CUST-WP-0074-T02 follow-up: blocked_on / wait_until reach the hub read model

Migration f9a0b1c2d3e4 (revises e8f9a0b1c2d3) adds tasks.blocked_on
(String 200) and tasks.wait_until (Date); TaskCreate/Update/Read carry both.

Read model (api/services/wait_kind.py): a wait task is external when it has
a dependency edge, a blocked_on matching ^message-from: (rule 6), or a
wait_until date (a window clears by itself). human/both/unqualified and
blocked_kind are unchanged in shape.

fix-consistency: _task_wait_fields carries blocked_on and wait_until (ISO
date, PyYAML date objects normalised), so the C-06/C-11 creates and the
C-10 status PATCH send them, and C-41 compares and syncs them like the
other qualifiers. C-39 accepts wait_until: YYYY-MM-DD as a qualifier; C-40
also fires when wait_until is before UTC today (report only).

/state/deps: depends_on stubs gain from_task_id / from_task_title so
consumers see task-scoped edges; both optional, response otherwise as before.

Co-Authored-By: Claude Fable 5.1 <noreply@anthropic.com>

Assistant: claude-code
Assistant-Model: sonnet
Assistant-Process: 237582@bnt-lap001
Assistant-Session: f2b3d9f1-8fb9-4b9c-bc2b-837ec5dfc826

api/models/task.py

@@ -60,6 +60,10 @@ class Task(Base, TimestampMixin):
     # "CCR-2026-0004" (CUST-WP-0074 Case B). Free text: the decision may live
     # in another repo and may not be indexed in the hub yet.
     decision_id: Mapped[str | None] = mapped_column(String(120), nullable=True)
+    # Owner-return marker "message-from:<agent>" (CUST-WP-0074 rule 6) and a
+    # date after which the wait clears by itself; either counts as external.
+    blocked_on: Mapped[str | None] = mapped_column(String(200), nullable=True)
+    wait_until: Mapped[date | None] = mapped_column(Date, nullable=True)
     parent_task_id: Mapped[uuid.UUID | None] = mapped_column(
         UUID(as_uuid=True),
         ForeignKey("tasks.id", ondelete="SET NULL", onupdate="CASCADE"),