diff --git a/src/yc_bench/db/base.py b/src/yc_bench/db/base.py
new file mode 100644
index 0000000..e493d0b
--- /dev/null
+++ b/src/yc_bench/db/base.py
@@ -0,0 +1,11 @@
+from __future__ import annotations
+
+from sqlalchemy.orm import DeclarativeBase
+
+class Base(DeclarativeBase):
+    pass
+
+class TimestampMixin:
+    pass
+
+__all__ = ["Base", "TimestampMixin"]
\ No newline at end of file
diff --git a/src/yc_bench/db/models/company.py b/src/yc_bench/db/models/company.py
new file mode 100644
index 0000000..d6a6db1
--- /dev/null
+++ b/src/yc_bench/db/models/company.py
@@ -0,0 +1,61 @@
+from __future__ import annotations
+
+from decimal import Decimal
+from uuid import uuid4
+from enum import Enum
+
+from sqlalchemy import BigInteger, CheckConstraint, Enum as SAEnum, ForeignKey, Numeric, String, Uuid
+from sqlalchemy.orm import mapped_column
+
+from ..base import Base
+
+class Domain(str, Enum):
+    SYSTEM = "system"
+    RESEARCH = "research"
+    DATA = "data"
+    FRONTEND = "frontend"
+    BACKEND = "backend"
+    TRAINING = "training"
+    HARDWARE = "hardware"
+
+class Company(Base):
+    __tablename__ = "companies"
+
+    id = mapped_column(
+        Uuid(as_uuid=True),
+        primary_key=True,
+        default=uuid4,
+    )
+    name = mapped_column(
+        String(255),
+        nullable=False,
+    )
+    funds_cents = mapped_column(
+        BigInteger,
+        nullable=False,
+    )
+    
+class CompanyPrestige(Base):
+    __tablename__ = "company_prestige"
+    __table_args__ = (
+        CheckConstraint("prestige_level >= 1 AND prestige_level <= 10", name="ck_company_prestige_prestige_level_range"),
+    )
+
+    company_id = mapped_column(
+        Uuid(as_uuid=True),
+        ForeignKey("companies.id", ondelete="CASCADE"),
+        primary_key=True,
+        nullable=False,
+    )
+    domain = mapped_column(
+        SAEnum(Domain, name="domain", values_callable=lambda e: [x.value for x in e]),
+        primary_key=True,
+        nullable=False,
+    )
+    prestige_level = mapped_column(
+        Numeric(6, 3),
+        nullable=False,
+        default=Decimal("1.000"),
+    )
+
+__all__ = ["Domain", "Company", "CompanyPrestige"]
diff --git a/src/yc_bench/db/models/employee.py b/src/yc_bench/db/models/employee.py
new file mode 100644
index 0000000..fb663f2
--- /dev/null
+++ b/src/yc_bench/db/models/employee.py
@@ -0,0 +1,66 @@
+from __future__ import annotations
+
+from uuid import uuid4
+
+from decimal import Decimal
+from sqlalchemy import BigInteger, CheckConstraint, Enum as SAEnum, ForeignKey, Numeric, String, Uuid
+from sqlalchemy.orm import mapped_column
+
+from ..base import Base
+from .company import Domain
+
+class Employee(Base):
+    __tablename__ = "employees"
+    __table_args__ = (
+        CheckConstraint("work_hours_per_day > 0", name="ck_employees_work_hours_per_day_gt_0"),
+        CheckConstraint("salary_cents >= 0", name="ck_employees_salary_cents_gte_0"),
+    )
+
+    id = mapped_column(
+        Uuid(as_uuid=True),
+        primary_key=True,
+        default=uuid4,
+    )
+    company_id = mapped_column(
+        Uuid(as_uuid=True),
+        ForeignKey("companies.id", ondelete="CASCADE"),
+        nullable=False,
+    )
+    name = mapped_column(
+        String(255),
+        nullable=False,
+    )
+    work_hours_per_day = mapped_column(
+        Numeric(5, 2),
+        nullable=False,
+        default=Decimal("9.00"),
+    )
+    salary_cents = mapped_column(
+        BigInteger,
+        nullable=False,
+    )
+
+class EmployeeSkillRate(Base):
+    __tablename__ = "employee_skill_rates"
+    __table_args__ = (
+        CheckConstraint("rate_domain_per_hour >= 0", name="ck_employee_skill_rates_rate_domain_per_hour_gte_0"),
+    )
+
+    employee_id = mapped_column(
