# Review, merge & conflict resolution

> **Explore-note — verify before trusting.** Distilled map of a subsystem, not authoritative.
> Last verified against `2f3f938` (2026-08-07), which finished the diff-viewer rework:
> Planning mode renders per file and `DiffLinesView` is retired.
> Drift check: `git log --oneline 20bce9b..HEAD -- src/ClaudeDo.Worker/Lifecycle src/ClaudeDo.Worker/State src/ClaudeDo.Worker/Planning src/ClaudeDo.Ui/ViewModels/Conflicts src/ClaudeDo.Worker/External`
> Stable structure only (no line numbers). See docs/explore-notes/README.md.

Covers the review→merge path: `TaskStateService` review transitions, `TaskMergeService`,
`PlanningMergeOrchestrator`, the post-merge verify gate, and the UI conflict resolver.

## Approve = merge the whole unit

`ApproveReview` (hub) and `review_task` approve (MCP) are the **single** review+merge action.
There is no separate "Merge all" entry.

- **Task with children** → drives `PlanningMergeOrchestrator`: merges the parent worktree if
  `Active`, then each `Done` child in order, then sets the parent `Done`. A mid-merge conflict
  pauses for `ContinuePlanningMerge` / `AbortPlanningMerge`.
- **Childless task** → `TaskMergeService.ApproveAndMergeAsync`. A conflict keeps the task in
  `WaitingForReview`.
- **No active worktree** (sandbox run) → straight to `Done`.

Review transitions all live in `TaskStateService`: `SubmitForReviewAsync`,
`SubmitForChildrenAsync`, `ApproveReviewAsync`, `RejectToQueueAsync`, `RejectToIdleAsync`,
`ClearReviewFeedbackAsync`.

`ReviewFeedback` (nullable string on `TaskEntity`) is the reviewer's rejection comment: set by
`RejectToQueueAsync`, consumed and cleared by `QueueService` on the next re-run, where it
becomes the next-turn prompt of the resumed Claude session.

## Unified parent model

Every parent — planning **or** improvement — flows
`… → WaitingForChildren → WaitingForReview → Done`, advanced by the single
`TaskStateService.TryAdvanceParentAsync`. It surfaces any `WaitingForChildren` parent for
review once all children are terminal; failed/cancelled children are **annotated on the
result, not wedged**.

- A planning parent enters `WaitingForChildren` at `FinalizePlanningAsync` (or
  `WaitingForReview` directly if it has no children).
- An improvement parent enters it from `TaskRunner.HandleSuccess` when its run spawned children.
- Planning/improvement **children** go straight to `Done` — no individual review. Only the
  parent is reviewed.

A child that hits a roadblock (fails, or reports `CLAUDEDO_BLOCKED` roadblocks) does **not**
advance the parent — the parent stays in `WaitingForChildren` until every child is terminal.
The UI surfaces blocked children on the parent's Session tab (`ChildOutcomes` + a "children
need attention" band) so the roadblock is visible without forcing a transition.

A blocked planning/improvement child still goes straight to `Done` per the unified parent model
above — it committed nothing, but nothing prevents its (empty) branch from being unit-merged
like any other `Done` child once the parent is approved. The MCP surface has no UI equivalent of
`ChildOutcomes`, so `review_task`'s approve on a parent additionally returns `emptyChildren` (the
`Done` children whose review range is empty) and every task-returning tool exposes
`TaskRefDto.roadblockCount` → [external-mcp.md](external-mcp.md) → `ReviewTask`/`PreviewMerge`.
An empty branch is still mergeable by design (some tasks — e.g. an audit — legitimately produce
no diff); this is a visibility fix, not a merge gate.

