diff --git a/Sources/KeyPathAppKit/Managers/ServiceLifecycleCoordinator+SessionRuntime.swift b/Sources/KeyPathAppKit/Managers/ServiceLifecycleCoordinator+SessionRuntime.swift
index 497484d5a..75e42d34e 100644
--- a/Sources/KeyPathAppKit/Managers/ServiceLifecycleCoordinator+SessionRuntime.swift
+++ b/Sources/KeyPathAppKit/Managers/ServiceLifecycleCoordinator+SessionRuntime.swift
@@ -521,6 +521,8 @@ extension ServiceLifecycleCoordinator {
         onStateChanged?()
         let recoveryStarted = Date()
         var lastBlocker: String?
+        var heldSince: Date?
+        var namedHeldKeys: [CGKeyCode]?
         while sessionStartIsCurrent(expectedGeneration) {
             // Screen wake can precede system wake by tens of seconds after a
             // quick lid close/open. Only a signal after this retirement counts;
@@ -533,6 +535,21 @@ extension ServiceLifecycleCoordinator {
                 AppLogger.shared.info("[SessionRuntime] Wake recovery gate: \(blocker ?? "ready") elapsedMs=\(Int(Date().timeIntervalSince(recoveryStarted) * 1000))")
                 lastBlocker = blocker
             }
+            // A key nobody is pressing can read as held indefinitely (a posted
+            // press whose release never came). Past a normal keystroke, name it.
+            if blocker == "held-keys" {
+                let since = heldSince ?? Date()
+                heldSince = since
+                let held = SessionCapsRuntimeSupport.heldKeys()
+                if Date().timeIntervalSince(since) >= 5, !held.isEmpty, held != namedHeldKeys {
+                    namedHeldKeys = held
+                    AppLogger.shared.warn("[SessionRuntime] Wake recovery waiting on held key codes \(held)")
+                    onWarning?(Self.heldKeysWarning(held))
+                }
+            } else {
+                heldSince = nil
+                namedHeldKeys = nil
+            }
             if blocker == nil {
                 AppLogger.shared.info("[SessionRuntime] Resuming after keyboard readiness")
                 sessionWakeRetryGeneration = nil
@@ -553,6 +570,14 @@ extension ServiceLifecycleCoordinator {
         return false
     }
 
+    static func heldKeysWarning(_ keys: [CGKeyCode]) -> String {
+        let names = keys.map { "\u{201C}\(KanataKeyCodeMap.overlayName(for: $0))\u{201D}" }
+        if names.count == 1 {
+            return "Remapping is waiting because macOS reports the \(names[0]) key as held down. Press and release it to resume."
+        }
+        return "Remapping is waiting because macOS reports these keys as held down: \(names.joined(separator: ", ")). Press and release each one to resume."
+    }
+
     static func canRetryWakeStartup(_ report: SessionRuntimeReport?, nonce: String,
                                     pid: Int32, uid: UInt32, cleanedUp: Bool) -> Bool
     {
diff --git a/Sources/KeyPathAppKit/Services/SessionRuntime/SessionCapsRuntimeSupport.swift b/Sources/KeyPathAppKit/Services/SessionRuntime/SessionCapsRuntimeSupport.swift
index 17a83a038..a6566b940 100644
--- a/Sources/KeyPathAppKit/Services/SessionRuntime/SessionCapsRuntimeSupport.swift
+++ b/Sources/KeyPathAppKit/Services/SessionRuntime/SessionCapsRuntimeSupport.swift
@@ -304,11 +304,22 @@ enum SessionCapsRuntimeSupport {
         return value
     }
 
-    /// Combined session state is conservative: all representable keys must be up
-    /// excluding Caps Lock’s persistent latch. It does not attribute a key to a device.
-    static func requirePhysicalAllUp() throws {
-        guard SessionKeyMap.keyCodeToUsage.keys.filter({ $0 != 57 }).allSatisfy({ !CGEventSource.keyState(.combinedSessionState, key: $0) })
-        else { throw Refusal.physicalKeysHeld }
+    /// All representable keys must be up in HID state, excluding Caps Lock’s
+    /// persistent latch. It does not attribute a key to a device. Combined
+    /// session state also keeps a posted press whose own release never came:
+    /// on 2026-10-20 it reported Space held for hours while HID state and every
+    /// keyboard had released it. Posted presses can still reach HID state, so a
+    /// caller that waits on this must say which key it is waiting for.
+    static func requirePhysicalAllUp(isDown: (CGKeyCode) -> Bool = hidKeyDown) throws {
+        guard heldKeys(isDown: isDown).isEmpty else { throw Refusal.physicalKeysHeld }
+    }
+
+    static func heldKeys(isDown: (CGKeyCode) -> Bool = hidKeyDown) -> [CGKeyCode] {
+        SessionKeyMap.keyCodeToUsage.keys.filter { $0 != 57 && isDown($0) }.sorted()
+    }
+
+    static func hidKeyDown(_ key: CGKeyCode) -> Bool {
+        CGEventSource.keyState(.hidSystemState, key: key)
     }
 
     static func configSHA256(_ path: String) throws -> String {
diff --git a/Tests/KeyPathTests/Services/SessionFailureRecoveryMessageTests.swift b/Tests/KeyPathTests/Services/SessionFailureRecoveryMessageTests.swift
index 64732ad0f..a4f77876a 100644
--- a/Tests/KeyPathTests/Services/SessionFailureRecoveryMessageTests.swift
+++ b/Tests/KeyPathTests/Services/SessionFailureRecoveryMessageTests.swift
@@ -4,6 +4,14 @@ import XCTest
 
