Update session-tree-plan.md with completed items

- Branch Summary Design: complete with fromId, fromHook, details fields
- Entry Labels: UI display and /label command complete in tree-selector
- UI Commands: /branch and /tree complete

packages/coding-agent/docs/session-tree-plan.md

@@ -73,22 +73,25 @@ Reference: [session-tree.md](./session-tree.md)
 
 Reference: [#314](https://github.com/badlogic/pi-mono/pull/314) - Structured compaction with anchored iterative summarization needs `details` field to store `ArtifactIndex` and version markers.
 
-### Branch Summary Design
+### Branch Summary Design ✅
 
 Current type:
 ```typescript
 export interface BranchSummaryEntry extends SessionEntryBase {
   type: "branch_summary";
   summary: string;
+  fromId: string;  // References the abandoned leaf
+  fromHook?: boolean;  // Whether summary was generated by a hook
+  details?: unknown;  // File tracking: { readFiles, modifiedFiles }
 }
 ```
 
-Questions to resolve:
-- [ ] Add `abandonedLeafId` field to reference what was abandoned?
-- [ ] Store metadata about why the branch happened?
-- [ ] Who generates the summary - user, LLM, or both options?
-- [ ] Design and implement branch summarizer
-- [ ] Add tests for `branchWithSummary()` flow
+- [x] `fromId` field references the abandoned leaf
+- [x] `fromHook` field distinguishes pi-generated vs hook-generated summaries
+- [x] `details` field for file tracking
+- [x] Branch summarizer implemented with structured output format
+- [x] Uses serialization approach (same as compaction) to prevent model confusion
+- [x] Tests for `branchWithSummary()` flow
 
 ### Entry Labels ✅
 
@@ -100,8 +103,8 @@ Questions to resolve:
 - [x] Update `createBranchedSession()` to filter out LabelEntry and recreate from resolved map
 - [x] `buildSessionContext()` already ignores LabelEntry (only handles message types)
 - [x] Add `label?: string` to `SessionTreeNode`, populated by `getTree()`
-- [ ] Display labels in UI (tree view, path view) - deferred to UI phase
-- [ ] `/label` command - deferred to UI phase
+- [x] Display labels in UI (tree-selector shows labels)
+- [x] `/label` command (implemented in tree-selector)
 
 ### CustomMessageEntry<T>
 
@@ -361,23 +364,14 @@ interface BeforeAgentStartResult {
 - [ ] Render full path (no compaction resolution needed)
 - [ ] Responsive: collapse sidebar on mobile
 
-### UI Commands
+### UI Commands ✅
 
-Design new commands based on refactored SessionManager:
-
-**`/branch`** - Current behavior (creates new session file from path)
-- [ ] Review if this is still the right UX with tree structure
-- [ ] Consider: should this use `createBranchedSession()` or `branch()`?
-
-**`/branch-here`** - In-place branching (new)
-- [ ] Use `branch(id)` to move leaf pointer without creating new file
-- [ ] Subsequent messages become new branch in same file
-- [ ] Design: how to select branch point? (similar to current `/branch` UI?)
-
-**`/branches`** - List/navigate branches (new)
-- [ ] Show tree structure or list of branch points
-- [ ] Allow switching between branches (move leaf pointer)
-- [ ] Show current position in tree
+- [x] `/branch` - Creates new session file from current path (uses `createBranchedSession()`)
+- [x] `/tree` - In-session tree navigation via tree-selector component
+  - Shows full tree structure with labels
+  - Navigate between branches (moves leaf pointer)
+  - Shows current position
+  - Generates branch summaries when switching branches
 
 ### Documentation