## Cancel is blocked while a unit merge is draining

`ApproveReview` on a task with children awaits `PlanningMergeOrchestrator.StartAsync` /
`DrainAsync` synchronously — the parent sits in `WaitingForReview` for the whole (potentially
minutes-long, one-child-at-a-time) drain. Without a guard, a concurrent `CancelReview` (UI or
`update_task_status`/`cancel_task` via MCP) could flip the parent to `Cancelled` mid-drain while
the orchestrator kept merging children's worktrees onto the target branch; `FinalizeParentDoneAsync`
then finds the parent no longer `WaitingForReview` and gives up, leaving the merged children's
diffs stranded with no rollback.

`TaskStateService.CancelAsync` now rejects with a `TransitionResult` reason whenever
`PlanningMergeOrchestrator.HasActiveMerge(taskId)` is true for the task being cancelled, before any
DB write. Cycle note: `TaskStateService` can't take a direct constructor dependency on
`PlanningMergeOrchestrator` (which itself depends on `ITaskStateService`), so it takes a lazily-resolved
`Func<IActiveMergeState>` instead — same cycle-breaking shape as the existing `Func<ITaskStateService>`
handed to `PlanningChainCoordinator`. `IActiveMergeState` (`Planning/Interfaces/`) is `PlanningMergeOrchestrator`'s
only public surface `TaskStateService` needs.

The UI mirrors this as polish: `DetailsIslandViewModel.IsMergeDraining` (set on
`PlanningMergeStartedEvent`, cleared on `PlanningMergeAborted`/`PlanningCompleted` for the bound
task) gates `CancelReviewCommand`'s `CanExecute` — same shape as `WorktreesOverviewModalViewModel.IsMerging`
gating `CanMergeAll`. The worker-side guard remains the actual correctness fix; the button gate
just avoids inviting a click the worker would reject. `CancelReviewAsync`'s catch now raises
`ErrorReported` (→ shell `FlashFooterError`) instead of swallowing the rejection silently.

## Post-merge verify gate

A list can set `ListConfigEntity.VerifyCommand` (List Settings modal → Verification).
Null/blank (the default) = **no gate**, behavior bit-identical to before the feature existed.

When set, `TaskMergeService` runs it via `VerifyCommandRunner` (`cmd.exe /c <command>`,
10-minute fixed timeout, output tail-captured) in `list.WorkingDir` right after a successful
`MergeNoFfAsync` / `ContinueMergeAsync` **and** worktree cleanup, but **before** the task is
allowed to reach `Done`.

| Outcome | Effect |
|---|---|
| Exit 0 | Unchanged flow — worktree `Merged`, task `Done` if it was `WaitingForReview`. |
| Non-zero exit or timeout | The git merge is **deliberately left in place** (no auto-revert — that's a separate, unbuilt feature). The worktree is still marked `Merged` (it's already gone from disk when `removeWorktree` was requested), but the task stays out of `Done`. |

On failure `MergeResult.Status` comes back `TaskMergeService.StatusVerifyFailed`
(`"verify_failed"`) with an output excerpt in `ErrorMessage`. This flows through
`MergeResultDto` (hub) and `ReviewTaskResult` (`review_task`) unchanged, because both already
treat any non-`blocked`/`conflict` status generically. All three UI merge entry points handle it
explicitly (detail-pane Approve, merge modal, worktrees batch) — a generic fallback there showed
the raw status string instead of the failure.

**Worktree-less approvals are gated too.** A task with no active `WorktreeEntity` — a sandbox run,
or a list-handler task that commits straight into `list.WorkingDir` — skips the merge entirely,
but `ApproveAndMergeAsync` still runs the verify command (same per-repo gate, working dir =
`list.WorkingDir`) before the task may reach `Done`. Without that, the run that lands the most on
the target branch at once would be the one run nothing checks.

**Serialization:** a process-wide `ConcurrentDictionary<string, SemaphoreSlim>` keyed by
`list.WorkingDir` serializes `MergeAsync` / `ContinueMergeAsync` (git ops + verify) per repo,
so a verify run can't be interrupted by a second merge landing in the same working dir
mid-build.

