diff --git a/.github/workflows/ci.yml b/.github/workflows/ci.yml
index e460d1ea..807c5bbe 100644
--- a/.github/workflows/ci.yml
+++ b/.github/workflows/ci.yml
@@ -78,4 +78,5 @@ jobs:
             -scheme macgit \
             -destination 'platform=macOS' \
             CODE_SIGNING_ALLOWED=NO \
+            -parallel-testing-enabled NO \
             test
diff --git a/macgit.xcodeproj/xcshareddata/xcschemes/macgit.xcscheme b/macgit.xcodeproj/xcshareddata/xcschemes/macgit.xcscheme
index 8b95d06a..4036b2a0 100644
--- a/macgit.xcodeproj/xcshareddata/xcschemes/macgit.xcscheme
+++ b/macgit.xcodeproj/xcshareddata/xcschemes/macgit.xcscheme
@@ -32,7 +32,7 @@
       <Testables>
          <TestableReference
             skipped = "NO"
-            parallelizable = "YES">
+            parallelizable = "NO">
             <BuildableReference
                BuildableIdentifier = "primary"
                BlueprintIdentifier = "6A843CBC2FC5342F0031F230"
diff --git a/macgit/App/FirebaseBootstrap.swift b/macgit/App/FirebaseBootstrap.swift
index b0466bf3..867a9584 100644
--- a/macgit/App/FirebaseBootstrap.swift
+++ b/macgit/App/FirebaseBootstrap.swift
@@ -25,6 +25,16 @@ import FirebaseCore
 import Foundation
 
 enum FirebaseBootstrap {
+    /// Unit tests launch the real app as their host. Anything that opens the
+    /// shared Firestore LevelDB cache makes concurrent/parallel test hosts abort
+    /// at launch with "Failed to open DB". Production stays unchanged; tests only
+    /// skip the cloud-backed stores. `FirebaseApp` is still configured so
+    /// Auth-backed members stay constructible.
+    static var isRunningUnitTests: Bool {
+        ProcessInfo.processInfo.environment["XCTestConfigurationFilePath"] != nil
+            || NSClassFromString("XCTestCase") != nil
+    }
+
     static func configure(bundle: Bundle = .main) -> FirebaseBootstrapStatus {
         if FirebaseApp.app() != nil {
             return .configured
diff --git a/macgit/App/macgitApp.swift b/macgit/App/macgitApp.swift
index 4ebdbfb7..ae788f04 100644
--- a/macgit/App/macgitApp.swift
+++ b/macgit/App/macgitApp.swift
@@ -38,34 +38,37 @@ struct macgitApp: App {
     init() {
         NSWindow.allowsAutomaticWindowTabbing = true
         let firebaseStatus = FirebaseBootstrap.configure()
+        // Unit-test hosts must not open Firestore: the shared LevelDB cache
+        // aborts when several test hosts (or a running app) use it at once.
+        let cloudFeaturesEnabled = firebaseStatus == .configured && !FirebaseBootstrap.isRunningUnitTests
         let appState = AppState.shared
         _appState = StateObject(wrappedValue: appState)
         let accountController = AccountSessionController(
             auth: FirebaseAuthService(),
             bootstrapStatus: firebaseStatus,
-            entitlementProvider: firebaseStatus == .configured
+            entitlementProvider: cloudFeaturesEnabled
                 ? FirestoreEntitlementStore()
                 : nil,
             entitlementCache: UserDefaultsEntitlementCache(),
-            webAccountSessionProvider: firebaseStatus == .configured
+            webAccountSessionProvider: cloudFeaturesEnabled
                 ? FirebaseWebAccountSessionService()
                 : nil,
             openWebURL: NSWorkspace.shared.open,
             appState: appState,
-            settingsStore: firebaseStatus == .configured
+            settingsStore: cloudFeaturesEnabled
                 ? FirestoreSettingsStore()
                 : nil,
-            deviceIdentity: firebaseStatus == .configured
+            deviceIdentity: cloudFeaturesEnabled
                 ? CommitPlusDeviceIdentityProvider()
                 : nil,
-            deviceAccessProvider: firebaseStatus == .configured
+            deviceAccessProvider: cloudFeaturesEnabled
                 ? FirestoreDeviceAccessService()
                 : nil,
             deviceSessionCache: UserDefaultsAccountDeviceSessionCache()
         )
         _accountController = StateObject(wrappedValue: accountController)
         let featureAccessController = FeatureAccessController(
-            provider: firebaseStatus == .configured
+            provider: cloudFeaturesEnabled
                 ? FirestoreFeaturePolicyStore()
