vNext: Fix DST Chart Handling and Add Configurable User Timezones

backend/alembic/versions/c8d1e2f3a4b5_add_timezone_configured_to_usersettings.py

@@ -0,0 +1,39 @@
+"""add timezone_configured to usersettings
+
+Revision ID: c8d1e2f3a4b5
+Revises: b4c5d6e7f8a9
+Create Date: 2026-11-03 00:00:00.000000
+
+"""
+from typing import Sequence, Union
+
+from alembic import op
+import sqlalchemy as sa
+
+
+revision: str = "c8d1e2f3a4b5"
+down_revision: Union[str, Sequence[str], None] = "b4c5d6e7f8a9"
+branch_labels: Union[str, Sequence[str], None] = None
+depends_on: Union[str, Sequence[str], None] = None
+
+
+def upgrade() -> None:
+    op.add_column(
+        "usersettings",
+        sa.Column(
+            "timezone_configured",
+            sa.Boolean(),
+            nullable=False,
+            server_default=sa.false(),
+        ),
+    )
+    # Preserve the old behaviour for existing accounts: a non-UTC value was
+    # either picked by the user or already auto-detected, while the UTC default
+    # still needs the one-time detection on the next login.
+    op.execute("UPDATE usersettings SET timezone_configured = true WHERE timezone != 'UTC'")
+
+
+def downgrade() -> None:
+    # The explicit-choice bit cannot be reconstructed by a later upgrade:
+    # UTC rows are treated as unconfigured again and re-detected once.
+    op.drop_column("usersettings", "timezone_configured")

backend/app/models.py

@@ -219,6 +219,10 @@ class UserSettings(SQLModel, table=True):
     user_id: int = Field(foreign_key="user.id", unique=True, index=True)
     language: str = Field(default="en", max_length=10)
     timezone: str = Field(default="UTC", max_length=64)
+    # False means the account still uses the default and the login/OIDC flows
+    # may replace it with the detected zone. True means the stored zone is
+    # authoritative, even when it is UTC.
+    timezone_configured: bool = Field(default=False)
     theme: str = Field(default="light", max_length=20)
     custom_theme: Optional[str] = Field(default=None, max_length=30)
     goal_pages_per_day_enabled: bool = Field(default=False)

backend/app/routers/profile.py

@@ -312,6 +312,7 @@ def get_settings(
         user_id=settings.user_id,
         language=settings.language,
         timezone=settings.timezone,
+        timezone_configured=settings.timezone_configured,
         theme=settings.theme,
         custom_theme=settings.custom_theme,
         goal_pages_per_day_enabled=settings.goal_pages_per_day_enabled,
@@ -357,6 +358,8 @@ def update_settings(
     if custom_from is not None and custom_to is not None and (custom_to - custom_from).days > MAX_CUSTOM_RANGE_DAYS:
         raise HTTPException(status_code=422, detail="Statistics custom range cannot exceed 25 years")
     settings.sqlmodel_update(update_data)
+    if update_data.get("timezone") is not None:
+        settings.timezone_configured = update_data.get("timezone_configured", True)
     if settings.theme != 'custom':
         settings.custom_theme = None
     session.add(settings)
@@ -367,6 +370,7 @@ def update_settings(
         user_id=settings.user_id,
         language=settings.language,
         timezone=settings.timezone,
+        timezone_configured=settings.timezone_configured,
         theme=settings.theme,
         custom_theme=settings.custom_theme,
         goal_pages_per_day_enabled=settings.goal_pages_per_day_enabled,

backend/app/schemas.py

@@ -4,6 +4,7 @@
 from datetime import date, datetime
 from enum import Enum
 from typing import Literal
+from zoneinfo import ZoneInfo, ZoneInfoNotFoundError
 
 from pydantic import BaseModel, field_validator, model_validator
 import pydantic
@@ -548,6 +549,7 @@ class UserSettingsRead(SQLModel):
     user_id: int
     language: str
     timezone: str
+    timezone_configured: bool
     theme: str
     custom_theme: Optional[str] = None
     goal_pages_per_day_enabled: bool
@@ -570,6 +572,7 @@ class UserSettingsUpdate(SQLModel):
     """User settings update request."""
     language: Optional[str] = None
     timezone: Optional[str] = None
+    timezone_configured: Optional[bool] = None
     theme: Optional[str] = None
     custom_theme: Optional[str] = None
     goal_pages_per_day_enabled: Optional[bool] = None
@@ -594,6 +597,24 @@ def validate_date_automation_setting(cls, value: Optional[bool]) -> Optional[boo
             raise ValueError("Reading date automation settings cannot be null")
         return value
 
