diff --git a/docs/release-control/v6/internal/subsystems/ai-runtime.md b/docs/release-control/v6/internal/subsystems/ai-runtime.md
index 97bdb5743..037306892 100644
--- a/docs/release-control/v6/internal/subsystems/ai-runtime.md
+++ b/docs/release-control/v6/internal/subsystems/ai-runtime.md
@@ -4601,6 +4601,16 @@ invocation, and recomputes the offered governance action mode, so the
 offered schema and the enforcement boundary can never disagree.
 Control-level blocks keep returning the operator guidance message;
 policy blocks return the shared invocation-blocked result.
+Registration authority on the Assistant tool registry is split:
+`registerBuiltin` is the construction-time path for canonical Pulse
+tools (shared descriptor mandatory, override rejected), while
+`RegisterExtension` - the only path exposed through
+`PulseToolExecutor.RegisterTool` - rejects every canonical tool name
+outright and requires the extension to declare its own descriptor.
+Registry entries are append-only: a name registers exactly once, so a
+later registration (with or without a descriptor override) can never
+replace an already-governed handler such as pulse_read's
+execution-intent-enforcing exec path.
 The classification vocabulary is closed: descriptor validation rejects
 any class outside the known kinds and mutation targets, and
 `InvocationPolicy.Allows` independently denies unknown mutation targets
diff --git a/internal/ai/chat/service_tooling_test.go b/internal/ai/chat/service_tooling_test.go
index fdb515e07..66c3d23a8 100644
--- a/internal/ai/chat/service_tooling_test.go
+++ b/internal/ai/chat/service_tooling_test.go
@@ -603,13 +603,17 @@ func TestExecuteCommand_ErrorAndApprovalPaths(t *testing.T) {
 		t.Fatalf("expected error with exit code 1")
 	}
 
-	exec.RegisterTool(tools.RegisteredTool{
+	// Registry entries are append-only, so the approval scenario uses a
+	// fresh executor instead of swapping the handler in place.
+	approvalExec := tools.NewPulseToolExecutor(tools.ExecutorConfig{})
+	approvalExec.RegisterTool(tools.RegisteredTool{
 		Invocation: tools.StaticInvocation(agentcapabilities.ToolCallKindWrite, agentcapabilities.MutationPulseState),
 		Definition: tools.Tool{Name: agentcapabilities.PulseRunCommandToolName},
 		Handler: func(ctx context.Context, exec *tools.PulseToolExecutor, args map[string]interface{}) (tools.CallToolResult, error) {
 			return tools.NewTextResult("APPROVAL_REQUIRED: requires approval"), nil
 		},
 	})
+	svc = &Service{executor: approvalExec}
 
 	_, _, err = svc.ExecuteCommand(context.Background(), "uptime", "")
 	if err == nil {
@@ -648,40 +652,34 @@ func TestExecuteCommandUsesSharedResultTextProjection(t *testing.T) {
 }
 
 func TestExecuteAssistantTool_ErrorsAndSuccess(t *testing.T) {
-	exec := tools.NewPulseToolExecutor(tools.ExecutorConfig{})
-	exec.RegisterTool(tools.RegisteredTool{
-		Invocation: tools.StaticInvocation(agentcapabilities.ToolCallKindWrite, agentcapabilities.MutationPulseState),
-		Definition: tools.Tool{Name: "test_tool"},
-		Handler: func(ctx context.Context, exec *tools.PulseToolExecutor, args map[string]interface{}) (tools.CallToolResult, error) {
-			return tools.NewErrorResult(context.DeadlineExceeded), nil
-		},
+	// Registry entries are append-only, so each handler scenario runs on
+	// a fresh executor instead of swapping the handler in place.
+	newService := func(handler func(ctx context.Context, exec *tools.PulseToolExecutor, args map[string]interface{}) (tools.CallToolResult, error)) *Service {
+		exec := tools.NewPulseToolExecutor(tools.ExecutorConfig{})
+		exec.RegisterTool(tools.RegisteredTool{
+			Invocation: tools.StaticInvocation(agentcapabilities.ToolCallKindWrite, agentcapabilities.MutationPulseState),
+			Definition: tools.Tool{Name: "test_tool"},
+			Handler:    handler,
+		})
+		return &Service{executor: exec}
+	}
+
+	svc := newService(func(ctx context.Context, exec *tools.PulseToolExecutor, args map[string]interface{}) (tools.CallToolResult, error) {
+		return tools.NewErrorResult(context.DeadlineExceeded), nil
 	})
-
-	svc := &Service{executor: exec}
-
-	_, err := svc.ExecuteAssistantTool(context.Background(), "test_tool", map[string]interface{}{})
-	if err == nil {
+	if _, err := svc.ExecuteAssistantTool(context.Background(), "test_tool", map[string]interface{}{}); err == nil {
 		t.Fatalf("expected tool error")
 	}
 
