ne $version) { throw "The packaged app does not say it is $version." }
 # A piece the packaged app refuses for its own reason shows its checker runs.
 $piece = Join-Path $Dir 'not-a-piece'
 New-Item -ItemType Directory -Path $piece | Out-Null
diff --git a/tests/studio_test.gd b/tests/studio_test.gd
index 34f1cac..7827b14 100644
--- a/tests/studio_test.gd
+++ b/tests/studio_test.gd
@@ -80,6 +80,7 @@ func run(tree: SceneTree) -> Array:
 	var verdict: Dictionary = await validator.check(folder.path_join("character.glb"), "character", lengths)
 	check(verdict.reason == "", "the piece did not pass the game's check: %s" % verdict.reason)
 	validator.free()
+	await _replaces(tree, piece, lengths)
 	_names()
 	await _rigs(tree, default, lengths)
 	await _companions(tree)
@@ -893,6 +894,64 @@ func _gltf(folder: String, name: String, images: Array, buffer: String) -> Strin
 	_put(folder.path_join(name), JSON.stringify(gltf).to_utf8_buffer())
 	return folder.path_join(name)
 
+func _replaces(tree: SceneTree, piece: Dictionary, lengths: Dictionary) -> void:
+	var where := { "world": "guild", "kind": "character", "crew": "anthropic" }
+	var folder := ProjectSettings.globalize_path(OUT.path_join("replaced"))
+	var beside := folder.get_base_dir()
+	var taken := [".replaced.part", ".replaced.previous"]
+	var staged := func():
+		var dir := DirAccess.open(beside)
+		if dir == null:
+			return []
+		dir.include_hidden = true
+		var dirs := Array(dir.get_directories()).filter(func(d): return d.begins_with(".replaced."))
+		dirs.sort()
+		return dirs
+	var theirs_kept := func(): return taken.all(func(d): return _files(beside.path_join(d)) == ["keep.txt"] and FileAccess.get_file_as_string(beside.path_join(d).path_join("keep.txt")) == "theirs")
+	for d in staged.call():
+		StudioFiles.remove_tree(beside.path_join(d))
+	StudioFiles.remove_tree(folder)
+	for d in taken:
+		_put(beside.path_join(d).path_join("keep.txt"), "theirs".to_utf8_buffer())
+	_put(folder.path_join("character.glb"), "old".to_utf8_buffer())
+	_put(folder.path_join("piece.json"), "old".to_utf8_buffer())
+	var failed := await Studio._save(tree.root, where, [StudioExport.scene(piece, "character")], { "walk": 99.0 }, "Fails", [], { "out": folder })
+	check(failed == 1 and _files(folder) == ["character.glb", "piece.json"] and FileAccess.get_file_as_string(folder.path_join("character.glb")) == "old",
+		"a piece that failed its check changed the files it would have replaced: %s" % [_files(folder)])
+	check(staged.call() == taken and theirs_kept.call(), "a failed save changed folders beside it that it did not make: %s" % [staged.call()])
+	_put(folder.path_join("notes.txt"), "mine".to_utf8_buffer())
+	var theirs := await Studio._save(tree.root, where, [StudioExport.scene(piece, "character")], lengths, "Theirs", [], { "out": folder })
+	check(theirs == 1 and "notes.txt" in String(Studio.said.reason) and _files(folder) == ["character.glb", "notes.txt", "piece.json"] and FileAccess.get_file_as_string(folder.path_join("character.glb")) == "old",
+		"a folder holding someone's own file was written into: %s" % [_files(folder)])
+	DirAccess.remove_absolute(folder.path_join("notes.txt"))
+	_put(folder.path_join("companion_0.glb"), "stale".to_utf8_buffer())
+	_put(folder.path_join("preview.jpg"), "stale".to_utf8_buffer())
+	var saved := await Studio._save(tree.root, where, [StudioExport.scene(piece, "character")], lengths, "Replaced", [], { "out": folder })
+	check(saved == 0 and _files(folder) == ["character.glb", "piece.json"] and not PieceLibrary.check_folder(folder).has("reason") and FileAccess.get_file_as_string(folder.path_join("character.glb")) != "old",
+		"a piece did not cleanly replace the one in its folder: %s %s" % [Studio.said.get("reason", ""), _files(folder)])
+	check(staged.call() == taken and theirs_kept.call(), "a save changed folders beside it that it did not make, or left its own: %s" % [staged.call()])
+
+	for d in taken:
+		StudioFiles.remove_tree(beside.path_join(d))
+
+	var moved := beside.path_join("moved")
+	var incoming := beside.path_join("incoming")
+	var backup := beside.path_join(".moved.previous")
+	for d in [moved, incoming, backup, beside.path_join(".moved.2.previous")]:
+		StudioFiles.remove_tree(d)
+	_put(backup.path_join("keep.txt"), "theirs".to_utf8_buffer())
+	_put(incoming.path_join("character.glb"), "new".to_utf8_buffer())
+	_put(incoming.path_join("piece.json"), "new".to_utf8_buffer())
