feat(workspace): add merge-conflict resolution UI

[liam-russell]

Type

• feat — new feature or user-visible capability

Summary

• Added a Conflicts tab, sidebar badge, and workspace banner that surface any worktree with unresolved merge/rebase conflicts.
• Added a per-file conflict resolution view with ours/theirs/result Monaco panes and per-block "Accept Ours" / "Accept Theirs" / "Accept Both" actions, plus a "Mark Resolved" action that stages the file once no conflict markers remain.
• Fixed a pre-existing bug where a lone unstaged file modification could be silently misread as staged, corrupting its reported path by one character.

Why

Closes #91 — today, resolving a merge conflict means dropping to a terminal or an external merge tool. This adds a minimal but real in-app resolution flow on top of the existing Monaco-based file editor (#57).

Screenshots / recordings

Captured via a WebdriverIO screenshot against the real Electron app (same mechanism as hero-screenshots.spec.ts), but this session's browser tooling for uploading it inline to the PR isn't available right now. Description of the captured view instead:

• Sidebar: the active worktree row shows a warning-triangle badge with the conflict count instead of the normal change-count badge.
• Tab bar: a "Conflicts" tab appears next to Files, with a count badge (e.g. "Conflicts 1").
• Workspace banner: an amber banner reading "N file(s) with unresolved merge conflicts" with a "Resolve Conflicts" button, shown on every tab except Conflicts itself.
• Conflicts tab: a left-hand list of conflicted files; selecting one opens the resolution view.
• Resolution view: a header with the file path, a "1 conflict remaining" / "All conflicts resolved" pill, Save and Mark Resolved buttons; below that, a per-block toolbar ("Conflict 1" with Accept Ours / Accept Theirs / Accept Both); below that, three Monaco panes side by side — Ours (read-only), Theirs (read-only), Result (editable, live-updates as blocks are accepted).

I'll attach the actual screenshot as a follow-up comment once browser tooling is available, or on request.

Breaking changes

None — adds a new IPC channel (git:conflictContent) and a conflicted field on StatusFileEntry; both are additive.

Test plan

• Added packages/git/src/__tests__/conflicts.test.ts — real merge conflicts (UU, both-added/AA) verifying conflicted detection and base/ours/theirs blob reads via index stages.
• Added app/src/renderer/workspace/__tests__/conflict-blocks.test.ts — conflict-marker parsing/resolution, including diff3-style markers and multi-block files.
• Added e2e/specs/merge-conflict-workflow.spec.ts — scripts a real merge conflict in a managed worktree, then drives the full UI flow (banner → Conflicts tab → accept-ours → mark resolved → banner disappears), asserting the on-disk result and that git no longer reports the path as unmerged.
• pnpm lint && pnpm typecheck && pnpm test all pass (362 unit tests + 15/15 E2E specs green, run 3x for flake-checking).

[Copilot]

Pull request overview

Adds an in-app merge-conflict resolution flow in the Workspace UI, backed by a new IPC endpoint that reads base/ours/theirs content from git index stages, and extends worktree status parsing to flag conflicted paths (while also addressing a porcelain parsing edge-case).

Changes:

• Introduces a new Conflicts tab (banner + sidebar badges) and a three-pane Monaco-based conflict resolution panel with per-block accept actions and “Mark Resolved”.
• Adds git:conflictContent IPC + git library support to read conflict stage blobs from the index (stages 1/2/3).
• Updates status parsing/types to expose StatusFileEntry.conflicted and fixes a porcelain parsing misclassification for unstaged-only entries.

Reviewed changes

Copilot reviewed 18 out of 18 changed files in this pull request and generated 4 comments.

Show a summary per file

File	Description
packages/types/src/ipc.ts	Adds IPC constant and IpcMap entry for git:conflictContent.
packages/types/src/git.ts	Extends status entries with conflicted and defines conflict stage/content result types.
packages/git/src/staging.ts	Adjusts porcelain status retrieval/parsing and flags conflicted XY codes.
packages/git/src/index.ts	Re-exports the new conflicts helper from the git package entrypoint.
packages/git/src/conflicts.ts	Implements index-stage reads for base/ours/theirs conflict content.
packages/git/src/tests/conflicts.test.ts	Adds unit tests for conflict detection and stage-blob reads.
packages/git/package.json	Exports the new ./conflicts module entry.
e2e/specs/merge-conflict-workflow.spec.ts	Adds E2E coverage for banner → Conflicts tab → resolve → mark resolved.
app/src/renderer/workspace/WorktreeSidebar.tsx	Shows conflict icon/badge per worktree and updates tooltip text.
app/src/renderer/workspace/ConflictResolutionPanel.tsx	Adds the conflict resolution UI (three panes + per-block actions + mark resolved).
app/src/renderer/workspace/ConflictedFilesPanel.tsx	Adds conflicted-file list panel for the Conflicts tab.
app/src/renderer/workspace/conflict-blocks.ts	Adds parsing/resolution logic for conflict markers (incl. diff3 tolerance).
app/src/renderer/workspace/tests/conflict-blocks.test.ts	Adds unit tests for conflict parsing and per-block resolution.
app/src/renderer/stores/workspace-store.ts	Adds conflicts to persisted workspace tab state.
app/src/renderer/routes/workspace.tsx	Wires up the banner/tab/panels and hooks for conflict counts/status.
app/src/renderer/queries.ts	Adds worktree conflict counts and a per-worktree status query hook.
app/src/preload/index.ts	Exposes getConflictFileContent to the renderer via preload API.
app/src/main/ipc/git.ts	Registers IPC handler for git:conflictContent with path assertion.

Comments suppressed due to low confidence (1)

packages/git/src/staging.ts:121

• parsePorcelainStatus trims the extracted file path (line.slice(3).trim()), which can silently corrupt valid filenames that begin/end with whitespace. Since porcelain v1 already has a fixed XY␠ prefix, it’s safer to take the substring as-is and only strip a trailing \r (for CRLF) if present.

      const indexStatus = line[0] ?? ' ';
      const worktreeStatus = line[1] ?? ' ';
      const filePath = line.slice(3).trim();