From 10a5c29702e7db4750cf4f87aaad77fa7ad98085 Mon Sep 17 00:00:00 2001
From: Alex Blank <alexblank@fastmail.com>
Date: Sun, 24 May 2026 09:18:29 +0000
Subject: [PATCH] docs: add session branch selection design spec

- Design for branch dropdown in session creation
- New local branch creation at clone time
- Frontend/backend changes overview
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 ...6-05-24-session-branch-selection-design.md | 155 ++++++++++++++++++
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 create mode 100644 docs/superpowers/specs/2026-05-24-session-branch-selection-design.md

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+# Session Branch Selection with New Branch Creation
+
+## Summary
+
+Replace the free-text branch input in the session creation form with a dropdown of available branches from the repository. Add the ability to create a new local branch at clone time by selecting "Create new branch..." from the dropdown.
+
+## Context
+
+The current session creation UI (`apps/web/src/pages/sessions.tsx`) has a free-text input for the branch name when "Clone fresh copy" mode is selected. Users must manually type the branch name, which is error-prone and doesn't show what branches are available.
+
+The backend already has:
+- A `GET /projects/{project_id}/repositories/{repo_id}/branches` endpoint that returns all branches and the default branch
+- A `clone_repository` service that clones a specific branch
+- Branch creation APIs for the original repository
+
+## Design
+
+### Frontend Changes
+
+#### 1. Branch API Integration
+
+Add a new API function in `apps/web/src/api/git_repositories.ts`:
+
+```typescript
+export interface Branch {
+  name: string;
+  is_default: boolean;
+  last_commit: string | null;
+}
+
+export interface BranchesResponse {
+  branches: Branch[];
+  default_branch: string;
+}
+
+export async function listRepositoryBranches(
+  projectId: string,
+  repoId: string
+): Promise<BranchesResponse> {
+  const response = await apiClient.get(
+    `/projects/${projectId}/repositories/${repoId}/branches`
+  );
+  return response.data;
+}
+```
+
+#### 2. UI State Management
+
+In `apps/web/src/pages/sessions.tsx`, add state for:
+- `branches`: `Branch[]` — loaded when a repository is selected and clone mode is active
+- `isLoadingBranches`: `boolean`
+- `isCreatingNewBranch`: `boolean` — toggled when "Create new branch..." is selected
+- `newBranchName`: `string` — the name for the new branch
+- `baseBranch`: `string` — the base branch for the new branch
+
+#### 3. Branch Loading
+
+When a repository is selected and clone mode is "clone", fetch branches:
+- Call `listRepositoryBranches(selectedProject, selectedRepo)`
+- Set `baseBranch` to `default_branch` from the response
+- If the current `branch` state is not in the list, reset it to `default_branch`
+
+#### 4. Branch Dropdown
+
+Replace the free-text input with a `<select>`:
+- Options populated from `branches` state
+- Default branch marked visually: `"main (default)"`
+- Last option: `"Create new branch..."` (disabled separator style or as a real option)
+- When selected, set `isCreatingNewBranch = true`
+
+#### 5. New Branch Form
+
+When `isCreatingNewBranch` is true, show:
+- **New branch name** input (required, validated for valid git branch name)
+- **Base branch** dropdown (populated from `branches`, defaulting to `default_branch`)
+
+#### 6. Form Submission
+
+Update `handleCreate` to handle new branch creation:
+- If `isCreatingNewBranch` is true, pass `newBranchName` and `baseBranch` to the API
+- The `branch` parameter sent to the API should be:
+  - `newBranchName` if creating a new branch
+  - The selected existing branch otherwise
+
+### Backend Changes
+
+#### 1. Update `CreateInstanceRequest`
+
+In `apps/api/src/api/tool_instances.py`, extend the request model:
+
+```python
+class CreateInstanceRequest(BaseModel):
+    model_config = {"extra": "ignore"}
+    
+    tool_type_id: str = Field(description="UUID of the tool type to instantiate")
+    display_name: str | None = Field(default=None, description="Optional display name")
+    clone_mode: str = Field(default="mount", description="'mount' or 'clone'")
+    branch: str | None = Field(default="main", description="Branch to clone")
+    new_branch: str | None = Field(default=None, description="Create a new branch from 'branch' after clone")
+```
+
+#### 2. Update Clone Logic
+
+In `create_instance`, after cloning:
+- If `data.new_branch` is provided:
+  1. Clone the `data.branch` (base branch) as usual
+  2. Run `git -C <clone_path> checkout -b <new_branch>` to create the local branch
+  3. Store `new_branch` in the `branch` field of the ToolInstance record
+
+#### 3. Update `clone_repository` Service
+
+No changes needed — it already clones a specific branch. The new branch creation happens after clone.
+
+#### 4. Database Schema
+
+No changes needed — the existing `branch` field on `ToolInstance` can store the new branch name.
+
+### Data Flow
+
+```
+User selects repo + "Clone fresh copy"
+  → Frontend fetches branches from GET /branches
+  → User selects "Create new branch..."
+  → User fills: newBranchName="feature-x", baseBranch="dev"
+  → Frontend sends: { branch: "dev", new_branch: "feature-x", ... }
+  → Backend clones "dev" branch
+  → Backend runs: git checkout -b feature-x
+  → Instance record stores branch="feature-x"
+  → Container starts with the new branch checked out
+```
+
+### Error Handling
+
+- **Branch fetch fails**: Show error, fallback to free-text input
+- **Invalid branch name**: Frontend validation (regex for valid git branch names)
+- **New branch creation fails**: Backend returns 400 with git error message
+- **Branch already exists locally**: Backend handles gracefully (git checkout -b will fail if branch exists)
+
+### Testing
+
+1. **Frontend**: Test branch dropdown loads correctly, "Create new branch" toggle works, form submission sends correct payload
+2. **Backend**: Test instance creation with `new_branch` parameter, verify git command runs correctly
+3. **Integration**: End-to-end test creating a session with a new branch
+
+## Files Changed
+
+- `apps/web/src/api/git_repositories.ts` — Add `listRepositoryBranches` function
+- `apps/web/src/pages/sessions.tsx` — Replace branch input with dropdown + new branch form
+- `apps/api/src/api/tool_instances.py` — Extend `CreateInstanceRequest` and clone logic
+- `apps/api/src/services/clone.py` — Add `create_local_branch` helper (optional)
+
+## Trade-offs
+
+- **Local branch only**: The new branch is created in the cloned workspace only, not pushed to the remote. This is intentional — it's a disposable work branch.
+- **No branch deletion**: When the instance is deleted, the branch is lost with the clone. This matches the "disposable" mental model.