diff --git a/roboco/api/deps.py b/roboco/api/deps.py
index cf43f8ba..05d591fb 100644
--- a/roboco/api/deps.py
+++ b/roboco/api/deps.py
@@ -502,7 +502,7 @@ def require_task_action(
 async def get_choreographer(
     db_session: DbSession,
 ) -> Choreographer:
-    """Build a Choreographer with all 7 service dependencies wired up."""
+    """Build a Choreographer with all service dependencies wired up."""
     return Choreographer(
         ChoreographerDeps(
             task=TaskService(db_session),
@@ -512,6 +512,7 @@ async def get_choreographer(
             journal=JournalService(db_session),
             audit=get_audit_service(),
             evidence_repo=EvidenceRepo(db_session),
+            messaging=MessagingService(db_session),
         )
     )
 
diff --git a/roboco/services/gateway/choreographer/_impl.py b/roboco/services/gateway/choreographer/_impl.py
index 57c0bbfd..ba83fd70 100644
--- a/roboco/services/gateway/choreographer/_impl.py
+++ b/roboco/services/gateway/choreographer/_impl.py
@@ -11,6 +11,7 @@ injection so later phases just fill in the bodies.
 
 from __future__ import annotations
 
+import contextlib
 from dataclasses import dataclass
 from datetime import UTC, datetime
 from typing import Any, ClassVar
@@ -173,6 +174,10 @@ class ChoreographerDeps:
     journal: Any
     audit: Any
     evidence_repo: Any
+    # Task #156: messaging is optional so existing callsites + tests that
+    # don't exercise session propagation don't have to plumb it in. The
+    # delegate() path uses it to thread parent sessions onto new subtasks.
+    messaging: Any = None
 
 
 @dataclass(frozen=True)
@@ -305,11 +310,39 @@ class Choreographer:
     def evidence_repo(self) -> Any:
         return self._deps.evidence_repo
 
+    @property
+    def messaging(self) -> Any:
+        return self._deps.messaging
+
     async def _touch(self, task_id: UUID | None) -> None:
         """Best-effort heartbeat write; silent on missing task."""
         if task_id is not None:
             await self.task.heartbeat(task_id)
 
+    async def _record_milestone_progress(
+        self,
+        task_id: UUID,
+        agent_id: UUID,
+        message: str,
+        percentage: int | None = None,
+    ) -> None:
+        """Append a server-emitted progress entry on a lifecycle milestone.
+
+        Task #155: agents call ``progress()`` inconsistently. Server-side
+        auto-emit on natural milestones (open_pr, i_am_done) guarantees
+        the panel + audit view always have entries at the major
+        transitions, regardless of how chatty the agent is. Best-effort:
+        a missing task_id or write failure must not break the verb path
+        — progress is observability, not correctness.
+        """
+        with contextlib.suppress(Exception):
+            await self.task.add_progress(
+                task_id=task_id,
+                agent_id=agent_id,
+                message=message,
+                percentage=percentage,
+            )
+
     @staticmethod
     def _reassigned_rejection(
         ctx: _ReassignedCtx,
@@ -1034,12 +1067,34 @@ class Choreographer:
                 task_id=task_id,
                 verb="open_pr",
             )
-        # Re-fetch: git_service.create_pr writes pr_number / pr_url onto
-        # the task row. The runner doesn't bubble that update back, so a
-        # fresh load is the simplest way to surface the new fields in the
-        # OK envelope's next-hint and introspection block.
+        return await self._open_pr_success_envelope(
+            agent_id, task_id, t, briefing, role_str
+        )
+
+    async def _open_pr_success_envelope(
+        self,
+        agent_id: UUID,
+        task_id: UUID,
+        t: Any,
+        briefing: dict[str, Any],
+        role_str: str,
+    ) -> Envelope:
+        """Refresh the task, auto-emit milestone progress, build the OK envelope.
+
+        git_service.create_pr writes pr_number / pr_url onto the task row;
+        the runner doesn't bubble that update back so we re-fetch. Task
+        #155 milestone progress fires server-side so the panel + audit
+        log always show "opened PR #N" regardless of agent chattiness.
+        """
         refreshed = await self.task.get(task_id)
         t = refreshed if refreshed is not None else t
+        if t.pr_number is not None:
+            await self._record_milestone_progress(
+                task_id,
+                agent_id,
+                f"opened PR #{t.pr_number}",
+                percentage=70,
+            )
         return Envelope.ok(
             status=str(t.status),
             task_id=str(task_id),
@@ -1266,6 +1321,14 @@ class Choreographer:
             )
         await self._notify_qa(ctx.agent_id, ctx.task_id, t)
         await self._touch(ctx.task_id)
+        # Task #155: server-side milestone progress so the panel always
+        # records the QA handoff regardless of agent's progress() habits.
+        await self._record_milestone_progress(
+            ctx.task_id,
+            ctx.agent_id,
+            "submitted for QA review",
+            percentage=90,
+        )
         return await self._build_i_am_done_ok(ctx.agent_id, ctx.task_id, t)
 