+        Uuid(as_uuid=True),
+        ForeignKey("employees.id", ondelete="CASCADE"),
+        primary_key=True,
+        nullable=False,
+    )
+    domain = mapped_column(
+        SAEnum(Domain, name="domain", values_callable=lambda e: [x.value for x in e]),
+        primary_key=True,
+        nullable=False,
+    )
+    rate_domain_per_hour = mapped_column(
+        Numeric(12, 4),
+        nullable=False,
+        default=Decimal("1.0000"),
+    )
+
+__all__ = ["Employee", "EmployeeSkillRate"]
diff --git a/src/yc_bench/db/models/event.py b/src/yc_bench/db/models/event.py
new file mode 100644
index 0000000..1fba9e4
--- /dev/null
+++ b/src/yc_bench/db/models/event.py
@@ -0,0 +1,53 @@
+from __future__ import annotations
+
+from enum import Enum
+from uuid import uuid4
+
+from sqlalchemy import Boolean, DateTime, Enum as SAEnum, ForeignKey, JSON, String, Uuid, text
+from sqlalchemy.orm import mapped_column
+
+from ..base import Base
+
+class EventType(str, Enum):
+    TASK_HALF_PROGRESS = "task_half_progress"
+    TASK_COMPLETED = "task_completed"
+    BANKRUPTCY = "bankruptcy"
+    HORIZON_END = "horizon_end"
+
+class SimEvent(Base):
+    __tablename__ = "sim_events"
+    
+    id = mapped_column(
+        Uuid(as_uuid=True),
+        primary_key=True,
+        default=uuid4,
+    )
+    company_id = mapped_column(
+        Uuid(as_uuid=True),
+        ForeignKey("companies.id", ondelete="CASCADE"),
+        nullable=False,
+    )
+    event_type = mapped_column(
+        SAEnum(EventType, name="event_type", values_callable=lambda e: [x.value for x in e]),
+        nullable=False,
+    )
+    scheduled_at = mapped_column(
+        DateTime(timezone=True),
+        nullable=False,
+    )
+    payload = mapped_column(
+        JSON,
+        nullable=False,
+    )
+    dedupe_key = mapped_column( # guardrail against duplicates in event recomputation
+        String(255),
+        nullable=True,
+    )
+    consumed = mapped_column(
+        Boolean,
+        nullable=False,
+        default=False,
+        server_default=text("false"),
+    )
+
+__all__ = ["EventType", "SimEvent"]
diff --git a/src/yc_bench/db/models/ledger.py b/src/yc_bench/db/models/ledger.py
new file mode 100644
index 0000000..7103f56
--- /dev/null
+++ b/src/yc_bench/db/models/ledger.py
@@ -0,0 +1,51 @@
+from __future__ import annotations
+
+from enum import Enum
+from uuid import uuid4
+
+from sqlalchemy import BigInteger, DateTime, Enum as SAEnum, ForeignKey, String, Uuid
+from sqlalchemy.orm import mapped_column
+
+from ..base import Base
+
+class LedgerCategory(str, Enum):
+    MONTHLY_PAYROLL = "monthly_payroll"
+    TASK_REWARD = "task_reward"
+    TASK_FAIL_PENALTY = "task_fail_penalty"
+    TASK_CANCEL_PENALTY = "task_cancel_penalty"
+
+class LedgerEntry(Base):
+    __tablename__ = "ledger_entries"
+    
+    id = mapped_column(
+        Uuid(as_uuid=True),
+        primary_key=True,
+        default=uuid4,
+    )
+    company_id = mapped_column(
+        Uuid(as_uuid=True),
+        ForeignKey("companies.id", ondelete="CASCADE"),
+        nullable=False,
+    )
+    occurred_at = mapped_column(  
+        DateTime(timezone=True),
+        nullable=False,
+    )
+    category = mapped_column(
+        SAEnum(LedgerCategory, name="ledger_category", values_callable=lambda e: [x.value for x in e]),
+        nullable=False,
+    )
+    amount_cents = mapped_column(
+        BigInteger,
+        nullable=False,
+    )
+    ref_type = mapped_column(
+        String(64),
+        nullable=True,
+    )
+    ref_id = mapped_column( # can refer multiple tables, no foreign key
+        Uuid(as_uuid=True),
+        nullable=True,
+    )
+
+__all__ = ["LedgerCategory", "LedgerEntry"]
\ No newline at end of file
