feat(R08): split ScheduleTaskTab, FolderTab, DashboardTab, StructureGraphView

Team Hoa, EPIC R08 (UI/Application Separation) - Team Hoa scope only
(R08-T11 -> T14; R08-T01->T10 belong to Team Duy/Team Nam).

- R08-T11: ui/schedule_task_tab.py (795 lines) -> presentation/scheduling/
  {kanban_board_widget,calendar_view_widget,ai_task_creator_dialog,
  ai_task_import_dialog,run_history_dialog}.py + schedule_task_tab.py
  shell. Kanban CRUD/drag-drop now goes through
  application/scheduling/task_application_service.py (R07-T04) instead of
  ~30 lines of inline if/elif per drag target.
- R08-T12: ui/folder_tab.py (1587 lines, the largest of the four) ->
  presentation/folder/{workspace_file_tree,document_preview_manager,
  code_editor,office_document_renderer,ai_file_editor_dialog,
  ai_edit_model_resolver,ai_edit_pipeline}.py + folder_tab.py shell.
  Closes the R06-T05 loop: FileWorkspaceService existed since R06 with
  zero production call sites (confirmed by grep); every plain-text write
  (save/create/write_content) now goes through it, gaining path
  containment and a Python-syntax warning the original code never had.
  Pure helpers (_read_text, _is_probably_text, _pptx_available,
  _split_code_block, _parse_ai_output) moved to
  application/workspaces/{file_preview_helpers,ai_edit_output}.py.
- R08-T13: ui/dashboard_tab.py (437 lines) -> presentation/dashboard/
  {token_usage_card_widget,usage_chart_widget,habits_widget}.py +
  dashboard_tab.py shell, backed by a new
  application/monitoring/dashboard_query_service.py (pricing/period/
  summary queries the three widgets used to each recompute separately).
  Directory-ownership note left in the checklist for Team Nam.
- R08-T14: ui/structure_graph_view.py (1035 lines) ->
  presentation/graph/{graph_scene_items,graph_renderer,
  graph_messages_view,graph_qa_widget}.py + structure_graph_view.py
  shell. Extraction helpers (_pdf_to_markdown, _extract_file_contents)
  moved to application/workspaces/graph_index_service.py (pure Python).
  Renderer and Q&A panel talk only through signals
  (node_selected/graph_rendered/raw_json_ready/project_changed) - neither
  imports the other.
- presentation/shared/web_engine_support.py: HAS_WEB_ENGINE, previously
  duplicated (folder_tab imported it FROM structure_graph_view.py) - now
  one shared flag instead of one screen importing another screen's module.

All four old ui/*.py files deleted; app.py and ui/workspace_tab.py updated
to the new import paths (each god-file only had 1-2 real construction
sites, so import sites were updated directly rather than kept as a
strangler-fig shim - unlike core/tools.py at R05, which had dozens).

pytest: 377 pass (+94 vs the R07 baseline of 328; same 4 pre-existing
failures as the R05/R06 baseline, unrelated to this work).
scripts/check_imports.py: PASS. python -c "import cowork_local.app": OK.
Every new file < 400 lines (largest: graph_renderer.py, 391).

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

presentation/dashboard/__init__.py

@@ -0,0 +1,3 @@
+"""Dashboard screen, split into single-responsibility widgets (R08-T13):
+``token_usage_card_widget``, ``usage_chart_widget``, ``habits_widget``,
+assembled by the ``dashboard_tab`` shell."""