## `MergeCommit` and revert

`WorktreeEntity.MergeCommit` (nullable) is the SHA of the merge commit this worktree's branch
produced on the target branch. Stamped by `TaskMergeService` the moment a merge/continue-merge
succeeds, written **only** by `WorktreeRepository.SetMergedAsync` (which atomically sets
`State=Merged` and stamps the SHA in one update).

It is the only thing that makes `revert_merge` possible without heuristically searching
`git log` — see [external-mcp.md](external-mcp.md) → `RevertMerge`. Null for any worktree
merged before the field existed.

## Review gate in the UI

**Approve & Merge is gated behind opening the diff.** When there is something to inspect
(worktree diff / merged range / children combined diff), the button stays disabled until the
diff or combined-diff viewer has been opened once. The gate **re-locks per run** — any state
change resets it. Tasks with nothing to inspect are never gated.

The row-level quick-approve in the task list is an **intentional bypass**.

Implementation: `MergeSectionViewModel` owns merge-target selection, the mergeability
indicator (`MergePreviewPresenter` over `PreviewMergeAsync`), and `OpenDiffAsync` /
`ReviewCombinedDiffCommand` — both build a `DiffViewerViewModel`, call `ShowDiffViewer`, and
fire the `DiffViewed` callback. `HasReviewableDiff` reports whether anything is inspectable
and feeds the gate.

## Conflict resolver (in-app Rider-style 3-pane merge editor)

`ConflictResolverViewModel` + `Views/Conflicts/ConflictResolverView`. Handles **both**
single-task and planning unit-merge conflicts.

### Model

Single-task mode starts the conflict merge, then parses each conflicted file into stable and
conflict `MergeFileSegment`s via the worker's `GetMergeConflictDocuments`. Types live in
`ConflictModels`: `MergeFile` / `MergeFileSegment` / `MergeConflictBlock`.

Exposed per active file: `ActiveOursText` / `ActiveResultText` / `ActiveTheirsText`
(reconstructed from `MergeFile.OursText/ResultText/TheirsText`; Result seeds unresolved
conflicts with Ours), plus `ActiveFile` / `SelectFileCommand` (multi-file switcher),
`Current` / `Next` / `Previous` (focused-conflict nav), a per-file `PositionText` readout,
per-block `AcceptOurs/Theirs/Both/Base` + `MergeFile.Compose`, and `CanContinue` gated on
**every file resolved + no binary**. Each file is written via `WriteConflictResolution`.

**Planning mode** via `OpenForPlanningAsync(parentId, subtaskId)` loads the current subtask's
mid-merge conflicts **without re-starting the merge** and routes continue/abort to
`ContinuePlanningMerge` / `AbortPlanningMerge`, so a unit-merge conflict re-opens the editor
per subtask via the `PlanningMergeConflict` broadcast.

**Except when an MCP session is driving the merge.** `PlanningMergeOrchestrator.StartAsync` takes
an `externallyDriven` bool (default `false`; `ExternalMcpService.review_task`'s parent-with-children
path passes `true`, since a running Claude session — not the UI — will resolve conflicts via
`continue_merge`/`abort_merge`). The flag rides along on the `PlanningMergeConflict` broadcast
(4th arg); `IslandsShellViewModel.OnPlanningMergeConflict` only auto-opens the resolver when it's
`false` — otherwise it shows a persistent, non-auto-dismissing banner
(`IsExternalMergeBannerVisible`) with a manual "Open resolver" button, cleared on
`PlanningMergeAborted`/`PlanningCompleted`. This exists because two parties (a human and the
driving session) could otherwise end up editing the same shared checkout at once.
`PlanningMergeOrchestrator.GetActiveExternalConflictsAsync` (hub: `GetActiveExternalPlanningMergeConflicts`)
re-derives this state by checking `GitService.IsMidMergeAsync` rather than trusting the in-memory
flag alone, so a UI restart mid-merge (or a stale entry left behind if something resolved the
repo outside the normal Continue/Abort path) can't show a phantom banner — the Ui calls it on
`ConnectionRestoredEvent`. The childless single-task conflict path
(`TaskMergeService.ApproveAndMergeAsync`) has no equivalent broadcast — it only sends the generic
`TaskUpdated` — so it never auto-opened the resolver and needed no change.