diff --git a/src/yc_bench/db/models/scratchpad.py b/src/yc_bench/db/models/scratchpad.py
new file mode 100644
index 0000000..39e6697
--- /dev/null
+++ b/src/yc_bench/db/models/scratchpad.py
@@ -0,0 +1,27 @@
+from __future__ import annotations
+
+from uuid import uuid4
+
+from sqlalchemy import ForeignKey, Text, Uuid
+from sqlalchemy.orm import mapped_column
+
+from ..base import Base
+
+
+class Scratchpad(Base):
+    __tablename__ = "scratchpads"
+
+    company_id = mapped_column(
+        Uuid(as_uuid=True),
+        ForeignKey("companies.id", ondelete="CASCADE"),
+        primary_key=True,
+        nullable=False,
+    )
+    content = mapped_column(
+        Text,
+        nullable=False,
+        default="",
+    )
+
+
+__all__ = ["Scratchpad"]
diff --git a/src/yc_bench/db/models/session.py b/src/yc_bench/db/models/session.py
new file mode 100644
index 0000000..497f3d4
--- /dev/null
+++ b/src/yc_bench/db/models/session.py
@@ -0,0 +1,68 @@
+from __future__ import annotations
+
+from uuid import uuid4
+
+from sqlalchemy import BigInteger, DateTime, ForeignKey, String, Uuid, Date, Enum as SAEnum
+from sqlalchemy.orm import mapped_column
+
+from ..base import Base
+from .event import EventType
+
+class Session(Base):
+    __tablename__ = "sessions"
+    
+    id = mapped_column(
+        Uuid(as_uuid=True),
+        primary_key=True,
+        default=uuid4,
+    )
+    company_id = mapped_column(
+        Uuid(as_uuid=True),
+        ForeignKey("companies.id", ondelete="CASCADE"),
+        nullable=False,
+    )
+    started_at = mapped_column(
+        DateTime(timezone=True),
+        nullable=False,
+    )
+    ended_at = mapped_column(
+        DateTime(timezone=True),
+        nullable=True,
+    )
+    wake_reason = mapped_column(
+        SAEnum(EventType, name="event_type", values_callable=lambda e: [x.value for x in e]),
+        nullable=False,
+    )
+    
+class MonthlyMetric(Base):
+    __tablename__ = "monthly_metrics"
+    
+    company_id = mapped_column(
+        Uuid(as_uuid=True),
+        ForeignKey("companies.id", ondelete="CASCADE"),
+        primary_key=True,
+        nullable=False,
+    )
+    month_start = mapped_column(
+        Date,
+        primary_key=True,
+        nullable=False,
+    )
+    revenue_cents = mapped_column(
+        BigInteger,
+        nullable=False,
+    )
+    cost_cents = mapped_column(
+        BigInteger,
+        nullable=False,
+    )
+    return_cents = mapped_column(
+        BigInteger,
+        nullable=False,
+    )
+    ending_funds_cents = mapped_column(
+        BigInteger,
+        nullable=False,
+    )
+
+__all__ = ["Session", "MonthlyMetric"]
\ No newline at end of file
diff --git a/src/yc_bench/db/models/sim_state.py b/src/yc_bench/db/models/sim_state.py
new file mode 100644
index 0000000..d6e9e54
--- /dev/null
+++ b/src/yc_bench/db/models/sim_state.py
@@ -0,0 +1,37 @@
+from __future__ import annotations
+
+from sqlalchemy import BigInteger, DateTime, ForeignKey, Integer, Uuid
+from sqlalchemy.orm import mapped_column
+
+from ..base import Base
+
+
+class SimState(Base):
+    __tablename__ = "sim_state"
+
+    company_id = mapped_column(
+        Uuid(as_uuid=True),
+        ForeignKey("companies.id", ondelete="CASCADE"),
+        primary_key=True,
+        nullable=False,
+    )
+    sim_time = mapped_column(
+        DateTime(timezone=True),
+        nullable=False,
+    )
+    run_seed = mapped_column(
+        Integer,
+        nullable=False,
+    )
+    horizon_end = mapped_column(
+        DateTime(timezone=True),
+        nullable=False,
+    )
+    replenish_counter = mapped_column(
+        Integer,
+        nullable=False,
+        default=0,
+        server_default="0",
+    )
+
+__all__ = ["SimState"]