presentation/dashboard/dashboard_tab.py

@@ -0,0 +1,91 @@
+"""DashboardTab shell (R08-T13) — assembles
+``token_usage_card_widget.py::TokenUsageCardWidget``,
+``usage_chart_widget.py::UsageChartWidget`` and
+``habits_widget.py::HabitsWidget`` behind the scroll area / header / 30s
+auto-refresh timer that used to be inline in
+``ui/dashboard_tab.py::DashboardTab.__init__`` (lines 40-193 of the original
+437-line file).
+
+The one ``DashboardQueryService`` (R08-T13) instance is built here and
+shared by all three children so pricing/currency stay consistent across the
+whole screen.
+"""
+from __future__ import annotations
+
+from PySide6.QtCore import QTimer, Signal
+from PySide6.QtWidgets import QHBoxLayout, QLabel, QPushButton, QScrollArea, QVBoxLayout, QWidget
+
+from cowork_local.application.monitoring import DashboardQueryService
+from cowork_local.i18n import on_language_changed, tr
+from cowork_local.presentation.dashboard.habits_widget import HabitsWidget
+from cowork_local.presentation.dashboard.token_usage_card_widget import TokenUsageCardWidget
+from cowork_local.presentation.dashboard.usage_chart_widget import UsageChartWidget
+from cowork_local.state import AppContext
+from cowork_local.ui.icons import icon
+
+
+class DashboardTab(QWidget):
+    status_message = Signal(str)
+
+    def __init__(self, ctx: AppContext):
+        super().__init__()
+        self.ctx = ctx
+        self._query = DashboardQueryService(ctx)
+
+        outer = QVBoxLayout(self)
+        scroll = QScrollArea()
+        scroll.setWidgetResizable(True)
+        scroll.setFrameShape(QScrollArea.NoFrame)
+        content = QWidget()
+        scroll.setWidget(content)
+        outer.addWidget(scroll)
+        root = QVBoxLayout(content)
+
+        head = QHBoxLayout()
+        self._title = QLabel()
+        self._title.setStyleSheet("font-weight:700; font-size:15px;")
+        self.refresh_btn = QPushButton("")
+        self.refresh_btn.setIcon(icon("refresh"))
+        self.refresh_btn.setFixedWidth(34)
+        self.refresh_btn.clicked.connect(self.refresh)
+        head.addWidget(self._title, 1)
+        head.addWidget(self.refresh_btn)
+        root.addLayout(head)
+
+        self.token_cards = TokenUsageCardWidget(ctx, self._query)
+        root.addWidget(self.token_cards)
+
+        self.chart = UsageChartWidget(ctx, self._query)
+        self.chart.period_changed.connect(self.refresh)
+        self.chart.currency_changed.connect(self.refresh)
+        root.addWidget(self.chart)
+
+        self.habits = HabitsWidget(ctx, self._query)
+        self.habits.status_message.connect(self.status_message.emit)
+        root.addWidget(self.habits, 1)
+
+        # Auto-refresh every 30s so numbers follow ongoing work.
+        self._timer = QTimer(self)
+        self._timer.setInterval(30_000)
+        self._timer.timeout.connect(self.refresh)
+        self._timer.start()
+
+        on_language_changed(self._retranslate)
+        self.refresh()
+
+    def _retranslate(self) -> None:
+        self._title.setText(tr("dashboard.title"))
+        self.refresh_btn.setToolTip(tr("dashboard.refresh_tooltip"))
+        self.token_cards.retranslate()
+        self.chart.retranslate()
+        self.habits.retranslate()
+        self.refresh()
+
+    def refresh(self, *_a) -> None:
+        start, end = self.chart.period_range()
+        self.token_cards.refresh(start, end)
+        self.chart.refresh()
+        self.habits.refresh(start, end)
+
+
+__all__ = ["DashboardTab"]