### View

Three **AvaloniaEdit** panes showing the whole file: MAIN/ours (read-only) | editable Result |
INCOMING/theirs (read-only). TextMate highlighting by extension (theme `StyleInclude` in
`App.axaml`).

- A code-behind `IBackgroundRenderer` tints each conflict block (unresolved/resolved) across
  panes. Tints live in `Tokens.axaml` (`Merge*TintBrush`).
- An `IReadOnlySectionProvider` + `TextAnchor` regions keep **only conflict spans** editable in
  Result; edits flow back to the block.
- Each unresolved conflict starts **EMPTY** (a thin marker bar).
- The between-pane gutter controls **toggle** each side in/out of the result: `›`/`‹` add
  MAIN/INCOMING in click order (first pick on top), clicking again removes that side — so a
  conflict can take main, incoming, both, or **neither**.
- `FilesSummary` shows how many files still have conflicts. The three panes share a
  proportional synced vertical scroll.
- A conflict overview ruler right of the Result pane (`ConflictMap`) maps every conflict in the
  file proportionally; click a tick to jump. Useful for long files.

### Entry points

Review **Approve** on conflict, and the **Merge** button in the Diff window (a conflicting
`MergeTask` hands off via `RequestConflictResolution`).

## Hub methods

- Review/merge: `ApproveReview(taskId, targetBranch) -> MergeResultDto`,
  `ContinuePlanningMerge` / `AbortPlanningMerge`, `PreviewMerge(taskId, targetBranch) ->
  MergePreviewDto`, `RejectReviewToQueue`, `RejectReviewToIdle`, `CancelReview`, `MergeTask`,
  `GetMergeTargets`
- Single-task conflict resolver: `StartConflictMerge`, `GetMergeConflictDocuments`,
  `WriteConflictResolution`, `ContinueConflictMerge`, `AbortConflictMerge` — note the
  service-level `TaskMergeService.ContinueMergeAsync` / `AbortMergeAsync` keep their own names.
- Broadcast events: `PlanningMergeStarted`, `PlanningSubtaskMerged`, `PlanningMergeConflict`,
  `PlanningMergeAborted`, `PlanningCompleted`

## Diff stack (UI)

`UnifiedDiffParser` (static) parses `git diff` output into `DiffFileViewModel`s, detecting
added/deleted/renamed/binary files and per-line numbers. `DiffModels.cs` holds the shared types
(`DiffLineViewModel`, `DiffFileViewModel`, `DiffLineKind`, `DiffFileStatus`, `SubtaskDiffRow`,
`DiffTreeNodeViewModel`, `DiffTree`).

`DiffViewerViewModel` is one unified read-only viewer with two modes:
- **Files** — dirty worktree / branch-vs-base / commit-range. Loads via `GitService`, folder
  file-tree left + per-file diff pane right, Merge button for a live branch source.
- **Planning** — per-subtask diffs via `GetPlanningAggregateAsync`, subtask list left + one
  editor per file right (`PlanningFiles`), combined integration-branch toggle.

Both modes render through `DiffAlignment` (pure — pairs diff lines into side-by-side rows and
computes word-diff spans) and `DiffTextView` (AvaloniaEdit + TextMate highlighting keyed off the
file extension, unified/split layout, optional line wrap, synced scrolling). Files mode hosts one
`DiffTextView` for the selected file; Planning mode hosts one per file in `PlanningFiles` so each
gets its own grammar (one editor can only carry one TextMate grammar). The split/wrap toggles
persist to `ui.config.json` via `AppSettings` and reach the per-file editors in Planning mode
too.