feat(chat): git branch indicator in chat header (Phase 2.4)

Hermes v2026.4.23's TUI shows the project's current git branch as a
sidebar pill. Mirror it in the chat header on both platforms.

ScarfCore GitBranchService:
- branch(at projectPath: String) async -> String? — runs
  `git -C <path> rev-parse --abbrev-ref HEAD` via the transport
  (works on local + remote SSH projects). Returns nil for
  non-git dirs, missing git, detached HEAD, or transport errors.
  No throwing — chat header omits the chip on any failure.

Mac:
- ChatViewModel.currentGitBranch populated alongside currentProjectPath
  in startACPSession's resolution branch.
- SessionInfoBar gains gitBranch: String? — renders a tinted
  `arrow.triangle.branch` chip after the project chip when set.
- RichChatView wires chatViewModel.currentGitBranch through.

iOS:
- ChatController.currentGitBranch on the same lifecycle hooks
  (resetAndStartInProject + startResuming + cleared on
  resetAndStartNewSession).
- projectContextBar renders the chip inline next to the project
  name.

Verified: ScarfCore + Mac + iOS builds clean.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

scarf/Packages/ScarfCore/Sources/ScarfCore/Services/GitBranchService.swift

@@ -0,0 +1,68 @@
+import Foundation
+#if canImport(os)
+import os
+#endif
+
+/// Resolves the current git branch of a project directory via the
+/// transport (so it works against local + remote SSH projects without
+/// any platform-specific branching). The result is informational —
+/// surfaced in the chat header alongside the project name as a small
+/// `branch` chip. No write operations.
+///
+/// Per-session caching lives on the chat view models (one read per chat
+/// session start); this service is stateless.
+///
+/// **Failure model.** Returns `nil` when the directory isn't a git
+/// repo, when `git` is missing on the host, or when the SSH connection
+/// drops. Never throws — the chat header simply omits the branch chip
+/// on any error.
+public struct GitBranchService: Sendable {
+    #if canImport(os)
+    private static let logger = Logger(
+        subsystem: "com.scarf",
+        category: "GitBranchService"
+    )
+    #endif
+
+    public let context: ServerContext
+
+    public nonisolated init(context: ServerContext = .local) {
+        self.context = context
+    }
+
+    /// Resolve the current branch name at `projectPath`. Returns nil
+    /// for non-git directories, missing `git`, or transport errors —
+    /// callers treat nil as "no branch chip to render."
+    ///
+    /// Internally runs `git -C <path> rev-parse --abbrev-ref HEAD`.
+    /// On a clean checkout that's a branch name like "main"; on a
+    /// detached HEAD it's literally "HEAD" (which we then return as
+    /// nil, since "HEAD" isn't a useful branch label).
+    public nonisolated func branch(at projectPath: String) async -> String? {
+        let ctx = context
+        return await Task.detached {
+            let transport = ctx.makeTransport()
+            do {
+                let result = try transport.runProcess(
+                    executable: "git",
+                    args: ["-C", projectPath, "rev-parse", "--abbrev-ref", "HEAD"],
+                    stdin: nil,
+                    timeout: 5
+                )
+                guard result.exitCode == 0 else {
+                    return nil
+                }
+                let raw = result.stdoutString.trimmingCharacters(in: .whitespacesAndNewlines)
+                if raw.isEmpty || raw == "HEAD" { return nil }
+                return raw
+            } catch {
+                #if canImport(os)
+                Self.logger.warning(
+                    "git branch lookup failed at \(projectPath, privacy: .public): \(error.localizedDescription, privacy: .public)"
+                )
+                #endif
+                return nil
+            }
+        }.value
+    }
+}

scarf/Scarf iOS/Chat/ChatView.swift

@@ -385,11 +385,23 @@ struct ChatView: View {
                     Text("Project chat")
                         .font(.caption2)
                         .foregroundStyle(.secondary)
+                    HStack(spacing: 6) {
                         Text(projectName)
                             .font(.callout.weight(.medium))
                             .foregroundStyle(.primary)
                             .lineLimit(1)
                             .truncationMode(.tail)
+                        if let branch = controller.currentGitBranch, !branch.isEmpty {
+                            Label(branch, systemImage: "arrow.triangle.branch")
+                                .font(.caption2)
+                                .foregroundStyle(.tint)
+                                .labelStyle(.titleAndIcon)
+                                .padding(.horizontal, 5)
+                                .padding(.vertical, 1)
+                                .background(.tint.opacity(0.15), in: Capsule())
+                                .lineLimit(1)
+                        }
+                    }
                 }
                 Spacer()
                 if !controller.vm.projectScopedCommands.isEmpty {
@@ -492,6 +504,12 @@ final class ChatController {
     /// the resumed session is attributed to a registered project.
     private(set) var currentProjectName: String?
 