presentation/dashboard/habits_widget.py

@@ -0,0 +1,171 @@
+"""HabitsWidget — the usage-habits summary + AI recommendations panel of the
+Dashboard (R08-T13, extracted from ``ui/dashboard_tab.py::DashboardTab``,
+lines 154-184/348-372/376-438 of the original 437-line file: the habits/AI
+layout, ``refresh()``'s habits-HTML section, ``_apply_saving_strategy``,
+``_ai_analyze``).
+"""
+from __future__ import annotations
+
+from datetime import date
+from typing import List, Optional
+
+from PySide6.QtWidgets import QHBoxLayout, QLabel, QPushButton, QTextBrowser, QVBoxLayout, QWidget
+from PySide6.QtCore import Signal
+
+from cowork_local.application.monitoring import DashboardQueryService
+from cowork_local.core.worker import AgentWorker
+from cowork_local.i18n import tr
+from cowork_local.ui.icons import icon
+from cowork_local.ui.widgets import fmt_tokens
+
+
+class HabitsWidget(QWidget):
+    status_message = Signal(str)
+
+    def __init__(self, ctx, query: DashboardQueryService, parent=None):
+        super().__init__(parent)
+        self.ctx = ctx
+        self._query = query
+        self._ai_worker: Optional[AgentWorker] = None
+        self._period_range = (None, None)   # set on each refresh(); _ai_analyze reuses it
+
+        root = QVBoxLayout(self)
+        root.setContentsMargins(0, 0, 0, 0)
+        self._habits_title = QLabel()
+        self._habits_title.setStyleSheet("font-weight:600;")
+        habits_head = QHBoxLayout()
+        self.ai_analyze_btn = QPushButton()
+        self.ai_analyze_btn.setIcon(icon("sparkle"))
+        self.ai_analyze_btn.clicked.connect(self._ai_analyze)
+        # Apply an AI-suggested cost-saving strategy — only after the user
+        # clicks to approve it.
+        self.apply_strategy_btn = QPushButton()
+        self.apply_strategy_btn.setIcon(icon("bolt"))
+        self.apply_strategy_btn.setVisible(False)
+        self.apply_strategy_btn.clicked.connect(self._apply_saving_strategy)
+        habits_head.addWidget(self._habits_title, 1)
+        habits_head.addWidget(self.apply_strategy_btn)
+        habits_head.addWidget(self.ai_analyze_btn)
+        root.addLayout(habits_head)
+        self.habits = QTextBrowser()
+        self.habits.setOpenExternalLinks(False)
+        self.habits.setMinimumHeight(160)
+        root.addWidget(self.habits, 1)
+        self._ai_title = QLabel()
+        self._ai_title.setStyleSheet("font-weight:600;")
+        self._ai_title.setVisible(False)
+        root.addWidget(self._ai_title)
+        self.ai_advice = QTextBrowser()
+        self.ai_advice.setOpenExternalLinks(False)
+        self.ai_advice.setMinimumHeight(140)
+        self.ai_advice.setVisible(False)
+        root.addWidget(self.ai_advice, 1)
+
+        self.retranslate()
+
+    def retranslate(self) -> None:
+        self.ai_analyze_btn.setText(tr("dashboard.ai_analyze_btn"))
+        self.ai_analyze_btn.setToolTip(tr("dashboard.ai_analyze_tooltip"))
+        self.apply_strategy_btn.setText(tr("dashboard.strategy_btn"))
+        self.apply_strategy_btn.setToolTip(tr("dashboard.strategy_tooltip"))
+        self._habits_title.setText(tr("dashboard.habits_title"))
+
+    def refresh(self, start: date, end: date) -> None:
+        self._period_range = (start, end)
+        summary = self._query.summary(start, end)
+        s, events = summary["stats"], summary["events"]
+
+        lines: List[str] = []
+        if not events:
+            lines.append(f"<i>{tr('dashboard.no_data')}</i>")
+        else:
+            lines.append(f"<b>{tr('dashboard.h_top')}</b>")
+            lines.append("<ol>")
+            for label, tok in s["top_labels"]:
+                pct = int(tok * 100 / s["total"]) if s["total"] else 0
+                lines.append(f"<li>{label[:60]} — {fmt_tokens(tok)} tokens ({pct}%)</li>")
+            lines.append("</ol>")
+            src_parts = ", ".join(
