Make settings restore crash-safe

config/dot/quickshell/scripts/panama-settings-backup

@@ -1,90 +1,625 @@
-#!/usr/bin/env bash
+#!/usr/bin/env python3
 
-# Snapshots of the Panama settings store.
-#
-# The whole desktop configuration is one JSON file, which makes a backup a copy
-# and a restore an overwrite. That is worth exposing: the settings app now
-# changes real things -- compositor geometry, idle timeouts, the dock -- and
-# being able to get back to a known-good state without hunting through git is
-# the difference between experimenting freely and being cautious.
-#
-#   panama-settings-backup save            snapshot the current settings
-#   panama-settings-backup list            JSON list of snapshots, newest first
-#   panama-settings-backup restore <name>  replace settings with a snapshot
-#
-# Snapshots are validated as JSON on the way in and on the way out, so a
-# truncated file can never be restored over a working configuration.
-#
-# Names carry milliseconds. At one-second resolution a save followed promptly by
-# a restore produced the same filename twice, and the restore's own safety
-# snapshot overwrote the very file it was about to read.
+"""Crash-safe snapshots of Panama's desktop and Home preference stores.
 
-set -euo pipefail
+A restore is a two-file transaction. Its fixed journal and artifacts live at
+`$XDG_STATE_HOME/panama/transactions/settings-restore`; they contain no
+caller-provided paths. The journal is fsynced before either destination changes
+and is removed only after both replacements are durable. Every invocation
+recovers an incomplete transaction before doing any other work.
+"""
 
-settings="${XDG_CONFIG_HOME:-$HOME/.config}/panama/settings.json"
-backup_dir="${XDG_STATE_HOME:-$HOME/.local/state}/panama/backups"
-keep=15
+from __future__ import annotations
 
-fail() {
-    printf '%s\n' "$1" >&2
-    exit 1
+import json
+import os
+import re
+import stat
+import sys
+import tempfile
+import time
+import fcntl
+from contextlib import contextmanager
+from datetime import datetime
+from pathlib import Path
+from typing import Any, Iterator, NoReturn
+
+
+HOME = Path(os.environ.get("HOME", str(Path.home())))
+CONFIG_ROOT = Path(os.environ.get("XDG_CONFIG_HOME", str(HOME / ".config")))
+STATE_ROOT = Path(os.environ.get("XDG_STATE_HOME", str(HOME / ".local/state")))
+SETTINGS = CONFIG_ROOT / "panama/settings.json"
+HOME_STATE = STATE_ROOT / "panama/panama-home.json"
+BACKUP_DIR = STATE_ROOT / "panama/backups"
+TRANSACTION_PARENT = STATE_ROOT / "panama/transactions"
+TRANSACTION_DIR = TRANSACTION_PARENT / "settings-restore"
+JOURNAL = TRANSACTION_DIR / "journal.json"
+LOCK_FILE = TRANSACTION_PARENT / "settings-backup.lock"
+KEEP = 15
+SNAPSHOT_RE = re.compile(r"^settings-[0-9]{8}-[0-9]{9}\.json$")
+ENTITY_RE = re.compile(r"^light\.[a-z0-9_]+$")
+
+
+class BackupError(RuntimeError):
+    pass
+
+
+def fail(message: str) -> NoReturn:
+    raise BackupError(message)
+
+
+def fsync_directory(path: Path) -> None:
+    descriptor = os.open(path, os.O_RDONLY | os.O_DIRECTORY)
+    try:
+        os.fsync(descriptor)
+    finally:
+        os.close(descriptor)
+
+
+def ensure_directory(path: Path) -> None:
+    path.mkdir(parents=True, exist_ok=True)
+    if path.is_symlink() or not path.is_dir():
+        fail(f"{path} is not a safe directory.")
+
+
+@contextmanager
+def process_lock() -> Iterator[None]:
+    ensure_directory(TRANSACTION_PARENT)
+    if LOCK_FILE.is_symlink():
+        fail("The settings transaction lock is a symbolic link.")
+    descriptor = os.open(
+        LOCK_FILE,
+        os.O_RDWR | os.O_CREAT | getattr(os, "O_NOFOLLOW", 0),
+        0o600,
+    )
+    try:
+        os.fchmod(descriptor, 0o600)
+        fcntl.flock(descriptor, fcntl.LOCK_EX)
+        yield
+    finally:
+        fcntl.flock(descriptor, fcntl.LOCK_UN)
+        os.close(descriptor)
+
+
+def is_present(path: Path) -> bool:
+    return path.exists() or path.is_symlink()
+
+
+def require_regular(path: Path, label: str) -> None:
+    if path.is_symlink():
+        fail(f"{label} is a symbolic link and cannot be used safely.")
+    try:
+        mode = path.stat().st_mode
+    except FileNotFoundError:
+        fail(f"{label} is missing.")
+    if not stat.S_ISREG(mode):
+        fail(f"{label} is not a regular file.")
+
+
+def read_json(path: Path, label: str) -> dict[str, Any]:
+    require_regular(path, label)
+    try:
+        value = json.loads(path.read_text(encoding="utf-8"))
+    except (OSError, UnicodeError, json.JSONDecodeError) as error:
+        raise BackupError(f"{label} is not valid JSON.") from error
+    if not isinstance(value, dict):
+        fail(f"{label} is not a JSON object.")
+    return value
+
+
+def valid_home(value: Any) -> bool:
+    if not isinstance(value, dict):
+        return False
+    initialized = value.get("initialized")
+    favorites = value.get("favorites")
+    if not isinstance(initialized, bool) or not isinstance(favorites, list):
+        return False
+    if not initialized and favorites:
+        return False
+    seen: set[str] = set()
+    for favorite in favorites:
+        if not isinstance(favorite, dict):
+            return False
+        entity_id = favorite.get("id")
+        alias = favorite.get("alias")
+        if (
+            not isinstance(entity_id, str)
+            or ENTITY_RE.fullmatch(entity_id) is None
+            or not isinstance(alias, str)
+            or entity_id in seen
+        ):
+            return False
+        seen.add(entity_id)
+    return True
+
+
+def validate_home(value: Any, label: str) -> dict[str, Any]:
+    if not valid_home(value):
+        fail(f"{label} does not contain valid Home favourites.")
+    return value
+
+
+def json_bytes(value: Any) -> bytes:
+    return (json.dumps(value, indent=2, ensure_ascii=False) + "\n").encode("utf-8")
+
+
+def atomic_write_bytes(path: Path, content: bytes) -> None:
+    ensure_directory(path.parent)
+    if path.is_symlink():
+        fail(f"{path} is a symbolic link and cannot be replaced safely.")
+    descriptor, temporary_name = tempfile.mkstemp(prefix=f".{path.name}.", dir=path.parent)
+    temporary = Path(temporary_name)
+    try:
+        os.fchmod(descriptor, 0o600)
+        with os.fdopen(descriptor, "wb") as stream:
+            stream.write(content)
+            stream.flush()
+            os.fsync(stream.fileno())
+        os.replace(temporary, path)
+        fsync_directory(path.parent)
+    finally:
+        if temporary.exists() or temporary.is_symlink():
+            temporary.unlink()
+
+
+def atomic_write_json(path: Path, value: Any) -> None:
+    atomic_write_bytes(path, json_bytes(value))
+
+
+def durable_remove(path: Path) -> None:
+    if path.exists() or path.is_symlink():
+        path.unlink()
+        fsync_directory(path.parent)
+
+
+def transaction_path(name: str) -> Path:
+    if name not in {
+        "journal.json",
+        "desktop.old",
+        "desktop.new",
+        "home.old",
+        "home.new",
+    }:
+        fail("The restore transaction contains an unknown artifact name.")
+    path = TRANSACTION_DIR / name
+    resolved_parent = path.parent.resolve(strict=False)
+    if resolved_parent != TRANSACTION_DIR.resolve(strict=False):
+        fail("The restore transaction escaped its contained state directory.")
+    return path
+
+
+def clean_transaction_artifacts() -> None:
+    if not TRANSACTION_DIR.exists() and not TRANSACTION_DIR.is_symlink():
+        return
+    if TRANSACTION_DIR.is_symlink() or not TRANSACTION_DIR.is_dir():
+        fail("The restore transaction path is not a safe directory.")
+    for child in list(TRANSACTION_DIR.iterdir()):
+        if child.name not in {
+            "journal.json",
+            "desktop.old",
+            "desktop.new",
+            "home.old",
+            "home.new",
+        } and not child.name.startswith(".journal.json."):
+            fail("The restore transaction directory contains an unknown artifact.")
+        if child.is_dir() and not child.is_symlink():
+            fail("The restore transaction contains an unexpected directory.")
+        child.unlink()
+    fsync_directory(TRANSACTION_DIR)
+    TRANSACTION_DIR.rmdir()
+    fsync_directory(TRANSACTION_PARENT)
+
+
+def clean_stale_atomic_files() -> None:
+    locations = (
+        (SETTINGS.parent, (".settings.json.",)),
+        (HOME_STATE.parent, (".panama-home.json.",)),
+        (BACKUP_DIR, (".settings-",)),
+    )
+    for directory, prefixes in locations:
+        if not directory.exists():
+            continue
+        if directory.is_symlink() or not directory.is_dir():
+            fail(f"{directory} is not a safe directory.")
+        changed = False
+        for child in directory.iterdir():
+            if not any(child.name.startswith(prefix) for prefix in prefixes):
+                continue
+            # Only Panama's hidden atomic-write names are eligible. A matching
+            # directory is unexpected and is never recursively removed.
+            if child.is_dir() and not child.is_symlink():
+                fail("A stale settings temporary path is an unexpected directory.")
+            child.unlink()
+            changed = True
+        if changed:
+            fsync_directory(directory)
+
+
+def validate_journal_side(value: Any) -> dict[str, bool]:
+    if not isinstance(value, dict):
+        fail("The restore journal is malformed.")
+    if set(value) != {"touch", "oldPresent", "newPresent"}:
+        fail("The restore journal is malformed.")
+    if not all(isinstance(value[key], bool) for key in value):
+        fail("The restore journal is malformed.")
+    return value
+
+
+def read_journal() -> dict[str, Any]:
+    value = read_json(JOURNAL, "The restore journal")
+    if set(value) != {"version", "desktop", "home"} or value.get("version") != 1:
+        fail("The restore journal uses an unsupported format.")
+    return {
+        "version": 1,
+        "desktop": validate_journal_side(value.get("desktop")),
+        "home": validate_journal_side(value.get("home")),
     }
 
