diff --git a/Palace/ErrorHandling/ProblemReportEmail.swift b/Palace/ErrorHandling/ProblemReportEmail.swift
index c07da6835..4eac46b32 100644
--- a/Palace/ErrorHandling/ProblemReportEmail.swift
+++ b/Palace/ErrorHandling/ProblemReportEmail.swift
@@ -65,6 +65,40 @@ import UIKit
         presentingViewController.present(mailComposeViewController, animated: true)
     }
 
+    /// The value rendered after `Library:` in a problem report. Never empty.
+    ///
+    /// PP-5078. This previously read `currentAccount?.name ?? ""`, so a nil
+    /// account emitted the bare line `Library:`. `currentAccount` resolves
+    /// through the library registry and is nil until that registry has loaded
+    /// the selected account — so a patron who reports a problem before it
+    /// settles sends a report with no library on it, while the patron ID (a
+    /// separate, per-library lookup) resolves normally.
+    ///
+    /// Real ticket 18864, app 3.2.3: `Library:` blank, `Patron ID:` populated.
+    /// The agent's triage summary read "Sign in prompt - no library?" — the
+    /// blank implied a patron with no library configured, and the patron had
+    /// written that they were a member of Park Ridge Public Library.
+    ///
+    /// Three outcomes, deliberately distinguishable by whoever reads the email:
+    ///   - a real name          — the common case, passed through verbatim
+    ///   - the identifier       — the app knows WHICH library but cannot name
+    ///                            it; support can resolve a UUID, not a blank
+    ///   - "(none selected)"    — the app genuinely has no library
+    ///
+    /// A blank could equally mean the line was lost in mail transit. None of
+    /// these can.
+    static func libraryFieldValue(name: String?, uuid: String?) -> String {
+        if let name = name?.trimmingCharacters(in: .whitespacesAndNewlines),
+           !name.isEmpty {
+            return name
+        }
+        if let uuid = uuid?.trimmingCharacters(in: .whitespacesAndNewlines),
+           !uuid.isEmpty {
+            return "(name unavailable — \(uuid))"
+        }
+        return "(none selected)"
+    }
+
     func generateBody(book: TPPBook?, patronIdentifier: String? = nil, accountsManager: AccountsManager = AppContainer.production().accountsManager) -> String {
         let nativeHeight = UIScreen.main.nativeBounds.height
         let systemVersion = UIDevice.current.systemVersion
@@ -91,7 +125,7 @@ import UIKit
         }
 
         let appVersion = Bundle.main.infoDictionary?["CFBundleShortVersionString"] as? String ?? "1.0"
-        var body = "\n\n---\nIdiom: \(idiom)\nPlatform: iOS\nOS: \(systemVersion)\nHeight: \(nativeHeight)\nPalace Version: \(appVersion)\nLibrary: \(accountsManager.currentAccount?.name ?? "")"
+        var body = "\n\n---\nIdiom: \(idiom)\nPlatform: iOS\nOS: \(systemVersion)\nHeight: \(nativeHeight)\nPalace Version: \(appVersion)\nLibrary: \(Self.libraryFieldValue(name: accountsManager.currentAccount?.name, uuid: accountsManager.currentAccountId))"
 
         if let patronIdentifier = patronIdentifier {
             body += "\nPatron ID: \(patronIdentifier)"
diff --git a/PalaceTests/ProblemReportEmailTests.swift b/PalaceTests/ProblemReportEmailTests.swift
index e021a0ae2..7f6bcb59d 100644
--- a/PalaceTests/ProblemReportEmailTests.swift
+++ b/PalaceTests/ProblemReportEmailTests.swift
@@ -157,4 +157,61 @@ final class ProblemReportEmailTests: XCTestCase {
         XCTAssertFalse(body.contains(sentinel),
                        "Sanity check that the body does not contain unrelated identifier-shaped text")
     }
+
+    // MARK: - PP-5078: the Library line must never arrive blank
+
+    /// The reported defect. `generateBody` rendered
+    /// `Library: \(accountsManager.currentAccount?.name ?? "")`, so whenever
+    /// `currentAccount` was nil the line went out as `Library:` with nothing
+    /// after it.
+    ///
+    /// Real ticket 18864 (1 Sep 2026, app 3.2.3) reached support as:
+    ///
+    ///     Palace Version: 3.2.3
+    ///     Library:
+    ///     Patron ID: 21467001510417
+    ///
+    /// The patron ID resolved and the library name did not, because they come
+    /// from different sources — the ID is looked up per-library, the name is
+    /// read from `currentAccount`, which is nil until the library registry has
+    /// loaded that account. The agent triaging it recorded the summary as
+    /// "Sign in prompt - no library?", so the blank actively implied the patron
+    /// had no library configured; the patron had written that they were a
+    /// member of Park Ridge Public Library.
+    func testPP5078_libraryFieldValue_withNoNameAndNoUUID_isNotBlank() {
+        let value = ProblemReportEmail.libraryFieldValue(name: nil, uuid: nil)
+        XCTAssertFalse(value.trimmingCharacters(in: .whitespacesAndNewlines).isEmpty,
+                       "Must render a placeholder, never an empty string. A blank cannot be "
+                       + "distinguished by support from a line lost in email transit.")
+    }
+
+    /// The case that actually produced ticket 18864: the app knows WHICH
+    /// library, it just cannot name it yet. Emitting the identifier turns a
+    /// dead end into something support can look up.
+    func testPP5078_libraryFieldValue_withUUIDButNoName_carriesTheIdentifier() {
+        let uuid = "urn:uuid:99d6a227-910c-484b-aaed-e323e247e959"
+        let value = ProblemReportEmail.libraryFieldValue(name: nil, uuid: uuid)
+        XCTAssertTrue(value.contains(uuid),
+                      "When the registry cannot name the library, the report must still say "
+                      + "which one it was — support can resolve a UUID, but not a blank.")
+    }
+
+    /// Whitespace is a blank line wearing a hat: identical in the email,
+    /// equally useless to the agent reading it.
+    func testPP5078_libraryFieldValue_withWhitespaceName_fallsBack() {
+        for candidate in ["", " ", "   ", "\n", " \t "] {
+            let value = ProblemReportEmail.libraryFieldValue(name: candidate, uuid: "urn:uuid:abc")
+            XCTAssertTrue(value.contains("urn:uuid:abc"),
+                          "Whitespace-only name \(candidate.debugDescription) must fall back, not pass through.")
+        }
+    }
+
+    /// The fix must not damage the common case — most reports do carry a name.
+    func testPP5078_libraryFieldValue_withRealName_isPassedThroughUnchanged() {
+        XCTAssertEqual(
+            ProblemReportEmail.libraryFieldValue(name: "Park Ridge Public Library",
+                                                 uuid: "urn:uuid:whatever"),
+            "Park Ridge Public Library",
+            "A real library name must reach support verbatim, with no decoration.")
+    }
 }