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/__init__.py

@@ -23,7 +23,7 @@ from api.models.technical_debt import TechnicalDebt, TDStatus
 from api.models.contribution import Contribution, ContributionType, ContributionStatus
 from api.models.sbom_snapshot import SBOMSnapshot
 from api.models.sbom_entry import SBOMEntry, Ecosystem
-from api.models.agent_message import AgentMessage
+from api.models.agent_message import AgentMessage, MessageReceipt
 from api.models.capability_catalog import CapabilityCatalog
 from api.models.capability_request import CapabilityRequest
 from api.models.tpsc import TPSCCatalog, TPSCSnapshot, TPSCEntry
@@ -76,6 +76,7 @@ __all__ = [
     "SBOMSnapshot",
     "SBOMEntry", "Ecosystem",
     "AgentMessage",
+    "MessageReceipt",
     "CapabilityCatalog",
     "CapabilityRequest",
     "TPSCCatalog", "TPSCSnapshot", "TPSCEntry",