Rename Foundry handoffs to tasks (#239)

* Restore foundry onboarding stack

* Consolidate foundry rename

* Create foundry tasks without prompts

* Rename Foundry handoffs to tasks

foundry/packages/backend/CLAUDE.md

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+# Backend Notes
+
+## Actor Hierarchy
+
+Keep the backend actor tree aligned with this shape unless we explicitly decide to change it:
+
+```text
+WorkspaceActor
+├─ HistoryActor(workspace-scoped global feed)
+├─ ProjectActor(repo)
+│  ├─ ProjectBranchSyncActor
+│  ├─ ProjectPrSyncActor
+│  └─ TaskActor(task)
+│     ├─ TaskSessionActor(session) × N
+│     │  └─ SessionStatusSyncActor(session) × 0..1
+│     └─ Task-local workbench state
+└─ SandboxInstanceActor(providerId, sandboxId) × N
+```
+
+## Ownership Rules
+
+- `WorkspaceActor` is the workspace coordinator and lookup/index owner.
+- `HistoryActor` is workspace-scoped. There is one workspace-level history feed.
+- `ProjectActor` is the repo coordinator and owns repo-local caches/indexes.
+- `TaskActor` is one branch. Treat `1 task = 1 branch` once branch assignment is finalized.
+- `TaskActor` can have many sessions.
+- `TaskActor` can reference many sandbox instances historically, but should have only one active sandbox/session at a time.
+- Session unread state and draft prompts are backend-owned workbench state, not frontend-local state.
+- Branch rename is a real git operation, not just metadata.
+- `SandboxInstanceActor` stays separate from `TaskActor`; tasks/sessions reference it by identity.
+- Sync actors are polling workers only. They feed parent actors and should not become the source of truth.
+
+## Maintenance
+
+- Keep this file up to date whenever actor ownership, hierarchy, or lifecycle responsibilities change.
+- If the real actor tree diverges from this document, update this document in the same change.