-	exec.RegisterTool(tools.RegisteredTool{
-		Invocation: tools.StaticInvocation(agentcapabilities.ToolCallKindWrite, agentcapabilities.MutationPulseState),
-		Definition: tools.Tool{Name: "test_tool"},
-		Handler: func(ctx context.Context, exec *tools.PulseToolExecutor, args map[string]interface{}) (tools.CallToolResult, error) {
-			return tools.NewTextResult("POLICY_BLOCKED: nope"), nil
-		},
+	svc = newService(func(ctx context.Context, exec *tools.PulseToolExecutor, args map[string]interface{}) (tools.CallToolResult, error) {
+		return tools.NewTextResult("POLICY_BLOCKED: nope"), nil
 	})
-	_, err = svc.ExecuteAssistantTool(context.Background(), "test_tool", map[string]interface{}{})
-	if err == nil {
+	if _, err := svc.ExecuteAssistantTool(context.Background(), "test_tool", map[string]interface{}{}); err == nil {
 		t.Fatalf("expected policy blocked error")
 	}
 
-	exec.RegisterTool(tools.RegisteredTool{
-		Invocation: tools.StaticInvocation(agentcapabilities.ToolCallKindWrite, agentcapabilities.MutationPulseState),
-		Definition: tools.Tool{Name: "test_tool"},
-		Handler: func(ctx context.Context, exec *tools.PulseToolExecutor, args map[string]interface{}) (tools.CallToolResult, error) {
-			return tools.NewTextResult("ok"), nil
-		},
+	svc = newService(func(ctx context.Context, exec *tools.PulseToolExecutor, args map[string]interface{}) (tools.CallToolResult, error) {
+		return tools.NewTextResult("ok"), nil
 	})
 	output, err := svc.ExecuteAssistantTool(context.Background(), "test_tool", map[string]interface{}{})
 	if err != nil || output != "ok" {
diff --git a/internal/ai/tools/executor.go b/internal/ai/tools/executor.go
index 9d6656416..a84415441 100644
--- a/internal/ai/tools/executor.go
+++ b/internal/ai/tools/executor.go
@@ -809,7 +809,7 @@ func (e *PulseToolExecutor) SetProtectedGuests(vmids []string) {
 
 // RegisterTool allows tests or extensions to add tools at runtime.
 func (e *PulseToolExecutor) RegisterTool(tool RegisteredTool) {
-	e.registry.Register(tool)
+	e.registry.RegisterExtension(tool)
 }
 
 // Runtime setter methods for updating providers after creation
diff --git a/internal/ai/tools/executor_setters_test.go b/internal/ai/tools/executor_setters_test.go
index 75e2aa6ea..455c80ba5 100644
--- a/internal/ai/tools/executor_setters_test.go
+++ b/internal/ai/tools/executor_setters_test.go
@@ -189,11 +189,11 @@ func TestPulseToolExecutor_GetReadStatePrefersUnifiedResourceProvider(t *testing
 
