From a23ca752303d2b8fad9b73c48f61a126927a6209 Mon Sep 17 00:00:00 2001
From: Ken Chau <kchau@outlook.com>
Date: Wed, 6 May 2026 15:20:51 -0700
Subject: [PATCH 1/8] feat: add _sum_cost_usd helper for spawn cost bridge

---
 amplifier_app_cli/session_spawner.py | 33 +++++++++++++++++--
 tests/test_cost_bridge.py            | 49 ++++++++++++++++++++++++++++
 2 files changed, 80 insertions(+), 2 deletions(-)
 create mode 100644 tests/test_cost_bridge.py

diff --git a/amplifier_app_cli/session_spawner.py b/amplifier_app_cli/session_spawner.py
index 190e3db..8e9dbb5 100644
--- a/amplifier_app_cli/session_spawner.py
+++ b/amplifier_app_cli/session_spawner.py
@@ -5,6 +5,7 @@
 
 import logging
 import sys
+from decimal import Decimal
 from pathlib import Path
 
 from amplifier_core import AmplifierSession
@@ -14,6 +15,27 @@
 
 logger = logging.getLogger(__name__)
 
+
+# Intentionally duplicated across provider-anthropic, foundation, and hooks-streaming-ui.
+# These are separate repos with no shared utility dependency. The function is 10 lines —
+# the coordination cost of sharing outweighs the duplication cost.
+def _sum_cost_usd(contributions: list) -> Decimal | None:
+    """Sum cost_usd values from collect_contributions() results.
+
+    Returns Decimal total, or None if no cost data is present.
+    None != 0: None means unknown cost (no rate data), 0 means known-free.
+    """
+    total: Decimal | None = None
+    for c in contributions:
+        if c and isinstance(c, dict):
+            cost = c.get("cost_usd")
+            if cost is not None:
+                total = (total or Decimal("0")) + (
+                    cost if isinstance(cost, Decimal) else Decimal(str(cost))
+                )
+    return total
+
+
 # Capture default sys.path entries at import time.
 # Used to filter out bundle-added paths when forwarding sys_paths to subprocess children.
 _DEFAULT_SYS_PATHS: frozenset[str] = frozenset(sys.path)
@@ -714,7 +736,11 @@ async def _capture_completion(event: str, data: dict) -> HookResult:
     }
 
 
-async def resume_sub_session(sub_session_id: str, instruction: str, parent_session: AmplifierSession | None = None) -> dict:
+async def resume_sub_session(
+    sub_session_id: str,
+    instruction: str,
+    parent_session: AmplifierSession | None = None,
+) -> dict:
     """Resume existing sub-session for multi-turn engagement.
 
     Loads previously saved sub-session state, recreates the session with
@@ -1016,7 +1042,10 @@ async def _capture_completion(event: str, data: dict) -> HookResult:
     finally:
         # Unregister child cancellation token before cleanup
         # MUST run even if execution was cancelled (CancelledError) or failed
-        if resume_parent_cancellation is not None and resume_child_cancellation is not None:
+        if (
+            resume_parent_cancellation is not None
+            and resume_child_cancellation is not None
+        ):
             resume_parent_cancellation.unregister_child(resume_child_cancellation)
             logger.debug(
                 f"Unregistered child cancellation token for resumed sub-session {sub_session_id}"
diff --git a/tests/test_cost_bridge.py b/tests/test_cost_bridge.py
new file mode 100644
index 0000000..0094b09
--- /dev/null
+++ b/tests/test_cost_bridge.py
@@ -0,0 +1,49 @@
+"""Tests for _sum_cost_usd helper in session_spawner."""
+
+from decimal import Decimal
+
+from amplifier_app_cli.session_spawner import _sum_cost_usd
+
+
+def test_sums_single_contribution():
+    result = _sum_cost_usd([{"cost_usd": Decimal("0.05")}])
+    assert result == Decimal("0.05")
+
+
+def test_sums_multiple_contributions():
+    result = _sum_cost_usd(
+        [
+            {"cost_usd": Decimal("0.03")},
+            {"cost_usd": Decimal("0.05")},
+            {"cost_usd": Decimal("0.01")},
+        ]
+    )
+    assert result == Decimal("0.09")
+
+
+def test_returns_none_for_empty_list():
+    result = _sum_cost_usd([])
+    assert result is None
+
+
+def test_returns_none_when_all_none():
+    result = _sum_cost_usd([{"cost_usd": None}, None, {}])
+    assert result is None
+
+
+def test_accepts_string_cost_usd():
+    result = _sum_cost_usd([{"cost_usd": "0.05"}])
+    assert result == Decimal("0.05")
+    assert isinstance(result, Decimal)
+
+
+def test_skips_none_entries_in_mixed_list():
+    result = _sum_cost_usd(
+        [
+            {"cost_usd": Decimal("0.03")},
+            None,
+            {"cost_usd": None},
+            {"cost_usd": Decimal("0.02")},
+        ]
+    )
+    assert result == Decimal("0.05")