+    /// Git branch of the project's working directory at session start
+    /// (v2.5). Nil for non-project sessions and projects that aren't
+    /// git repos / have git missing on the host. Surfaced as a small
+    /// chip on the right side of the project context bar.
+    private(set) var currentGitBranch: String?
+
     private let context: ServerContext
     private var client: ACPClient?
     private var eventTask: Task<Void, Never>?
@@ -656,6 +674,7 @@ final class ChatController {
         await stop()
         vm.reset()
         currentProjectName = nil
+        currentGitBranch = nil
         // Quick-chat sessions don't have a project; clear any leftover
         // project-scoped slash commands from a prior session.
         vm.loadProjectScopedCommands(at: nil)
@@ -671,18 +690,27 @@ final class ChatController {
         await stop()
         vm.reset()
         currentProjectName = project.name
+        currentGitBranch = nil
         // Pull any project-authored slash commands at
         // <project.path>/.scarf/slash-commands/ into the chat menu.
         // Async + non-fatal — degrades cleanly on SFTP failures (logged).
         vm.loadProjectScopedCommands(at: project.path)
+        // v2.5 git branch indicator. Async + nil on failure — the chip
+        // simply doesn't render if the project isn't a git repo.
+        let ctx = context
+        let projectPath = project.path
+        Task { @MainActor [weak self] in
+            let branch = await GitBranchService(context: ctx).branch(at: projectPath)
+            if self?.currentProjectName == project.name {
+                self?.currentGitBranch = branch
+            }
+        }
         // Synchronously load the slash command NAMES so we can list them
         // in the AGENTS.md block (the agent needs to know what commands
         // are available). This is a separate read from the async one
         // above because the block has to land on disk BEFORE `hermes acp`
         // boots — async loads might lose the race. Blocking load on a
         // detached task to keep the MainActor responsive.
-        let ctx = context
-        let projectPath = project.path
         let slashNames: [String] = await Task.detached {
             ProjectSlashCommandService(context: ctx)
                 .loadCommands(at: projectPath)
@@ -845,7 +873,20 @@ final class ChatController {
             return (path: path, name: name)
         }.value
         currentProjectName = resolved?.name
+        currentGitBranch = nil
         vm.loadProjectScopedCommands(at: resolved?.path)
+        // v2.5 git branch indicator for the resumed-session header.
+        if let resumePath = resolved?.path {
+            let resolvedName = resolved?.name
+            Task { @MainActor [weak self] in
+                let branch = await GitBranchService(context: ctx).branch(at: resumePath)
+                // Guard against a project switch landing while we
+                // were resolving — only set if the chat hasn't moved.
+                if self?.currentProjectName == resolvedName {
+                    self?.currentGitBranch = branch
+                }
+            }
+        }
 
         state = .connecting
         let client = ACPClient.forIOSApp(

scarf/scarf/Features/Chat/ViewModels/ChatViewModel.swift

@@ -49,6 +49,13 @@ final class ChatViewModel {
     /// indicator in SessionInfoBar + the `Chat · <Name>` nav title.
     private(set) var currentProjectPath: String?
 
+    /// Git branch the project's working directory is currently on, or
+    /// nil when the dir isn't a git repo / git isn't installed / the
+    /// resolution failed. Populated alongside `currentProjectPath`;
+    /// surfaced as a small chip after the project name in
+    /// `SessionInfoBar`. v2.5.
+    private(set) var currentGitBranch: String?
+
     /// Human-readable name of the active project, resolved from the
     /// projects registry at session-start time. Stored alongside the
     /// path so the view renders without hitting disk on every update.
@@ -477,11 +484,21 @@ final class ChatViewModel {
                     // the menu degrades to ACP + quick commands only on
                     // any failure (logged inside the service).
                     self.richChatViewModel.loadProjectScopedCommands(at: path)
+                    // Resolve the project's current git branch (v2.5)
+                    // for the chat header chip. Async + nil on failure
+                    // (not a git repo / git missing / SSH error) — the
+                    // chip just doesn't render.
+                    let svc = GitBranchService(context: context)
+                    Task { @MainActor [weak self] in
+                        let branch = await svc.branch(at: path)
+                        self?.currentGitBranch = branch
+                    }
                 } else {
                     // Explicit clear on non-project sessions so the
                     // indicator doesn't leak from a previous chat.
                     self.currentProjectPath = nil
                     self.currentProjectName = nil
+                    self.currentGitBranch = nil
                     self.richChatViewModel.loadProjectScopedCommands(at: nil)
                 }
 

scarf/scarf/Features/Chat/Views/RichChatView.swift

@@ -30,7 +30,9 @@ struct RichChatView: View {
                 // ChatViewModel.currentProjectName which is set in
                 // startACPSession on both new project chats and
                 // resumed project-attributed sessions.
-                projectName: chatViewModel.currentProjectName
+                projectName: chatViewModel.currentProjectName,
+                // v2.5: git branch indicator alongside the project chip.
+                gitBranch: chatViewModel.currentGitBranch
             )
             Divider()
 

scarf/scarf/Features/Chat/Views/SessionInfoBar.swift

@@ -14,6 +14,11 @@ struct SessionInfoBar: View {
     /// `ChatViewModel.currentProjectName` — the view just passes it
     /// through.
     var projectName: String? = nil
+    /// Current git branch of the project's working directory, when
+    /// resolved (v2.5). Renders as a tinted chip after the project
+    /// name. Nil for non-project chats and for projects that aren't
+    /// git repos.
+    var gitBranch: String? = nil
 
     var body: some View {
         HStack(spacing: 16) {
@@ -28,6 +33,13 @@ struct SessionInfoBar: View {
                         .foregroundStyle(.tint)
                         .lineLimit(1)
                         .help("Chat is scoped to Scarf project \"\(projectName)\"")
+                    if let gitBranch {
+                        Label(gitBranch, systemImage: "arrow.triangle.branch")
+                            .font(.caption)
+                            .foregroundStyle(.tint)
+                            .lineLimit(1)
+                            .help("Project's current git branch")
+                    }
                 }
 
                 HStack(spacing: 4) {