                 : nil,
             cache: UserDefaultsFeaturePolicyCache()
@@ -73,7 +76,7 @@ struct macgitApp: App {
         _featureAccessController = StateObject(wrappedValue: featureAccessController)
         let providerConfiguration = GitHubProviderAuthConfiguration.appConfiguration()
         let gitLabProviderConfiguration = GitLabProviderAuthConfiguration.appConfiguration()
-        let providerCloudStore: GitProviderAccountCloudStore? = firebaseStatus == .configured
+        let providerCloudStore: GitProviderAccountCloudStore? = cloudFeaturesEnabled
             ? FirestoreGitProviderAccountStore()
             : nil
         let providerStore = LocalFirstGitProviderAccountStore(cloudStore: providerCloudStore)
@@ -131,14 +134,14 @@ struct macgitApp: App {
         )
         _repositoryBookmarkController = StateObject(
             wrappedValue: RepositoryBookmarkController(
-                cloudStore: firebaseStatus == .configured
+                cloudStore: cloudFeaturesEnabled
                     ? FirestoreRepositoryBookmarkStore()
                     : nil
             )
         )
         _gitFlowConfigurationSyncController = StateObject(
             wrappedValue: GitFlowConfigurationSyncController(
-                cloudStore: firebaseStatus == .configured
+                cloudStore: cloudFeaturesEnabled
                     ? FirestoreGitFlowConfigurationStore()
                     : nil
             )
diff --git a/macgit/Models/RepositoryAIFileContext.swift b/macgit/Models/RepositoryAIFileContext.swift
index 5f600c41..28a3d741 100644
--- a/macgit/Models/RepositoryAIFileContext.swift
+++ b/macgit/Models/RepositoryAIFileContext.swift
@@ -216,6 +216,10 @@ nonisolated enum RepositoryAIAnswerDecoder {
         let content: String
         if let suffixRange = body.range(of: #"\"\s*\}\s*$"#, options: [.regularExpression, .backwards]) {
             content = String(body[..<suffixRange.lowerBound])
+        } else if body.hasSuffix("\"") {
+            // The provider hit its output cap before closing the JSON wrapper, so
+            // the text value still carries its closing quote.
+            content = String(body.dropLast())
         } else {
             // A provider can reach its output cap before the JSON wrapper is
             // closed. The text value remains safe to display as prose.
diff --git a/macgit/Services/GitStatusService+BranchForcePush.swift b/macgit/Services/GitStatusService+BranchForcePush.swift
index ed62961a..7ba1720b 100644
--- a/macgit/Services/GitStatusService+BranchForcePush.swift
+++ b/macgit/Services/GitStatusService+BranchForcePush.swift
@@ -120,6 +120,16 @@ extension GitStatusService {
         }
         let expected = restoring ? plan.localHash : plan.remoteHash
         let target = restoring ? plan.remoteHash : plan.localHash
+        // `--force-with-lease` is skipped by Git when the push is a no-op, so
+        // verify the reviewed remote tip explicitly before replacing anything.
+        let currentRemoteTip = try await remoteBranchTip(
+            plan.remoteBranch, at: plan.remoteURL, in: repositoryURL, injection: injection
+        )
+        guard currentRemoteTip == expected else {
+            throw GitError.commandFailed(
+                "The remote branch changed since Force Push was reviewed. Review it again before replacing it."
+            )
+        }
         _ = try await forcePushCommit(target, in: repositoryURL)
         do {
             // A URL and one full refspec avoid remote.push/mirror config expanding the scope.
@@ -144,4 +154,18 @@ extension GitStatusService {
         try await runGit(arguments: ["rev-parse", "--verify", "\(ref)^{commit}"], in: repositoryURL)
             .trimmingCharacters(in: .whitespacesAndNewlines)
     }
+
+    private func remoteBranchTip(
+        _ branch: String,
+        at url: String,
+        in repositoryURL: URL,
+        injection: GitCredentialInjection?
+    ) async throws -> String? {
+        let output = try await runRemoteGit(
+            arguments: ["ls-remote", "--heads", "--", url, "refs/heads/\(branch)"],
+            in: repositoryURL, injection: injection
+        )
+        return output.split(whereSeparator: \.isNewline).first?