From c66f0a3a5af215f75d063b9cd1d3d5f6c8ee200b Mon Sep 17 00:00:00 2001
From: Ken Chau <kchau@outlook.com>
Date: Wed, 6 May 2026 15:29:45 -0700
Subject: [PATCH 2/8] feat: bridge child session costs to parent in
 spawn_sub_session()

---
 amplifier_app_cli/session_spawner.py | 29 ++++++++++++++++
 tests/test_cost_bridge.py            | 51 ++++++++++++++++++++++++++++
 tests/test_session_spawner.py        |  8 +++++
 3 files changed, 88 insertions(+)

diff --git a/amplifier_app_cli/session_spawner.py b/amplifier_app_cli/session_spawner.py
index 8e9dbb5..e50ad4a 100644
--- a/amplifier_app_cli/session_spawner.py
+++ b/amplifier_app_cli/session_spawner.py
@@ -36,6 +36,28 @@ def _sum_cost_usd(contributions: list) -> Decimal | None:
     return total
 
 
+async def _bridge_child_cost(
+    child_coordinator,
+    parent_coordinator,
+    child_session_id: str,
+) -> None:
+    """Propagate child session cost to parent's session.cost channel.
+
+    Called after child_session.execute() returns and before child_session.cleanup().
+    The child coordinator is still alive in this window.
+    """
+    child_contributions = await child_coordinator.collect_contributions("session.cost")
+    child_total = _sum_cost_usd(child_contributions)
+
+    if child_total is not None:
+        # Freeze value in default arg — child coordinator will be torn down after this
+        parent_coordinator.register_contributor(
+            "session.cost",
+            f"delegate:{child_session_id}",
+            lambda total=child_total: {"cost_usd": total},
+        )
+
+
 # Capture default sys.path entries at import time.
 # Used to filter out bundle-added paths when forwarding sys_paths to subprocess children.
 _DEFAULT_SYS_PATHS: frozenset[str] = frozenset(sys.path)
@@ -710,6 +732,13 @@ async def _capture_completion(event: str, data: dict) -> HookResult:
         store.save(sub_session_id, transcript, metadata)
         logger.debug(f"Sub-session {sub_session_id} state persisted")
 
+        # Bridge child session costs to parent coordinator before child is torn down
+        await _bridge_child_cost(
+            child_coordinator=child_session.coordinator,
+            parent_coordinator=parent_session.coordinator,
+            child_session_id=sub_session_id,
+        )
+
     finally:
         # Unregister child cancellation token before cleanup
         # MUST run even if execution was cancelled (CancelledError) or failed
diff --git a/tests/test_cost_bridge.py b/tests/test_cost_bridge.py
index 0094b09..8ba930d 100644
--- a/tests/test_cost_bridge.py
+++ b/tests/test_cost_bridge.py
@@ -1,6 +1,9 @@
 """Tests for _sum_cost_usd helper in session_spawner."""
 
 from decimal import Decimal
+from unittest.mock import AsyncMock, MagicMock
+
+import pytest
 
 from amplifier_app_cli.session_spawner import _sum_cost_usd
 
@@ -47,3 +50,51 @@ def test_skips_none_entries_in_mixed_list():
         ]
     )
     assert result == Decimal("0.05")
+
+
+@pytest.mark.asyncio
+async def test_spawn_bridge_registers_child_cost_on_parent():
+    """After spawn_sub_session completes, parent coordinator has a delegate contributor."""
+    child_coord = MagicMock()
+    child_coord.collect_contributions = AsyncMock(
+        return_value=[{"cost_usd": Decimal("0.07")}]
+    )
+
+    parent_coord = MagicMock()
+    registered = {}
+
+    def capture_register(channel, name, callback):
+        registered[(channel, name)] = callback
+
+    parent_coord.register_contributor = capture_register
+
+    from amplifier_app_cli.session_spawner import _bridge_child_cost
+    await _bridge_child_cost(
+        child_coordinator=child_coord,
+        parent_coordinator=parent_coord,
+        child_session_id="test-child-123",
+    )
+
+    key = ("session.cost", "delegate:test-child-123")
+    assert key in registered
+    result = registered[key]()
+    assert result == {"cost_usd": Decimal("0.07")}
+
+
+@pytest.mark.asyncio
+async def test_spawn_bridge_skips_registration_when_no_cost():
+    """If child has no cost data, no contributor is registered on parent."""
+    child_coord = MagicMock()
+    child_coord.collect_contributions = AsyncMock(return_value=[])
+
+    parent_coord = MagicMock()
+    parent_coord.register_contributor = MagicMock()
+
+    from amplifier_app_cli.session_spawner import _bridge_child_cost
+    await _bridge_child_cost(
+        child_coordinator=child_coord,
+        parent_coordinator=parent_coord,
+        child_session_id="test-child-456",
+    )
+
+    parent_coord.register_contributor.assert_not_called()
diff --git a/tests/test_session_spawner.py b/tests/test_session_spawner.py
index 1e5e593..4bc8e2c 100644
--- a/tests/test_session_spawner.py
+++ b/tests/test_session_spawner.py
@@ -659,6 +659,7 @@ def child_get(name):
 
         child_coordinator.get = child_get
         child_coordinator.mount = AsyncMock()
+        child_coordinator.collect_contributions = AsyncMock(return_value=[])
 
