diff --git a/internal/agent/agent.go b/internal/agent/agent.go
index efdc4808..cd570255 100644
--- a/internal/agent/agent.go
+++ b/internal/agent/agent.go
@@ -7,6 +7,7 @@ import (
 	"fmt"
 	"log/slog"
 	"strings"
+	"sync"
 	"time"
 
 	sdk "github.com/memohai/twilight-ai/sdk"
@@ -99,7 +100,7 @@ func (a *Agent) runStream(ctx context.Context, cfg RunConfig, ch chan<- StreamEv
 	var textLoopGuard *TextLoopGuard
 	var textLoopProbeBuffer *TextLoopProbeBuffer
 	var toolLoopGuard *ToolLoopGuard
-	toolLoopAbortCallIDs := make(map[string]struct{})
+	toolLoopAbortCallIDs := newToolAbortRegistry()
 	if cfg.LoopDetection.Enabled {
 		textLoopGuard = NewTextLoopGuard(LoopDetectedStreakThreshold, LoopDetectedMinNewGramsPerChunk, SentialOptions{})
 		textLoopProbeBuffer = NewTextLoopProbeBuffer(LoopDetectedProbeChars, func(text string) {
@@ -314,11 +315,7 @@ func (a *Agent) runStream(ctx context.Context, cfg RunConfig, ch chan<- StreamEv
 			}
 
 		case *sdk.StreamToolResultPart:
-			shouldAbort := false
-			if _, ok := toolLoopAbortCallIDs[p.ToolCallID]; ok {
-				delete(toolLoopAbortCallIDs, p.ToolCallID)
-				shouldAbort = true
-			}
+			shouldAbort := toolLoopAbortCallIDs.Take(p.ToolCallID)
 			stepNumber++
 			if !sendEvent(ctx, ch, StreamEvent{
 				Type:       EventToolCallEnd,
@@ -440,7 +437,10 @@ func (a *Agent) runStream(ctx context.Context, cfg RunConfig, ch chan<- StreamEv
 func (a *Agent) runGenerate(ctx context.Context, cfg RunConfig) (*GenerateResult, error) {
 	// Collecting emitter: tools push side-effect events here during generation.
 	var collected []tools.ToolStreamEvent
+	var collectedMu sync.Mutex
 	collectEmitter := tools.StreamEmitter(func(evt tools.ToolStreamEvent) {
+		collectedMu.Lock()
+		defer collectedMu.Unlock()
 		collected = append(collected, evt)
 	})
 
@@ -456,7 +456,7 @@ func (a *Agent) runGenerate(ctx context.Context, cfg RunConfig) (*GenerateResult
 
 	var toolLoopGuard *ToolLoopGuard
 	var textLoopGuard *TextLoopGuard
-	toolLoopAbortCallIDs := make(map[string]struct{})
+	toolLoopAbortCallIDs := newToolAbortRegistry()
 	if cfg.LoopDetection.Enabled {
 		toolLoopGuard = NewToolLoopGuard(ToolLoopRepeatThreshold, ToolLoopWarningsBeforeAbort)
 		textLoopGuard = NewTextLoopGuard(LoopDetectedStreakThreshold, LoopDetectedMinNewGramsPerChunk, SentialOptions{})
@@ -490,7 +490,7 @@ func (a *Agent) runGenerate(ctx context.Context, cfg RunConfig) (*GenerateResult
 	opts = append(opts,
 		sdk.WithOnStep(func(step *sdk.StepResult) *sdk.GenerateParams {
 			if cfg.LoopDetection.Enabled {
-				if len(toolLoopAbortCallIDs) > 0 {
+				if toolLoopAbortCallIDs.Any() {
 					return nil // stop
 				}
 				if textLoopGuard != nil && isNonEmptyString(step.Text) {
@@ -701,7 +701,7 @@ func drainBackgroundNotifications(
 	return p
 }
 
