diff --git a/CoreAILabCore/AppleModels/Diffusion/AppleDiffusionPipelineEngine.swift b/CoreAILabCore/AppleModels/Diffusion/AppleDiffusionPipelineEngine.swift
index 0507794..29f3011 100644
--- a/CoreAILabCore/AppleModels/Diffusion/AppleDiffusionPipelineEngine.swift
+++ b/CoreAILabCore/AppleModels/Diffusion/AppleDiffusionPipelineEngine.swift
@@ -2,6 +2,9 @@ import CoreAIDiffusionPipeline
 import Foundation
 
 actor AppleDiffusionPipelineEngine: AppleDiffusionGenerating {
+    // Safe: all stored properties are immutable after init, and the class is
+    // only stored on this actor; deinit merely balances the security-scoped
+    // access started in init, so there is no shared mutable state to race on.
     private final class ScopedResourceLease: @unchecked Sendable {
         let url: URL
         private let isAccessing: Bool
diff --git a/CoreAILabCore/AppleModels/ObjectDetection/AppleObjectDetectorEngine.swift b/CoreAILabCore/AppleModels/ObjectDetection/AppleObjectDetectorEngine.swift
index 7c4e37f..6b023ab 100644
--- a/CoreAILabCore/AppleModels/ObjectDetection/AppleObjectDetectorEngine.swift
+++ b/CoreAILabCore/AppleModels/ObjectDetection/AppleObjectDetectorEngine.swift
@@ -37,9 +37,11 @@ actor AppleObjectDetectorEngine: AppleObjectDetecting {
     }
 }
 
-// ObjectDetector is a value wrapper around Core AI runtime handles, and its
-// inference function supports concurrent calls. Keep that unchecked boundary
-// local instead of adding a retroactive conformance to Apple's public type.
+// Safe: ObjectDetector is a value wrapper around Core AI runtime handles, and
+// its inference function supports concurrent calls; instances are additionally
+// confined to AppleObjectDetectorEngine's actor-isolated methods. Keep that
+// unchecked boundary local instead of adding a retroactive conformance to
+// Apple's public type.
 private struct SendableObjectDetector: @unchecked Sendable {
     let value: ObjectDetector
 }
diff --git a/CoreAILabCore/AppleModels/Segmentation/AppleImageSegmenterEngine.swift b/CoreAILabCore/AppleModels/Segmentation/AppleImageSegmenterEngine.swift
index 0ae7e9c..9e134e8 100644
--- a/CoreAILabCore/AppleModels/Segmentation/AppleImageSegmenterEngine.swift
+++ b/CoreAILabCore/AppleModels/Segmentation/AppleImageSegmenterEngine.swift
@@ -72,6 +72,9 @@ actor AppleImageSegmenterEngine: AppleImageSegmenting {
     }
 }
 
+// Safe: ImageSegmenter is not Sendable, but every instance is created and
+// queried exclusively from AppleImageSegmenterEngine's actor-isolated methods,
+// so the wrapped value never crosses an isolation boundary concurrently.
 private struct SendableImageSegmenter: @unchecked Sendable {
     let value: ImageSegmenter
 }
diff --git a/CoreAILabCore/Chatterbox/ChatterboxSampling.swift b/CoreAILabCore/Chatterbox/ChatterboxSampling.swift
index 2122e04..33c7f2a 100644
--- a/CoreAILabCore/Chatterbox/ChatterboxSampling.swift
+++ b/CoreAILabCore/Chatterbox/ChatterboxSampling.swift
@@ -1,37 +1,62 @@
 import Foundation
+import os
 
+/// A deterministic SplitMix64-based generator whose mutable state is guarded by
+/// an unfair lock, which is what makes the `@unchecked Sendable` conformance
+/// sound. Draw order still determines the sequence, so callers that need
+/// reproducibility must serialize their draws (the Chatterbox engine does, by
+/// confining each generator to a single generation pass).
 final class ChatterboxRandomGenerator: @unchecked Sendable, RandomNumberGenerator {
-    private var state: UInt64
-    private var spareNormal: Double?
+    private struct State {
+        var state: UInt64
+        var spareNormal: Double?
+    }
+
+    private let protectedState: OSAllocatedUnfairLock<State>
 