+                f"{tr(f'app.tab.{k}') if k in ('cowork', 'code') else k}: {fmt_tokens(v)}"
+                for k, v in s["by_source"])
+            lines.append(f"<b>{tr('dashboard.h_by_source')}</b>: {src_parts}<br>")
+            lines.append(f"<b>{tr('dashboard.h_avg')}</b>: "
+                         f"{fmt_tokens(s['avg_per_turn'])} tokens<br>")
+            if s["busiest_day"]:
+                lines.append(f"<b>{tr('dashboard.h_busiest_day')}</b>: {s['busiest_day']}<br>")
+            if s["busiest_hour"] is not None:
+                lines.append(f"<b>{tr('dashboard.h_busiest_hour')}</b>: "
+                             f"{s['busiest_hour']:02d}:00–{s['busiest_hour']:02d}:59<br>")
+            if s["estimated_share"] > 0:
+                lines.append(f"<i>{tr('dashboard.estimated_note', pct=int(s['estimated_share'] * 100))}</i>")
+        self.habits.setHtml("".join(lines))
+
+    def _apply_saving_strategy(self) -> None:
+        """Apply an AI-suggested cost-saving strategy AFTER the user
+        approves: turn on auto-compress and compress earlier (lower
+        threshold) + compress content before sending it to the agent."""
+        from PySide6.QtWidgets import QMessageBox
+        if QMessageBox.question(self, tr("dashboard.strategy_title"),
+                                tr("dashboard.strategy_confirm")) != QMessageBox.Yes:
+            return
+        cx = self.ctx.config.data.setdefault("context", {})
+        cx["auto_compact"] = True
+        cx["compact_threshold"] = 0.6          # compress at 60% of the window (was ~80%)
+        cx["compress_before_send"] = True      # digest context before each turn
+        self.ctx.save()
+        self.status_message.emit(tr("dashboard.strategy_applied"))
+
+    def _ai_analyze(self) -> None:
+        """✨ Send the aggregated numbers (never raw prompt text) to the
+        active provider and show habit feedback + token-saving
+        recommendations."""
+        if self._ai_worker is not None:
+            return
+        start, end = self._period_range
+        if start is None:
+            return
+        summary = self._query.summary(start, end)
+        if not summary["events"]:
+            self.status_message.emit(tr("dashboard.no_data"))
+            return
+        stats = summary["stats"]
+        self.ai_analyze_btn.setEnabled(False)
+        self.ai_analyze_btn.setText(tr("dashboard.ai_analyzing"))
+        ctx = self.ctx
+
+        def job(worker: AgentWorker):
+            from cowork_local.core import usage_tracker as ut
+            from cowork_local.i18n import get_language
+
+            prompt = ut.build_ai_analysis_prompt(stats, get_language())
+            provider = ctx.build_active_provider()
+            reply = provider.chat([{"role": "user", "content": prompt}],
+                                  cancel=worker.stop_event)
+            return {"text": (reply.get("content") or "").strip()}
+
+        def done(result: dict) -> None:
+            self._ai_worker = None
+            self.ai_analyze_btn.setEnabled(True)
+            self.ai_analyze_btn.setText(tr("dashboard.ai_analyze_btn"))
+            text = result.get("text") or ""
+            if text:
+                self._ai_title.setText(tr("dashboard.ai_advice_title"))
+                self._ai_title.setVisible(True)
+                self.ai_advice.setMarkdown(text)
+                self.ai_advice.setVisible(True)
+                self.apply_strategy_btn.setVisible(True)
+
+        def failed(err: str) -> None:
+            self._ai_worker = None
+            self.ai_analyze_btn.setEnabled(True)
+            self.ai_analyze_btn.setText(tr("dashboard.ai_analyze_btn"))
+            self.status_message.emit(str(err))
+
+        w = AgentWorker(job)
+        w.finished_ok.connect(done)
+        w.failed.connect(failed)
+        self._ai_worker = w
+        w.start()
+
+
+__all__ = ["HabitsWidget"]