+            .split(whereSeparator: \.isWhitespace).first.map(String.init)
+    }
 }
diff --git a/macgit/Services/RepositoryAIGitCommandPolicy.swift b/macgit/Services/RepositoryAIGitCommandPolicy.swift
index c6a87364..80bba8d2 100644
--- a/macgit/Services/RepositoryAIGitCommandPolicy.swift
+++ b/macgit/Services/RepositoryAIGitCommandPolicy.swift
@@ -41,6 +41,12 @@ nonisolated enum RepositoryAIGitCommandPolicy {
         "verify-pack", "whatchanged",
     ]
 
+    /// Commands that can render a diff, and therefore must not invoke an
+    /// external diff driver or textconv filter.
+    private static let diffProducingBuiltins: Set<String> = [
+        "diff", "diff-files", "diff-index", "diff-tree", "log", "show", "whatchanged",
+    ]
+
     static func validatedArguments(_ arguments: [String]) throws -> [String] {
         guard let command = arguments.first?.trimmingCharacters(in: .whitespacesAndNewlines),
               !command.isEmpty else {
@@ -57,7 +63,7 @@ nonisolated enum RepositoryAIGitCommandPolicy {
             )
         }
 
-        let builtinSafetyArguments = command.hasPrefix("diff")
+        let builtinSafetyArguments = diffProducingBuiltins.contains(command)
             ? ["--no-ext-diff", "--no-textconv"]
             : []
         return safeGlobalArguments + [command] + builtinSafetyArguments + commandArguments
diff --git a/macgitTests/AICommitMessageTests.swift b/macgitTests/AICommitMessageTests.swift
index bac728ce..1ea3e817 100644
--- a/macgitTests/AICommitMessageTests.swift
+++ b/macgitTests/AICommitMessageTests.swift
@@ -113,7 +113,7 @@ final class AICommitMessageTests: XCTestCase {
             ids,
             [.appleIntelligence, .openAI, .googleGemini, .anthropic, .deepSeek, .openRouter]
         )
-        XCTAssertEqual(registry.provider(for: .appleIntelligence)?.descriptor.billing, .none)
+        XCTAssertEqual(registry.provider(for: .appleIntelligence)?.descriptor.billing, AIProviderBilling.none)
         for id in [AIProviderID.openAI, .anthropic, .googleGemini, .deepSeek, .openRouter] {
             let provider = registry.provider(for: id)
             let availability = await provider?.availability()
diff --git a/macgitTests/ConflictAIResolutionTests.swift b/macgitTests/ConflictAIResolutionTests.swift
index dbf814cc..1bbc8989 100644
--- a/macgitTests/ConflictAIResolutionTests.swift
+++ b/macgitTests/ConflictAIResolutionTests.swift
@@ -28,7 +28,7 @@ final class ConflictAIResolutionTests: XCTestCase {
                 {
                   "sectionIndex": 1,
                   "action": "replace",
-                  "replacementText": "merged()\n",
+                  "replacementText": "merged()\\n",
                   "reason": "Combines both behaviors",
                   "question": "",
                   "options": []
diff --git a/macgitTests/RepositoryAIPullRequestContextServiceTests.swift b/macgitTests/RepositoryAIPullRequestContextServiceTests.swift
index a3f4b92e..c3b480ba 100644
--- a/macgitTests/RepositoryAIPullRequestContextServiceTests.swift
+++ b/macgitTests/RepositoryAIPullRequestContextServiceTests.swift
@@ -40,7 +40,7 @@ final class RepositoryAIPullRequestContextServiceTests: XCTestCase {
         XCTAssertEqual(provider.detailNumber, 12)
         XCTAssertEqual(provider.changesNumber, 12)
         XCTAssertEqual(result.toolName, "pull_request_context")
-        XCTAssertTrue(result.content.contains("PR #12"))
+        XCTAssertTrue(result.content.contains("Number: #12"))
         XCTAssertFalse(result.content.contains("secret-token"))
         XCTAssertFalse(result.content.contains("refresh-secret"))
         XCTAssertFalse(result.content.contains("Authorization"))
diff --git a/macgitTests/RepositoryBookmarkTests.swift b/macgitTests/RepositoryBookmarkTests.swift
index b0f31f0a..57ca0f50 100644
--- a/macgitTests/RepositoryBookmarkTests.swift
+++ b/macgitTests/RepositoryBookmarkTests.swift
@@ -102,7 +102,7 @@ final class RepositoryBookmarkTests: XCTestCase {
             )
         )
         let bookmark = RepositoryBookmark(identity: identity)
-        let localURL = URL(fileURLWithPath: "/Users/test/Project/codex")
+        let localURL = URL(fileURLWithPath: "/Users/test/Project/codex", isDirectory: true)
 
         controller.link(bookmark, to: localURL)