STATE-WP-0093: per-recipient broadcast receipts and standing notices (T01-T06).

Founder approved T01 on 2026-09-22 (D2, D3, D6 as recommended).
- T02: message_receipts table; kind/expires_at/supersedes_id on
  agent_messages; migration d7e8f9a0b1c2 archives existing broadcasts,
  leaves direct messages untouched, reversible.
- T03: reader-aware mark-read (unattributed broadcast mark-read is a
  metered, deprecated no-op), delivery receipts on the scoped unread inbox,
  POST /messages/{id}/ack, news/standing kinds, expiry, supersede, broadcast
  archive no longer stamps read_at, reply writes the replier's receipt.
- T04 (state-hub part): Codex MCP reader param and acknowledge_notice;
  hub-core part handed off (message 69fc387c).
- T05: GET /messages/notices, standing_notices in /state/summary,
  dashboard standing-notices panel.
- T06: 17 new tests; full suite green.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

Assistant: claude-code
Assistant-Model: opus
Assistant-Process: 63291@bnt-lap001
Assistant-Session: 8bd77868-ca68-4f49-bb1e-d539ecc0d703

api/models/agent_message.py

@@ -1,15 +1,22 @@
 import uuid
 from datetime import datetime
 
-from sqlalchemy import DateTime, ForeignKey, String, Text, text
+from sqlalchemy import DateTime, ForeignKey, Index, String, Text, text
 from sqlalchemy.dialects.postgresql import UUID
 from sqlalchemy.orm import Mapped, mapped_column, relationship
 
 from api.models.base import Base, new_uuid
 
 
+BROADCAST = "broadcast"
+MESSAGE_KINDS = ("message", "news", "standing")
+
+
 class AgentMessage(Base):
     __tablename__ = "agent_messages"
+    __table_args__ = (
+        Index("ix_agent_messages_to_kind_archived", "to_agent", "kind", "archived_at"),
+    )
 
     id: Mapped[uuid.UUID] = mapped_column(
         UUID(as_uuid=True), primary_key=True, default=new_uuid
@@ -30,6 +37,19 @@ class AgentMessage(Base):
     archived_at: Mapped[datetime | None] = mapped_column(
         DateTime(timezone=True), nullable=True
     )
+    # STATE-WP-0093: kind is only meaningful for broadcasts
+    # (message | news | standing); direct messages stay "message".
+    kind: Mapped[str] = mapped_column(
+        String(20), nullable=False, default="message", server_default="message"
+    )
+    expires_at: Mapped[datetime | None] = mapped_column(
+        DateTime(timezone=True), nullable=True
+    )
+    supersedes_id: Mapped[uuid.UUID | None] = mapped_column(
+        UUID(as_uuid=True),
+        ForeignKey("agent_messages.id", ondelete="SET NULL"),
+        nullable=True,
+    )
     created_at: Mapped[datetime] = mapped_column(
         DateTime(timezone=True),
         server_default=text("now()"),
@@ -42,3 +62,29 @@ class AgentMessage(Base):
         foreign_keys=[thread_id],
         lazy="select",
     )
+
+
+class MessageReceipt(Base):
+    """Per-reader state for broadcast messages (STATE-WP-0093).
+
+    Written only for broadcasts; direct messages keep the global
+    ``AgentMessage.read_at``.
+    """
+
+    __tablename__ = "message_receipts"
+
+    message_id: Mapped[uuid.UUID] = mapped_column(
+        UUID(as_uuid=True),
+        ForeignKey("agent_messages.id", ondelete="CASCADE"),
+        primary_key=True,
+    )
+    agent: Mapped[str] = mapped_column(String(100), primary_key=True, index=True)
+    delivered_at: Mapped[datetime | None] = mapped_column(
+        DateTime(timezone=True), nullable=True
+    )
+    read_at: Mapped[datetime | None] = mapped_column(
+        DateTime(timezone=True), nullable=True
+    )
+    acknowledged_at: Mapped[datetime | None] = mapped_column(
+        DateTime(timezone=True), nullable=True
+    )