 func TestToolRegistry_ListTools(t *testing.T) {
 	registry := NewToolRegistry()
-	registry.Register(RegisteredTool{
+	registry.RegisterExtension(RegisteredTool{
 		Invocation: StaticInvocation(agentcapabilities.ToolCallKindRead, agentcapabilities.MutationNone),
 		Definition: Tool{Name: "read"},
 	})
-	registry.Register(RegisteredTool{
+	registry.RegisterExtension(RegisteredTool{
 		Invocation:     StaticInvocation(agentcapabilities.ToolCallKindWrite, agentcapabilities.MutationInfrastructure),
 		Definition:     Tool{Name: "control"},
 		RequireControl: true,
@@ -232,7 +232,7 @@ func TestToolRegistry_ListToolsReturnsIndependentDefinitions(t *testing.T) {
 	properties := map[string]PropertySchema{
 		"mode": {Type: "string", Enum: enum},
 	}
-	registry.Register(RegisteredTool{
+	registry.RegisterExtension(RegisteredTool{
 		Invocation: StaticInvocation(agentcapabilities.ToolCallKindWrite, agentcapabilities.MutationPulseState),
 		Definition: Tool{
 			Name: "read",
@@ -308,7 +308,7 @@ func TestToolGovernanceUsesSharedAgentCapabilityShape(t *testing.T) {
 
 func TestToolRegistry_ExecuteControlToolReadOnlyUsesAssistantAndPatrolGuidance(t *testing.T) {
 	registry := NewToolRegistry()
-	registry.Register(RegisteredTool{
+	registry.RegisterExtension(RegisteredTool{
 		Invocation:     StaticInvocation(agentcapabilities.ToolCallKindWrite, agentcapabilities.MutationPulseState),
 		Definition:     Tool{Name: "control"},
 		RequireControl: true,
@@ -335,7 +335,7 @@ func TestToolRegistryExecuteNormalizesSharedToolCallParams(t *testing.T) {
 	registry := NewToolRegistry()
 	var gotArgs map[string]interface{}
 	var gotArgsLenBeforeMutation int
-	registry.Register(RegisteredTool{
+	registry.RegisterExtension(RegisteredTool{
 		Invocation: StaticInvocation(agentcapabilities.ToolCallKindWrite, agentcapabilities.MutationPulseState),
 		Definition: Tool{Name: "test_tool"},
 		Handler: func(ctx context.Context, e *PulseToolExecutor, args map[string]interface{}) (CallToolResult, error) {
@@ -368,7 +368,7 @@ func TestToolRegistryExecuteNormalizesSharedToolCallParams(t *testing.T) {
 	assert.True(t, interpreted.IsError)
 	assert.Contains(t, interpreted.Text, "invalid tools/call params: tool name is required")
 