presentation/dashboard/token_usage_card_widget.py

@@ -0,0 +1,108 @@
+"""TokenUsageCardWidget — the stat-card grid + budget card of the Dashboard
+(R08-T13, extracted from ``ui/dashboard_tab.py::DashboardTab``, lines
+116-141/226-254/337-346 of the original 437-line file: the card grid layout,
+``_apply_budget``, ``_refresh_budget``, and ``refresh()``'s card-filling
+section).
+"""
+from __future__ import annotations
+
+from datetime import date
+
+from PySide6.QtWidgets import QGridLayout, QWidget
+
+from cowork_local.application.monitoring import DashboardQueryService
+from cowork_local.i18n import tr
+from cowork_local.ui.icons import icon
+from cowork_local.ui.widgets import BudgetCard, StatCard, fmt_tokens
+
+
+class TokenUsageCardWidget(QWidget):
+    """Cost is the headline this screen exists for, so it gets a card twice
+    the height of the rest instead of being the fifth of five identical
+    tiles — with six equal cards nothing said which number mattered."""
+
+    def __init__(self, ctx, query: DashboardQueryService, parent=None):
+        super().__init__(parent)
+        self.ctx = ctx
+        self._query = query
+
+        cards_grid = QGridLayout(self)
+        cards_grid.setSpacing(8)
+        self.card_total = StatCard()
+        self.card_in = StatCard()
+        self.card_out = StatCard()
+        self.card_cache = StatCard()
+        self.card_cost = StatCard().as_hero()
+        # Hero on the left, spanning both rows; the four supporting figures
+        # fill a 2x2 block beside it.
+        cards_grid.addWidget(self.card_cost, 0, 0, 2, 1)
+        for i, card in enumerate((self.card_total, self.card_in,
+                                  self.card_out, self.card_cache)):
+            cards_grid.addWidget(card, i // 2, 1 + i % 2)
+        # Budget: remaining/budget, direct entry, auto-warns red past 85% used.
+        self.budget_card = BudgetCard()
+        self.budget_card.apply_btn.setIcon(icon("check"))
+        self.budget_card.apply_btn.clicked.connect(self._apply_budget)
+        cards_grid.addWidget(self.budget_card, 0, 3, 2, 1)
+        for col, stretch in ((0, 3), (1, 2), (2, 2), (3, 3)):
+            cards_grid.setColumnStretch(col, stretch)
+
+        self.retranslate()
+
+    def retranslate(self) -> None:
+        self.budget_card.apply_btn.setToolTip(tr("usage.budget_apply_tooltip"))
+        self.budget_card.budget_spin.setToolTip(tr("usage.budget_spin_tooltip"))
+
+    def refresh(self, start: date, end: date) -> None:
+        summary = self._query.summary(start, end)
+        s, pricing, costs = summary["stats"], summary["pricing"], summary["costs"]
+        from cowork_local.core import usage_tracker as ut
+
+        est_note = (tr("dashboard.estimated_note", pct=int(s["estimated_share"] * 100))
+                    if s["estimated_share"] > 0 else "")
+        self.card_total.set(tr("dashboard.card_total"), fmt_tokens(s["total"]),
+                            tr("dashboard.card_turns", n=s["turns"]))
+        self.card_in.set(tr("dashboard.card_in"), fmt_tokens(s["in"]),
+                         ut.format_cost(costs["in"], pricing))
+        self.card_out.set(tr("dashboard.card_out"), fmt_tokens(s["out"]),
+                          ut.format_cost(costs["out"], pricing))
+        self.card_cache.set(tr("dashboard.card_cache"), fmt_tokens(s["cache"]),
+                            ut.format_cost(costs["cache"], pricing))
+        self.card_cost.set(tr("dashboard.card_cost"),
+                           ut.format_cost(summary["total_cost"], pricing, digits=2), est_note)
+        self._refresh_budget()
+
+    def _apply_budget(self) -> None:
+        """Persist the spin box's value as the new budget — starts a fresh
+        remaining-balance window (spend before now is no longer counted)."""
+        ccy = (self.ctx.config.data.get("usage") or {}).get("currency", "USD")
+        self._query.set_budget(self.budget_card.budget_spin.value(), ccy)
+        self.ctx.save()
+        self._refresh_budget()
+
+    def _refresh_budget(self) -> None:
+        from cowork_local.core import model_pricing as mp
+        from cowork_local.core import usage_tracker as ut
+
+        pricing = self._query.pricing()
+        status = self._query.budget_status()
+        if status is None:
+            self.budget_card.set(tr("usage.budget_title"), "—", tr("usage.budget_no_budget"))
+            self.budget_card.budget_spin.setValue(0.0)
+            return
+        remaining_disp = mp.convert(status["remaining_usd"], "USD",
+                                    pricing.get("currency", "USD"), self.ctx.config)
+        amount_disp = mp.convert(status["amount_usd"], "USD",
+                                 pricing.get("currency", "USD"), self.ctx.config)
+        value = (f"{ut.format_cost(status['remaining_usd'], pricing, digits=2)}"
+                 f" / {ut.format_cost(status['amount_usd'], pricing, digits=2)}")
+        pct = int(round(status["pct_used"] * 100))
+        sub = tr("usage.budget_over_warning") if status["over_85"] else tr("usage.budget_used_pct", pct=pct)
+        self.budget_card.set(tr("usage.budget_title"), value, sub, warn=status["over_85"])
+        # keep the entry field showing the CURRENT budget (in display currency)
+        # — only when it doesn't already have unsaved focus/edits from the user.
+        if not self.budget_card.budget_spin.hasFocus():
+            self.budget_card.budget_spin.setValue(round(amount_disp, 2))
+
+
+__all__ = ["TokenUsageCardWidget"]