 @MainActor
 final class SessionFailureRecoveryMessageTests: XCTestCase {
+    func testHeldKeysWarningNamesTheKeyToRelease() {
+        XCTAssertEqual(ServiceLifecycleCoordinator.heldKeysWarning([49]),
+                       "Remapping is waiting because macOS reports the \u{201C}space\u{201D} key as held down. Press and release it to resume.")
+        let several = ServiceLifecycleCoordinator.heldKeysWarning([0, 49])
+        XCTAssertTrue(several.contains("these keys as held down: \u{201C}a\u{201D}, \u{201C}space\u{201D}."), several)
+        XCTAssertTrue(several.hasSuffix("Press and release each one to resume."), several)
+    }
+
     func testConfirmedDenialExplainsBothGrantsAndRelaunch() {
         let message = ServiceLifecycleCoordinator.sessionFailureRecoveryMessage("missing-current-process-permission")
         XCTAssertTrue(message.hasPrefix("Enable \(AccessibilityPermissionPresentation.current.name)"))
diff --git a/Tests/KeyPathTests/SessionRuntime/SessionCapsRuntimeSupportTests.swift b/Tests/KeyPathTests/SessionRuntime/SessionCapsRuntimeSupportTests.swift
index 86d50ca17..41865916d 100644
--- a/Tests/KeyPathTests/SessionRuntime/SessionCapsRuntimeSupportTests.swift
+++ b/Tests/KeyPathTests/SessionRuntime/SessionCapsRuntimeSupportTests.swift
@@ -1,3 +1,4 @@
+import CoreGraphics
 import Darwin
 import Foundation
 @testable import KeyPathAppKit
@@ -153,6 +154,16 @@ final class SessionCapsRuntimeSupportTests: XCTestCase {
         XCTAssertFalse(full.managedCaps)
     }
 
+    func testPhysicalAllUpRefusesAnyHeldKeyButCapsLatch() throws {
+        XCTAssertNoThrow(try SessionCapsRuntimeSupport.requirePhysicalAllUp(isDown: { _ in false }))
+        // Caps Lock's latch persists while it is not pressed; it never blocks.
+        XCTAssertNoThrow(try SessionCapsRuntimeSupport.requirePhysicalAllUp(isDown: { $0 == 57 }))
+        XCTAssertThrowsError(try SessionCapsRuntimeSupport.requirePhysicalAllUp(isDown: { $0 == 49 })) { error in
+            XCTAssertEqual(error as? SessionCapsRuntimeSupport.Refusal, .physicalKeysHeld)
+        }
+        XCTAssertEqual(SessionCapsRuntimeSupport.heldKeys(isDown: { [49, 57, 0].contains($0) }), [0, 49])
+    }
+
     func testOrphanMutationMarkerBlocksRecoveryEvenWithoutIntent() throws {
         let root = FileManager.default.temporaryDirectory.appendingPathComponent(UUID().uuidString)
         try FileManager.default.createDirectory(at: root, withIntermediateDirectories: false)
diff --git a/docs/bugs/stale-synthetic-key-blocks-startup.md b/docs/bugs/stale-synthetic-key-blocks-startup.md
new file mode 100644
index 000000000..c542ad2de
--- /dev/null
+++ b/docs/bugs/stale-synthetic-key-blocks-startup.md
@@ -0,0 +1,55 @@
+# A key nobody was pressing left remapping off with no explanation
+
+## Symptom (mini, 2026-10-20)
+
+KeyPath started without its engine three times in one day (11:01, 14:09,
+14:18). Each start logged:
+
+```
+Managed Caps activation refused: physicalKeysHeld
+Wake recovery gate: held-keys elapsedMs=0
+```
+
+and nothing after that. Port 37001 refused connections for hours, and the only
+visible message was "Remapping will resume when your keyboard session is ready."
+
+## Cause
+
+`SessionCapsRuntimeSupport.requirePhysicalAllUp()` read
+`CGEventSource.keyState(.combinedSessionState, …)`. It reported Space
+(keycode 49) held while HID state did not:
+
+```
+combined: [49]   hid: []
+```
+
+No keyboard was holding Space. Pressing and releasing Space on the cl80 and
+unplugging the fixture and the X2A changed nothing. One Space key-up posted at
+the session tap (`kCGSessionEventTap`, from a combined-state source) cleared it
+immediately.
+
+The wake recovery loop polls the same check every 250 ms and logs only when the
+blocker changes, so it waited silently for as long as the stale state lasted.
+
+How the state diverged is not established. Posted events reach both records: a
+key-down posted at the session tap from a private source set HID state as well,
+and a key-up from a different source cleared both. That experiment did not
+reproduce a combined-only press, and which program posted the original press is
+unknown.
+
+## Fix
+
+- The check reads `.hidSystemState`, which was clear throughout this incident.
+  It exists so a Caps Lock hidutil mapping never changes mid-press, and hidutil
+  acts on HID events.
+- Because HID state can also be held by a posted press, the wake recovery loop
+  no longer waits silently: after 5 seconds on `held-keys` it logs the key codes
+  and shows "Remapping is waiting because macOS reports the “space” key as held
+  down. Press and release it to resume."
+
+## Clearing it by hand
+
+Post one key-up for the stuck key code at the session tap, for example from
+Python with `ctypes`: `CGEventSourceCreate(0)`, then
+`CGEventCreateKeyboardEvent(src, 49, False)` and `CGEventPost(1, event)`. A
+key-up on its own types nothing. Logging out also clears it.