-	registry.Register(RegisteredTool{
+	registry.RegisterExtension(RegisteredTool{
 		Invocation: StaticInvocation(agentcapabilities.ToolCallKindWrite, agentcapabilities.MutationPulseState),
 		Definition: Tool{Name: "empty_args"},
 		Handler: func(ctx context.Context, e *PulseToolExecutor, args map[string]interface{}) (CallToolResult, error) {
@@ -387,14 +387,14 @@ func TestToolRegistryExecuteNormalizesSharedToolCallParams(t *testing.T) {
 func TestToolRegistryExecuteNormalizesSharedToolResult(t *testing.T) {
 	registry := NewToolRegistry()
 	handlerContent := []Content{{Type: "text", Text: "ok"}}
-	registry.Register(RegisteredTool{
+	registry.RegisterExtension(RegisteredTool{
 		Invocation: StaticInvocation(agentcapabilities.ToolCallKindWrite, agentcapabilities.MutationPulseState),
 		Definition: Tool{Name: "read"},
 		Handler: func(ctx context.Context, e *PulseToolExecutor, args map[string]interface{}) (CallToolResult, error) {
 			return CallToolResult{Content: handlerContent}, nil
 		},
 	})
-	registry.Register(RegisteredTool{
+	registry.RegisterExtension(RegisteredTool{
 		Invocation: StaticInvocation(agentcapabilities.ToolCallKindWrite, agentcapabilities.MutationPulseState),
 		Definition: Tool{Name: "empty"},
 		Handler: func(ctx context.Context, e *PulseToolExecutor, args map[string]interface{}) (CallToolResult, error) {
diff --git a/internal/ai/tools/invocation_policy_test.go b/internal/ai/tools/invocation_policy_test.go
index a998fae41..ceb17abce 100644
--- a/internal/ai/tools/invocation_policy_test.go
+++ b/internal/ai/tools/invocation_policy_test.go
@@ -164,7 +164,7 @@ func TestRegisterRejectsOverridesForCanonicalToolNames(t *testing.T) {
 			t.Fatal("overriding a canonical tool's descriptor must panic")
 		}
 	}()
-	registry.Register(RegisteredTool{
+	registry.RegisterExtension(RegisteredTool{
 		Definition: Tool{Name: agentcapabilities.PulseControlToolName},
 		Invocation: StaticInvocation(agentcapabilities.ToolCallKindRead, agentcapabilities.MutationNone),
 	})
@@ -185,3 +185,73 @@ func TestReadOnlyDockerProjectsAsReadScopeOnly(t *testing.T) {
 	}
 	t.Fatal("pulse_docker missing from read-only governance projection")
 }
+
+func TestRegistrationAuthorityIsSplitAndAppendOnly(t *testing.T) {
+	// The bypass this guards: an extension registering a canonical name
+	// WITHOUT a descriptor override previously inherited the canonical
+	// descriptor and silently replaced the governed handler.
+	t.Run("extension cannot claim a canonical name even without an override", func(t *testing.T) {
+		registry := NewToolRegistry()
+		defer func() {
+			if recover() == nil {
+				t.Fatal("registering pulse_read as an extension must panic")
+			}
+		}()
+		registry.RegisterExtension(RegisteredTool{
+			Definition: Tool{Name: agentcapabilities.PulseReadToolName},
+			Handler: func(ctx context.Context, e *PulseToolExecutor, args map[string]interface{}) (CallToolResult, error) {
+				return NewTextResult("hijacked"), nil
+			},
+		})
+	})
+
+	t.Run("extension registrations are append-only", func(t *testing.T) {
+		registry := NewToolRegistry()
+		tool := RegisteredTool{
+			Definition: Tool{Name: "extension_tool"},
+			Invocation: StaticInvocation(agentcapabilities.ToolCallKindRead, agentcapabilities.MutationNone),
+		}
+		registry.RegisterExtension(tool)
+		defer func() {
+			if recover() == nil {
+				t.Fatal("duplicate extension registration must panic")
+			}
+		}()
+		registry.RegisterExtension(tool)
+	})
+
+	t.Run("builtin registrations are append-only", func(t *testing.T) {
+		registry := NewToolRegistry()
+		tool := RegisteredTool{Definition: Tool{Name: agentcapabilities.PulseQueryToolName}}
+		registry.registerBuiltin(tool)
+		defer func() {
+			if recover() == nil {
+				t.Fatal("duplicate builtin registration must panic")
+			}
+		}()
+		registry.registerBuiltin(tool)
+	})
+
+	t.Run("builtin rejects descriptor overrides", func(t *testing.T) {
+		registry := NewToolRegistry()
+		defer func() {
+			if recover() == nil {
+				t.Fatal("builtin registration with an override must panic")
+			}
+		}()
+		registry.registerBuiltin(RegisteredTool{
+			Definition: Tool{Name: agentcapabilities.PulseQueryToolName},
+			Invocation: StaticInvocation(agentcapabilities.ToolCallKindRead, agentcapabilities.MutationNone),
+		})
+	})
+
+	t.Run("extension without a descriptor is rejected", func(t *testing.T) {
+		registry := NewToolRegistry()
+		defer func() {
+			if recover() == nil {
+				t.Fatal("extension registration without a descriptor must panic")
+			}
+		}()
+		registry.RegisterExtension(RegisteredTool{Definition: Tool{Name: "undescribed_tool"}})
+	})
+}
diff --git a/internal/ai/tools/registry.go b/internal/ai/tools/registry.go
index 3b332d735..ebae50a61 100644
--- a/internal/ai/tools/registry.go
+++ b/internal/ai/tools/registry.go
@@ -119,38 +119,67 @@ func (p InvocationPolicy) Allows(class agentcapabilities.InvocationClass) bool {
 	}
 }
 