         async def mock_execute(instruction):
             # Simulate orchestrator emitting orchestrator:complete during execute
@@ -769,6 +770,7 @@ def child_get(name):
 
         child_coordinator.get = child_get
         child_coordinator.mount = AsyncMock()
+        child_coordinator.collect_contributions = AsyncMock(return_value=[])
 
         child_session = MagicMock()
         child_session.coordinator = child_coordinator
@@ -1052,6 +1054,7 @@ def child_get(name):
 
         child_coordinator.get = child_get
         child_coordinator.mount = AsyncMock()
+        child_coordinator.collect_contributions = AsyncMock(return_value=[])
 
         child_session = MagicMock()
         child_session.coordinator = child_coordinator
@@ -1217,6 +1220,7 @@ def child_get(name):
 
         child_coordinator.get = child_get
         child_coordinator.mount = AsyncMock()
+        child_coordinator.collect_contributions = AsyncMock(return_value=[])
 
         child_session = MagicMock()
         child_session.coordinator = child_coordinator
@@ -1335,6 +1339,7 @@ def child_get(name):
 
         child_coordinator.get = child_get
         child_coordinator.mount = AsyncMock()
+        child_coordinator.collect_contributions = AsyncMock(return_value=[])
 
         child_session = MagicMock()
         child_session.coordinator = child_coordinator
@@ -1445,6 +1450,7 @@ def child_get(name):
 
         child_coordinator.get = child_get
         child_coordinator.mount = AsyncMock()
+        child_coordinator.collect_contributions = AsyncMock(return_value=[])
 
         child_session = MagicMock()
         child_session.coordinator = child_coordinator
@@ -1561,6 +1567,7 @@ def child_get(name):
 
         child_coordinator.get = child_get
         child_coordinator.mount = AsyncMock()
+        child_coordinator.collect_contributions = AsyncMock(return_value=[])
 
         child_session = MagicMock()
         child_session.coordinator = child_coordinator
@@ -1657,6 +1664,7 @@ def child_get(name):
 
         child_coordinator.get = child_get
         child_coordinator.mount = AsyncMock()
+        child_coordinator.collect_contributions = AsyncMock(return_value=[])
 
         child_session = MagicMock()
         child_session.coordinator = child_coordinator

From 9c19733e18a9fb9b3bbf22d39553aaea95ba4fb3 Mon Sep 17 00:00:00 2001
From: Ken Chau <kchau@outlook.com>
Date: Wed, 6 May 2026 15:33:36 -0700
Subject: [PATCH 3/8] feat: bridge child session costs in resume_sub_session()

---
 amplifier_app_cli/session_spawner.py |  8 ++++++++
 tests/test_cost_bridge.py            | 26 ++++++++++++++++++++++++++
 2 files changed, 34 insertions(+)

diff --git a/amplifier_app_cli/session_spawner.py b/amplifier_app_cli/session_spawner.py
index e50ad4a..f3e79a5 100644
--- a/amplifier_app_cli/session_spawner.py
+++ b/amplifier_app_cli/session_spawner.py
@@ -1068,6 +1068,14 @@ async def _capture_completion(event: str, data: dict) -> HookResult:
             f"Sub-session {sub_session_id} state updated (turn {metadata['turn_count']})"
         )
 
+        # Bridge child session costs to parent coordinator before child is torn down
+        if parent_session is not None:
+            await _bridge_child_cost(
+                child_coordinator=child_session.coordinator,
+                parent_coordinator=parent_session.coordinator,
+                child_session_id=sub_session_id,
+            )
+
     finally:
         # Unregister child cancellation token before cleanup
         # MUST run even if execution was cancelled (CancelledError) or failed
diff --git a/tests/test_cost_bridge.py b/tests/test_cost_bridge.py
index 8ba930d..343a148 100644
--- a/tests/test_cost_bridge.py
+++ b/tests/test_cost_bridge.py
@@ -98,3 +98,29 @@ async def test_spawn_bridge_skips_registration_when_no_cost():
     )
 
     parent_coord.register_contributor.assert_not_called()
+
+
+@pytest.mark.asyncio
+async def test_resume_bridge_registers_child_cost_on_parent():
+    """resume_sub_session also bridges child costs after execute()."""
+    child_coord = MagicMock()
+    child_coord.collect_contributions = AsyncMock(
+        return_value=[{"cost_usd": Decimal("0.04")}]
+    )
+
+    parent_coord = MagicMock()
+    registered = {}
+
+    def capture_register(channel, name, callback):
+        registered[(channel, name)] = callback
+
+    parent_coord.register_contributor = capture_register
+
+    from amplifier_app_cli.session_spawner import _bridge_child_cost
+    await _bridge_child_cost(
+        child_coordinator=child_coord,
+        parent_coordinator=parent_coord,
+        child_session_id="resumed-child-789",
+    )
+
+    assert ("session.cost", "delegate:resumed-child-789") in registered

From 2dc6828d4d03ac72ae7ce91b270422729f75d7f7 Mon Sep 17 00:00:00 2001
From: Ken Chau <kchau@outlook.com>
Date: Wed, 6 May 2026 16:01:49 -0700
Subject: [PATCH 4/8] style: fix ruff formatting in test_cost_bridge.py

---
 tests/test_cost_bridge.py | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/tests/test_cost_bridge.py b/tests/test_cost_bridge.py
index 343a148..709e0e7 100644
--- a/tests/test_cost_bridge.py
+++ b/tests/test_cost_bridge.py
@@ -69,6 +69,7 @@ def capture_register(channel, name, callback):
     parent_coord.register_contributor = capture_register
 
     from amplifier_app_cli.session_spawner import _bridge_child_cost
+
     await _bridge_child_cost(
         child_coordinator=child_coord,
         parent_coordinator=parent_coord,
@@ -91,6 +92,7 @@ async def test_spawn_bridge_skips_registration_when_no_cost():
     parent_coord.register_contributor = MagicMock()
 
     from amplifier_app_cli.session_spawner import _bridge_child_cost
+
     await _bridge_child_cost(
         child_coordinator=child_coord,
         parent_coordinator=parent_coord,
@@ -117,6 +119,7 @@ def capture_register(channel, name, callback):
     parent_coord.register_contributor = capture_register
 
     from amplifier_app_cli.session_spawner import _bridge_child_cost
+
     await _bridge_child_cost(
         child_coordinator=child_coord,
         parent_coordinator=parent_coord,

From 5bbe66e0fb3679da5b5964014b92afe9407b7cf8 Mon Sep 17 00:00:00 2001
From: Ken Chau <kchau@outlook.com>
Date: Wed, 6 May 2026 23:38:06 -0700
Subject: [PATCH 5/8] refactor: improve _sum_cost_usd comment to describe
 purpose rather than implementation note

---
 .../brainstorm/77298-1776142637/state/server-stopped         | 1 +
 amplifier_app_cli/session_spawner.py                         | 5 ++---
 2 files changed, 3 insertions(+), 3 deletions(-)
 create mode 100644 .superpowers/brainstorm/77298-1776142637/state/server-stopped

diff --git a/.superpowers/brainstorm/77298-1776142637/state/server-stopped b/.superpowers/brainstorm/77298-1776142637/state/server-stopped
new file mode 100644
index 0000000..d59b8f7
--- /dev/null
+++ b/.superpowers/brainstorm/77298-1776142637/state/server-stopped
@@ -0,0 +1 @@
+{"reason":"idle timeout","timestamp":1776146178059}
diff --git a/amplifier_app_cli/session_spawner.py b/amplifier_app_cli/session_spawner.py
index f3e79a5..8abeaa7 100644
--- a/amplifier_app_cli/session_spawner.py
+++ b/amplifier_app_cli/session_spawner.py
@@ -16,9 +16,8 @@
 logger = logging.getLogger(__name__)
 
 
-# Intentionally duplicated across provider-anthropic, foundation, and hooks-streaming-ui.
-# These are separate repos with no shared utility dependency. The function is 10 lines —
-# the coordination cost of sharing outweighs the duplication cost.
+# Collects cost_usd contributions from a session.cost channel and returns the
+# total as Decimal, or None when no cost data is present (e.g. self-hosted models).
 def _sum_cost_usd(contributions: list) -> Decimal | None:
     """Sum cost_usd values from collect_contributions() results.
 

From 32ea8fde50217f44dd25e2365e5611ab5432e2f0 Mon Sep 17 00:00:00 2001
From: Ken Chau <kchau@outlook.com>
Date: Thu, 7 May 2026 01:33:38 -0700
Subject: [PATCH 6/8] fix: wrap _bridge_child_cost in try/except, fix test
 description, remove stray artifact

---
 .../77298-1776142637/state/server-stopped     |  1 -
 amplifier_app_cli/session_spawner.py          | 34 ++++++---
 tests/test_cost_bridge.py                     | 75 +++++++++++++++++++
 3 files changed, 99 insertions(+), 11 deletions(-)
 delete mode 100644 .superpowers/brainstorm/77298-1776142637/state/server-stopped

diff --git a/.superpowers/brainstorm/77298-1776142637/state/server-stopped b/.superpowers/brainstorm/77298-1776142637/state/server-stopped
deleted file mode 100644
index d59b8f7..0000000
--- a/.superpowers/brainstorm/77298-1776142637/state/server-stopped
+++ /dev/null
@@ -1 +0,0 @@
-{"reason":"idle timeout","timestamp":1776146178059}
diff --git a/amplifier_app_cli/session_spawner.py b/amplifier_app_cli/session_spawner.py
index 8abeaa7..2072def 100644
--- a/amplifier_app_cli/session_spawner.py
+++ b/amplifier_app_cli/session_spawner.py
@@ -732,11 +732,18 @@ async def _capture_completion(event: str, data: dict) -> HookResult:
         logger.debug(f"Sub-session {sub_session_id} state persisted")
 