+	DirAccess.make_dir_recursive_absolute(moved.path_join("character.glb"))
+	_put(moved.path_join("piece.json"), "old".to_utf8_buffer())
+	var blocked := StudioFiles.move_in(incoming, moved, StudioExport.names())
+	check(blocked != "" and _files(moved) == ["piece.json"] and DirAccess.dir_exists_absolute(moved.path_join("character.glb")) and FileAccess.get_file_as_string(moved.path_join("piece.json")) == "old",
+		"a move that failed did not put back what the folder held: %s %s" % [blocked, _files(moved)])
+	check(_files(backup) == ["keep.txt"] and FileAccess.get_file_as_string(backup.path_join("keep.txt")) == "theirs" and not DirAccess.dir_exists_absolute(beside.path_join(".moved.2.previous")),
+		"a move that failed changed a folder beside it that it did not make, or left its own")
+	for d in [moved, incoming, backup]:
+		StudioFiles.remove_tree(d)
+
 func _put(path: String, bytes: PackedByteArray) -> void:
 	DirAccess.make_dir_recursive_absolute(path.get_base_dir())
 	FileAccess.open(path, FileAccess.WRITE).store_buffer(bytes)
diff --git a/tests/window_test.gd b/tests/window_test.gd
index ac7ff70..352b7aa 100644
--- a/tests/window_test.gd
+++ b/tests/window_test.gd
@@ -45,6 +45,12 @@ func run(tree: SceneTree) -> Array:
 	var home: HomePanel = main.home
 	check(home != null and home.visible and not main.panel.visible, "the window did not open on its first screen")
 	check(home.world == "guild" and home.art == "missing" and home.art_bytes == 300000, "the first screen does not say guild's art is a 300000 byte download: %s %d" % [home.art, home.art_bytes])
+	check(_shows(home, "Development build"), "the first screen does not say it is a development build")
+	ProjectSettings.set_setting("application/config/version", "0.1.7")
+	main._show_home()
+	check(_shows(home, "Build 7"), "the first screen does not show its build")
+	ProjectSettings.set_setting("application/config/version", null)
+	main._show_home()
 
 	home.download_requested.emit("guild")
 	check(home.art == "downloading", "a download did not show as under way")
@@ -87,10 +93,15 @@ func run(tree: SceneTree) -> Array:
 	main.add_child(saving)
 	saving.start(main.panel, main.stage, main.pieces, main.TOOLS, "guild", "light")
 	saving._made = { "where": { "kind": "character", "world": "guild", "crew": "anthropic" } }
+	var theirs := out.path_join(".Failed save.part")
+	DirAccess.make_dir_recursive_absolute(theirs)
+	FileAccess.open(theirs.path_join("keep.txt"), FileAccess.WRITE).store_string("theirs")
 	saving._save(out, "Failed save")
 	main.close()
 	check(quits[0] == 0, "closing interrupted an in-progress save")
 	check(await TestRunner.until(tree, func(): return saving._keeping == ""), "a failed save never finished")
+	check(FileAccess.get_file_as_string(theirs.path_join("keep.txt")) == "theirs" and not DirAccess.dir_exists_absolute(out.path_join(".Failed save.2.part")),
+		"a failed save changed a folder beside it that it did not make, or left its own")
 	check(quits[0] == 0 and saving.active and not main._closing, "a failed save did not cancel closing and leave the window usable")
 	main.close()
 	main.close()
@@ -119,12 +130,38 @@ func _window_processes(tree: SceneTree, main: Node, out: String) -> void:
 			main._window_pids.append(pid)
 	check(await TestRunner.until(tree, func(): return main._window_pids.is_empty()), "closed window processes were not collected")
 	check(pids.all(func(pid): return OS.get_process_exit_code(pid) == 0), "a window process exit code was lost")
+	var asked := OS.execute_with_pipe(OS.get_executable_path(), main.window_args() + ["--headless", "--no-header", "--", "--version"], false)
+	var answer := await _piped(tree, asked)
+	check(answer.ended, "Studio did not answer --version")
+	check(answer.code == 0 and answer.out.strip_edges() == "dev", "--version says %s, not dev" % answer.out)
 	if OS.get_name() != "Windows":
 		var writer := out.path_join("Bill's $cash `tools`.gd")
-		FileAccess.open(writer, FileAccess.WRITE).store_string("extends SceneTree\nfunc _initialize():\n\tprint('window stdout')\n\tprinterr('window stderr')\n\tquit(0)\n")
+		var ran := out.path_join("ran")
+		FileAccess.open(writer, FileAccess.WRITE).store_string("extends SceneTree\nfunc _initialize():\n\tFileAccess.open(%s, FileAccess.WRITE).store_string('ran')\n\tprint('window stdout')\n\tprinterr('window stderr')\n\tquit(0)\n" % var_to_str(ran))
 		command = main.window_command(OS.get_executable_path(), ["--headless", "--no-header", "--script", writer])