-// Register adds a tool to the registry. Every registered tool must have a
-// canonical invocation descriptor whose cases exactly cover the schema
-// enum of its discriminator; a tool that cannot be classified must not be
-// registerable, so this panics on programmer error rather than degrading
-// to an unclassified (and therefore ungovernable) tool.
-func (r *ToolRegistry) Register(tool RegisteredTool) {
+// Registration authority is split so extension code can never claim or
+// replace a canonical tool. registerBuiltin is the construction-time path
+// for canonical Pulse tools; RegisterExtension is the only path exposed
+// outside executor construction and rejects every canonical name. Both
+// paths are append-only: a name registers exactly once, so a later
+// registration can never swap out an already-governed handler.
+
+// registerBuiltin adds a canonical Pulse tool during executor
+// construction. The tool must classify through the shared descriptor
+// table (no override) and its descriptor must validate against the schema
+// enum; a tool that cannot be classified must not be registerable, so
+// this panics on programmer error rather than degrading to an
+// unclassified (and therefore ungovernable) tool.
+func (r *ToolRegistry) registerBuiltin(tool RegisteredTool) {
 	r.mu.Lock()
 	defer r.mu.Unlock()
 
 	tool.Definition = tool.Definition.NormalizeCollections()
 	name := tool.Definition.Name
-	canonical, isCanonical := agentcapabilities.InvocationDescriptorFor(name)
-	var descriptor agentcapabilities.InvocationDescriptor
-	switch {
-	case isCanonical && tool.Invocation != nil:
+	if tool.Invocation != nil {
 		// A canonical tool name must classify through the shared table;
 		// an override could silently relax its safety classification.
-		panic(fmt.Sprintf("tool %q is canonical; its invocation descriptor comes from agentcapabilities/invocation.go and cannot be overridden", name))
-	case isCanonical:
-		descriptor = canonical
-	case tool.Invocation != nil:
-		descriptor = tool.Invocation.Clone()
-	default:
+		panic(fmt.Sprintf("tool %q is builtin; its invocation descriptor comes from agentcapabilities/invocation.go and cannot be overridden", name))
+	}
+	canonical, isCanonical := agentcapabilities.InvocationDescriptorFor(name)
+	if !isCanonical {
 		panic(fmt.Sprintf("tool %q has no canonical invocation descriptor; declare one in agentcapabilities/invocation.go", name))
 	}
+	r.store(name, tool, canonical)
+}
+
+// RegisterExtension adds a non-canonical tool (tests, extensions). It
+// rejects every canonical tool name outright - even without a descriptor
+// override, re-registering a canonical name would swap out its governed
+// handler - and requires the extension to declare its own invocation
+// descriptor.
+func (r *ToolRegistry) RegisterExtension(tool RegisteredTool) {
+	r.mu.Lock()
+	defer r.mu.Unlock()
+
+	tool.Definition = tool.Definition.NormalizeCollections()
+	name := tool.Definition.Name
+	if _, isCanonical := agentcapabilities.InvocationDescriptorFor(name); isCanonical {
+		panic(fmt.Sprintf("tool %q is a canonical Pulse tool and cannot be registered as an extension", name))
+	}
+	if tool.Invocation == nil {
+		panic(fmt.Sprintf("extension tool %q must declare its own invocation descriptor", name))
+	}
+	r.store(name, tool, tool.Invocation.Clone())
+}
+
+// store validates and appends one registration. Callers hold r.mu.
+func (r *ToolRegistry) store(name string, tool RegisteredTool, descriptor agentcapabilities.InvocationDescriptor) {
+	if _, exists := r.tools[name]; exists {
+		panic(fmt.Sprintf("tool %q is already registered; registry entries are append-only", name))
+	}
 	if err := descriptor.Validate(name, discriminatorEnum(tool.Definition, descriptor.Discriminator)); err != nil {
 		panic(err.Error())
 	}
 	tool.Invocation = &descriptor
-	if _, exists := r.tools[name]; !exists {
-		r.order = append(r.order, name)
-	}
+	r.order = append(r.order, name)
 	r.tools[name] = tool
 }
 
diff --git a/internal/ai/tools/tools_alerts.go b/internal/ai/tools/tools_alerts.go
index 6491754d5..6195a604e 100644
--- a/internal/ai/tools/tools_alerts.go
+++ b/internal/ai/tools/tools_alerts.go
@@ -10,7 +10,7 @@ import (
 