     async def _i_am_done_resume_from_verifying(self, ctx: _IAmDoneContext) -> Envelope:
@@ -2886,7 +2949,20 @@ class Choreographer:
             nature=nature_enum,
             estimated_complexity=complexity_enum,
         )
-        return await self.task.create_subtask(req)
+        new_task = await self.task.create_subtask(req)
+        # Task #156: thread the parent's existing session links onto the
+        # new subtask so the assigned agent (dev/qa/doc) lands in the
+        # group chat the PM has already been talking in. Pre-gateway
+        # parity — sessions were wired to the whole tree at creation
+        # time; the gateway path created subtasks one-by-one and forgot
+        # this step. Idempotent on re-runs; no-op when no parent session.
+        if self.messaging is not None:
+            await self.messaging.propagate_sessions_to_subtask(
+                parent_task_id=parent_task_id,
+                subtask_id=new_task.id,
+                added_by=pm_agent_id,
+            )
+        return new_task
 
     @staticmethod
     def _validate_delegation_chain(pm_role: str, target_slug: str) -> str | None:
diff --git a/roboco/services/messaging.py b/roboco/services/messaging.py
index 9eacc0d4..455d085a 100644
--- a/roboco/services/messaging.py
+++ b/roboco/services/messaging.py
@@ -1008,6 +1008,44 @@ class MessagingService(BaseService):
         )
         return list(result.scalars().all())
 
+    async def propagate_sessions_to_subtask(
+        self,
+        parent_task_id: UUID,
+        subtask_id: UUID,
+        added_by: UUID,
+    ) -> list[SessionTaskTable]:
+        """Link every session attached to ``parent_task_id`` onto ``subtask_id``.
+
+        Task #156: pre-gateway flow created a session with the whole task
+        tree at once, so subtasks were visible in the parent's group chat
+        the moment they existed. The gateway creates subtasks one at a
+        time via ``delegate()``, so this step re-attaches every existing
+        parent session link to the new child.
+
+        ``link_session_to_task`` is idempotent on duplicate (session, task)
+        pairs, so re-runs are no-ops. Primary status is NOT propagated —
+        each subtask owns its own primary slot, and a primary on the
+        parent should not auto-claim the subtask's primary too.
+        """
+        parent_links = await self.get_sessions_for_task(parent_task_id)
+        propagated: list[SessionTaskTable] = []
+        for parent_link in parent_links:
+            session_id = cast("UUID", parent_link.session_id)
+            rel_raw = parent_link.relationship_type
+            try:
+                rel = SessionTaskRelationshipType(rel_raw)
+            except (TypeError, ValueError):
+                rel = SessionTaskRelationshipType.DISCUSSION
+            link = await self.link_session_to_task(
+                session_id=session_id,
+                task_id=subtask_id,
+                added_by=added_by,
+                is_primary=False,
+                relationship_type=rel,
+            )
+            propagated.append(link)
+        return propagated
+
     async def _walk_task_ancestors(self, task_id: UUID) -> list["TaskTable"]:  # type: ignore[name-defined]  # noqa: F821
         """Return [parent, grandparent, ..., root] for a task, empty if none.
 
diff --git a/tests/unit/gateway/test_delegate_propagates_sessions.py b/tests/unit/gateway/test_delegate_propagates_sessions.py
new file mode 100644
index 00000000..2b26d304
--- /dev/null
+++ b/tests/unit/gateway/test_delegate_propagates_sessions.py
@@ -0,0 +1,138 @@
+"""Task #156: delegate() must thread parent sessions onto the new subtask.
+
+Pre-gateway flow created sessions for whole task trees at once, so subtasks
+were visible in the group chat the PM was already using. The gateway's
+delegate() creates subtasks one-by-one — without this step the new agent
+spawns into an empty channel and can't see the PM's prior discussion.
+"""
+
+from __future__ import annotations
+
+from datetime import UTC, datetime
+from typing import Any
+from unittest.mock import AsyncMock, MagicMock
+from uuid import uuid4
+
+import pytest
+from roboco.services.gateway.choreographer import Choreographer, ChoreographerDeps
+from roboco.services.gateway.choreographer._impl import DelegateInputs
+
+
+def _make_deps(**overrides: Any) -> ChoreographerDeps:
+    base: dict[str, Any] = {
+        "task": AsyncMock(),
+        "work_session": AsyncMock(),
+        "git": AsyncMock(),
+        "a2a": AsyncMock(),
+        "journal": AsyncMock(),
+        "audit": AsyncMock(),
+        "evidence_repo": AsyncMock(),
+        "messaging": AsyncMock(),
+    }
+    base.update(overrides)
+    task = base["task"]
+    task.session = MagicMock()
+    task.session.begin_nested = MagicMock(
+        return_value=MagicMock(
+            __aenter__=AsyncMock(return_value=None),
+            __aexit__=AsyncMock(return_value=False),
+        )
+    )
+    repo = base["evidence_repo"]
+    for method in (
+        "list_unread_a2a",
+        "list_unread_mentions",
+        "list_pending_notifications",
+        "task_metadata_gaps",
+        "recent_team_activity",
+        "blockers_in_lane",
+        "journal_highlights_for_task",
+    ):
+        getattr(repo, method).return_value = []
+    _ldef = base["journal"].latest_decision_at.return_value
+    if type(_ldef).__name__ in ("MagicMock", "AsyncMock"):
+        base["journal"].latest_decision_at.return_value = datetime.now(UTC)
+    return ChoreographerDeps(**base)
+
+
+@pytest.mark.asyncio
+async def test_create_subtask_propagates_parent_sessions() -> None:
+    """When the choreographer creates a subtask, the parent's session
+    links are auto-attached to it via MessagingService.propagate_sessions_to_subtask.
+    """
+    pm_id = uuid4()
+    parent_id = uuid4()
+    new_task_id = uuid4()
+    parent = MagicMock(
+        id=parent_id,
+        project_id=uuid4(),
+        team="backend",
+        status="in_progress",
+        task_type="planning",
+        sequence=0,
+        assigned_to=pm_id,
+    )
+    new_task = MagicMock(id=new_task_id, status="pending")
+    task_svc = AsyncMock()
+    task_svc.create_subtask.return_value = new_task
+    messaging = AsyncMock()
+    messaging.propagate_sessions_to_subtask.return_value = []
+    deps = _make_deps(task=task_svc, messaging=messaging)
+    c = Choreographer(deps)
+
+    inputs = DelegateInputs(
+        title="Backend slice",
+        description="API + DB",
+        acceptance_criteria=["api works", "schema migrated"],
+        assigned_to="be-dev-1",
+        team="backend",
+        task_type="code",
+        nature="technical",
+        estimated_complexity="medium",
+    )
+    result = await c._create_subtask_from_inputs(pm_id, parent_id, parent, inputs)
+    assert result is new_task
+
+    messaging.propagate_sessions_to_subtask.assert_awaited_once_with(
+        parent_task_id=parent_id,
+        subtask_id=new_task_id,
+        added_by=pm_id,
+    )
+
+
+@pytest.mark.asyncio
+async def test_create_subtask_no_messaging_skips_propagation() -> None:
+    """When messaging dep is None (e.g. lightweight test wiring), the
