Split the tasks feature out of the calendar widget into its own widget type

Task lists used to be a week-view-only sub-feature bolted onto calendar
widgets (CalendarWidgetConfig.tasks_*), so a task list could only exist
tied to a calendar's view and only inside its footprint. Tasks are now
a standalone widget type (TaskWidgetConfig, app/widgets/tasks.py) that
can be placed and sized independently, same as photos/calendar/
whiteboard -- no separate "enabled" flag either, since being on the
grid at all is the on/off switch, matching every other widget type.

Migration 17 creates task_widget_configs, extracts any existing
calendar widget's configured task source into a new sibling tasks
widget (auto-placed in open grid space, source dropped+logged if truly
none is left), then drops calendar_widget_configs' now-dead tasks_*
columns in the same migration -- this project's usual same-migration-
drop convention. Also handles the rarer case of a database jumping
straight from before the widget system existed to after this split in
one boot, via the legacy Frame.calendar_tasks_* columns.

Verified live in the browser at desktop and mobile widths: adding a
Tasks widget, its own dialog (task-list source picker + preview), and
confirming the calendar widget's dialog no longer mentions tasks at
all. Full test suite (180 tests, including new coverage for the widget
render/actions, the migration's data-extraction path, and the
permission-boundary shape for tasks-source) passes.

server/app/migration.py

@@ -27,6 +27,7 @@ from .models import (
     FrameButtonAction,
     PhotoWidgetConfig,
     ServerSettings,
+    TaskWidgetConfig,
     WhiteboardWidgetConfig,
     Widget,
 )
@@ -333,6 +334,110 @@ def _migration_16(conn) -> None:
     ))
 