presentation/dashboard/usage_chart_widget.py

@@ -0,0 +1,179 @@
+"""UsageChartWidget — the period pager + granularity/metric/currency
+controls + spline chart of the Dashboard (R08-T13, extracted from
+``ui/dashboard_tab.py::DashboardTab``, lines 53-114/143-152/201-207/
+263-323 of the original 437-line file).
+
+Owns the period SELECTOR (granularity + prev/next offset) that the whole
+screen follows — ``token_usage_card_widget.py`` and ``habits_widget.py``
+read :meth:`period_range`/:meth:`granularity` rather than keeping their own
+copy, and the shell re-refreshes them on :attr:`period_changed`.
+"""
+from __future__ import annotations
+
+from typing import Tuple
+
+from PySide6.QtCore import Qt, Signal
+from PySide6.QtWidgets import QComboBox, QHBoxLayout, QLabel, QPushButton, QVBoxLayout, QWidget
+
+from cowork_local.application.monitoring import DashboardQueryService
+from cowork_local.i18n import tr
+from cowork_local.theme import current_palette
+from cowork_local.ui.icons import icon
+from cowork_local.ui.spline_chart import SplineChart
+from cowork_local.ui.widgets import fmt_tokens
+
+
+class UsageChartWidget(QWidget):
+    period_changed = Signal()     # granularity or offset changed — re-run every widget
+    currency_changed = Signal()   # display currency changed — same, cost text depends on it
+
+    def __init__(self, ctx, query: DashboardQueryService, parent=None):
+        super().__init__(parent)
+        self.ctx = ctx
+        self._query = query
+        self._chart_offset = 0    # 0 = current period; <0 = a past period
+
+        root = QVBoxLayout(self)
+        root.setContentsMargins(0, 0, 0, 0)
+        controls = QHBoxLayout()
+        controls.setSpacing(6)
+        self.chart_prev_btn = QPushButton()
+        self.chart_prev_btn.setIcon(icon("chevron-left"))
+        self.chart_prev_btn.setFixedWidth(30)
+        self.chart_prev_btn.clicked.connect(self._chart_prev)
+        controls.addWidget(self.chart_prev_btn)
+        self._chart_period_lbl = QLabel()
+        self._chart_period_lbl.setObjectName("hint")
+        self._chart_period_lbl.setAlignment(Qt.AlignCenter)
+        self._chart_period_lbl.setMinimumWidth(170)
+        controls.addWidget(self._chart_period_lbl)
+        self.chart_next_btn = QPushButton()
+        self.chart_next_btn.setIcon(icon("chevron-right"))
+        self.chart_next_btn.setFixedWidth(30)
+        self.chart_next_btn.clicked.connect(self._chart_next)
+        controls.addWidget(self.chart_next_btn)
+        controls.addSpacing(12)
+        self.gran_combo = QComboBox()
+        for g in ("week", "month", "year"):
+            self.gran_combo.addItem(tr(f"dashboard.gran_{g}"), g)
+        self.gran_combo.currentIndexChanged.connect(self._on_gran_changed)
+        controls.addWidget(self.gran_combo)
+        self.metric_combo = QComboBox()
+        for m in ("cost", "tokens"):
+            self.metric_combo.addItem(tr(f"dashboard.metric_{m}"), m)
+        self.metric_combo.currentIndexChanged.connect(self.refresh)
+        controls.addWidget(self.metric_combo)
+        controls.addStretch(1)
+        # Display-currency picker — both Dashboard and Monitoring read/write
+        # the same usage.currency config key, so changing it here updates
+        # cost text everywhere.
+        self.currency_lbl = QLabel()
+        self.currency_lbl.setObjectName("hint")
+        controls.addWidget(self.currency_lbl)
+        self.currency_combo = QComboBox()
+        from cowork_local.core import usage_tracker as ut
+        for cur in ut.SUPPORTED_CURRENCIES:
+            self.currency_combo.addItem(cur, cur)
+        idx = self.currency_combo.findData(
+            (self.ctx.config.data.get("usage") or {}).get("currency", "USD"))
+        self.currency_combo.setCurrentIndex(max(0, idx))
+        self.currency_combo.currentIndexChanged.connect(self._on_currency_changed)
+        controls.addWidget(self.currency_combo)
+        root.addLayout(controls)
+
+        chart_head = QHBoxLayout()
+        self._chart_title = QLabel()
+        self._chart_title.setStyleSheet("font-weight:600;")
+        chart_head.addWidget(self._chart_title, 1)