-case "${1:-list}" in
-    save)
-        [[ -r "$settings" ]] || fail "No settings file to back up."
-        jq -e . "$settings" >/dev/null 2>&1 || fail "The current settings file is not valid JSON."
-        mkdir -p "$backup_dir"
-        stamp="$(date +%Y%m%d-%H%M%S%3N)"
-        cp "$settings" "$backup_dir/settings-$stamp.json"
-        # Keep the most recent few. A snapshot per change would otherwise grow
-        # without bound in a directory nobody ever looks at.
-        ls -1t "$backup_dir"/settings-*.json 2>/dev/null | tail -n +$((keep + 1)) | while read -r old; do
-            rm -f "$old"
-        done
-        printf '{"saved":"settings-%s.json"}\n' "$stamp"
-        ;;
 
-    list)
-        mkdir -p "$backup_dir"
-        first=true
-        printf '['
-        for file in $(ls -1t "$backup_dir"/settings-*.json 2>/dev/null); do
-            name="$(basename "$file")"
-            # settings-20260818-004512.json -> 2026-08-18 00:45
-            raw="${name#settings-}"; raw="${raw%.json}"
-            pretty="${raw:0:4}-${raw:4:2}-${raw:6:2} ${raw:9:2}:${raw:11:2}:${raw:13:2}"
-            keys="$(jq -r 'keys | length' "$file" 2>/dev/null || printf 0)"
-            [[ "$first" == true ]] || printf ','
-            first=false
-            printf '{"name":"%s","when":"%s","keys":%s}' "$name" "$pretty" "$keys"
-        done
-        printf ']\n'
-        ;;
+def target_for(store: str) -> Path:
+    if store == "desktop":
+        return SETTINGS
+    if store == "home":
+        return HOME_STATE
+    fail("The restore journal names an unknown store.")
 
-    restore)
-        name="${2:-}"
-        [[ -n "$name" ]] || fail "Which snapshot?"
-        # Only a bare filename from the backup directory, so a caller cannot
-        # walk out of it with a path.
-        [[ "$name" =~ ^settings-[0-9]{8}-[0-9]{9}\.json$ ]] || fail "Not a snapshot name."
-        source_file="$backup_dir/$name"
-        [[ -r "$source_file" ]] || fail "That snapshot is missing."
-        jq -e . "$source_file" >/dev/null 2>&1 || fail "That snapshot is not valid JSON."
 