 
+def _migration_17(conn) -> None:
+    """Splits the calendar widget's old week-view-only task list out into
+    its own standalone widget type (see models.TaskWidgetConfig,
+    app/widgets/tasks.py) -- a task list is no longer tied to a
+    calendar's view or footprint, and can be placed/sized on its own.
+
+    Every calendar_widget_configs row that still has a task source
+    configured gets a new sibling `tasks` widget carrying that source
+    over, auto-placed in whatever open grid space is left on its frame
+    (same find_open_rect logic a manual "add widget" uses; if truly none
+    is left, the source is dropped and logged -- rare enough, and with
+    no interactive way to ask during a boot-time migration, that this is
+    an acceptable edge case). calendar_widget_configs then drops its now
+    -dead tasks_* columns -- this project's usual same-migration-drop
+    convention (see docs/widgets.md's Known Gaps for the one deliberate,
+    much-larger-blast-radius exception)."""
+    conn.execute(text(
+        "CREATE TABLE task_widget_configs ("
+        "widget_id INTEGER PRIMARY KEY REFERENCES widgets(id) ON DELETE CASCADE, "
+        "user_id INTEGER REFERENCES users(id) ON DELETE SET NULL, "
+        "calendar_key TEXT, "
+        "checked_at REAL NOT NULL DEFAULT 0.0, "
+        "cached TEXT)"
+    ))
+
+    rows = conn.execute(text(
+        "SELECT cwc.widget_id, w.frame_id, f.orientation, "
+        "cwc.tasks_user_id, cwc.tasks_calendar_key, cwc.tasks_checked_at, cwc.tasks_cached "
+        "FROM calendar_widget_configs cwc "
+        "JOIN widgets w ON w.id = cwc.widget_id "
+        "JOIN frames f ON f.id = w.frame_id "
+        "WHERE cwc.tasks_calendar_key IS NOT NULL"
+    )).mappings().all()
+
+    skipped = 0
+    now = time.time()
+    for row in rows:
+        existing = conn.execute(text(
+            "SELECT x, y, w, h FROM widgets WHERE frame_id = :frame_id"
+        ), {"frame_id": row["frame_id"]}).all()
+        min_w, min_h = grid.MIN_FOOTPRINT["tasks"]
+        rect = grid.find_open_rect(row["orientation"], [tuple(r) for r in existing], min_w, min_h)
+        if rect is None:
+            skipped += 1
+            continue
+        x, y, w, h = rect
+        max_sort = conn.execute(text(
+            "SELECT COALESCE(MAX(sort_order), 0) FROM widgets WHERE frame_id = :frame_id"
+        ), {"frame_id": row["frame_id"]}).scalar()
+        result = conn.execute(text(
+            "INSERT INTO widgets (frame_id, widget_type, x, y, w, h, sort_order, created_at) "
+            "VALUES (:frame_id, 'tasks', :x, :y, :w, :h, :sort_order, :created_at)"
+        ), {"frame_id": row["frame_id"], "x": x, "y": y, "w": w, "h": h,
+            "sort_order": max_sort + 1, "created_at": now})
+        new_widget_id = result.lastrowid
+        conn.execute(text(
+            "INSERT INTO task_widget_configs (widget_id, user_id, calendar_key, checked_at, cached) "
+            "VALUES (:widget_id, :user_id, :calendar_key, :checked_at, :cached)"
+        ), {"widget_id": new_widget_id, "user_id": row["tasks_user_id"],
+            "calendar_key": row["tasks_calendar_key"], "checked_at": row["tasks_checked_at"],
+            "cached": row["tasks_cached"]})
+
+    if skipped:
+        logger.warning(
+            "%d calendar widget(s) had a task list configured but no open grid space for a "
+            "standalone tasks widget -- their task source was dropped", skipped
+        )
+
+    # Rebuild calendar_widget_configs without the now-dead tasks_*
+    # columns -- SQLite can't drop tasks_user_id directly (it's part of
+    # an FK constraint), same situation frame_calendars hit in
+    # _migration_9, same rebuild-create-copy-drop-rename fix.
+    conn.execute(text(
+        "CREATE TABLE calendar_widget_configs_new ("
+        "widget_id INTEGER PRIMARY KEY REFERENCES widgets(id) ON DELETE CASCADE, "
+        "view TEXT NOT NULL DEFAULT 'agenda', "
+        "week_start INTEGER NOT NULL DEFAULT 0, "
+        "browse_offset INTEGER NOT NULL DEFAULT 0, "
+        "checked_at REAL NOT NULL DEFAULT 0.0, "
+        "cached_events TEXT, "
+        "fetch_summary TEXT NOT NULL DEFAULT '', "
+        "weather_enabled INTEGER NOT NULL DEFAULT 0, "
+        "weather_units TEXT NOT NULL DEFAULT 'fahrenheit', "
+        "weather_cities TEXT, "
+        "weather_checked_at REAL NOT NULL DEFAULT 0.0, "
+        "weather_cached TEXT, "
+        "week_days INTEGER NOT NULL DEFAULT 7, "
+        "week_layout TEXT NOT NULL DEFAULT 'horizontal', "
+        "week_start_offset INTEGER NOT NULL DEFAULT 0)"
+    ))
+    conn.execute(text(
+        "INSERT INTO calendar_widget_configs_new "
+        "(widget_id, view, week_start, browse_offset, checked_at, cached_events, fetch_summary, "
+        "weather_enabled, weather_units, weather_cities, weather_checked_at, weather_cached, "
+        "week_days, week_layout, week_start_offset) "
+        "SELECT widget_id, view, week_start, browse_offset, checked_at, cached_events, fetch_summary, "
+        "weather_enabled, weather_units, weather_cities, weather_checked_at, weather_cached, "
+        "week_days, week_layout, week_start_offset "
+        "FROM calendar_widget_configs"
+    ))
+    conn.execute(text("DROP TABLE calendar_widget_configs"))
+    conn.execute(text("ALTER TABLE calendar_widget_configs_new RENAME TO calendar_widget_configs"))
+
+
 MIGRATIONS = [
     (1, _migration_1),
     (2, _migration_2),
@@ -350,6 +455,7 @@ MIGRATIONS = [
     (14, _migration_14),
     (15, _migration_15),
     (16, _migration_16),
+    (17, _migration_17),
 ]
 
