# Exploration: ~ / $HOME Expansion in Mount Paths

## User Request
Allow `~` and `$HOME` in mount paths for both regular mounts and git mounts.

## Where This Applies

### Container target paths (where it makes sense)
- **Regular mounts** (`mount.target`): The absolute path inside the container where files are bind-mounted
- **Git mount mappings** (`mapping.target_path`): The absolute path inside the container where repo subdirectories are mounted

### Where it does NOT apply
- **Regular mount file paths** (`mount.files` keys): These are relative to the mount target
- **Git mount source paths** (`mapping.source_path`): These are relative to the cloned repo
- **Host-side source paths**: The API runs in a container; `~` on the host would mean the Docker host's home, which the API container cannot access

## Complexity Assessment

### The Core Problem
`~` means "user's home directory". But whose home?

| Context | Home Directory | Knowable at Mount Time? |
|---------|---------------|------------------------|
| API container | `/root` or `/app` | Yes |
| Target container (manifest, user=root) | `/root` | Yes (from manifest) |
| Target container (manifest, user=user) | `/home/user` | Yes (from manifest) |
| Target container (legacy tool type) | Unknown | No (assume `/root`) |
| Docker host | `/home/alex` or similar | No (API is containerized) |

### Docker Compose Reality Check
Docker Compose **does not expand** `~` or `$HOME` in volume targets. These are passed literally to the Docker daemon. So `~/workspace` becomes a directory literally named `~` in the container root.

This means **we must resolve the path ourselves** before writing the compose file.

## Design Options

### Option A: Simple `/root` default (minimal change)
- Replace `~` and `$HOME` with `/root` in all container target paths
- Apply during compose modification and git mount resolution
- **Effort**: ~30 min, ~20 lines
- **Pros**: Dead simple, works for root-running containers (most legacy setups)
- **Cons**: Wrong for pi-agent (runs as `user`, home `/home/user`)

### Option B: Manifest-aware home directory (recommended)
- For manifest-based tools: read `user.name` from manifest, compute home as `/home/{name}` or `/root`
- For legacy tools: default to `/root`
- Pass `home_dir` through the mount resolution pipeline
- Apply expansion in `apply_resolved_profile()` and `_resolve_git_mount_mappings()`
- **Effort**: ~2 hours, touches 3-4 files
- **Pros**: Correct for all container types
- **Cons**: Slightly more plumbing

### Option C: Configurable home per profile
- Add `home_directory` field to ConfigProfile
- User can override the container home directory
- **Effort**: ~3 hours, schema change
- **Cons**: Overkill, clutters UI

## Recommendation

**Option B** — manifest-aware expansion. The pi-agent manifest already declares `user.name`, so we can compute the correct home directory. For backward compatibility, legacy tool types default to `/root`.

## Files to Touch

1. `apps/api/src/services/config_profile_resolver.py` — add `expand_container_path()` helper
2. `apps/api/src/api/tool_instances.py` — pass `home_dir` to `apply_resolved_profile()` and git mount functions; determine home from manifest/tool type
3. `apps/api/src/services/manifest_compiler.py` — expose helper to extract user from manifest
4. Tests for expansion logic

## Risks

| Risk | Mitigation |
|------|------------|
| Wrong home for custom containers | Document that manifest should declare `user.name` |
| `$HOME` env var not set in container | We resolve it at compose generation time, so no runtime dependency |
| Breaking existing profiles with literal `~` in path | Very unlikely; we can add an escape hatch if needed |
