## Review 001: Session Endpoints and Models (sessions.py, models.py)

**Files reviewed:** src/backend/api/sessions.py, src/backend/models.py
**Verdict:** request-changes

### Findings

#### block: start_session 409 response doesn't include session data
**Location:** src/backend/api/sessions.py:48-52
**Quote:**

```
raise HTTPException(
    status_code=409,
    detail=f"Session already active (id={active.id})",
)
```

**Read:** When concurrent start is attempted, the code raises HTTPException with status 409 and a detail string. FastAPI serializes this to {"detail": "Session already active..."}, not as a session object.
**Concern:** The test test_concurrent_start_requests_return_409_on_second_attempt (test_session_001_start_and_complete.py:110) expects data["id"] in the 409 response. The current implementation returns {"detail": "..."}, so accessing data["id"] raises KeyError and the test fails.
**Request:** Return the full session dict with 409 status. Do not raise HTTPException. Instead, import JSONResponse and return JSONResponse(status_code=409, content=active.to_dict()). The client needs the session state to recover gracefully.

#### block: Model name 'Session' shadows sqlalchemy.orm.Session
**Location:** src/backend/models.py:19
**Quote:**

```
class Session(Base):
```

**Read:** The model class is named Session, but sqlalchemy.orm.Session (imported at line 9) is the ORM's connection manager. The code works around this collision by aliasing SessionModel in sessions.py, but the problem persists across the codebase.
**Concern:** Name shadowing is a maintainability hazard. Future readers will find 'Session' used in two conflicting ways. IDE autocompletion, grep, and documentation become harder to navigate. The model should have a distinct name that clarifies its domain.
**Request:** Rename the model class to clearly distinguish it from the ORM Session. Examples: FocusSession, PomodoroSession, SessionRecord. Avoid generic names that shadow stdlib or framework concepts. The name should self-document: a reader should understand what it is without cross-referencing imports.

#### block: Timezone handling in date queries ignores user config
**Location:** src/backend/api/sessions.py:162-175 (get_today_sessions), 208-210 (get_sessions_range)
**Quote:**

```
now = datetime.now(timezone.utc)
today_start = now.replace(hour=0, minute=0, second=0, microsecond=0)
```

**Read:** Both /sessions/today and /sessions/range use UTC midnight as the day boundary. But the Config model includes a configurable timezone field. The code fetches Config elsewhere (e.g., start_session line 53) but ignores it in date-boundary queries.
**Concern:** If a user in Asia/Tokyo (UTC+9) completes sessions at 11:59 PM and 12:01 AM (next day in Tokyo), the /sessions/today endpoint returns both even though one is 'tomorrow' in the user's timezone. This is a silent-wrongness bug: the user sees the wrong calendar date. The feature contract says users can configure their timezone; ignoring it violates that contract.
**Request:** Fetch the user's timezone from Config and compute day boundaries in user-local time, not UTC. Use Python's zoneinfo.ZoneInfo to convert. Example (pseudocode): tz = ZoneInfo(config.timezone); today_local = datetime.now(tz).date(); today_start_utc = datetime.combine(today_local, datetime.min.time(), tzinfo=tz).astimezone(timezone.utc). Apply the same fix to get_sessions_range lines 208-210.

#### change-required: start_session hardcodes current_elapsed_seconds instead of computing it
**Location:** src/backend/api/sessions.py:78
**Quote:**

```
"current_elapsed_seconds": 0,
```

**Read:** The response hardcodes current_elapsed_seconds as 0. But the SessionModel defines get_current_elapsed_seconds() (models.py:67) which computes actual elapsed time. This method is never called.
**Concern:** Contract drift: the model has a method to compute elapsed time correctly, but the endpoint hardcodes 0. This indicates either dead code or inconsistent response contracts. For start_session, elapsed is always near 0, so this is minor. But it suggests the method's purpose is unclear.
**Request:** Use session.get_current_elapsed_seconds() instead of hardcoding 0. Or, if the method is unnecessary, delete it from the model. Keep response computation consistent across all endpoints.

#### change-required: Session.to_dict() includes undocumented fields
**Location:** src/backend/models.py:46-58
**Quote:**

```
"created_at": self.created_at.isoformat() if self.created_at else None,
"updated_at": self.updated_at.isoformat() if self.updated_at else None,
```

**Read:** The to_dict() method returns created_at and updated_at. But the API contracts (endpoint docstrings and test scenarios) specify only: id, start_time, end_time, target_duration_seconds, duration_seconds, is_active, is_completed, is_deleted.
**Concern:** Bloat: the response includes undocumented fields that inflate response size and add noise to the API surface. If tests don't validate these fields, bugs in their computation won't be caught. Clients might accidentally rely on them, creating fragile dependencies.
**Request:** Remove created_at and updated_at from to_dict(). These are database metadata, not API contracts. If needed for debugging, create a separate .debug_dict() or log them server-side. Keep the API contract minimal and predictable.

#### suggestion: Magic numbers for config validation ranges
**Location:** src/backend/api/sessions.py:287-294
**Quote:**

```
if not isinstance(val, int) or val < 1 or val > 120:
    raise HTTPException(status_code=400, detail="session_length_minutes must be in [1, 120]")
...
if not isinstance(val, int) or val < 1 or val > 60:
    raise HTTPException(status_code=400, detail="break_length_minutes must be in [1, 60]")
```

**Read:** Config validation uses hardcoded numbers: 1, 120, 1, 60. These business rules are hidden in the code.
**Concern:** Maintainability: magic numbers hide intent. If requirements change (allow 180-minute sessions), the constant is hard to find. The hardcoded ranges are repeated in error messages, making them fragile.
**Request:** Define ranges as module-level constants at the top of sessions.py: SESSION_LENGTH_MIN = 1; SESSION_LENGTH_MAX = 120; BREAK_LENGTH_MIN = 1; BREAK_LENGTH_MAX = 60. Use these constants in validation and error messages. This makes constraints explicit and centralizes changes.

#### note: Idempotence language in docstring is uncertain
**Location:** src/backend/api/sessions.py:94
**Quote:**

```
Idempotent: if already completed, return 409 or 200 (accepting idempotency).
```

**Read:** The docstring contains 'or', indicating the author wasn't sure whether to return 409 or 200 for idempotent requests. The code returns 200 (implicit), and the test accepts either.
**Concern:** Uncertainty in the docstring is a clarity issue. A future reader won't know what the intended behavior is.
**Request:** Decide on one behavior: strict (409 Conflict: cannot complete twice) or lenient (200 OK: idempotent). For a timer app, lenient (200) is more user-friendly. Update the docstring to be definitive: 'If already completed, return 200 with the session (idempotent).'

### Approvals

- Error handling structure is solid: 404 for not found, 409 for conflicts, 400 for validation. Each error includes appropriate detail messages.
- Soft delete pattern (is_deleted field) is correctly implemented. Abandoned sessions are properly excluded from all relevant queries.
- Session state machine is correctly enforced: is_active and is_completed states transition correctly. Completed/deleted sessions are immutable.
- Query ordering (by start_time descending) is correct and matches feature expectations (newest-first in lists).
- Pagination in get_sessions_range is correct: offset=(page-1)*limit, with total_count reported so client knows if more pages exist.
- Config auto-initialization gracefully handles missing rows by creating defaults rather than crashing.

### Cross-domain references

- Frontend (Tweedledee) should be aware of the model name change recommendation (Session → FocusSession) to align on domain terminology.
- Timezone handling fix will affect frontend rendering of day boundaries. Changes to how 'today' is computed might require frontend updates.