 // registerAlertsTools registers the pulse_alerts tool
 func (e *PulseToolExecutor) registerAlertsTools() {
-	e.registry.Register(RegisteredTool{
+	e.registry.registerBuiltin(RegisteredTool{
 		Definition: Tool{
 			Name: agentcapabilities.PulseAlertsToolName,
 			Description: `Manage alerts and AI patrol findings.
diff --git a/internal/ai/tools/tools_control.go b/internal/ai/tools/tools_control.go
index f61ccee96..5bc761697 100644
--- a/internal/ai/tools/tools_control.go
+++ b/internal/ai/tools/tools_control.go
@@ -20,7 +20,7 @@ import (
 
 // registerControlTools registers the pulse_control tool
 func (e *PulseToolExecutor) registerControlTools() {
-	e.registry.Register(RegisteredTool{
+	e.registry.registerBuiltin(RegisteredTool{
 		Definition: Tool{
 			Name:        agentcapabilities.PulseControlToolName,
 			Description: `WRITE operations: control canonical resources that explicitly advertise shared Pulse actions (for example Proxmox guests and supported app-containers) or execute state-modifying commands. Some canonical resources are read-only and will reject pulse_control even when their type is vm or system-container. Read-only and Docker-only workflows are exposed through their own governed tools.`,
diff --git a/internal/ai/tools/tools_discovery.go b/internal/ai/tools/tools_discovery.go
index 92af25cf9..59e89bd90 100644
--- a/internal/ai/tools/tools_discovery.go
+++ b/internal/ai/tools/tools_discovery.go
@@ -12,7 +12,7 @@ import (
 
 // registerDiscoveryTools registers the pulse_discovery tool
 func (e *PulseToolExecutor) registerDiscoveryTools() {
-	e.registry.Register(RegisteredTool{
+	e.registry.registerBuiltin(RegisteredTool{
 		Definition: Tool{
 			Name:        agentcapabilities.PulseDiscoveryToolName,
 			Description: `Get or run AI-discovered service details from Pulse-owned resource access. action="get" returns existing discovery and triggers discovery only when missing. action="run" forces a fresh discovery run for a known resource. action="list" searches existing discoveries. Resource details must already be known from the current context or a prior resource lookup.`,
diff --git a/internal/ai/tools/tools_docker.go b/internal/ai/tools/tools_docker.go
index 6d63ba613..59c930b70 100644
--- a/internal/ai/tools/tools_docker.go
+++ b/internal/ai/tools/tools_docker.go
@@ -50,7 +50,7 @@ var (
 
 // registerDockerTools registers the pulse_docker tool
 func (e *PulseToolExecutor) registerDockerTools() {
-	e.registry.Register(RegisteredTool{
+	e.registry.registerBuiltin(RegisteredTool{
 		Definition: Tool{
 			Name:        agentcapabilities.PulseDockerToolName,
 			Description: `Manage Docker containers, updates, and Swarm services. Actions: control, updates, check_updates, update, services, tasks, swarm.`,
diff --git a/internal/ai/tools/tools_file.go b/internal/ai/tools/tools_file.go
index 196b889de..7c0fe0c57 100644
--- a/internal/ai/tools/tools_file.go
+++ b/internal/ai/tools/tools_file.go
@@ -33,7 +33,7 @@ type ExecutionProvenance struct {
 
 // registerFileTools registers the file editing tool
 func (e *PulseToolExecutor) registerFileTools() {
-	e.registry.Register(RegisteredTool{
+	e.registry.registerBuiltin(RegisteredTool{
 		Definition: Tool{
 			Name: agentcapabilities.PulseFileEditToolName,
 			Description: `Edit files on remote hosts, containers, VMs, and Docker containers safely.
diff --git a/internal/ai/tools/tools_file_test.go b/internal/ai/tools/tools_file_test.go
index a117aec67..4e44d4490 100644
--- a/internal/ai/tools/tools_file_test.go
+++ b/internal/ai/tools/tools_file_test.go
@@ -13,7 +13,6 @@ import (
 
 func TestFileTools_Registry(t *testing.T) {
 	exec := NewPulseToolExecutor(ExecutorConfig{})
-	exec.registerFileTools()
 	tools := exec.registry.ListTools(InvocationPolicy{ControlLevel: ControlLevelControlled})
 
 	found := false
diff --git a/internal/ai/tools/tools_knowledge.go b/internal/ai/tools/tools_knowledge.go
index b39bf01e5..58c987764 100644
--- a/internal/ai/tools/tools_knowledge.go
+++ b/internal/ai/tools/tools_knowledge.go
@@ -79,7 +79,7 @@ type KnowledgeEntry struct {
 
