# Session Tree Navigation

The `/tree` command provides tree-based navigation of the session history.

## Overview

Sessions are stored as trees where each entry has an `id` and `parentId`. The "leaf" pointer tracks the current position. `/tree` lets you navigate to any point and optionally summarize the branch you're leaving.

### Comparison with `/branch`

| Feature | `/branch` | `/tree` |
|---------|-----------|---------|
| View | Flat list of user messages | Full tree structure |
| Action | Extracts path to **new session file** | Changes leaf in **same session** |
| Summary | Never | Optional (user prompted) |
| Events | `session_before_branch` / `session_branch` | `session_before_tree` / `session_tree` |

## Tree UI

```
├─ user: "Hello, can you help..."
│  └─ assistant: "Of course! I can..."
│     ├─ user: "Let's try approach A..."
│     │  └─ assistant: "For approach A..."
│     │     └─ [compaction: 12k tokens]
│     │        └─ user: "That worked..."  ← active
│     └─ user: "Actually, approach B..."
│        └─ assistant: "For approach B..."
```

### Controls

| Key | Action |
|-----|--------|
| ↑/↓ | Navigate (depth-first order) |
| Enter | Select node |
| Escape/Ctrl+C | Cancel |
| Ctrl+U | Toggle: user messages only |
| Ctrl+O | Toggle: show all (including custom/label entries) |

### Display

- Height: half terminal height
- Current leaf marked with `← active`
- Labels shown inline: `[label-name]`
- Default filter hides `label` and `custom` entries (shown in Ctrl+O mode)
- Children sorted by timestamp (oldest first)

## Selection Behavior

### User Message or Custom Message
1. Leaf set to **parent** of selected node (or `null` if root)
2. Message text placed in **editor** for re-submission
3. User edits and submits, creating a new branch

### Non-User Message (assistant, compaction, etc.)
1. Leaf set to **selected node**
2. Editor stays empty
3. User continues from that point

### Selecting Root User Message
If user selects the very first message (has no parent):
1. Leaf reset to `null` (empty conversation)
2. Message text placed in editor
3. User effectively restarts from scratch

## Branch Summarization

When switching, user is prompted: "Summarize the branch you're leaving?"

### What Gets Summarized

Path from old leaf back to common ancestor with target:

```
A → B → C → D → E → F  ← old leaf
        ↘ G → H        ← target
```

Abandoned path: D → E → F (summarized)

Summarization stops at:
1. Common ancestor (always)
2. Compaction node (if encountered first)

### Summary Storage

Stored as `BranchSummaryEntry`:

```typescript
interface BranchSummaryEntry {
  type: "branch_summary";
  id: string;
  parentId: string;      // New leaf position
  timestamp: string;
  fromId: string;        // Old leaf we abandoned
  summary: string;       // LLM-generated summary
  details?: unknown;     // Optional hook data
}
```

## Implementation

### AgentSession.navigateTree()

```typescript
async navigateTree(
  targetId: string,
  options?: { summarize?: boolean; customInstructions?: string }
): Promise<{ editorText?: string; cancelled: boolean }>
```

Flow:
1. Validate target, check no-op (target === current leaf)
2. Find common ancestor between old leaf and target
3. Collect entries to summarize (if requested)
4. Fire `session_before_tree` event (hook can cancel or provide summary)
5. Run default summarizer if needed
6. Switch leaf via `branch()` or `branchWithSummary()`
7. Update agent: `agent.replaceMessages(sessionManager.buildSessionContext().messages)`
8. Fire `session_tree` event
9. Notify custom tools via session event
10. Return result with `editorText` if user message was selected

### SessionManager

- `getLeafUuid(): string | null` - Current leaf (null if empty)
- `resetLeaf(): void` - Set leaf to null (for root user message navigation)
- `getTree(): SessionTreeNode[]` - Full tree with children sorted by timestamp
- `branch(id)` - Change leaf pointer
- `branchWithSummary(id, summary)` - Change leaf and create summary entry

### InteractiveMode

`/tree` command shows `TreeSelectorComponent`, then:
1. Prompt for summarization
2. Call `session.navigateTree()`
3. Clear and re-render chat
4. Set editor text if applicable

## Hook Events

### `session_before_tree`

```typescript
interface TreePreparation {
  targetId: string;
  oldLeafId: string | null;
  commonAncestorId: string | null;
  entriesToSummarize: SessionEntry[];
  userWantsSummary: boolean;
}

interface SessionBeforeTreeEvent {
  type: "session_before_tree";
  preparation: TreePreparation;
  model: Model;
  signal: AbortSignal;
}

interface SessionBeforeTreeResult {
  cancel?: boolean;
  summary?: { summary: string; details?: unknown };
}
```

### `session_tree`

```typescript
interface SessionTreeEvent {
  type: "session_tree";
  newLeafId: string | null;
  oldLeafId: string | null;
  summaryEntry?: BranchSummaryEntry;
  fromHook?: boolean;
}
```

### Example: Custom Summarizer

```typescript
export default function(pi: HookAPI) {
  pi.on("session_before_tree", async (event, ctx) => {
    if (!event.preparation.userWantsSummary) return;
    if (event.preparation.entriesToSummarize.length === 0) return;
    
    const summary = await myCustomSummarizer(event.preparation.entriesToSummarize);
    return { summary: { summary, details: { custom: true } } };
  });
}
```

## Error Handling

- Summarization failure: cancels navigation, shows error
- User abort (Escape): cancels navigation
- Hook returns `cancel: true`: cancels navigation silently