-        # Snapshot what is being replaced, so restore is itself undoable.
-        if [[ -r "$settings" ]] && jq -e . "$settings" >/dev/null 2>&1; then
-            mkdir -p "$backup_dir"
-            cp "$settings" "$backup_dir/settings-$(date +%Y%m%d-%H%M%S%3N).json"
-        fi
+def apply_artifact(store: str, generation: str, present: bool) -> None:
+    target = target_for(store)
+    if present:
+        artifact = transaction_path(f"{store}.{generation}")
+        require_regular(artifact, "A restore transaction artifact")
+        atomic_write_bytes(target, artifact.read_bytes())
+    else:
+        ensure_directory(target.parent)
+        if target.is_symlink():
+            fail(f"{target} is a symbolic link and cannot be replaced safely.")
+        durable_remove(target)
 
-        mkdir -p "$(dirname "$settings")"
-        cp "$source_file" "$settings.tmp"
-        mv "$settings.tmp" "$settings"
-        printf '{"restored":"%s"}\n' "$name"
-        ;;
 
-    *)
-        fail "usage: panama-settings-backup [save|list|restore <name>]"
-        ;;
-esac
+def recover_transaction() -> None:
+    ensure_directory(TRANSACTION_PARENT)
+    if not TRANSACTION_DIR.exists() and not TRANSACTION_DIR.is_symlink():
+        return
+    if TRANSACTION_DIR.is_symlink() or not TRANSACTION_DIR.is_dir():
+        fail("The restore transaction path is not a safe directory.")
+    if not JOURNAL.exists() and not JOURNAL.is_symlink():
+        clean_transaction_artifacts()
+        return
+
+    journal = read_journal()
+    for store in ("desktop", "home"):
+        side = journal[store]
+        if side["touch"]:
+            apply_artifact(store, "old", side["oldPresent"])
+
+    # Journal absence is the durable commit marker for recovery too. If a
+    # second power loss occurs above, the journal remains and recovery retries.
+    durable_remove(JOURNAL)
+    clean_transaction_artifacts()
+
+
+def is_v2_side(value: Any) -> bool:
+    return (
+        isinstance(value, dict)
+        and isinstance(value.get("present"), bool)
+        and (not value["present"] or isinstance(value.get("data"), dict))
+    )
+
+
+def is_v2_envelope(value: Any) -> bool:
+    return (
+        isinstance(value, dict)
+        and value.get("version") == 2
+        and is_v2_side(value.get("desktop"))
+        and is_v2_side(value.get("home"))
+    )
+
+
+def validate_snapshot(value: dict[str, Any]) -> tuple[str, dict[str, Any]]:
+    if not is_v2_envelope(value):
+        return "legacy", value
+    if value["home"]["present"]:
+        validate_home(value["home"]["data"], "That snapshot")
+    return "versioned", value
+
+
+def current_store(path: Path, label: str, *, home_store: bool = False) -> tuple[bool, Any]:
+    if not is_present(path):
+        return False, None
+    value = read_json(path, label)
+    if home_store:
+        validate_home(value, label)
+    return True, value
+
+
+def next_snapshot_path() -> Path:
+    ensure_directory(BACKUP_DIR)
+    while True:
+        stamp = datetime.now().strftime("%Y%m%d-%H%M%S%f")[:18]
+        candidate = BACKUP_DIR / f"settings-{stamp}.json"
+        if not is_present(candidate):
+            return candidate
+        time.sleep(0.002)
+
+
+def prune_snapshots() -> None:
+    snapshots = sorted(
+        (
+            path
+            for path in BACKUP_DIR.iterdir()
+            if SNAPSHOT_RE.fullmatch(path.name)
+            and path.is_file()
+            and not path.is_symlink()
+        ),
+        key=lambda path: path.stat().st_mtime_ns,
+        reverse=True,
+    )
+    for old in snapshots[KEEP:]:
+        durable_remove(old)
+
+
+def save_snapshot(*, require_any: bool, validate: bool) -> Path | None:
+    try:
+        desktop_present, desktop = current_store(
+            SETTINGS, "The current settings file"
+        )
+        home_present, home = current_store(
+            HOME_STATE, "The current Home state file", home_store=True
+        )
+    except BackupError:
+        if validate:
+            raise
+        return None
+
+    if not desktop_present and not home_present:
+        if require_any:
+            fail("No Panama settings exist to back up.")
+        return None
+
+    envelope: dict[str, Any] = {
+        "version": 2,
+        "desktop": {"present": desktop_present},
+        "home": {"present": home_present},
+    }
+    if desktop_present:
+        envelope["desktop"]["data"] = desktop
+    if home_present:
+        envelope["home"]["data"] = home
+
+    destination = next_snapshot_path()
+    atomic_write_json(destination, envelope)
+    prune_snapshots()
+    return destination
+
+
+def snapshot_source(name: str) -> Path:
+    if SNAPSHOT_RE.fullmatch(name) is None:
+        fail("Not a snapshot name.")
+    ensure_directory(BACKUP_DIR)
+    candidate = BACKUP_DIR / name
+    require_regular(candidate, "That snapshot")
+    if candidate.resolve(strict=True).parent != BACKUP_DIR.resolve(strict=True):
+        fail("That snapshot is outside the backup directory.")
+    return candidate
+
+
+def stage_artifact(name: str, content: bytes) -> None:
+    path = transaction_path(name)
+    if path.exists() or path.is_symlink():
+        fail("A stale restore transaction artifact was not recovered.")
+    descriptor = os.open(path, os.O_WRONLY | os.O_CREAT | os.O_EXCL, 0o600)
+    try:
+        with os.fdopen(descriptor, "wb") as stream:
+            stream.write(content)
+            stream.flush()
+            os.fsync(stream.fileno())
+    finally:
+        # fdopen owns the descriptor after construction.
+        pass
+    fsync_directory(TRANSACTION_DIR)
+
+
+def capture_old(store: str, target: Path) -> bool:
+    if not is_present(target):
+        return False
+    require_regular(target, f"The current {store} settings file")
+    stage_artifact(f"{store}.old", target.read_bytes())
+    return True
+
+
+def prepare_transaction(
+    desktop_present: bool,
+    desktop_data: dict[str, Any] | None,
+    home_touch: bool,
+    home_present: bool,
+    home_data: dict[str, Any] | None,
+) -> dict[str, Any]:
+    # Cleanup is active before the first artifact is created. A pre-journal
+    # error removes every staged/rollback file; a process death is recovered as
+    # stale preparation by the next invocation.