diff --git a/src/yc_bench/db/models/task.py b/src/yc_bench/db/models/task.py
new file mode 100644
index 0000000..26deda2
--- /dev/null
+++ b/src/yc_bench/db/models/task.py
@@ -0,0 +1,140 @@
+from __future__ import annotations
+
+from enum import Enum
+from uuid import uuid4
+
+from sqlalchemy import BigInteger, Boolean, CheckConstraint, DateTime, Enum as SAEnum, ForeignKey, Integer, Numeric, String, Uuid, text
+from sqlalchemy.orm import mapped_column
+
+from ..base import Base
+from .company import Domain
+
+class TaskStatus(str, Enum):
+    MARKET = "market"
+    PLANNED = "planned"
+    ACTIVE = "active"
+    COMPLETED_SUCCESS = "completed_success"
+    COMPLETED_FAIL = "completed_fail"
+    CANCELLED = "cancelled"
+
+class Task(Base):
+    __tablename__ = "tasks"
+    __table_args__ = (
+        CheckConstraint("required_prestige >= 1 AND required_prestige <= 10", name="ck_tasks_required_prestige_range"),
+        CheckConstraint("skill_boost_pct >= 0", name="ck_tasks_skill_boost_pct_range"),
+        CheckConstraint("reward_funds_cents >= 0", name="ck_tasks_reward_funds_cents_gte_0"),
+        CheckConstraint("reward_prestige_delta >= 0 AND reward_prestige_delta <= 5", name="ck_tasks_reward_prestige_delta_range"),
+    )
+
+    id = mapped_column(
+        Uuid(as_uuid=True),
+        primary_key=True,
+        default=uuid4,
+    )
+    company_id = mapped_column(
+        Uuid(as_uuid=True),
+        ForeignKey("companies.id", ondelete="CASCADE"),
+        nullable=True,
+    )
+    status = mapped_column(
+        SAEnum(TaskStatus, name="task_status", values_callable=lambda e: [x.value for x in e]),
+        nullable=False,
+        default=TaskStatus.MARKET,
+    )
+    title = mapped_column(
+        String(255),
+        nullable=False,
+    )
+    description = mapped_column(
+        String,
+        nullable=False,
+    )
+    required_prestige = mapped_column(
+        Integer,
+        nullable=False,
+    )
+    reward_funds_cents = mapped_column(
+        BigInteger,
+        nullable=False,
+    )
+    reward_prestige_delta = mapped_column(
+        Numeric(6, 3),
+        nullable=False,
+    )
+    skill_boost_pct = mapped_column(
+        Numeric(6, 4),
+        nullable=False,
+    )
+    accepted_at = mapped_column(
+        DateTime(timezone=True),
+        nullable=True,
+    )
+    deadline = mapped_column(
+        DateTime(timezone=True),
+        nullable=True,
+    )
+    completed_at = mapped_column(
+        DateTime(timezone=True),
+        nullable=True,
+    )
+    success = mapped_column(
+        Boolean,
+        nullable=True,
+    )
+    halfway_event_emitted = mapped_column(
+        Boolean,
+        nullable=False,
+        default=False,
+        server_default=text("false"),
+    )
+
+class TaskRequirement(Base):
+    __tablename__ = "task_requirements"
+    __table_args__ = (
+        CheckConstraint("required_qty >= 200 AND required_qty <= 3000", name="ck_task_requirements_required_qty_range"),
+        CheckConstraint("completed_qty >= 0", name="ck_task_requirements_completed_qty_gte_0"),
+        CheckConstraint("completed_qty <= required_qty", name="ck_task_requirements_completed_qty_lte_required_qty"),
+    )
+
+    task_id = mapped_column(
+        Uuid(as_uuid=True),
+        ForeignKey("tasks.id", ondelete="CASCADE"),
+        primary_key=True,
+        nullable=False,
+    )
+    domain = mapped_column(
+        SAEnum(Domain, name="domain", values_callable=lambda e: [x.value for x in e]),
+        primary_key=True,
+        nullable=False,
+    )
+    required_qty = mapped_column(
+        Numeric(14, 4),
+        nullable=False,
+    )
+    completed_qty = mapped_column(
+        Numeric(14, 4),
+        nullable=False,
+        default=0,
+    )
+
+class TaskAssignment(Base):