+    @field_validator("timezone")
+    @classmethod
+    def validate_timezone(cls, value: Optional[str]) -> Optional[str]:
+        if value is None:
+            raise ValueError("timezone cannot be null")
+        try:
+            ZoneInfo(value)
+        except (ZoneInfoNotFoundError, ValueError):
+            raise ValueError("timezone must be a valid IANA zone name")
+        return value
+
+    @field_validator("timezone_configured")
+    @classmethod
+    def validate_timezone_configured(cls, value: Optional[bool]) -> Optional[bool]:
+        if value is None:
+            raise ValueError("timezone_configured cannot be null")
+        return value
+
     @field_validator('theme')
     @classmethod
     def validate_theme(cls, v: Optional[str]) -> Optional[str]:

backend/tests/test_auth_profile_users.py

@@ -220,6 +220,7 @@ def test_profile_settings_get_and_update(client: TestClient) -> None:
     assert current.status_code == 200
     assert current.json()["language"] == "en"
     assert current.json()["timezone"] == "UTC"
+    assert current.json()["timezone_configured"] is False
     assert current.json()["theme"] == "light"
     assert current.json()["custom_theme"] is None
 
@@ -231,6 +232,7 @@ def test_profile_settings_get_and_update(client: TestClient) -> None:
     tz_updated = client.patch("/api/profile/settings", json={"timezone": "Europe/Berlin"})
     assert tz_updated.status_code == 200
     assert tz_updated.json()["timezone"] == "Europe/Berlin"
+    assert tz_updated.json()["timezone_configured"] is True
 
     theme_updated = client.patch("/api/profile/settings", json={"theme": "dark"})
     assert theme_updated.status_code == 200
@@ -243,6 +245,69 @@ def test_profile_settings_get_and_update(client: TestClient) -> None:
     assert custom_updated.json()["custom_theme"] == "dracula"
 
 
+def test_profile_settings_explicit_utc_marks_timezone_configured(client: TestClient) -> None:
+    current = client.get("/api/profile/settings")
+    assert current.status_code == 200
+    assert current.json()["timezone"] == "UTC"
+    assert current.json()["timezone_configured"] is False
+
+    updated = client.patch("/api/profile/settings", json={"timezone": "UTC"})
+    assert updated.status_code == 200
+    assert updated.json()["timezone"] == "UTC"
+    assert updated.json()["timezone_configured"] is True
+
+    reloaded = client.get("/api/profile/settings")
+    assert reloaded.status_code == 200
+    assert reloaded.json()["timezone_configured"] is True
+
+
+def test_profile_settings_rejects_invalid_timezone(client: TestClient) -> None:
+    for value in ("", "Not/AZone", None):
+        response = client.patch("/api/profile/settings", json={"timezone": value})
+        assert response.status_code == 422, value
+
+
+def test_profile_settings_keep_configured_flag_without_timezone(client: TestClient) -> None:
+    client.patch("/api/profile/settings", json={"timezone": "America/New_York"})
+
+    updated = client.patch("/api/profile/settings", json={"language": "de"})
+    assert updated.status_code == 200
+    assert updated.json()["timezone"] == "America/New_York"
+    assert updated.json()["timezone_configured"] is True
+
+
+def test_profile_settings_reject_null_timezone_configured(client: TestClient) -> None:
+    response = client.patch("/api/profile/settings", json={"timezone_configured": None})
+    assert response.status_code == 422
+
+
+def test_profile_settings_can_return_to_automatic_timezone(client: TestClient) -> None:
+    client.patch("/api/profile/settings", json={"timezone": "UTC"})
+    pinned = client.get("/api/profile/settings").json()
+    assert pinned["timezone_configured"] is True
+
+    reset = client.patch(
+        "/api/profile/settings",
+        json={"timezone": "America/New_York", "timezone_configured": False},
+    )
+    assert reset.status_code == 200
+    assert reset.json()["timezone"] == "America/New_York"
+    assert reset.json()["timezone_configured"] is False
+
+    reloaded = client.get("/api/profile/settings").json()
+    assert reloaded["timezone"] == "America/New_York"
+    assert reloaded["timezone_configured"] is False
+
+
+def test_profile_settings_flag_resets_without_changing_timezone(client: TestClient) -> None:
+    client.patch("/api/profile/settings", json={"timezone": "America/New_York"})
+
+    reset = client.patch("/api/profile/settings", json={"timezone_configured": False})
+    assert reset.status_code == 200
+    assert reset.json()["timezone"] == "America/New_York"
+    assert reset.json()["timezone_configured"] is False
+
+
 def test_profile_api_key_lifecycle(client: TestClient) -> None:
     listed = client.get("/api/profile/api-keys")
     assert listed.status_code == 200

backend/tests/test_profile.py

@@ -42,6 +42,7 @@ def test_get_settings_creates_default_when_missing(client: TestClient, session:
     data = resp.json()
     assert data["language"] == "en"
     assert data["user_id"] == user.id
+    assert data["timezone_configured"] is False
     assert data["auto_set_date_started"] is True
     assert data["auto_set_date_finished"] is True
 