+    ensure_directory(TRANSACTION_PARENT)
+    clean_transaction_artifacts()
+    ensure_directory(TRANSACTION_DIR)
+    fsync_directory(TRANSACTION_PARENT)
+    try:
+        desktop_old = capture_old("desktop", SETTINGS)
+        if desktop_present:
+            stage_artifact("desktop.new", json_bytes(desktop_data))
+        if os.environ.get("PANAMA_SETTINGS_BACKUP_TEST_FAIL") == "after-desktop-stage":
+            fail("Injected failure after desktop staging.")
+
+        home_old = capture_old("home", HOME_STATE) if home_touch else False
+        if home_touch and home_present:
+            stage_artifact("home.new", json_bytes(home_data))
+
+        journal = {
+            "version": 1,
+            "desktop": {
+                "touch": True,
+                "oldPresent": desktop_old,
+                "newPresent": desktop_present,
+            },
+            "home": {
+                "touch": home_touch,
+                "oldPresent": home_old,
+                "newPresent": home_present,
+            },
+        }
+        atomic_write_json(JOURNAL, journal)
+        return journal
+    except BaseException:
+        # SIGKILL/os._exit bypass this block by design; the next invocation
+        # cleans a pre-journal directory or recovers a journalled transaction.
+        if not JOURNAL.exists() and not JOURNAL.is_symlink():
+            clean_transaction_artifacts()
+        raise
+
+
+def commit_restore(journal: dict[str, Any]) -> None:
+    try:
+        desktop = journal["desktop"]
+        apply_artifact("desktop", "new", desktop["newPresent"])
+        if os.environ.get("PANAMA_SETTINGS_BACKUP_TEST_CRASH") == "after-desktop":
+            os._exit(86)
+
+        home = journal["home"]
+        if home["touch"]:
+            apply_artifact("home", "new", home["newPresent"])
+
+        # Both targets and their parent directories are durable. Removing and
+        # fsyncing the journal is the transaction's commit record.
+        durable_remove(JOURNAL)
+        clean_transaction_artifacts()
+    except BaseException:
+        # Ordinary failures roll back immediately. Process death leaves the
+        # journal in place and takes this same path on the next invocation.
+        recover_transaction()
+        raise
+
+
+def write_live_home(text: str) -> None:
+    try:
+        value = json.loads(text)
+    except json.JSONDecodeError as error:
+        raise BackupError("The live Home state is not valid JSON.") from error
+    validate_home(value, "The live Home state")
+    atomic_write_json(HOME_STATE, value)
+
+
+def command_save(arguments: list[str]) -> None:
+    if arguments:
+        write_live_home(arguments[0])
+    destination = save_snapshot(require_any=True, validate=True)
+    assert destination is not None
+    print(json.dumps({"saved": destination.name}, separators=(",", ":")))
+
+
+def snapshot_files() -> list[Path]:
+    ensure_directory(BACKUP_DIR)
+    return sorted(
+        (
+            path
+            for path in BACKUP_DIR.iterdir()
+            if SNAPSHOT_RE.fullmatch(path.name)
+            and path.is_file()
+            and not path.is_symlink()
+        ),
+        key=lambda path: path.stat().st_mtime_ns,
+        reverse=True,
+    )
+
+
+def command_list() -> None:
+    output: list[dict[str, Any]] = []
+    for path in snapshot_files():
+        try:
+            value = read_json(path, "A snapshot")
+            if is_v2_envelope(value):
+                desktop = value["desktop"]
+                keys = len(desktop["data"]) if desktop["present"] else 0
+            else:
+                keys = len(value)
+        except BackupError:
+            keys = 0
+        raw = path.name.removeprefix("settings-").removesuffix(".json")
+        pretty = (
+            f"{raw[0:4]}-{raw[4:6]}-{raw[6:8]} "
+            f"{raw[9:11]}:{raw[11:13]}:{raw[13:15]}"
+        )
+        output.append({"name": path.name, "when": pretty, "keys": keys})
+    print(json.dumps(output, separators=(",", ":")))
+
+
+def command_restore(arguments: list[str]) -> None:
+    if not arguments:
+        fail("Which snapshot?")
+    name = arguments[0]
+    source = snapshot_source(name)
+    snapshot = read_json(source, "That snapshot")
+    snapshot_format, value = validate_snapshot(snapshot)
+
+    if snapshot_format == "versioned":
+        desktop_present = value["desktop"]["present"]
+        desktop_data = value["desktop"].get("data")
+        home_touch = True
+        home_present = value["home"]["present"]
+        home_data = value["home"].get("data")
+    else:
+        desktop_present = True
+        desktop_data = value
+        home_touch = False
+        home_present = False
+        home_data = None
+
+    # Restoring remains undoable, but a corrupt current file must not prevent a
+    # known-good snapshot from recovering the desktop.
+    save_snapshot(require_any=False, validate=False)
+    journal = prepare_transaction(
+        desktop_present,
+        desktop_data,
+        home_touch,
+        home_present,
+        home_data,
+    )
+    commit_restore(journal)
+
+    if not home_touch:
+        home_result: dict[str, Any] = {"preserve": True}
+    elif home_present:
+        home_result = {"present": True, "data": home_data}
+    else:
+        home_result = {"present": False}
+    print(
+        json.dumps(
+            {"restored": name, "home": home_result},
+            separators=(",", ":"),
+        )
+    )
+
+
+def main() -> None:
+    with process_lock():
+        clean_stale_atomic_files()
+        recover_transaction()
+        command = sys.argv[1] if len(sys.argv) > 1 else "list"
+        arguments = sys.argv[2:]
+        if command == "save":
+            command_save(arguments)
+        elif command == "list":
+            command_list()
+        elif command == "restore":
+            command_restore(arguments)
+        else:
+            fail("usage: panama-settings-backup [save|list|restore <name>]")
+
+
+if __name__ == "__main__":
+    try:
+        main()
+    except BackupError as error:
+        print(str(error), file=sys.stderr)
+        raise SystemExit(1) from error
+    except OSError as error:
+        print("The settings backup could not access its state files.", file=sys.stderr)
+        raise SystemExit(1) from error

