Implement State Hub v0.2: dependency graph, next-steps suggestions, design boundary

S0 — Design boundary formalised across all integration surfaces:
- TOOLS.md restructured with Design Boundary section, Sanctioned Write Tools,
  and Bootstrap-Only Tools (create_workstream, create_task) with explicit note
- project_claude_md.template and railiance CLAUDE.md updated with boundary note
  and get_next_steps() in session start protocol
- Global ~/.claude/CLAUDE.md updated accordingly

S1 — Workstream dependency graph:
- WorkstreamDependency model (directed edge, CASCADE on delete, unique pair constraint)
- Alembic migration 0b547c153153; script.py.mako added (was missing)
- REST API: POST/GET /workstreams/{id}/dependencies/, DELETE …/{dep_id} (hard delete)
- StateSummary open_workstreams enriched with depends_on/blocks lists
- MCP tools: create_dependency(), list_dependencies()
- Dashboard workstreams page: Dependencies section with relationship cards
- Seeded: custodian-agent-runtime → llm-shared-library + phase-0-operational-baseline

S2 — Suggesting Next Steps (sanctioned write use case #2):
- GET /state/next_steps derives suggestions from recently resolved decisions
  (→ first open task in same workstream) and cleared dependencies
  (→ first todo task in now-unblocked workstream)
- StateSummary.next_steps included on every summary call
- MCP tool: get_next_steps()
- Dashboard: "What's next?" card grid above Registered Projects

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

api/models/__init__.py

@@ -1,6 +1,7 @@
 from api.models.base import Base
 from api.models.topic import Topic, TopicStatus, Domain
 from api.models.workstream import Workstream, WorkstreamStatus
+from api.models.workstream_dependency import WorkstreamDependency
 from api.models.task import Task, TaskStatus, TaskPriority
 from api.models.decision import Decision, DecisionType, DecisionStatus
 from api.models.progress_event import ProgressEvent
@@ -9,6 +10,7 @@ __all__ = [
     "Base",
     "Topic", "TopicStatus", "Domain",
     "Workstream", "WorkstreamStatus",
+    "WorkstreamDependency",
     "Task", "TaskStatus", "TaskPriority",
     "Decision", "DecisionType", "DecisionStatus",
     "ProgressEvent",

api/models/workstream_dependency.py

@@ -0,0 +1,45 @@
+import uuid
+
+from sqlalchemy import ForeignKey, Text, UniqueConstraint
+from sqlalchemy.dialects.postgresql import UUID
+from sqlalchemy.orm import Mapped, mapped_column, relationship
+
+from api.models.base import Base, TimestampMixin, new_uuid
+
+
+class WorkstreamDependency(Base, TimestampMixin):
+    """Directed dependency edge: `from_workstream` depends on `to_workstream`.
+
+    Semantics: `to_workstream` must reach a satisfactory state before
+    `from_workstream` can fully proceed.  Hard deletes are intentional —
+    removing an edge removes a constraint, not information.
+    """
+
+    __tablename__ = "workstream_dependencies"
+    __table_args__ = (
+        UniqueConstraint("from_workstream_id", "to_workstream_id", name="uq_ws_dep_pair"),
+    )
+
+    id: Mapped[uuid.UUID] = mapped_column(
+        UUID(as_uuid=True), primary_key=True, default=new_uuid
+    )
+    from_workstream_id: Mapped[uuid.UUID] = mapped_column(
+        UUID(as_uuid=True),
+        ForeignKey("workstreams.id", ondelete="CASCADE"),
+        nullable=False,
+        index=True,
+    )
+    to_workstream_id: Mapped[uuid.UUID] = mapped_column(
+        UUID(as_uuid=True),
+        ForeignKey("workstreams.id", ondelete="CASCADE"),
+        nullable=False,
+        index=True,
+    )
+    description: Mapped[str | None] = mapped_column(Text, nullable=True)
+
+    from_workstream: Mapped["Workstream"] = relationship(  # noqa: F821
+        "Workstream", foreign_keys=[from_workstream_id]
+    )
+    to_workstream: Mapped["Workstream"] = relationship(  # noqa: F821
+        "Workstream", foreign_keys=[to_workstream_id]
+    )