@@ -70,6 +71,7 @@ def test_update_settings_creates_default_when_missing(client: TestClient, sessio
     data = resp.json()
     assert data["language"] == "de"
     assert data["user_id"] == user.id
+    assert data["timezone_configured"] is False
 
 
 def test_statistics_range_settings_are_persisted(client: TestClient) -> None:

docs/guide/database-layout.md

@@ -164,6 +164,7 @@ erDiagram
         integer user_id UK
         varchar(10) language
         varchar(64) timezone
+        boolean timezone_configured
         varchar(20) theme
         varchar(30) custom_theme
         boolean goal_pages_per_day_enabled
@@ -417,6 +418,7 @@ Per-user settings such as language, timezone, and theme.
 | `user_id` | `INTEGER` | FK → user.id, UNIQUE, NOT NULL |  |
 | `language` | `VARCHAR(10)` | NOT NULL | default `en` |
 | `timezone` | `VARCHAR(64)` | NOT NULL | default `UTC` |
+| `timezone_configured` | `BOOLEAN` | NOT NULL | default False; true once a timezone was saved explicitly, false means automatic detection on login |
 | `theme` | `VARCHAR(20)` | NOT NULL | default `light` |
 | `custom_theme` | `VARCHAR(30)` |  |  |
 | `goal_pages_per_day_enabled` | `BOOLEAN` | NOT NULL | default False |
@@ -434,6 +436,8 @@ Per-user settings such as language, timezone, and theme.
 | `statistics_custom_from` | `DATE` |  |  |
 | `statistics_custom_to` | `DATE` |  |  |
 
+On upgrade, existing non-UTC values are marked as configured, including values that were auto-detected before this flag existed. Rows still on the `UTC` default remain in automatic detection.
+
 ### `book_author`
 
 Many-to-many association between books and authors.

docs/guide/using-librislog/profile.md

@@ -55,7 +55,7 @@ Switch the UI language between available locales. The change applies immediately
 
 ## Timezone
 
-Set your preferred timezone for date/time displays (e.g., for the calendar heatmap and progress log timestamps). Your browser's detected timezone is shown as a reference.
+Set your preferred timezone for date/time displays (e.g., for the calendar heatmap and progress log timestamps). Your browser's detected timezone is shown as a reference. Saving a timezone pins that choice, including UTC, so the app will not replace it with the detected zone on the next login. Use **Use detected timezone** to switch back to automatic detection, which follows the browser's zone on each login. Accounts that never saved a timezone follow the detected zone automatically.
 
 ## Theme
 

docs/releases.md

@@ -8,14 +8,15 @@ You can also browse the [GitHub Releases](https://github.com/codebude/librislog/
 
 ## Latest Release
 
-::: tip ⭐ v1.12.0 - Mass Tag Editor, Profile Pictures & Authentication Methods
-LibrisLog v1.12.0 adds a Mass Tag Editor page for adding or removing tags on many books at once, and profile pictures with three selectable sources: the existing animal avatar, a locally cached OIDC picture, and a manually uploaded image with a built-in cropper. Public profiles gain a separate profile picture toggle. It also adds two opt-in authentication options: password login can be disabled once single sign-on is in use, and a trusted reverse proxy can sign users in from a forwarded header. Existing accounts keep their animal avatar and existing share links stay unchanged after upgrading, and the new options need no manual data migration.
+::: tip ⭐ v1.12.1 - DST Chart & Timezone Fixes
+LibrisLog v1.12.1 fixes a browser freeze in the book detail view. When a book's reading progress chart crossed a daylight-saving fall-back in the user's profile time zone, the chart's time axis could loop forever and lock up the page. Time steps now keep advancing across the transition, day, week, and month ticks stay on their local calendar boundaries, and an explicitly chosen UTC timezone is no longer replaced with the detected zone on the next login. The timezone card also has a **Use detected timezone** button to switch back to automatic detection. The new timezone flag is added by an automatic database migration.
 :::
 
 ### All releases
 
 | Version | Date | Type |
 |---|---|---|
+| [v1.12.1](#v1-12-1-dst-chart-timezone-fixes) | 2026-11-03 | Maintenance |
 | [v1.12.0](#v1-12-0-mass-tag-editor-profile-pictures-authentication-methods) | 2026-11-02 | Feature release |
 | [v1.11.0](#v1-11-0-reading-sessions-re-reads) | 2026-10-24 | Feature release |
 | [v1.10.0](#v1-10-0-more-book-sources-upgrades) | 2026-10-18 | Feature release |
@@ -38,6 +39,26 @@ LibrisLog v1.12.0 adds a Mass Tag Editor page for adding or removing tags on man
 