     init(seed: UInt64) {
-        state = seed
+        protectedState = OSAllocatedUnfairLock(
+            initialState: State(state: seed, spareNormal: nil)
+        )
     }
 
     func next() -> UInt64 {
-        state &+= 0x9E3779B97F4A7C15
-        var value = state
-        value = (value ^ (value >> 30)) &* 0xBF58476D1CE4E5B9
-        value = (value ^ (value >> 27)) &* 0x94D049BB133111EB
-        return value ^ (value >> 31)
+        protectedState.withLock { Self.nextValue(&$0) }
     }
 
     func nextUnitDouble() -> Double {
-        Double(next() >> 11) * 0x1.0p-53
+        protectedState.withLock { Self.nextUnitDouble(&$0) }
     }
 
     func nextNormal() -> Double {
-        if let spareNormal {
-            self.spareNormal = nil
-            return spareNormal
+        protectedState.withLock { state in
+            if let spareNormal = state.spareNormal {
+                state.spareNormal = nil
+                return spareNormal
+            }
+
+            let first = max(
+                Self.nextUnitDouble(&state),
+                Double.leastNonzeroMagnitude
+            )
+            let second = Self.nextUnitDouble(&state)
+            let magnitude = sqrt(-2 * log(first))
+            let angle = 2 * Double.pi * second
+            state.spareNormal = magnitude * sin(angle)
+            return magnitude * cos(angle)
         }
+    }
+
+    private static func nextValue(_ state: inout State) -> UInt64 {
+        state.state &+= 0x9E3779B97F4A7C15
+        var value = state.state
+        value = (value ^ (value >> 30)) &* 0xBF58476D1CE4E5B9
+        value = (value ^ (value >> 27)) &* 0x94D049BB133111EB
+        return value ^ (value >> 31)
+    }
 
-        let first = max(nextUnitDouble(), Double.leastNonzeroMagnitude)
-        let second = nextUnitDouble()
-        let magnitude = sqrt(-2 * log(first))
-        let angle = 2 * Double.pi * second
-        spareNormal = magnitude * sin(angle)
-        return magnitude * cos(angle)
+    private static func nextUnitDouble(_ state: inout State) -> Double {
+        Double(nextValue(&state) >> 11) * 0x1.0p-53
     }
 }
 
diff --git a/CoreAILabCore/Conversion/CoreAIConversionProcessRunner.swift b/CoreAILabCore/Conversion/CoreAIConversionProcessRunner.swift
index 317ac35..e954d59 100644
--- a/CoreAILabCore/Conversion/CoreAIConversionProcessRunner.swift
+++ b/CoreAILabCore/Conversion/CoreAIConversionProcessRunner.swift
@@ -126,14 +126,38 @@ actor CoreAIConversionProcessRunner {
 
     private func stop(_ process: Process) async {
         guard process.isRunning else { return }
+
         process.interrupt()
-        try? await Task.sleep(for: .seconds(1))
-        if process.isRunning {
-            process.terminate()
-        }
-        if process.isRunning {
-            process.waitUntilExit()
+        if await waitForExit(of: process, within: .seconds(1)) { return }
+
+        process.terminate()
+        if await waitForExit(of: process, within: .seconds(1)) { return }
+
+        kill(process.processIdentifier, SIGKILL)
+        _ = await waitForExit(of: process, within: .seconds(1))
+    }
+
+    /// Waits for the process to exit without blocking the actor. Polling is
+    /// used because `execute` already owns the process's `terminationHandler`,
+    /// so installing a second handler here would break the termination stream.
+    /// Returns `false` as soon as the grace period lapses (or the surrounding
+    /// task is cancelled) so the caller can escalate to the next signal.
+    private func waitForExit(
+        of process: Process,
+        within gracePeriod: Duration
+    ) async -> Bool {
+        let clock = ContinuousClock()
+        let deadline = clock.now.advanced(by: gracePeriod)
+        while process.isRunning {
+            guard clock.now < deadline else { return false }
+            do {
+                try await Task.sleep(for: .milliseconds(50))
+            } catch {
+                // Cancelled: skip the remaining grace period and escalate.
+                return !process.isRunning
+            }
         }
+        return true
     }
 
     private func childEnvironment(for executableURL: URL) -> [String: String] {