         # Bridge child session costs to parent coordinator before child is torn down
-        await _bridge_child_cost(
-            child_coordinator=child_session.coordinator,
-            parent_coordinator=parent_session.coordinator,
-            child_session_id=sub_session_id,
-        )
+        try:
+            await _bridge_child_cost(
+                child_coordinator=child_session.coordinator,
+                parent_coordinator=parent_session.coordinator,
+                child_session_id=sub_session_id,
+            )
+        except Exception:
+            logger.warning(
+                "Failed to bridge child session cost for %s; skipping",
+                sub_session_id,
+                exc_info=True,
+            )
 
     finally:
         # Unregister child cancellation token before cleanup
@@ -1069,11 +1076,18 @@ async def _capture_completion(event: str, data: dict) -> HookResult:
 
         # Bridge child session costs to parent coordinator before child is torn down
         if parent_session is not None:
-            await _bridge_child_cost(
-                child_coordinator=child_session.coordinator,
-                parent_coordinator=parent_session.coordinator,
-                child_session_id=sub_session_id,
-            )
+            try:
+                await _bridge_child_cost(
+                    child_coordinator=child_session.coordinator,
+                    parent_coordinator=parent_session.coordinator,
+                    child_session_id=sub_session_id,
+                )
+            except Exception:
+                logger.warning(
+                    "Failed to bridge child session cost for %s; skipping",
+                    sub_session_id,
+                    exc_info=True,
+                )
 
     finally:
         # Unregister child cancellation token before cleanup
diff --git a/tests/test_cost_bridge.py b/tests/test_cost_bridge.py
index 709e0e7..206a1a6 100644
--- a/tests/test_cost_bridge.py
+++ b/tests/test_cost_bridge.py
@@ -127,3 +127,78 @@ def capture_register(channel, name, callback):
     )
 
     assert ("session.cost", "delegate:resumed-child-789") in registered
+
+
+@pytest.mark.asyncio
+async def test_resume_bridge_accumulates_incremental_costs():
+    """Resuming the same session twice correctly accumulates incremental costs.
+
+    Each resume_sub_session call creates a FRESH child coordinator.  The provider
+    re-mounts from zero, so the child's session.cost channel only contains costs
+    for THAT resume's turns — not the full session history.
+
+    _bridge_child_cost therefore passes the incremental cost for each resume.
+
+    register_contributor in amplifier-core APPENDS (coordinator.rs: .push(entry)) —
+    it does NOT overwrite on duplicate name.  Both entries are returned by
+    collect_contributions and summed correctly by _sum_cost_usd.
+
+    Verified properties:
+    - Both calls use the same (channel, name) key — standard contributor identity.
+    - Each callback carries only the incremental cost of its resume.
+    - _sum_cost_usd([cb1(), cb2()]) == first_cost + second_cost (no double-count).
+    """
+    from amplifier_app_cli.session_spawner import _bridge_child_cost, _sum_cost_usd
+
+    parent_coord = MagicMock()
+    all_register_calls: list[tuple] = []
+
+    def capture_register(channel, name, callback):
+        all_register_calls.append((channel, name, callback))
+
+    parent_coord.register_contributor = capture_register
+
+    # First resume: fresh child coordinator accumulated $0.04 (turn 1 only)
+    child_coord_1 = MagicMock()
+    child_coord_1.collect_contributions = AsyncMock(
+        return_value=[{"cost_usd": Decimal("0.04")}]
+    )
+    await _bridge_child_cost(
+        child_coordinator=child_coord_1,
+        parent_coordinator=parent_coord,
+        child_session_id="test-child-xyz",
+    )
+
+    # Second resume: fresh child coordinator accumulated $0.06 (turn 2 only)
+    child_coord_2 = MagicMock()
+    child_coord_2.collect_contributions = AsyncMock(
+        return_value=[{"cost_usd": Decimal("0.06")}]
+    )
+    await _bridge_child_cost(
+        child_coordinator=child_coord_2,
+        parent_coordinator=parent_coord,
+        child_session_id="test-child-xyz",
+    )
+
+    assert len(all_register_calls) == 2, "Expected exactly two register_contributor calls"
+
+    channel1, name1, _ = all_register_calls[0]
+    channel2, name2, _ = all_register_calls[1]
+
+    # Same channel + name: register_contributor appends both, collect_contributions
+    # returns both, _sum_cost_usd sums them — no key uniqueness required.
+    assert channel1 == channel2 == "session.cost"
+    assert name1 == name2 == "delegate:test-child-xyz"
+
+    # Verify incremental values and that their sum is correct
+    _, _, cb1 = all_register_calls[0]
+    _, _, cb2 = all_register_calls[1]
+    assert cb1()["cost_usd"] == Decimal("0.04")
+    assert cb2()["cost_usd"] == Decimal("0.06")
+
+    # Simulate what collect_contributions + _sum_cost_usd would produce:
+    # both entries are returned, summed to $0.10 (no double-counting)
+    total = _sum_cost_usd([cb1(), cb2()])
+    assert total == Decimal("0.10"), (
+        f"Expected $0.10 from two incremental contributions, got {total!r}"
+    )

From d1b6d7daf8280393729933a795e3cbfd2e59a912 Mon Sep 17 00:00:00 2001
From: Ken Chau <kchau@outlook.com>
Date: Thu, 7 May 2026 09:44:40 -0700
Subject: [PATCH 7/8] refactor: import _bridge_child_cost from foundation
 instead of reimplementing; remove outer try/except wrappers

---
 amplifier_app_cli/session_spawner.py | 81 +++++-----------------------
 tests/test_cost_bridge.py            | 36 +++++++++----
 2 files changed, 40 insertions(+), 77 deletions(-)

diff --git a/amplifier_app_cli/session_spawner.py b/amplifier_app_cli/session_spawner.py
index 2072def..e91694e 100644
--- a/amplifier_app_cli/session_spawner.py
+++ b/amplifier_app_cli/session_spawner.py
@@ -5,58 +5,17 @@
 
 import logging
 import sys
-from decimal import Decimal
 from pathlib import Path
 
 from amplifier_core import AmplifierSession
 from amplifier_foundation import generate_sub_session_id
+from amplifier_foundation.bundle._prepared import _bridge_child_cost
 
 from .agent_config import merge_configs
 
 logger = logging.getLogger(__name__)
 
 
-# Collects cost_usd contributions from a session.cost channel and returns the
-# total as Decimal, or None when no cost data is present (e.g. self-hosted models).
-def _sum_cost_usd(contributions: list) -> Decimal | None:
-    """Sum cost_usd values from collect_contributions() results.
-
-    Returns Decimal total, or None if no cost data is present.
-    None != 0: None means unknown cost (no rate data), 0 means known-free.
-    """
-    total: Decimal | None = None
-    for c in contributions:
-        if c and isinstance(c, dict):
-            cost = c.get("cost_usd")
-            if cost is not None:
-                total = (total or Decimal("0")) + (
-                    cost if isinstance(cost, Decimal) else Decimal(str(cost))
-                )
-    return total
-
-
-async def _bridge_child_cost(
-    child_coordinator,
-    parent_coordinator,
-    child_session_id: str,
-) -> None:
-    """Propagate child session cost to parent's session.cost channel.
-
-    Called after child_session.execute() returns and before child_session.cleanup().
-    The child coordinator is still alive in this window.
-    """
-    child_contributions = await child_coordinator.collect_contributions("session.cost")
-    child_total = _sum_cost_usd(child_contributions)
-
-    if child_total is not None:
-        # Freeze value in default arg — child coordinator will be torn down after this
-        parent_coordinator.register_contributor(
-            "session.cost",
-            f"delegate:{child_session_id}",
-            lambda total=child_total: {"cost_usd": total},
-        )
-
-
 # Capture default sys.path entries at import time.
 # Used to filter out bundle-added paths when forwarding sys_paths to subprocess children.
 _DEFAULT_SYS_PATHS: frozenset[str] = frozenset(sys.path)
@@ -731,19 +690,12 @@ async def _capture_completion(event: str, data: dict) -> HookResult:
         store.save(sub_session_id, transcript, metadata)
         logger.debug(f"Sub-session {sub_session_id} state persisted")
 
-        # Bridge child session costs to parent coordinator before child is torn down
-        try:
-            await _bridge_child_cost(
-                child_coordinator=child_session.coordinator,
-                parent_coordinator=parent_session.coordinator,
-                child_session_id=sub_session_id,
-            )
-        except Exception:
-            logger.warning(
-                "Failed to bridge child session cost for %s; skipping",
-                sub_session_id,
-                exc_info=True,
-            )
+        # Bridge child session costs to parent coordinator (_bridge_child_cost never raises)
+        await _bridge_child_cost(
+            child_coordinator=child_session.coordinator,
+            parent_coordinator=parent_session.coordinator,
+            child_session_id=sub_session_id,
+        )
 
     finally:
         # Unregister child cancellation token before cleanup
@@ -1074,20 +1026,13 @@ async def _capture_completion(event: str, data: dict) -> HookResult:
             f"Sub-session {sub_session_id} state updated (turn {metadata['turn_count']})"
         )
 
-        # Bridge child session costs to parent coordinator before child is torn down
+        # Bridge child session costs to parent coordinator (_bridge_child_cost never raises)
         if parent_session is not None:
-            try:
-                await _bridge_child_cost(
-                    child_coordinator=child_session.coordinator,
-                    parent_coordinator=parent_session.coordinator,
-                    child_session_id=sub_session_id,
-                )
-            except Exception:
-                logger.warning(
-                    "Failed to bridge child session cost for %s; skipping",
-                    sub_session_id,
-                    exc_info=True,
-                )
+            await _bridge_child_cost(
+                child_coordinator=child_session.coordinator,
+                parent_coordinator=parent_session.coordinator,
+                child_session_id=sub_session_id,
+            )
 
     finally:
         # Unregister child cancellation token before cleanup
diff --git a/tests/test_cost_bridge.py b/tests/test_cost_bridge.py
index 206a1a6..3a5cc0e 100644
--- a/tests/test_cost_bridge.py
+++ b/tests/test_cost_bridge.py
@@ -1,11 +1,15 @@
-"""Tests for _sum_cost_usd helper in session_spawner."""
+"""Tests for spawn cost bridge helpers.
+
+_sum_cost_usd and _bridge_child_cost live in amplifier_foundation.bundle._prepared
+and are imported directly from there (app-cli delegates, not reimplements).
+"""
 
 from decimal import Decimal
 from unittest.mock import AsyncMock, MagicMock
 
 import pytest
 
-from amplifier_app_cli.session_spawner import _sum_cost_usd
+from amplifier_foundation.bundle._prepared import _bridge_child_cost, _sum_cost_usd
 
 
 def test_sums_single_contribution():
@@ -68,8 +72,6 @@ def capture_register(channel, name, callback):
 
     parent_coord.register_contributor = capture_register
 
-    from amplifier_app_cli.session_spawner import _bridge_child_cost
-
     await _bridge_child_cost(
         child_coordinator=child_coord,
         parent_coordinator=parent_coord,
@@ -82,6 +84,27 @@ def capture_register(channel, name, callback):
     assert result == {"cost_usd": Decimal("0.07")}
 
 
+@pytest.mark.asyncio
+async def test_bridge_swallows_exception_and_logs():
+    """_bridge_child_cost never raises — errors are logged as warnings."""
+    child_coord = MagicMock()
+    # Simulate a failure inside collect_contributions
+    child_coord.collect_contributions = AsyncMock(side_effect=RuntimeError("simulated"))
+
+    parent_coord = MagicMock()
+    parent_coord.register_contributor = MagicMock()
+
+    # Must not raise
+    await _bridge_child_cost(
+        child_coordinator=child_coord,
+        parent_coordinator=parent_coord,
+        child_session_id="test-child-err",
+    )
+
+    # No contributor registered because the bridge failed before it could register
+    parent_coord.register_contributor.assert_not_called()
+
+
 @pytest.mark.asyncio
 async def test_spawn_bridge_skips_registration_when_no_cost():
     """If child has no cost data, no contributor is registered on parent."""
@@ -91,8 +114,6 @@ async def test_spawn_bridge_skips_registration_when_no_cost():
     parent_coord = MagicMock()
     parent_coord.register_contributor = MagicMock()
 
-    from amplifier_app_cli.session_spawner import _bridge_child_cost
-
     await _bridge_child_cost(
         child_coordinator=child_coord,
         parent_coordinator=parent_coord,
@@ -118,8 +139,6 @@ def capture_register(channel, name, callback):
 
     parent_coord.register_contributor = capture_register
 
-    from amplifier_app_cli.session_spawner import _bridge_child_cost
-
     await _bridge_child_cost(
         child_coordinator=child_coord,
         parent_coordinator=parent_coord,
@@ -148,7 +167,6 @@ async def test_resume_bridge_accumulates_incremental_costs():
     - Each callback carries only the incremental cost of its resume.
     - _sum_cost_usd([cb1(), cb2()]) == first_cost + second_cost (no double-count).
     """
-    from amplifier_app_cli.session_spawner import _bridge_child_cost, _sum_cost_usd
 
     parent_coord = MagicMock()
     all_register_calls: list[tuple] = []

From 397d137b1d1e081cac816d4e0decfc5e79e34dd4 Mon Sep 17 00:00:00 2001
From: Ken Chau <kchau@microsoft.com>
Date: Thu, 7 May 2026 13:58:56 -0700
Subject: [PATCH 8/8] refactor: import bridge_child_cost from public
 amplifier_foundation API
MIME-Version: 1.0
Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: 8bit

🤖 Generated with [Amplifier](https://github.com/microsoft/amplifier)

Co-Authored-By: Amplifier <240397093+microsoft-amplifier@users.noreply.github.com>
---
 amplifier_app_cli/session_spawner.py | 10 +++++-----
 tests/test_cost_bridge.py            | 30 ++++++++++++++--------------
 2 files changed, 20 insertions(+), 20 deletions(-)

diff --git a/amplifier_app_cli/session_spawner.py b/amplifier_app_cli/session_spawner.py
index e91694e..e17fe84 100644
--- a/amplifier_app_cli/session_spawner.py
+++ b/amplifier_app_cli/session_spawner.py
@@ -9,7 +9,7 @@
 
 from amplifier_core import AmplifierSession
 from amplifier_foundation import generate_sub_session_id
-from amplifier_foundation.bundle._prepared import _bridge_child_cost
+from amplifier_foundation import bridge_child_cost
 
 from .agent_config import merge_configs
 
@@ -690,8 +690,8 @@ async def _capture_completion(event: str, data: dict) -> HookResult:
         store.save(sub_session_id, transcript, metadata)
         logger.debug(f"Sub-session {sub_session_id} state persisted")
 
-        # Bridge child session costs to parent coordinator (_bridge_child_cost never raises)
-        await _bridge_child_cost(
+        # Bridge child session costs to parent coordinator (bridge_child_cost never raises)
+        await bridge_child_cost(
             child_coordinator=child_session.coordinator,
             parent_coordinator=parent_session.coordinator,
             child_session_id=sub_session_id,
@@ -1026,9 +1026,9 @@ async def _capture_completion(event: str, data: dict) -> HookResult:
             f"Sub-session {sub_session_id} state updated (turn {metadata['turn_count']})"
         )
 
-        # Bridge child session costs to parent coordinator (_bridge_child_cost never raises)
+        # Bridge child session costs to parent coordinator (bridge_child_cost never raises)
         if parent_session is not None:
-            await _bridge_child_cost(
+            await bridge_child_cost(
                 child_coordinator=child_session.coordinator,
                 parent_coordinator=parent_session.coordinator,
                 child_session_id=sub_session_id,
diff --git a/tests/test_cost_bridge.py b/tests/test_cost_bridge.py
index 3a5cc0e..7f9bc77 100644
--- a/tests/test_cost_bridge.py
+++ b/tests/test_cost_bridge.py
@@ -9,16 +9,16 @@
 
 import pytest
 
-from amplifier_foundation.bundle._prepared import _bridge_child_cost, _sum_cost_usd
+from amplifier_foundation import bridge_child_cost, sum_cost_usd
 
 
 def test_sums_single_contribution():
-    result = _sum_cost_usd([{"cost_usd": Decimal("0.05")}])
+    result = sum_cost_usd([{"cost_usd": Decimal("0.05")}])
     assert result == Decimal("0.05")
 
 
 def test_sums_multiple_contributions():
-    result = _sum_cost_usd(
+    result = sum_cost_usd(
         [
             {"cost_usd": Decimal("0.03")},
             {"cost_usd": Decimal("0.05")},
@@ -29,23 +29,23 @@ def test_sums_multiple_contributions():
 
 
 def test_returns_none_for_empty_list():
-    result = _sum_cost_usd([])
+    result = sum_cost_usd([])
     assert result is None
 
 
 def test_returns_none_when_all_none():
-    result = _sum_cost_usd([{"cost_usd": None}, None, {}])
+    result = sum_cost_usd([{"cost_usd": None}, None, {}])
     assert result is None
 
 
 def test_accepts_string_cost_usd():
-    result = _sum_cost_usd([{"cost_usd": "0.05"}])
+    result = sum_cost_usd([{"cost_usd": "0.05"}])
     assert result == Decimal("0.05")
     assert isinstance(result, Decimal)
 
 
 def test_skips_none_entries_in_mixed_list():
-    result = _sum_cost_usd(
+    result = sum_cost_usd(
         [
             {"cost_usd": Decimal("0.03")},
             None,
@@ -72,7 +72,7 @@ def capture_register(channel, name, callback):
 
     parent_coord.register_contributor = capture_register
 
-    await _bridge_child_cost(
+    await bridge_child_cost(
         child_coordinator=child_coord,
         parent_coordinator=parent_coord,
         child_session_id="test-child-123",
@@ -95,7 +95,7 @@ async def test_bridge_swallows_exception_and_logs():
     parent_coord.register_contributor = MagicMock()
 
     # Must not raise
-    await _bridge_child_cost(
+    await bridge_child_cost(
         child_coordinator=child_coord,
         parent_coordinator=parent_coord,
         child_session_id="test-child-err",
@@ -114,7 +114,7 @@ async def test_spawn_bridge_skips_registration_when_no_cost():
     parent_coord = MagicMock()
     parent_coord.register_contributor = MagicMock()
 
-    await _bridge_child_cost(
+    await bridge_child_cost(
         child_coordinator=child_coord,
         parent_coordinator=parent_coord,
         child_session_id="test-child-456",
@@ -139,7 +139,7 @@ def capture_register(channel, name, callback):
 
     parent_coord.register_contributor = capture_register
 
-    await _bridge_child_cost(
+    await bridge_child_cost(
         child_coordinator=child_coord,
         parent_coordinator=parent_coord,
         child_session_id="resumed-child-789",
@@ -165,7 +165,7 @@ async def test_resume_bridge_accumulates_incremental_costs():
     Verified properties:
     - Both calls use the same (channel, name) key — standard contributor identity.
     - Each callback carries only the incremental cost of its resume.
-    - _sum_cost_usd([cb1(), cb2()]) == first_cost + second_cost (no double-count).
+    - sum_cost_usd([cb1(), cb2()]) == first_cost + second_cost (no double-count).
     """
 
     parent_coord = MagicMock()
@@ -181,7 +181,7 @@ def capture_register(channel, name, callback):
     child_coord_1.collect_contributions = AsyncMock(
         return_value=[{"cost_usd": Decimal("0.04")}]
     )
-    await _bridge_child_cost(
+    await bridge_child_cost(
         child_coordinator=child_coord_1,
         parent_coordinator=parent_coord,
         child_session_id="test-child-xyz",
@@ -192,7 +192,7 @@ def capture_register(channel, name, callback):
     child_coord_2.collect_contributions = AsyncMock(
         return_value=[{"cost_usd": Decimal("0.06")}]
     )
-    await _bridge_child_cost(
+    await bridge_child_cost(
         child_coordinator=child_coord_2,
         parent_coordinator=parent_coord,
         child_session_id="test-child-xyz",
@@ -216,7 +216,7 @@ def capture_register(channel, name, callback):
 
     # Simulate what collect_contributions + _sum_cost_usd would produce:
     # both entries are returned, summed to $0.10 (no double-counting)
-    total = _sum_cost_usd([cb1(), cb2()])
+    total = sum_cost_usd([cb1(), cb2()])
     assert total == Decimal("0.10"), (
         f"Expected $0.10 from two incremental contributions, got {total!r}"
     )