diff --git a/supacode/Domain/Worktree.swift b/supacode/Domain/Worktree.swift
index 26089e3c..a65d827d 100644
--- a/supacode/Domain/Worktree.swift
+++ b/supacode/Domain/Worktree.swift
@@ -7,6 +7,7 @@ nonisolated struct Worktree: Identifiable, Hashable, Sendable {
   let workingDirectory: URL
   let repositoryRootURL: URL
   let createdAt: Date?
+  let isMain: Bool
 
   nonisolated init(
     id: String,
@@ -22,6 +23,14 @@ nonisolated struct Worktree: Identifiable, Hashable, Sendable {
     self.workingDirectory = workingDirectory
     self.repositoryRootURL = repositoryRootURL
     self.createdAt = createdAt
+    // Pre-compute the main-worktree flag at construction time so that hot SwiftUI
+    // paths never call the expensive `URL.standardizedFileURL` getter during view
+    // updates. The fast equality check covers the common case where callers
+    // already pass normalized URLs; the standardized fallback protects against
+    // any future call site that forgets to normalize first.
+    self.isMain =
+      workingDirectory == repositoryRootURL
+      || workingDirectory.standardizedFileURL == repositoryRootURL.standardizedFileURL
   }
 }
 
diff --git a/supacode/Features/Repositories/Reducer/RepositoriesFeature.swift b/supacode/Features/Repositories/Reducer/RepositoriesFeature.swift
index 1de469de..f6fd46a7 100644
--- a/supacode/Features/Repositories/Reducer/RepositoriesFeature.swift
+++ b/supacode/Features/Repositories/Reducer/RepositoriesFeature.swift
@@ -1573,7 +1573,7 @@ extension RepositoriesFeature.State {
   }
 
   func isMainWorktree(_ worktree: Worktree) -> Bool {
-    worktree.workingDirectory.standardizedFileURL == worktree.repositoryRootURL.standardizedFileURL
+    worktree.isMain
   }
 
   func isWorktreeMerged(_ worktree: Worktree) -> Bool {
diff --git a/supacodeTests/WorktreeIsMainTests.swift b/supacodeTests/WorktreeIsMainTests.swift
new file mode 100644
index 00000000..e2bf31f0
--- /dev/null
+++ b/supacodeTests/WorktreeIsMainTests.swift
@@ -0,0 +1,66 @@
+import Foundation
+import Testing
+
+@testable import supacode
+
+@MainActor
+struct WorktreeIsMainTests {
+  @Test func identicalURLsAreMain() {
+    let root = URL(fileURLWithPath: "/tmp/repo")
+    let worktree = Worktree(
+      id: "/tmp/repo",
+      name: "main",
+      detail: ".",
+      workingDirectory: root,
+      repositoryRootURL: root,
+    )
+    #expect(worktree.isMain == true)
+  }
+
+  @Test func subdirectoryWorktreeIsNotMain() {
+    let worktree = Worktree(
+      id: "/tmp/repo/wt-1",
+      name: "feature",
+      detail: "wt-1",
+      workingDirectory: URL(fileURLWithPath: "/tmp/repo/wt-1"),
+      repositoryRootURL: URL(fileURLWithPath: "/tmp/repo"),
+    )
+    #expect(worktree.isMain == false)
+  }
+
+  @Test func siblingWorktreeIsNotMain() {
+    let worktree = Worktree(
+      id: "/tmp/repo.wt/feature",
+      name: "feature",
+      detail: "../repo.wt/feature",
+      workingDirectory: URL(fileURLWithPath: "/tmp/repo.wt/feature"),
+      repositoryRootURL: URL(fileURLWithPath: "/tmp/repo"),
+    )
+    #expect(worktree.isMain == false)
+  }
+
+  @Test func dotComponentEquivalentURLsAreMain() {
+    // `/tmp/./repo` and `/tmp/repo` are semantically the same directory.
+    // The standardization fallback in Worktree.init covers this case even
+    // if the caller forgot to normalize the URL beforehand.
+    let worktree = Worktree(
+      id: "/tmp/repo",
+      name: "main",
+      detail: ".",
+      workingDirectory: URL(fileURLWithPath: "/tmp/./repo"),
+      repositoryRootURL: URL(fileURLWithPath: "/tmp/repo"),
+    )
+    #expect(worktree.isMain == true)
+  }
+
+  @Test func dotDotComponentEquivalentURLsAreMain() {
+    let worktree = Worktree(
+      id: "/tmp/repo",
+      name: "main",
+      detail: ".",
+      workingDirectory: URL(fileURLWithPath: "/tmp/nested/../repo"),
+      repositoryRootURL: URL(fileURLWithPath: "/tmp/repo"),
+    )
+    #expect(worktree.isMain == true)
+  }
+}