 ---
 
+## v1.12.1: DST Chart & Timezone Fixes
+
+<Badge type="info" text="Maintenance" /> <Badge type="info" text="2026-11-03" />
+
+**Summary:** LibrisLog v1.12.1 fixes a browser freeze in the book detail view when a book's reading progress chart spans a daylight-saving fall-back in the profile time zone. Sub-day time steps now run on the UTC timeline, so tick generation always completes, and day, week, and month steps keep their local wall-clock time, so calendar ticks no longer drift after a transition. It also keeps an explicitly chosen UTC profile timezone instead of replacing it with the detected zone on the next login, and adds a **Use detected timezone** button that switches an account back to automatic detection.
+
+**Bug fixes**
+- 🕒 **No more freeze across a DST fall-back.** When the device and profile time zones were the same zone that observes daylight saving, a time step inside the repeated hour could stall or move backwards. Chart.js then kept generating ticks forever, which froze the book detail dialog in Firefox and Chromium-based browsers. Millisecond, second, minute, and hour steps now use the UTC epoch value, so they always move forward. Hour ticks still start on local hour boundaries and show the repeated hour correctly when ticks are hourly, for example 1AM twice.
+- 📅 **Calendar ticks stay aligned.** Day, week, month, quarter, and year steps now keep the local wall-clock time instead of adding a fixed number of milliseconds, so day and month ticks no longer land at 23:00 or drift into the wrong month after a DST change.
+- 🌍 **Explicit UTC choice is kept.** The timezone picker now offers UTC in every browser, including Chromium-based ones that omit it from `Intl.supportedValuesOf`. The login and OIDC callback used to treat a stored UTC value as "not configured" and replaced it with the detected zone. Saving any timezone now marks it as explicitly chosen, so UTC stays UTC. Existing accounts keep their current behaviour: non-UTC values are untouched, and a legacy UTC default follows the detected zone on login.
+- 🔄 **Back to automatic detection.** The timezone card has a **Use detected timezone** button that saves the browser's zone and switches the account back to automatic detection, which follows the browser on each login. Saving a zone still pins it, including UTC.
+- 🛡️ **Invalid timezones are rejected.** Saving an empty or unknown timezone name now returns a validation error instead of storing a value that breaks date rendering.
+- 🧪 **Regression coverage.** A new test pins the device and profile time zones to `America/New_York` and covers fall-back and spring-forward tick sequences, monotonic time steps, local `startOf` and `endOf` boundaries, non-whole-hour zones, and calendar-unit steps. Login and OIDC callback tests cover unconfigured, explicitly chosen, and version-skew cases, and backend tests cover invalid input and switching back to automatic detection.
+
+**Breaking changes:** None. The new `timezone_configured` flag is added by an automatic database migration. `GET /api/profile/settings` gains one additive field, and `PATCH` accepts an optional `timezone_configured` flag to pin or reset automatic detection. `PATCH` now rejects empty or unknown timezone names with a validation error. Downgrading drops the explicit-choice bit, so a later upgrade treats UTC as unconfigured again.
+
+[Compare with v1.12.0](https://github.com/codebude/librislog/compare/v1.12.0...v1.12.1)
+
+---
+
 ## v1.12.0: Mass Tag Editor, Profile Pictures & Authentication Methods
 
 <Badge type="tip" text="Feature release" /> <Badge type="info" text="2026-11-02" />
@@ -103,7 +124,7 @@ LibrisLog v1.12.0 adds a Mass Tag Editor page for adding or removing tags on man
 
 **Breaking changes:** None. Existing installs keep working untouched: every book with a single session behaves and scores identically to before, and data migrates automatically on upgrade. Downgrading to a previous release drops re-read history (the `reading_session` table is removed).
 
-[Compare with v1.10.0](https://github.com/codebude/librislog/compare/v1.10.0...HEAD)
+[Compare with v1.10.0](https://github.com/codebude/librislog/compare/v1.10.0...v1.11.0)
 
 ---
 

frontend/src/lib/api.test.ts

@@ -263,6 +263,7 @@ describe('api.statistics.gamification', () => {
 				user_id: 1,
 				language: 'en',
 				timezone: 'UTC',
+				timezone_configured: true,
 				theme: 'light',
 				custom_theme: null,
 				goal_pages_per_day_enabled: true,

frontend/src/lib/api.ts

@@ -211,7 +211,7 @@ export const api = {
 			return request<UserSettings>('/profile/settings');
 		},
 
-		updateSettings(data: Partial<UserSettings>): Promise<UserSettings> {
+		updateSettings(data: Partial<Omit<UserSettings, 'user_id'>>): Promise<UserSettings> {
 			return request<UserSettings>('/profile/settings', {
 				method: 'PATCH',
 				body: JSON.stringify(data)