 
@@ -518,11 +624,26 @@ def _calendar_config_from_frame(frame: Frame, widget_id: int) -> CalendarWidgetC
         week_days=frame.calendar_week_days,
         week_layout=frame.calendar_week_layout,
         week_start_offset=frame.calendar_week_start_offset,
-        tasks_enabled=frame.calendar_tasks_enabled,
-        tasks_user_id=frame.calendar_tasks_user_id,
-        tasks_calendar_key=frame.calendar_tasks_calendar_key,
-        tasks_checked_at=frame.calendar_tasks_checked_at,
-        tasks_cached=list(frame.calendar_tasks_cached) if frame.calendar_tasks_cached else None,
+        # tasks_* deliberately not carried over -- see _task_config_from_frame,
+        # a sibling standalone widget now, not part of this config.
+    )
+
+
+def _task_config_from_frame(frame: Frame, widget_id: int) -> TaskWidgetConfig:
+    """Only ever called for a frame whose legacy calendar_tasks_* columns
+    (see Frame's own docstring on those -- a dead pre-widget-system
+    field set, same status as calendar_photo_inlay below) still carry a
+    configured source -- i.e. a database jumping straight from before
+    the widget system existed to after tasks became its own widget type
+    in a single upgrade, skipping the intermediate period where it would
+    have lived on CalendarWidgetConfig instead (see _migration_17's own
+    extraction of *that* case)."""
+    return TaskWidgetConfig(
+        widget_id=widget_id,
+        user_id=frame.calendar_tasks_user_id,
+        calendar_key=frame.calendar_tasks_calendar_key,
+        checked_at=frame.calendar_tasks_checked_at,
+        cached=list(frame.calendar_tasks_cached) if frame.calendar_tasks_cached else None,
     )
 
 
@@ -556,6 +677,33 @@ def _default_button_actions(frame_id: int, widget_id: int, widget_type: str) ->
     ]
 
 
+def _maybe_add_legacy_tasks_widget(db, frame: Frame, existing: list[grid.Rect], next_sort_order: int) -> None:
+    """Only relevant for a database jumping straight from before the
+    widget system existed to after tasks became its own widget type in
+    one upgrade (see _task_config_from_frame) -- frame.calendar_tasks_*
+    is the dead legacy field set otherwise. Auto-placed in whatever open
+    space is left after the widget(s) above it in _backfill_frame_
+    widgets claimed theirs, same find_open_rect logic a manual "add
+    widget" uses; silently dropped (logged) if none fits, same as this
+    migration having nowhere else to put it either."""
+    if not frame.calendar_tasks_calendar_key:
+        return
+    min_w, min_h = grid.MIN_FOOTPRINT["tasks"]
+    rect = grid.find_open_rect(frame.orientation, existing, min_w, min_h)
+    if rect is None:
+        logger.warning(
+            "Frame %d had a legacy task list configured but no open grid space for a "
+            "standalone tasks widget during backfill -- its task source was dropped", frame.id
+        )
+        return
+    x, y, w, h = rect
+    task_widget = Widget(frame_id=frame.id, widget_type="tasks", x=x, y=y, w=w, h=h,
+                         sort_order=next_sort_order, created_at=time.time())
+    db.add(task_widget)
+    db.flush()
+    db.add(_task_config_from_frame(frame, task_widget.id))
+
+
 def _backfill_frame_widgets(db, frame: Frame) -> None:
     cols, rows = grid.grid_dims(frame.orientation)
     mode = frame.mode if frame.mode in ("photos", "calendar", "whiteboard") else "photos"
@@ -575,6 +723,9 @@ def _backfill_frame_widgets(db, frame: Frame) -> None:
         db.add(_calendar_config_from_frame(frame, cal_widget.id))
         db.add(_photo_config_from_frame(frame, photo_widget.id))
         db.add_all(_default_button_actions(frame.id, cal_widget.id, "calendar"))
+        _maybe_add_legacy_tasks_widget(
+            db, frame, [(0, 0, cols - half, rows), (cols - half, 0, half, rows)], next_sort_order=2
+        )
         return
 
     widget = Widget(frame_id=frame.id, widget_type=mode, x=0, y=0, w=cols, h=rows,
@@ -588,6 +739,8 @@ def _backfill_frame_widgets(db, frame: Frame) -> None:
     elif mode == "whiteboard":
         db.add(_whiteboard_config_from_frame(frame, widget.id))
     db.add_all(_default_button_actions(frame.id, widget.id, mode))
+    if mode == "calendar":
+        _maybe_add_legacy_tasks_widget(db, frame, [(0, 0, cols, rows)], next_sort_order=1)
 
 
 def _ensure_widgets_backfilled() -> None: