fix: README structure and code quality nits

README.md

@@ -204,20 +204,22 @@ Add `V=1` for verbose output: `make check V=1`
 cli-tools/
 ├── src/
 │   └── copilot_usage/
-│       ├── cli.py          # Click commands + interactive loop + watchdog auto-refresh
-│       ├── models.py       # Pydantic data models
-│       ├── parser.py       # events.jsonl parsing
-│       ├── pricing.py      # Model cost multipliers
-│       ├── logging_config.py # Loguru configuration
-│       └── report.py       # Rich terminal output
+│       ├── cli.py              # Click commands + interactive loop + watchdog auto-refresh
+│       ├── models.py           # Pydantic data models
+│       ├── parser.py           # events.jsonl parsing
+│       ├── pricing.py          # Model cost multipliers
+│       ├── logging_config.py   # Loguru configuration
+│       ├── report.py           # Rich terminal output
+│       └── docs/               # Developer docs
+│           ├── architecture.md
+│           ├── changelog.md
+│           ├── implementation.md
+│           └── plan.md
 ├── tests/
-│   ├── copilot_usage/      # Unit tests
-│   └── e2e/                # End-to-end tests with fixtures
+│   ├── copilot_usage/          # Unit tests
+│   └── e2e/                    # End-to-end tests with fixtures
 ├── docs/
-│   ├── plan.md
-│   ├── architecture.md
-│   ├── changelog.md
-│   └── implementation.md
+│   └── changelog.md            # Top-level changelog
 ├── Makefile
 └── pyproject.toml
 ```

src/copilot_usage/cli.py

@@ -388,20 +388,11 @@ def cost(
     try:
         sessions = get_all_sessions(path)
 
-        # Filter by date range
-        since_aware = _ensure_aware(since)
-        until_aware = _ensure_aware(until)
-        filtered = sessions
-        if since_aware is not None or until_aware is not None:
-            filtered = [
-                s
-                for s in sessions
-                if s.start_time is not None
-                and (since_aware is None or s.start_time >= since_aware)
-                and (until_aware is None or s.start_time <= until_aware)
-            ]
-
-        render_cost_view(filtered)
+        render_cost_view(
+            sessions,
+            since=_ensure_aware(since),
+            until=_ensure_aware(until),
+        )
     except Exception as exc:  # noqa: BLE001
         click.echo(f"Error: {exc}", err=True)
         sys.exit(1)

src/copilot_usage/report.py

@@ -848,14 +848,18 @@ def render_full_summary(
 def render_cost_view(
     sessions: list[SessionSummary],
     *,
+    since: datetime | None = None,
+    until: datetime | None = None,
     target_console: Console | None = None,
 ) -> None:
     """Render per-session, per-model cost breakdown.
 
+    Filters sessions by date range when *since* and/or *until* are given.
     For active sessions, appends a "↳ Since last shutdown" row with N/A
     for premium and the active model calls / output tokens.
     """
     console = target_console or Console()
+    sessions = _filter_sessions(sessions, since, until)
 
     if not sessions:
         console.print("[yellow]No sessions found.[/yellow]")

tests/copilot_usage/test_report.py

@@ -1134,11 +1134,15 @@ def test_no_historical_data(self) -> None:
 # ---------------------------------------------------------------------------
 
 
-def _capture_cost_view(sessions: list[SessionSummary]) -> str:
+def _capture_cost_view(
+    sessions: list[SessionSummary],
+    since: datetime | None = None,
+    until: datetime | None = None,
+) -> str:
     """Capture Rich output from render_cost_view to a plain string."""
     buf = StringIO()
     console = Console(file=buf, force_terminal=True, width=120)
-    render_cost_view(sessions, target_console=console)
+    render_cost_view(sessions, since=since, until=until, target_console=console)
     return buf.getvalue()
 
 
@@ -1321,3 +1325,15 @@ def test_historical_model_table_present(self) -> None:
         output = _capture_full_summary([session])
         assert "Per-Model Breakdown" in output
         assert "claude-sonnet-4" in output
+
+    def test_since_until_filters_sessions(self) -> None:
+        """render_cost_view since/until params exclude sessions outside range."""
+        early = _make_session(
+            start_time=datetime(2025, 1, 10, tzinfo=UTC), name="Early"
+        )
+        late = _make_session(start_time=datetime(2025, 1, 20, tzinfo=UTC), name="Late")
+        since = datetime(2025, 1, 15, tzinfo=UTC)
+        until = datetime(2025, 1, 25, tzinfo=UTC)
+        output = _capture_cost_view([early, late], since=since, until=until)
+        assert "Late" in output
+        assert "Early" not in output