Implement Milestone 4: Synchronization and Remote Interaction

This milestone adds comprehensive remote synchronization and stacked-diff
publishing capabilities to Onyx.

## New Features

### Rebase Engine (internal/git/rebase.go)
- Stacked rebase with sequential commit rebasing
- Conflict detection and handling
- Integration with rerere for automatic conflict resolution
- Support for rebase continuation and abort operations

### Rerere Integration (internal/git/rerere.go)
- Conflict resolution recording and replay
- Cache location: .onx/rerere_cache
- Automatic application of previous conflict resolutions
- Normalized conflict pattern matching via SHA1 hashing

### Conflict Resolution UI (internal/git/conflicts.go)
- Index-based conflict detection (stage 1/2/3)
- Clear conflict presentation with file paths and hashes
- User-friendly resolution guidance
- Conflict marker extraction and analysis

### Remote Commands

#### onx sync (internal/commands/sync.go)
- Fetch latest changes from remote
- Rebase workstream stack onto updated base branch
- Automatic rerere conflict resolution
- Transaction-based with full undo support
- Progress reporting and clear error messages

#### onx push (internal/commands/push.go)
- Push all workstream branches to remote
- Support for force push operations
- Per-branch progress reporting
- Clear summary of pushed branches

### Remote Helpers (internal/git/remote.go)
- Remote validation and configuration
- Support for multiple remotes with origin default
- URL retrieval and remote existence checking

## Implementation Details

- All operations wrapped in oplog transactions for undo support
- Comprehensive error handling and user feedback
- Integration with existing workstream management
- CLI commands registered in cmd/onx/main.go

## Status

Milestone 4 is now complete. All core synchronization and remote
interaction features are implemented and tested.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude <noreply@anthropic.com>

notes/checklist.md

@@ -1,54 +1,45 @@
-## Milestone 3: Workstreams ✓ COMPLETE
+## Milestone 4: Synchronization and Remote Interaction ✓ COMPLETE
 
-### Workstream Data Model
+### Rebase Engine ✓
 
-28. ✓ **Implement workstream storage** (`internal/storage/workstreams.go`)
-    - `LoadWorkstreams(path string) (*WorkstreamCollection, error)`
-    - `SaveWorkstreams(path string, collection *WorkstreamCollection) error`
+34. **Implement stacked rebase** (`internal/git/rebase.go`) ✓
+    - Implemented RebaseStack function
+    - Sequential rebase with conflict handling
+    - Integration with rerere for automatic conflict resolution
+    - Support for rebase continuation and abort
 
-29. ✓ **Create workstream manager** (`internal/core/workstream_manager.go`)
-    - `CreateWorkstream(name string, base string) error`
-    - `GetCurrentWorkstream() (*Workstream, error)`
-    - `SwitchWorkstream(name string) error`
-    - `ListWorkstreams() ([]*Workstream, error)`
-    - `AddCommitToWorkstream(sha, message string) error`
-    - `GetCurrentWorkstreamName() (string, error)`
+35. **Integrate rerere** (`internal/git/rerere.go`) ✓
+    - Configured rerere cache location (.onx/rerere_cache)
+    - Enabled rerere for rebase operations
+    - Implemented conflict detection and recording
+    - Apply recorded resolutions automatically
 
-### Workstream Commands
+36. **Create conflict resolution UI** (`internal/git/conflicts.go`) ✓
+    - Detect merge conflicts via index stages
+    - Present clear conflict markers with file paths
+    - Guide user through resolution process
+    - Record resolutions for rerere
 
-30. ✓ **Implement onx new** (`internal/commands/new.go`)
-    - Validates workstream name
-    - Creates workstream entry
-    - Sets as current workstream
-    - Updates workspace to base commit
-    - Logs to oplog with transaction wrapper
-    - Provides helpful next-step guidance
+### Sync and Push Commands ✓
 
-31. ✓ **Implement onx list** (`internal/commands/list.go`)
-    - Reads workstreams.json via storage layer
-    - Formats output with current indicator (*)
-    - Shows commit count per workstream
-    - Color-coded output for status (active=green, merged/abandoned/archived=gray)
-    - `--all` flag to show non-active workstreams
-    - Alias: `ls`
+37. **Implement onx sync** (`internal/commands/sync.go`) ✓
+    - Begin oplog transaction for undo support
+    - Fetch from remote (origin by default)
+    - Get workstream commit stack
+    - Sequential rebase with rerere support
+    - Handle and present conflicts clearly
+    - Update workstreams.json with new SHAs
+    - Finalize oplog transaction
 
-32. ✓ **Implement onx switch** (`internal/commands/switch.go`)
-    - Validates target workstream exists
-    - Checkouts latest commit in target workstream
-    - Updates current_workstream pointer
-    - Logs to oplog with transaction wrapper
-    - Shows helpful info about target workstream
-
-33. ✓ **Add workstream validation**
-    - Validates workstream names (alphanumeric, hyphens, underscores, slashes only)
-    - Prevents duplicate workstream names
-    - Prevents reserved names (HEAD, main, master, etc.)
-    - Integrated in `ValidateWorkstreamName()` function
-
-### Integration & Refactoring
-
-- ✓ Refactored `onx save` to use WorkstreamManager
-- ✓ All commands properly wired in `cmd/onx/main.go`
-- ✓ All tests passing
-- ✓ Build successful
+38. **Implement onx push** (`internal/commands/push.go`) ✓
+    - Get all branches in current workstream
+    - Push each workstream branch to remote
+    - Support for force push flag
+    - Progress reporting for each branch
+    - Clear summary of pushed branches
 
+39. **Add remote configuration** (`internal/git/remote.go`) ✓
+    - Read git remote configuration
+    - Support multiple remotes
+    - Default to "origin"
+    - Validate remote existence and URLs