-func wrapToolsWithLoopGuard(tools []sdk.Tool, guard *ToolLoopGuard, abortCallIDs map[string]struct{}) []sdk.Tool {
+func wrapToolsWithLoopGuard(tools []sdk.Tool, guard *ToolLoopGuard, abortCallIDs *toolAbortRegistry) []sdk.Tool {
 	wrapped := make([]sdk.Tool, len(tools))
 	for i, tool := range tools {
 		originalExecute := tool.Execute
@@ -710,7 +710,7 @@ func wrapToolsWithLoopGuard(tools []sdk.Tool, guard *ToolLoopGuard, abortCallIDs
 		wrapped[i].Execute = func(ctx *sdk.ToolExecContext, input any) (any, error) {
 			warn, abort := guard.Guard(toolName, input)
 			if abort {
-				abortCallIDs[ctx.ToolCallID] = struct{}{}
+				abortCallIDs.Add(ctx.ToolCallID)
 				return map[string]any{
 					"isError": true,
 					"content": []map[string]any{{
diff --git a/internal/agent/guard_state.go b/internal/agent/guard_state.go
new file mode 100644
index 00000000..f54fe902
--- /dev/null
+++ b/internal/agent/guard_state.go
@@ -0,0 +1,48 @@
+package agent
+
+import "sync"
+
+type toolAbortRegistry struct {
+	mu  sync.Mutex
+	ids map[string]struct{}
+}
+
+func newToolAbortRegistry() *toolAbortRegistry {
+	return &toolAbortRegistry{
+		ids: make(map[string]struct{}),
+	}
+}
+
+func (r *toolAbortRegistry) Add(toolCallID string) {
+	if r == nil || toolCallID == "" {
+		return
+	}
+
+	r.mu.Lock()
+	defer r.mu.Unlock()
+	r.ids[toolCallID] = struct{}{}
+}
+
+func (r *toolAbortRegistry) Take(toolCallID string) bool {
+	if r == nil || toolCallID == "" {
+		return false
+	}
+
+	r.mu.Lock()
+	defer r.mu.Unlock()
+	if _, ok := r.ids[toolCallID]; !ok {
+		return false
+	}
+	delete(r.ids, toolCallID)
+	return true
+}
+
+func (r *toolAbortRegistry) Any() bool {
+	if r == nil {
+		return false
+	}
+
+	r.mu.Lock()
+	defer r.mu.Unlock()
+	return len(r.ids) > 0
+}
diff --git a/internal/agent/guard_state_test.go b/internal/agent/guard_state_test.go
new file mode 100644
index 00000000..f4b6b5f8
--- /dev/null
+++ b/internal/agent/guard_state_test.go
@@ -0,0 +1,32 @@
+package agent
+
+import (
+	"fmt"
+	"sync"
+	"testing"
+)
+
+func TestToolAbortRegistryConcurrentAccess(t *testing.T) {
+	registry := newToolAbortRegistry()
+
+	var wg sync.WaitGroup
+	for i := 0; i < 32; i++ {
+		wg.Add(1)
+		go func(i int) {
+			defer wg.Done()
+			id := fmt.Sprintf("call-%d", i)
+			registry.Add(id)
+			if !registry.Any() {
+				t.Error("expected registry to report pending aborts")
+			}
+			if !registry.Take(id) {
+				t.Errorf("expected to take %s", id)
+			}
+		}(i)
+	}
+	wg.Wait()
+
+	if registry.Any() {
+		t.Fatal("expected registry to be empty")
+	}
+}
diff --git a/internal/agent/sential.go b/internal/agent/sential.go
index 51d5784d..23ec52f7 100644
--- a/internal/agent/sential.go
+++ b/internal/agent/sential.go
@@ -7,6 +7,7 @@ import (
 	"fmt"
 	"sort"
 	"strings"
+	"sync"
 	"unicode"
 	"unicode/utf8"
 )
@@ -322,6 +323,7 @@ type ToolLoopResult struct {
 
 // ToolLoopGuard detects repeated identical tool calls.
 type ToolLoopGuard struct {
+	mu                  sync.Mutex
 	repeatThreshold     int
 	warningsBeforeAbort int
 	volatileKeySet      map[string]struct{}
@@ -352,8 +354,17 @@ func NewToolLoopGuard(repeatThreshold, warningsBeforeAbort int) *ToolLoopGuard {
 
 // Inspect checks a tool call for repetition.
 func (g *ToolLoopGuard) Inspect(input ToolLoopInput) ToolLoopResult {
+	if g == nil {
+		return ToolLoopResult{
+			Hash: computeToolLoopHash(input, nil),
+		}
+	}
+
 	hash := computeToolLoopHash(input, g.volatileKeySet)
 
+	g.mu.Lock()
+	defer g.mu.Unlock()
+
 	if hash == g.lastHash {
 		g.repeatCount++
 	} else {
@@ -391,6 +402,13 @@ func (g *ToolLoopGuard) Inspect(input ToolLoopInput) ToolLoopResult {
 
 // Reset clears the guard state.
 func (g *ToolLoopGuard) Reset() {
+	if g == nil {
+		return
+	}
+
+	g.mu.Lock()
+	defer g.mu.Unlock()
+
 	g.lastHash = ""
 	g.repeatCount = 0
 	g.breachCount = 0
diff --git a/internal/agent/sential_test.go b/internal/agent/sential_test.go
new file mode 100644
index 00000000..acef5ec8
--- /dev/null
+++ b/internal/agent/sential_test.go
@@ -0,0 +1,57 @@
+package agent
+
+import (
+	"sync"
+	"testing"
+)
+
+func TestToolLoopGuardNilReceiver(t *testing.T) {
+	var guard *ToolLoopGuard
+
+	result := guard.Inspect(ToolLoopInput{
+		ToolName: "search",
+		Input: map[string]any{
+			"query": "memoh",
+		},
+	})
+
+	if result.Hash == "" {
+		t.Fatal("expected hash for nil receiver")
+	}
+	if result.Warn {
+		t.Fatal("did not expect warning for nil receiver")
+	}
+	if result.Abort {
+		t.Fatal("did not expect abort for nil receiver")
+	}
+}
+
+func TestToolLoopGuardConcurrentInspectAndReset(t *testing.T) {
+	guard := NewToolLoopGuard(2, 1)
+	input := ToolLoopInput{
+		ToolName: "web_search",
+		Input: map[string]any{
+			"query":     "memoh logs",
+			"requestId": "volatile",
+		},
+	}
+
+	var wg sync.WaitGroup
+	for i := 0; i < 16; i++ {
+		wg.Add(1)
+		go func(i int) {
+			defer wg.Done()
+			for j := 0; j < 200; j++ {
+				result := guard.Inspect(input)
+				if result.Hash == "" {
+					t.Error("expected non-empty hash")
+					return
+				}
+				if (i+j)%25 == 0 {
+					guard.Reset()
+				}
+			}
+		}(i)
+	}
+	wg.Wait()
+}