+    __tablename__ = "task_assignments"
+
+    task_id = mapped_column(
+        Uuid(as_uuid=True),
+        ForeignKey("tasks.id", ondelete="CASCADE"),
+        primary_key=True,
+        nullable=False,
+    )
+    employee_id = mapped_column(
+        Uuid(as_uuid=True),
+        ForeignKey("employees.id", ondelete="CASCADE"),
+        primary_key=True,
+        nullable=False,
+    )
+    assigned_at = mapped_column(
+        DateTime(timezone=True),
+        nullable=False,
+    )
+
+__all__ = ["TaskStatus", "Task", "TaskRequirement", "TaskAssignment"]
diff --git a/src/yc_bench/db/session.py b/src/yc_bench/db/session.py
new file mode 100644
index 0000000..bffb061
--- /dev/null
+++ b/src/yc_bench/db/session.py
@@ -0,0 +1,94 @@
+from __future__ import annotations
+
+import os
+from contextlib import contextmanager
+
+from sqlalchemy import create_engine
+from sqlalchemy.orm import Session, sessionmaker
+
+
+def _get_database_url() -> str:
+    default = "sqlite:///db/yc_bench.db"
+    url = os.environ.get("DATABASE_URL", default)
+    # Auto-create parent directory for sqlite:/// relative paths
+    if url.startswith("sqlite:///") and not url.startswith("sqlite:////"):
+        import pathlib
+        db_path = pathlib.Path(url[len("sqlite:///"):])
+        db_path.parent.mkdir(parents=True, exist_ok=True)
+    return url
+
+
+def _maybe_register_psycopg_enum_dumpers(url: str) -> None:
+    """Register psycopg3 enum value dumpers — only needed for PostgreSQL.
+
+    psycopg3 sends enum .name (uppercase) by default; the DB stores .value
+    (lowercase). This adapter fixes that mismatch. SQLite doesn't need it
+    because SQLAlchemy stores enums as plain VARCHAR using .value directly.
+    """
+    if not url.startswith("postgresql"):
+        return
+
+    import enum
+    import psycopg
+    from psycopg.adapt import Dumper
+    from psycopg.pq import Format
+
+    class _EnumValueDumper(Dumper):
+        format = Format.TEXT
+
+        def dump(self, obj):
+            return obj.value.encode("utf-8") if isinstance(obj, enum.Enum) else str(obj).encode("utf-8")
+
+    from .models.company import Domain
+    from .models.event import EventType
+    from .models.ledger import LedgerCategory
+    from .models.task import TaskStatus
+
+    for cls in (Domain, EventType, LedgerCategory, TaskStatus):
+        psycopg.adapters.register_dumper(cls, _EnumValueDumper)
+
+
+def build_engine(url: str | None = None):
+    db_url = url or _get_database_url()
+    _maybe_register_psycopg_enum_dumpers(db_url)
+
+    kwargs: dict = {"echo": False, "future": True}
+    if db_url.startswith("sqlite"):
+        # Required for SQLAlchemy's connection pool when used across threads
+        kwargs["connect_args"] = {"check_same_thread": False}
+
+    return create_engine(db_url, **kwargs)
+
+
+def build_session_factory(engine):
+    return sessionmaker(
+        bind=engine,
+        autoflush=False,
+        autocommit=False,
+        expire_on_commit=False,
+        class_=Session,
+    )
+
+
+@contextmanager
+def session_scope(session_factory):
+    session = session_factory()
+    try:
+        yield session
+        session.commit()
+    except Exception:
+        session.rollback()
+        raise
+    finally:
+        session.close()
+
+
+def init_db(engine) -> None:
+    """Create all tables that do not yet exist. Safe to call on every startup."""
+    from .base import Base
+    # Import all models so SQLAlchemy registers them with Base.metadata before create_all.
+    from .models import company, employee, event, ledger, scratchpad, session, sim_state, task  # noqa: F401
+    Base.metadata.create_all(engine)
+
+
+__all__ = ["build_engine", "build_session_factory", "session_scope", "init_db"]