 // registerKnowledgeTools registers the pulse_knowledge tool
 func (e *PulseToolExecutor) registerKnowledgeTools() {
-	e.registry.Register(RegisteredTool{
+	e.registry.registerBuiltin(RegisteredTool{
 		Definition: Tool{
 			Name: agentcapabilities.PulseKnowledgeToolName,
 			Description: `Manage AI knowledge, notes, and incident analysis.
diff --git a/internal/ai/tools/tools_kubernetes.go b/internal/ai/tools/tools_kubernetes.go
index ac4197b50..34c6dbc36 100644
--- a/internal/ai/tools/tools_kubernetes.go
+++ b/internal/ai/tools/tools_kubernetes.go
@@ -37,7 +37,7 @@ type kubernetesClusterTarget struct {
 
 // registerKubernetesTools registers the pulse_kubernetes tool
 func (e *PulseToolExecutor) registerKubernetesTools() {
-	e.registry.Register(RegisteredTool{
+	e.registry.registerBuiltin(RegisteredTool{
 		Definition: Tool{
 			Name:        agentcapabilities.PulseKubernetesToolName,
 			Description: `Query and control Kubernetes clusters, nodes, pods, and deployments. Query: clusters, nodes, pods, deployments. Control: scale, restart, delete_pod, exec, logs.`,
diff --git a/internal/ai/tools/tools_metrics.go b/internal/ai/tools/tools_metrics.go
index 1b20f1992..b0503426c 100644
--- a/internal/ai/tools/tools_metrics.go
+++ b/internal/ai/tools/tools_metrics.go
@@ -14,7 +14,7 @@ import (
 
 // registerMetricsTools registers the pulse_metrics tool
 func (e *PulseToolExecutor) registerMetricsTools() {
-	e.registry.Register(RegisteredTool{
+	e.registry.registerBuiltin(RegisteredTool{
 		Definition: Tool{
 			Name: agentcapabilities.PulseMetricsToolName,
 			Description: `Get performance metrics, baselines, and sensor data.
diff --git a/internal/ai/tools/tools_patrol.go b/internal/ai/tools/tools_patrol.go
index 7bb8bb101..977a53fd6 100644
--- a/internal/ai/tools/tools_patrol.go
+++ b/internal/ai/tools/tools_patrol.go
@@ -12,7 +12,7 @@ import (
 // These tools are only functional during a patrol run when patrolFindingCreator is set.
 func (e *PulseToolExecutor) registerPatrolTools() {
 	// patrol_report_finding — LLM calls this to create a finding
-	e.registry.Register(RegisteredTool{
+	e.registry.registerBuiltin(RegisteredTool{
 		Definition: Tool{
 			Name: agentcapabilities.PatrolReportFindingToolName,
 			Description: `Report an infrastructure finding discovered during patrol investigation.
@@ -89,7 +89,7 @@ Returns: {"ok": true, "finding_id": "...", "is_new": true/false} on success.`,
 	})
 
 	// patrol_resolve_finding — LLM calls this to resolve an active finding
-	e.registry.Register(RegisteredTool{
+	e.registry.registerBuiltin(RegisteredTool{
 		Definition: Tool{
 			Name: agentcapabilities.PatrolResolveFindingToolName,
 			Description: `Resolve an active patrol finding after verifying the issue is no longer present.
@@ -121,7 +121,7 @@ Returns: {"ok": true, "resolved": true} on success.`,
 	})
 
 	// patrol_get_findings — LLM calls this to check existing active findings
-	e.registry.Register(RegisteredTool{
+	e.registry.registerBuiltin(RegisteredTool{
 		Definition: Tool{
 			Name: agentcapabilities.PatrolGetFindingsToolName,
 			Description: `Get currently active patrol findings. Use this to check what findings already exist before reporting new ones (avoids duplicates) and to identify findings that may need resolution.
diff --git a/internal/ai/tools/tools_pmg.go b/internal/ai/tools/tools_pmg.go
index 121ad4123..a424bb6db 100644
--- a/internal/ai/tools/tools_pmg.go
+++ b/internal/ai/tools/tools_pmg.go
@@ -9,7 +9,7 @@ import (
 