+        root.addLayout(chart_head)
+        self.chart = SplineChart()
+        root.addWidget(self.chart)
+
+        self.retranslate()
+
+    def retranslate(self) -> None:
+        self.currency_lbl.setText(tr("monitoring.overview_currency"))
+        self.currency_combo.setToolTip(tr("dashboard.currency_tooltip"))
+        self._chart_title.setText(tr("dashboard.chart_title"))
+        self.chart_prev_btn.setToolTip(tr("dashboard.chart_prev"))
+        self.chart_next_btn.setToolTip(tr("dashboard.chart_next"))
+
+    # ---- public: the period selector every other widget follows ------------- #
+    def granularity(self) -> str:
+        return self.gran_combo.currentData() or "week"
+
+    @property
+    def chart_offset(self) -> int:
+        return self._chart_offset
+
+    def period_range(self) -> Tuple:
+        return self._query.period_range(self.granularity(), self._chart_offset)
+
+    # ---- navigation ------------------------------------------------------------ #
+    def _on_gran_changed(self, *_a) -> None:
+        self._chart_offset = 0            # period size changed → back to current
+        self.period_changed.emit()
+
+    def _chart_prev(self) -> None:
+        self._chart_offset -= 1
+        self.period_changed.emit()
+
+    def _chart_next(self) -> None:
+        self._chart_offset = min(0, self._chart_offset + 1)   # never past the present
+        self.period_changed.emit()
+
+    def _on_currency_changed(self, _idx: int) -> None:
+        cur = self.currency_combo.currentData()
+        if not cur:
+            return
+        self.ctx.config.data.setdefault("usage", {})["currency"] = cur
+        self.ctx.save()
+        self.currency_changed.emit()
+
+    @staticmethod
+    def _delta_txt(cur: float, prev: float) -> str:
+        """▲/▼ percent change of ``cur`` vs ``prev`` (empty if no baseline)."""
+        if not prev:
+            return ""
+        pct = (cur - prev) / prev * 100
+        arrow = "▲" if pct > 0.5 else ("▼" if pct < -0.5 else "•")
+        return f"{arrow}{abs(pct):.0f}%"
+
+    # ---- rendering --------------------------------------------------------------- #
+    def refresh(self, *_a) -> None:
+        """Break the SELECTED period into its parts: WEEK -> 7 days (Mon-Sun)
+        - MONTH -> weeks W1..Wn - YEAR -> 12 months. A dashed line marks the
+        previous same-granularity period's average per point with the %
+        change of the totals."""
+        from cowork_local.core import usage_tracker as ut
+
+        gran = self.granularity()
+        metric = self.metric_combo.currentData() or "cost"
+        pts = self._query.chart_series(gran, self._chart_offset, metric)
+        pricing = self._query.pricing()
+        mi = 0 if metric == "tokens" else 1
+        # Compact cost format (2 decimals, K/M above 1,000/1,000,000) — the
+        # chart's y-axis label box is narrow; format_cost's full precision
+        # overflowed it, clipping/obscuring the amount.
+        fmt = fmt_tokens if metric == "tokens" else (lambda v: ut.format_cost_compact(v, pricing))
+
+        cur = self._query.period_totals(gran, self._chart_offset)
+        prev = self._query.period_totals(gran, self._chart_offset - 1)
+        ref_key = {"week": "dashboard.ref_last_week",
+                   "month": "dashboard.ref_last_month",
+                   "year": "dashboard.ref_last_year"}.get(gran, "dashboard.ref_last_week")
+        n_points = max(1, len(pts))
+        refs = []
+        if prev[mi] > 0:
+            # Muted on purpose: the comparison line is a reference, not the
+            # series — it must not compete with the accent-coloured spline.
+            refs.append((prev[mi] / n_points,
+                         f"{tr(ref_key)} {self._delta_txt(cur[mi], prev[mi])}",
+                         current_palette().text_muted))
+        self.chart.set_reference_lines(refs)
+        self.chart.set_data(pts, fmt, tr(f"dashboard.metric_{metric}"))
+        self._chart_period_lbl.setText(self._query.period_range_label(gran, self._chart_offset))
+        self.chart_next_btn.setEnabled(self._chart_offset < 0)
+
+
+__all__ = ["UsageChartWidget"]