config/dot/quickshell/services/SettingsBackup.qml

@@ -1,14 +1,15 @@
 pragma Singleton
 
-// Snapshots of the settings store.
+// Snapshots of Panama's durable settings stores.
 //
-// The whole desktop configuration is one JSON file, so a backup is a copy and a
-// restore is an overwrite. Worth exposing now that the settings app changes
-// real things -- compositor geometry, idle timeouts, the dock -- because being
-// able to return to a known-good state is what makes experimenting feel safe.
+// DesktopPreferences and HomePreferences use separate files. The helper owns
+// the transactional filesystem boundary; this service owns settling the live
+// desktop after those files have changed underneath it.
 //
-// Restoring rewrites the file underneath the running shell, so the store is
-// told to re-read afterwards rather than waiting for the next change.
+// HomePreferences intentionally keeps its FileView in Quickshell's private
+// state directory while snapshots use Panama's canonical state directory. This
+// service bridges them through HomePreferences' public mutation API, then soft
+// reloads once external consumers have settled.
 
 import Quickshell
 import Quickshell.Io
@@ -24,7 +25,31 @@ Singleton {
     property string lastError: ""
     property string lastAction: ""
 
+    // Narrow service boundaries keep restore sequencing explicit and make it
+    // possible to verify the real handler in an isolated shell without ever
+    // calling the daily-driver compositor or wallpaper services.
+    property var readHomeState: function() {
+        return {
+            initialized: HomePreferences.initialized,
+            favorites: HomePreferences.favorites
+        };
+    }
+    property var resetHome: function() { HomePreferences.resetHomeDefaults(); }
+    property var initializeHome: function(ids) { HomePreferences.initialize(ids); }
+    property var aliasHome: function(id, alias) { HomePreferences.setAlias(id, alias); }
+    property var reloadDesktop: function() { DesktopPreferences.reload(); }
+    property var applyCompositor: function() { SystemSettings.applyPersistedDisplayPolicy(); }
+    property var reloadKeybinds: function() { Keybinds.applyReload(); }
+    property var keybindsReloading: function() { return Keybinds.reloading; }
+    property var systemBusy: function() { return SystemSettings.busy; }
+    property var currentWallpaper: function() {
+        return String(DesktopPreferences.get("wallpaperPath") ?? "");
+    }
+    property var applyWallpaper: function(path) { Wallpaper.set(path); }
+    property var reloadShell: function() { Quickshell.reload(false); }
+
     readonly property bool busy: listQuery.running || actionRun.running
+        || applyRestoredState.running || settleReload.running
 
     Process {
         id: listQuery
@@ -34,6 +59,7 @@ Singleton {
                 try {
                     const parsed = JSON.parse(this.text);
                     root.snapshots = Array.isArray(parsed) ? parsed : [];
+                    if (root.lastError === "Could not read the list of snapshots.")
                         root.lastError = "";
                 } catch (error) {
                     root.lastError = "Could not read the list of snapshots.";
@@ -45,6 +71,11 @@ Singleton {
     Process {
         id: actionRun
         property bool restoring: false
+        property string outputText: ""
+        stdout: StdioCollector {
+            onStreamFinished: actionRun.outputText = this.text
+        }
+        onStarted: actionRun.outputText = ""
         onExited: (exitCode, exitStatus) => {
             if (exitCode !== 0) {
                 root.lastError = actionRun.restoring
@@ -52,14 +83,52 @@ Singleton {
                     : "The settings could not be backed up.";
                 return;
             }
-            root.lastError = "";
             root.lastAction = actionRun.restoring ? "restored" : "saved";
-            if (actionRun.restoring)
-                DesktopPreferences.reload();
+            if (actionRun.restoring) {
+                const homeReloaded = root.handleRestoreOutput(actionRun.outputText);
+                root.lastError = homeReloaded
+                    ? ""
+                    : "Desktop settings were restored, but Home favourites could not be reloaded.";
+            } else
+                root.lastError = "";
             root.refresh();
         }
     }
 
+    Timer {
+        id: applyRestoredState
+        interval: 80
+        repeat: false
+        onTriggered: {
+            // DesktopPreferences.reload() invalidates reactive shell bindings.
+            // These services also own state outside QML and need an explicit
+            // replay: compositor options, Lua-generated binds, and hyprpaper.
+            root.applyCompositor();
+            root.reloadKeybinds();
+            root.applyWallpaper(root.currentWallpaper());
+
+            settleReload.attempts = 0;
+            settleReload.restart();
+        }
+    }
+
+    Timer {
+        id: settleReload
+        property int attempts: 0
+        interval: 100
+        repeat: true
+        onTriggered: {
+            attempts++;
+            // Let the current instances finish their external writes before a
+            // soft reload replaces them. The cap keeps a failed external tool
+            // from leaving restored Home state stale indefinitely.
+            if ((!root.keybindsReloading() && !root.systemBusy()) || attempts >= 30) {
+                stop();
+                root.reloadShell();
+            }
+        }
+    }
+
     Component.onCompleted: root.refresh()
 
     function refresh(): void {
@@ -71,7 +140,81 @@ Singleton {
         if (actionRun.running)
             return;
         actionRun.restoring = false;
-        actionRun.exec([root.helperPath, "save"]);
+        actionRun.exec([root.helperPath, "save", root.serialiseHomeState()]);
+    }
+
+    function serialiseHomeState(): string {
+        const current = root.readHomeState();
+        const favorites = [];
+        for (const favorite of current.favorites ?? []) {
+            favorites.push({
+                id: String(favorite.id ?? ""),
+                alias: String(favorite.alias ?? "")
+            });
+        }
+        return JSON.stringify({
+            initialized: current.initialized === true,
+            favorites: favorites
+        });
+    }
+
+    function handleRestoreOutput(text: string): bool {
+        if (!root.reloadHomeState(text))
+            return false;
+        root.reloadDesktop();
+        applyRestoredState.restart();
+        return true;
+    }
+
+    // Restore output carries the canonical Home state. Reconstructing through
+    // these methods keeps validation and persistence inside HomePreferences;
+    // this service never mutates its aliases or private FileView directly.
+    function reloadHomeState(text: string): bool {
+        try {
+            const result = JSON.parse(text);
+            const restored = result?.home;
+            if (!restored || restored.preserve === true)
+                return true;
+
+            if (restored.present !== true)
+                return restored.present === false
+                    ? root.resetHomeState()
+                    : false;
+
+            const data = restored.data;
+            if (!data || typeof data.initialized !== "boolean" || !Array.isArray(data.favorites))
+                return false;
+            const ids = [];
+            const aliases = [];
+            const seen = {};
+            for (const favorite of data.favorites) {
+                const id = favorite?.id;
+                const alias = favorite?.alias;
+                if (typeof id !== "string" || !/^light\.[a-z0-9_]+$/.test(id)
+                        || typeof alias !== "string" || seen[id])
+                    return false;
+                seen[id] = true;
+                ids.push(id);
+                aliases.push(alias);
+            }
+            if (!data.initialized && ids.length > 0)
+                return false;
+
+            root.resetHome();
+            if (!data.initialized)
+                return true;
+            root.initializeHome(ids);
+            for (let index = 0; index < ids.length; index++)
+                root.aliasHome(ids[index], aliases[index]);
+            return true;
+        } catch (error) {
+            return false;
+        }
+    }
+
+    function resetHomeState(): bool {
+        root.resetHome();
+        return true;
     }
 
     // The name is matched against the snapshot list rather than trusted, so no

config/dot/quickshell/settings-backup-harness.qml

@@ -0,0 +1,76 @@
+// Isolated behavioral harness for SettingsBackup's live restore handoff.
+// Every external consumer is replaced before restore output is exercised, so
+// this file never writes the real compositor, wallpaper, keymap, or shell.
+import Quickshell
+import Quickshell.Io
+import QtQuick
+
+import qs.services
+
+ShellRoot {
+    id: root
+
+    property var calls: []
+    property bool homeInitialized: false
+    property var homeFavorites: []
+
+    function record(name: string): void {
+        const next = root.calls.slice();
+        next.push(name);
+        root.calls = next;
+    }
+
+    Component.onCompleted: {
+        SettingsBackup.readHomeState = function() {
+            return {
+                initialized: root.homeInitialized,
+                favorites: root.homeFavorites
+            };
+        };
+        SettingsBackup.resetHome = function() {
+            root.record("home.reset");
+            root.homeInitialized = false;
+            root.homeFavorites = [];
+        };
+        SettingsBackup.initializeHome = function(ids) {
+            root.record("home.initialize:" + ids.join(","));
+            root.homeInitialized = true;
+            root.homeFavorites = ids.map(id => ({ id: id, alias: "" }));
+        };
+        SettingsBackup.aliasHome = function(id, alias) {
+            root.record("home.alias:" + id + "=" + alias);
+            root.homeFavorites = root.homeFavorites.map(favorite =>
+                favorite.id === id ? { id: id, alias: alias } : favorite);
+        };
+        SettingsBackup.reloadDesktop = function() { root.record("desktop.reload"); };
+        SettingsBackup.applyCompositor = function() { root.record("system.apply"); };
+        SettingsBackup.reloadKeybinds = function() { root.record("keybinds.reload"); };
+        SettingsBackup.keybindsReloading = function() { return false; };
+        SettingsBackup.systemBusy = function() { return false; };
+        SettingsBackup.currentWallpaper = function() { return "/tmp/restored-wallpaper.jpg"; };
+        SettingsBackup.applyWallpaper = function(path) { root.record("wallpaper.set:" + path); };
+        SettingsBackup.reloadShell = function() { root.record("shell.reload"); };
+    }
+
+    IpcHandler {
+        target: "settings-backup-behavior"
+
+        function reset(): void {
+            root.calls = [];
+            root.homeInitialized = false;
+            root.homeFavorites = [];
+        }
+
+        function apply(output: string): bool {
+            return SettingsBackup.handleRestoreOutput(output);
+        }
+
+        function status(): string {
+            return JSON.stringify({
+                calls: root.calls,
+                initialized: root.homeInitialized,
+                favorites: root.homeFavorites
+            });
+        }
+    }
+}

tests/quickshell/settings-backup-contract.sh

@@ -22,10 +22,26 @@ cleanup() { rm -rf "$work"; }
 trap cleanup EXIT
 
 settings="$work/config/panama/settings.json"
+home="$work/state/panama/panama-home.json"
 backups="$work/state/panama/backups"
+transaction_dir="$work/state/panama/transactions/settings-restore"
 mkdir -p "$(dirname "$settings")"
 
 run() { XDG_CONFIG_HOME="$work/config" XDG_STATE_HOME="$work/state" "$helper" "$@"; }
+run_with() { XDG_CONFIG_HOME="$work/config" XDG_STATE_HOME="$work/state" env "$@"; }
+
+assert_transaction_clean() {
+    if [[ -d "$transaction_dir" ]] && find "$transaction_dir" -mindepth 1 -print -quit | rg -q .; then
+        fail 'restore left staged, rollback, or journal files behind'
+    fi
+    if find "$work" -type f \( \
+            -name '.settings-restore.*' -o -name '.home-restore.*' \
+            -o -name '*rollback*' -o -name '.journal.json.*' \
+            -o -name '.settings.json.*' -o -name '.panama-home.json.*' \
+        \) -print -quit | rg -q .; then
+        fail 'restore left a temporary target or journal file behind'
+    fi
+}
 
 # ── Nothing to back up ───────────────────────────────────────────────────────
 run save >/dev/null 2>&1 && fail 'backing up a missing settings file reported success'
@@ -33,15 +49,96 @@ run save >/dev/null 2>&1 && fail 'backing up a missing settings file reported su
 
 # ── A snapshot round-trips ───────────────────────────────────────────────────
 printf '{"gapsOut":24,"windowRounding":6}' >"$settings"
+mkdir -p "$(dirname "$home")"
+printf '{"initialized":true,"favorites":[{"id":"light.desk","alias":"Desk"}]}' >"$home"
 run save >/dev/null || fail 'save failed on a valid settings file'
 name="$(run list | jq -r '.[0].name')"
 [[ "$name" =~ ^settings-[0-9]{8}-[0-9]{9}\.json$ ]] || fail "unexpected snapshot name: $name"
 [[ "$(run list | jq -r '.[0].keys')" == "2" ]] || fail 'snapshot key count is wrong'
 