+    subtask is still created — propagation is a soft enhancement, not a
+    hard requirement."""
+    pm_id = uuid4()
+    parent_id = uuid4()
+    new_task_id = uuid4()
+    parent = MagicMock(
+        id=parent_id,
+        project_id=uuid4(),
+        team="backend",
+        status="in_progress",
+        task_type="planning",
+        sequence=0,
+        assigned_to=pm_id,
+    )
+    new_task = MagicMock(id=new_task_id, status="pending")
+    task_svc = AsyncMock()
+    task_svc.create_subtask.return_value = new_task
+    deps = _make_deps(task=task_svc, messaging=None)
+    c = Choreographer(deps)
+
+    inputs = DelegateInputs(
+        title="Backend slice",
+        description="API + DB",
+        acceptance_criteria=["api works"],
+        assigned_to="be-dev-1",
+        team="backend",
+        task_type="code",
+        nature="technical",
+        estimated_complexity="medium",
+    )
+    # Must not raise even though messaging is None.
+    result = await c._create_subtask_from_inputs(pm_id, parent_id, parent, inputs)
+    assert result is new_task
diff --git a/tests/unit/gateway/test_milestone_progress.py b/tests/unit/gateway/test_milestone_progress.py
new file mode 100644
index 00000000..036b4b10
--- /dev/null
+++ b/tests/unit/gateway/test_milestone_progress.py
@@ -0,0 +1,68 @@
+"""Task #155: server-side auto-progress on lifecycle milestones.
+
+Smoke-9 ended with zero progress entries because the dev never called
+progress() explicitly. The fix: server emits progress entries at
+deterministic lifecycle milestones (open_pr → "opened PR #N",
+i_am_done → "submitted for QA review") so the panel + audit have entries
+regardless of agent chattiness. Progress is observability — write failures
+must not break the verb path.
+"""
+
+from __future__ import annotations
+
+from unittest.mock import AsyncMock
+from uuid import uuid4
+
+import pytest
+from roboco.services.gateway.choreographer import Choreographer, ChoreographerDeps
+
+
+@pytest.mark.asyncio
+async def test_record_milestone_progress_calls_add_progress() -> None:
+    """The helper proxies to TaskService.add_progress with the right args."""
+    task_svc = AsyncMock()
+    deps = ChoreographerDeps(
+        task=task_svc,
+        work_session=AsyncMock(),
+        git=AsyncMock(),
+        a2a=AsyncMock(),
+        journal=AsyncMock(),
+        audit=AsyncMock(),
+        evidence_repo=AsyncMock(),
+        messaging=AsyncMock(),
+    )
+    c = Choreographer(deps)
+
+    task_id = uuid4()
+    agent_id = uuid4()
+    await c._record_milestone_progress(task_id, agent_id, "opened PR #20", 70)
+
+    task_svc.add_progress.assert_awaited_once_with(
+        task_id=task_id,
+        agent_id=agent_id,
+        message="opened PR #20",
+        percentage=70,
+    )
+
+
+@pytest.mark.asyncio
+async def test_record_milestone_progress_swallows_errors() -> None:
+    """Progress is observability. A failing add_progress must not raise
+    so the verb body's main flow is unaffected."""
+    task_svc = AsyncMock()
+    task_svc.add_progress.side_effect = RuntimeError("db lock contention")
+    deps = ChoreographerDeps(
+        task=task_svc,
+        work_session=AsyncMock(),
+        git=AsyncMock(),
+        a2a=AsyncMock(),
+        journal=AsyncMock(),
+        audit=AsyncMock(),
+        evidence_repo=AsyncMock(),
+        messaging=AsyncMock(),
+    )
+    c = Choreographer(deps)
+
+    # Must NOT raise.
+    await c._record_milestone_progress(uuid4(), uuid4(), "submitted for QA review", 90)
+    task_svc.add_progress.assert_awaited_once()
diff --git a/tests/unit/services/test_propagate_sessions_to_subtask.py b/tests/unit/services/test_propagate_sessions_to_subtask.py
new file mode 100644
index 00000000..456ae7ac
--- /dev/null
+++ b/tests/unit/services/test_propagate_sessions_to_subtask.py
