feat: agent coordination system (workflows, locks, components, messages)

Adds /api/coord/* endpoints for real-time cross-session coordination:
- coord_workflows: named units of work per project
- coord_work_items: tasks within workflows with dependency chains
- coord_session_locks: exclusive resource locks with auto-expiry (TTL)
- coord_component_states: live component state per project (upsert)
- coord_messages: cross-session messaging and broadcasts
- /api/coord/status: cross-project snapshot endpoint

Replaces PROJECT_STATE.md as the coordination layer for Claude sessions.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

api/models/coord_work_item.py

@@ -0,0 +1,87 @@
+"""Coordination work item model."""
+
+from datetime import datetime
+from typing import Optional
+
+from sqlalchemy import CHAR, CheckConstraint, ForeignKey, Index, Integer, String, Text, DateTime
+from sqlalchemy.orm import Mapped, mapped_column
+
+from .base import Base, TimestampMixin, UUIDMixin
+
+
+class CoordWorkItem(Base, UUIDMixin, TimestampMixin):
+    """A discrete task within a coordination workflow."""
+
+    __tablename__ = "coord_work_items"
+
+    workflow_id: Mapped[str] = mapped_column(
+        CHAR(36),
+        ForeignKey("coord_workflows.id", ondelete="CASCADE"),
+        nullable=False,
+        doc="Parent workflow"
+    )
+
+    project_key: Mapped[str] = mapped_column(
+        String(200),
+        nullable=False,
+        doc="Denormalized project key for filtering without join"
+    )
+
+    title: Mapped[str] = mapped_column(
+        String(500),
+        nullable=False,
+        doc="Short title"
+    )
+
+    description: Mapped[Optional[str]] = mapped_column(
+        Text,
+        doc="Full description, markdown ok — store design specs, schemas, etc."
+    )
+
+    status: Mapped[str] = mapped_column(
+        String(20),
+        nullable=False,
+        default="pending",
+        doc="Status: pending, in_progress, blocked, completed, cancelled"
+    )
+
+    priority: Mapped[int] = mapped_column(
+        Integer,
+        nullable=False,
+        default=0,
+        doc="Higher value = more urgent"
+    )
+
+    assigned_session: Mapped[Optional[str]] = mapped_column(
+        String(200),
+        doc="Session currently working this item"
+    )
+
+    depends_on_id: Mapped[Optional[str]] = mapped_column(
+        CHAR(36),
+        ForeignKey("coord_work_items.id", ondelete="SET NULL"),
+        doc="Blocking predecessor item"
+    )
+
+    started_at: Mapped[Optional[datetime]] = mapped_column(
+        DateTime,
+        doc="When work began"
+    )
+
+    completed_at: Mapped[Optional[datetime]] = mapped_column(
+        DateTime,
+        doc="When item reached a terminal state"
+    )
+
+    __table_args__ = (
+        CheckConstraint(
+            "status IN ('pending', 'in_progress', 'blocked', 'completed', 'cancelled')",
+            name="ck_coord_work_items_status"
+        ),
+        Index("idx_coord_work_items_workflow", "workflow_id"),
+        Index("idx_coord_work_items_project_status", "project_key", "status"),
+        Index("idx_coord_work_items_assigned", "assigned_session"),
+    )
+
+    def __repr__(self) -> str:
+        return f"<CoordWorkItem(title='{self.title}', status='{self.status}')>"