 printf '{"gapsOut":99}' >"$settings"
-run restore "$name" >/dev/null || fail 'restore failed'
+printf '{"initialized":false,"favorites":[]}' >"$home"
+restore_result="$(run restore "$name")" || fail 'restore failed'
 [[ "$(jq -r .gapsOut "$settings")" == "24" ]] || fail 'restore did not bring back the snapshot contents'
 [[ "$(jq -r .windowRounding "$settings")" == "6" ]] || fail 'restore lost a key'
+[[ "$(jq -r '.favorites[0].id' "$home")" == "light.desk" ]] || fail 'restore did not bring back Home favourites'
+[[ "$(jq -r '.favorites[0].alias' "$home")" == "Desk" ]] || fail 'restore lost a Home alias'
+jq -e '.home.present == true and .home.data.favorites[0].id == "light.desk"' <<<"$restore_result" >/dev/null \
+    || fail 'restore did not return Home state for the live service to reload'
+
+# ── Absence is part of a snapshot ───────────────────────────────────────────
+rm -f "$home"
+printf '{"gapsOut":30}' >"$settings"
+run save >/dev/null || fail 'save failed when Home state was absent'
+absent_name="$(run list | jq -r '.[0].name')"
+printf '{"initialized":true,"favorites":[{"id":"light.living_room","alias":"Living room"}]}' >"$home"
+absent_result="$(run restore "$absent_name")" || fail 'restore failed for a snapshot without Home state'
+[[ ! -e "$home" ]] || fail 'restore did not preserve the snapshot’s absent Home state'
+jq -e '.home.present == false and (.home | has("data") | not)' <<<"$absent_result" >/dev/null \
+    || fail 'restore did not return absent Home state for the live service to reload'
+
+# Desktop absence is symmetric: a Home-only snapshot removes a desktop file
+# created later and restores the Home store.
+rm -f "$settings"
+printf '{"initialized":true,"favorites":[{"id":"light.porch","alias":"Porch"}]}' >"$home"
+run save >/dev/null || fail 'save failed when desktop settings were absent'
+desktop_absent_name="$(run list | jq -r '.[0].name')"
+printf '{"gapsOut":47}' >"$settings"
+printf '{"initialized":false,"favorites":[]}' >"$home"
+run restore "$desktop_absent_name" >/dev/null || fail 'Home-only snapshot restore failed'
+[[ ! -e "$settings" ]] || fail 'restore did not preserve the snapshot’s absent desktop state'
+[[ "$(jq -r '.favorites[0].id' "$home")" == "light.porch" ]] \
+    || fail 'Home-only snapshot did not restore Home state'
+assert_transaction_clean
+
+printf '{"gapsOut":17}' >"$settings"
+
+# A legacy settings-only snapshot predates presence metadata. Its safest
+# interpretation is to restore desktop settings without deleting current Home
+# state that the old format knew nothing about.
+legacy="settings-20000101-010203004.json"
+printf '{"gapsOut":17}' >"$backups/$legacy"
+printf '{"initialized":true,"favorites":[{"id":"light.office","alias":"Office"}]}' >"$home"
+run restore "$legacy" >/dev/null || fail 'legacy snapshot restore failed'
+[[ "$(jq -r .gapsOut "$settings")" == "17" ]] || fail 'legacy snapshot did not restore desktop settings'
+[[ "$(jq -r '.favorites[0].id' "$home")" == "light.office" ]] || fail 'legacy snapshot destroyed Home state it did not describe'
+
+# `version` is a valid unknown desktop preference. It is only an envelope when
+# the complete v2 shape is present.
+legacy_version="settings-20000101-010203005.json"
+printf '{"version":77,"gapsOut":19}' >"$backups/$legacy_version"
+run restore "$legacy_version" >/dev/null || fail 'a legacy snapshot with an unknown version key was rejected'
+[[ "$(jq -r '.version' "$settings")" == "77" ]] || fail 'legacy version key was not restored as desktop data'
+[[ "$(jq -r '.favorites[0].id' "$home")" == "light.office" ]] || fail 'legacy version key changed Home state'
+
+# ── A durable journal recovers a process/power-loss split ────────────────────
+printf '{"gapsOut":28,"windowRounding":12}' >"$settings"
+printf '{"initialized":true,"favorites":[{"id":"light.desk","alias":"Snapshot"}]}' >"$home"
+run save >/dev/null || fail 'could not create crash-recovery snapshot'
+crash_name="$(run list | jq -r '.[0].name')"
+
+printf '{"gapsOut":91,"windowRounding":3}' >"$settings"
+printf '{"initialized":true,"favorites":[{"id":"light.office","alias":"Before crash"}]}' >"$home"
+run_with PANAMA_SETTINGS_BACKUP_TEST_CRASH=after-desktop "$helper" restore "$crash_name" >/dev/null 2>&1 \
+    && fail 'crash injection completed restore instead of terminating after the first replacement'
+[[ "$(jq -r '.gapsOut' "$settings")" == "28" ]] || fail 'crash did not occur after desktop replacement'
+[[ "$(jq -r '.favorites[0].alias' "$home")" == "Before crash" ]] || fail 'crash unexpectedly replaced Home state'
+[[ -f "$transaction_dir/journal.json" ]] || fail 'crash left no durable recovery journal'
+
+# Every entry point must recover before doing its own work. `list` is the least
+# invasive proof and must put both stores back to the pre-restore generation.
+run list >/dev/null || fail 'next invocation could not recover the interrupted restore'
+[[ "$(jq -r '.gapsOut' "$settings")" == "91" ]] || fail 'recovery did not roll desktop settings back'
+[[ "$(jq -r '.favorites[0].alias' "$home")" == "Before crash" ]] || fail 'recovery did not keep Home state in the same generation'
+assert_transaction_clean
+
+# Cleanup is installed before staging. A deterministic pre-journal failure
+# must leave both destinations untouched and no hidden artifacts behind.
+run_with PANAMA_SETTINGS_BACKUP_TEST_FAIL=after-desktop-stage "$helper" restore "$crash_name" >/dev/null 2>&1 \
+    && fail 'staging failure injection unexpectedly restored the snapshot'
+[[ "$(jq -r '.gapsOut' "$settings")" == "91" ]] || fail 'staging failure changed desktop settings'
+[[ "$(jq -r '.favorites[0].alias' "$home")" == "Before crash" ]] || fail 'staging failure changed Home state'
+assert_transaction_clean
 
 # ── Restoring snapshots what it replaced, so it is undoable ──────────────────
 count="$(run list | jq 'length')"
@@ -52,12 +149,44 @@ bad="settings-19990101-000000000.json"
 mkdir -p "$backups"
 printf '{ truncated' >"$backups/$bad"
 run restore "$bad" >/dev/null 2>&1 && fail 'a corrupt snapshot was restored'
-[[ "$(jq -r .gapsOut "$settings")" == "24" ]] || fail 'a refused restore still damaged the settings file'
+[[ "$(jq -r .gapsOut "$settings")" == "91" ]] || fail 'a refused restore still damaged the settings file'
+
+invalid_home="settings-19990101-000000001.json"
+jq -n '{
+    version: 2,
+    desktop: {present: true, data: {gapsOut: 88}},
+    home: {present: true, data: {
+        initialized: true,
+        favorites: [
+            {id: "light.desk", alias: "Desk"},
+            {id: "light.desk", alias: "Duplicate"}
+        ]
+    }}
+}' >"$backups/$invalid_home"
+run restore "$invalid_home" >/dev/null 2>&1 && fail 'a snapshot with duplicate Home favourites was restored'
+[[ "$(jq -r .gapsOut "$settings")" == "91" ]] || fail 'an invalid Home snapshot still damaged desktop settings'
+
+printf '{ truncated' >"$home"
+run save >/dev/null 2>&1 && fail 'a corrupt Home state file was backed up'
+printf '{"initialized":true,"favorites":[]}' >"$home"
+
+# ── The live service can sync its private Home state before save ─────────────
+rm -f "$home"
+printf '{"gapsOut":21}' >"$settings"
+live_home='{"initialized":true,"favorites":[{"id":"light.studio","alias":"Studio"}]}'
+run save "$live_home" >/dev/null || fail 'save rejected valid live Home state'
+live_name="$(run list | jq -r '.[0].name')"
+jq -e '.home.present == true and .home.data.favorites[0].alias == "Studio"' \
+    "$backups/$live_name" >/dev/null \
+    || fail 'live Home state was not written to the canonical snapshot'
 