@@ -0,0 +1,98 @@
+"""Task #156: MessagingService.propagate_sessions_to_subtask.
+
+Tests the helper's call shape and idempotency contract without going
+through the DB. Integration coverage (real DB, real linking) lives in
+``tests/integration/test_messaging_service.py``.
+"""
+
+from __future__ import annotations
+
+from typing import Any
+from unittest.mock import AsyncMock, MagicMock
+from uuid import uuid4
+
+import pytest
+from roboco.models.session import SessionTaskRelationshipType
+from roboco.services.messaging import MessagingService
+
+
+def _link(session_id: object, relationship_type: str) -> MagicMock:
+    link = MagicMock()
+    link.session_id = session_id
+    link.relationship_type = relationship_type
+    return link
+
+
+@pytest.mark.asyncio
+async def test_propagate_links_every_parent_session_to_subtask() -> None:
+    """Every link on the parent gets re-attached to the new subtask."""
+    svc = MessagingService.__new__(MessagingService)
+    parent_session = uuid4()
+    review_session = uuid4()
+    svc.get_sessions_for_task = AsyncMock(  # type: ignore[method-assign]
+        return_value=[
+            _link(parent_session, "discussion"),
+            _link(review_session, "review"),
+        ]
+    )
+
+    calls: list[dict[str, Any]] = []
+
+    async def fake_link(**kwargs: Any) -> Any:
+        calls.append(kwargs)
+        link = MagicMock()
+        link.session_id = kwargs["session_id"]
+        link.task_id = kwargs["task_id"]
+        return link
+
+    svc.link_session_to_task = fake_link  # type: ignore[method-assign]
+
+    parent_id = uuid4()
+    subtask_id = uuid4()
+    added_by = uuid4()
+    expected_sessions = {parent_session, review_session}
+    out = await svc.propagate_sessions_to_subtask(parent_id, subtask_id, added_by)
+    assert len(out) == len(expected_sessions)
+    assert {c["session_id"] for c in calls} == expected_sessions
+    # Every propagated link must be non-primary — primary is the subtask's
+    # own slot, never inherited from the parent.
+    assert all(c["is_primary"] is False for c in calls)
+    # Every call must target the new subtask (not the parent).
+    assert {c["task_id"] for c in calls} == {subtask_id}
+    # Relationship types preserved.
+    rels = {c["relationship_type"] for c in calls}
+    assert SessionTaskRelationshipType.DISCUSSION in rels
+    assert SessionTaskRelationshipType.REVIEW in rels
+
+
+@pytest.mark.asyncio
+async def test_propagate_no_parent_sessions_returns_empty() -> None:
+    """When the parent has no session links, propagation is a no-op."""
+    svc = MessagingService.__new__(MessagingService)
+    svc.get_sessions_for_task = AsyncMock(return_value=[])  # type: ignore[method-assign]
+    svc.link_session_to_task = AsyncMock()  # type: ignore[method-assign]
+
+    out = await svc.propagate_sessions_to_subtask(uuid4(), uuid4(), uuid4())
+    assert out == []
+    svc.link_session_to_task.assert_not_awaited()
+
+
+@pytest.mark.asyncio
+async def test_propagate_unknown_relationship_type_defaults_to_discussion() -> None:
+    """Garbage relationship_type on the parent link doesn't crash; it
+    defaults to DISCUSSION so the subtask is still linked."""
+    svc = MessagingService.__new__(MessagingService)
+    svc.get_sessions_for_task = AsyncMock(  # type: ignore[method-assign]
+        return_value=[_link(uuid4(), "definitely-not-a-real-type")]
+    )
+    calls: list[dict[str, Any]] = []
+
+    async def fake_link(**kwargs: Any) -> Any:
+        calls.append(kwargs)
+        return MagicMock()
+
+    svc.link_session_to_task = fake_link  # type: ignore[method-assign]
+
+    await svc.propagate_sessions_to_subtask(uuid4(), uuid4(), uuid4())
+    assert len(calls) == 1
+    assert calls[0]["relationship_type"] == SessionTaskRelationshipType.DISCUSSION