-		var output := []
-		check(OS.execute(command[0], command[1], output, true) == 0 and "".join(output) == "", "the standalone window wrote to MCP's stdout or stderr")
+		var child := OS.execute_with_pipe(command[0], command[1], false)
+		var window := await _piped(tree, child)
+		check(window.ended, "the standalone window did not end")
+		check(window.code == 0 and FileAccess.file_exists(ran) and window.out + window.err == "", "the standalone window did not run its script, or wrote to MCP's stdout or stderr: %s" % (window.out + window.err))
+
+func _piped(tree: SceneTree, child: Dictionary) -> Dictionary:
+	var said := { "ended": false, "code": -1, "out": "", "err": "" }
+	if child.is_empty():
+		return said
+	var read := func():
+		said.out += child.stdio.get_buffer(4096).get_string_from_utf8()
+		said.err += child.stderr.get_buffer(4096).get_string_from_utf8()
+	said.ended = await TestRunner.until(tree, func():
+		read.call()
+		return not OS.is_process_running(child.pid))
+	if not said.ended:
+		OS.kill(child.pid)
+	read.call()
+	said.code = OS.get_process_exit_code(child.pid)
+	return said
+
+func _shows(home: HomePanel, text: String) -> bool:
+	return home.rows.get_children().any(func(c): return c is Label and c.text == text and not c.is_queued_for_deletion())
 
 func _folder(name: String) -> String:
 	var dir := ProjectSettings.globalize_path(OUT + "folders/" + name)
diff --git a/tools/package.ps1 b/tools/package.ps1
index 1f1b392..281ff8e 100644
--- a/tools/package.ps1
+++ b/tools/package.ps1
@@ -1,4 +1,4 @@
-param([string]$Godot = 'godot', [ValidateSet('Windows', 'macOS')][string]$Platform = 'Windows')
+param([string]$Godot = 'godot', [ValidateSet('Windows', 'macOS')][string]$Platform = 'Windows', [ValidateRange(0, 65535)][int]$Release = 0)
 
 $ErrorActionPreference = 'Stop'
 $project = (Resolve-Path (Join-Path $PSScriptRoot '..')).Path
@@ -16,7 +16,29 @@ $mac = $Platform -eq 'macOS'
 $app = Join-Path $stage 'AgentGuildStudio.app'
 $bundle = if ($mac) { Join-Path $app 'Contents/Resources' } else { Join-Path $stage 'AgentGuildStudio' }
 New-Item -ItemType Directory -Path $(if ($mac) { $stage } else { $bundle }) -Force | Out-Null
+$settings = Join-Path $project 'project.godot'
+$exportPresets = Join-Path $project 'export_presets.cfg'
+$keptSettings = [IO.File]::ReadAllBytes($settings)
+$keptPresets = [IO.File]::ReadAllBytes($exportPresets)
 try {
+    if ($Release -gt 0) {
+        $version = "0.1.$Release"
+        $text = [IO.File]::ReadAllText($settings)
+        $nl = if ($text.Contains("`r`n")) { "`r`n" } else { "`n" }
+        $section = "[application]$nl"
+        if ($text -match '(?m)^config/version=' -or -not $text.Contains($section)) { throw 'project.godot cannot take a version.' }
+        [IO.File]::WriteAllText($settings, $text.Replace($section, "$section" + "config/version=`"$version`"$nl"))
+        $cfg = [IO.File]::ReadAllText($exportPresets)
+        $fields = [ordered]@{ 'Windows Desktop' = [ordered]@{ file_version = "$version.0"; product_version = "$version.0" }; 'macOS' = [ordered]@{ short_version = $version; version = $version } }
+        foreach ($target in $fields.Keys) {
+            $found = [regex]::Match($cfg, "(?m)^\[preset\.(\d+)\]\r?\n(?:[^\[\r\n].*\r?\n|\r?\n)*?platform=`"$target`"")
+            $header = "[preset.$($found.Groups[1].Value).options]$nl"
+            if (-not $found.Success -or -not $cfg.Contains($header)) { throw "export_presets.cfg has no $target options." }
+            $lines = ($fields[$target].GetEnumerator() | ForEach-Object { "application/$($_.Key)=`"$($_.Value)`"$nl" }) -join ''
+            $cfg = $cfg.Replace($header, $header + $lines)
+        }
+        [IO.File]::WriteAllText($exportPresets, $cfg)
+    }
     $importLog = & $Godot --headless --path $project --editor --import --quit 2>&1
     $importExit = $LASTEXITCODE
     $importLog | Write-Output
@@ -44,6 +66,8 @@ try {
     Move-Item -LiteralPath $zip -Destination $output -Force
     Write-Output "Packaged $output"
 } finally {
+    [IO.File]::WriteAllBytes($settings, $keptSettings)
+    [IO.File]::WriteAllBytes($exportPresets, $keptPresets)
     $resolvedStage = [IO.Path]::GetFullPath($stage)
     if (-not $resolvedStage.StartsWith([IO.Path]::GetFullPath($build) + [IO.Path]::DirectorySeparatorChar, [StringComparison]::OrdinalIgnoreCase)) { throw 'Staging path escaped the build directory.' }
     Remove-Item -LiteralPath $resolvedStage -Recurse -Force