 # ── A snapshot cannot name a path outside the backup directory ───────────────
 printf '{"pwned":true}' >"$work/outside.json"
 run restore "../../outside.json" >/dev/null 2>&1 && fail 'a traversing snapshot name was accepted'
 run restore "/etc/passwd" >/dev/null 2>&1 && fail 'an absolute snapshot path was accepted'
+link_name="settings-20000101-000000001.json"
+ln -s "$work/outside.json" "$backups/$link_name"
+run restore "$link_name" >/dev/null 2>&1 && fail 'a snapshot symlink escaping the backup directory was accepted'
 jq -e 'has("pwned") | not' "$settings" >/dev/null || fail 'a file outside the backup directory was restored'
 
 # ── A snapshot that is not listed is refused ─────────────────────────────────

tests/quickshell/settings-backup-live-contract.sh

@@ -0,0 +1,132 @@
+#!/usr/bin/env bash
+
+# Behavioral coverage for the QML handoff after the helper commits a restore.
+# The harness has a unique shell identity, isolated XDG roots, and fake external
+# consumers. It records the real SettingsBackup call order without touching the
+# daily-driver shell, compositor, keymap, or wallpaper.
+
+set -euo pipefail
+
+repo_dir="$(cd "$(dirname "${BASH_SOURCE[0]}")/../.." && pwd)"
+service="$repo_dir/config/dot/quickshell/services/SettingsBackup.qml"
+harness="$repo_dir/config/dot/quickshell/settings-backup-harness.qml"
+work="$(mktemp -d /tmp/panama-settings-backup-live.XXXXXX)"
+
+fail() {
+    printf 'settings backup live contract: %s\n' "$1" >&2
+    exit 1
+}
+
+qs_test() {
+    XDG_CONFIG_HOME="$work/config" XDG_STATE_HOME="$work/state" qs -p "$harness" "$@"
+}
+
+cleanup() {
+    qs_test kill >/dev/null 2>&1 || true
+    rm -rf "$work"
+}
+trap cleanup EXIT
+
+# The production command boundary must remain argv-only.
+rg -Fq 'actionRun.exec([root.helperPath, "save", root.serialiseHomeState()]);' "$service" \
+    || fail 'save does not pass live Home state as one argument'
+rg -Fq 'actionRun.exec([root.helperPath, "restore", name]);' "$service" \
+    || fail 'restore is not executed through an argument array'
+if rg -q 'bash.*-c|sh.*-c' "$service"; then
+    fail 'the restore service constructs a shell command'
+fi
+
+# The harness replaces these seams, while these mappings prove the production
+# defaults still delegate to Panama's existing public service APIs.
+for mapping in \
+    'HomePreferences.resetHomeDefaults();' \
+    'HomePreferences.initialize(ids);' \
+    'HomePreferences.setAlias(id, alias);' \
+    'DesktopPreferences.reload();' \
+    'SystemSettings.applyPersistedDisplayPolicy();' \
+    'Keybinds.applyReload();' \
+    'Wallpaper.set(path);' \
+    'Quickshell.reload(false);'; do
+    rg -Fq "$mapping" "$service" || fail "production restore seam is missing: $mapping"
+done
+
+qs_test --daemonize >"$work/quickshell.log" 2>&1
+ready=false
+for _ in $(seq 1 60); do
+    if qs_test ipc show 2>/dev/null | rg -q '^target settings-backup-behavior$'; then
+        ready=true
+        break
+    fi
+    sleep 0.1
+done
+if [[ "$ready" != true ]]; then
+    sed -n '1,200p' "$work/quickshell.log" >&2
+    fail 'isolated SettingsBackup harness did not start'
+fi
+
+qs_test ipc call settings-backup-behavior reset >/dev/null
+payload='{"restored":"settings-20260818-010203004.json","home":{"present":true,"data":{"initialized":true,"favorites":[{"id":"light.desk","alias":"Desk"},{"id":"light.office","alias":"Office"}]}}}'
+[[ "$(qs_test ipc call settings-backup-behavior apply "$payload")" == "true" ]] \
+    || fail 'valid restore output was rejected'
+
+status=""
+for _ in $(seq 1 50); do
+    status="$(qs_test ipc call settings-backup-behavior status)"
+    jq -e '.calls[-1] == "shell.reload"' <<<"$status" >/dev/null 2>&1 && break
+    sleep 0.1
+done
+jq -e '
+    .calls == [
+        "home.reset",
+        "home.initialize:light.desk,light.office",
+        "home.alias:light.desk=Desk",
+        "home.alias:light.office=Office",
+        "desktop.reload",
+        "system.apply",
+        "keybinds.reload",
+        "wallpaper.set:/tmp/restored-wallpaper.jpg",
+        "shell.reload"
+    ]
+    and .initialized == true
+    and .favorites == [
+        {"id":"light.desk","alias":"Desk"},
+        {"id":"light.office","alias":"Office"}
+    ]
+' <<<"$status" >/dev/null || fail "restore handoff order/state was wrong: $status"
+
+# Invalid output is rejected before Home state or external consumers change.
+qs_test ipc call settings-backup-behavior reset >/dev/null
+invalid='{"home":{"present":true,"data":{"initialized":true,"favorites":[{"id":"light.desk","alias":"One"},{"id":"light.desk","alias":"Two"}]}}}'
+[[ "$(qs_test ipc call settings-backup-behavior apply "$invalid")" == "false" ]] \
+    || fail 'duplicate Home state was accepted'
+status="$(qs_test ipc call settings-backup-behavior status)"
+jq -e '.calls == [] and .initialized == false and .favorites == []' <<<"$status" >/dev/null \
+    || fail 'invalid restore output caused partial live mutations'
+
+# An absent Home generation uses the same ordered external handoff but leaves
+# the live Home service reset rather than manufacturing an initialized store.
+qs_test ipc call settings-backup-behavior reset >/dev/null
+absent='{"restored":"settings-20260818-010203005.json","home":{"present":false}}'
+[[ "$(qs_test ipc call settings-backup-behavior apply "$absent")" == "true" ]] \
+    || fail 'absent Home restore output was rejected'
+for _ in $(seq 1 50); do
+    status="$(qs_test ipc call settings-backup-behavior status)"
+    jq -e '.calls[-1] == "shell.reload"' <<<"$status" >/dev/null 2>&1 && break
+    sleep 0.1
+done
+jq -e '
+    .calls == [
+        "home.reset",
+        "desktop.reload",
+        "system.apply",
+        "keybinds.reload",
+        "wallpaper.set:/tmp/restored-wallpaper.jpg",
+        "shell.reload"
+    ]
+    and .initialized == false
+    and .favorites == []
+' <<<"$status" >/dev/null || fail "absent Home handoff was wrong: $status"
+
+trap - EXIT
+cleanup
+printf 'settings backup live contract: PASS\n'