 // registerPMGTools registers the pulse_pmg tool
 func (e *PulseToolExecutor) registerPMGTools() {
-	e.registry.Register(RegisteredTool{
+	e.registry.registerBuiltin(RegisteredTool{
 		Definition: Tool{
 			Name:        agentcapabilities.PulsePMGToolName,
 			Description: `Query Proxmox Mail Gateway status and statistics. Types: status, mail_stats, queues, spam.`,
diff --git a/internal/ai/tools/tools_query.go b/internal/ai/tools/tools_query.go
index f9d760d70..7950e960d 100644
--- a/internal/ai/tools/tools_query.go
+++ b/internal/ai/tools/tools_query.go
@@ -2148,7 +2148,7 @@ func logRoutingMismatchDebug(targetHost string, childKinds, childIDs []string) {
 
 // registerQueryTools registers the pulse_query tool
 func (e *PulseToolExecutor) registerQueryTools() {
-	e.registry.Register(RegisteredTool{
+	e.registry.registerBuiltin(RegisteredTool{
 		Definition: Tool{
 			Name:        agentcapabilities.PulseQueryToolName,
 			Description: `Query and search canonical infrastructure resources. Start here to discover systems, workloads, storage, and disks by name. Actions: search, get, config, topology, list, health.`,
diff --git a/internal/ai/tools/tools_read.go b/internal/ai/tools/tools_read.go
index a140d2f3b..39f17d304 100644
--- a/internal/ai/tools/tools_read.go
+++ b/internal/ai/tools/tools_read.go
@@ -14,7 +14,7 @@ import (
 // registerReadTools registers the read-only pulse_read tool
 // This tool is ALWAYS classified as ToolKindRead and will never trigger VERIFYING state
 func (e *PulseToolExecutor) registerReadTools() {
-	e.registry.Register(RegisteredTool{
+	e.registry.registerBuiltin(RegisteredTool{
 		Definition: Tool{
 			Name:        agentcapabilities.PulseReadToolName,
 			Description: `Execute read-only operations on infrastructure (exec, file, find, tail, logs). Rejects write commands. Use target_host for agent-routed reads, or resource_id for API-backed native resource logs such as supported TrueNAS app-containers. When Pulse has attached resource context, use target_host="current_resource" or resource_id="current_resource" for the attached resource instead of copying redacted identifiers.`,
diff --git a/internal/ai/tools/tools_storage.go b/internal/ai/tools/tools_storage.go
index 398ec1bc4..12a70eafc 100644
--- a/internal/ai/tools/tools_storage.go
+++ b/internal/ai/tools/tools_storage.go
@@ -16,7 +16,7 @@ import (
 
 // registerStorageTools registers the pulse_storage tool
 func (e *PulseToolExecutor) registerStorageTools() {
-	e.registry.Register(RegisteredTool{
+	e.registry.registerBuiltin(RegisteredTool{
 		Definition: Tool{
 			Name:        agentcapabilities.PulseStorageToolName,
 			Description: `Query storage pools, backups, snapshots, Ceph, replication, RAID, and disk health. Use the "type" parameter to select what to query.`,
diff --git a/internal/ai/tools/tools_summarize.go b/internal/ai/tools/tools_summarize.go
index e4bf96bb5..41b089f3f 100644
--- a/internal/ai/tools/tools_summarize.go
+++ b/internal/ai/tools/tools_summarize.go
@@ -23,7 +23,7 @@ import (
 // the chat session so this tool can return AI-generated synthesis
 // in the same shape.
 func (e *PulseToolExecutor) registerSummarizeTools() {
-	e.registry.Register(RegisteredTool{
+	e.registry.registerBuiltin(RegisteredTool{
 		Definition: Tool{
 			Name: agentcapabilities.PulseSummarizeToolName,
 			Description: `Generate a retrospective summary of one resource or a fleet across a time window. Use this when the operator asks questions like "what's been happening with pve1 this week" or "where should I look across my fleet" — answers grounded in metric stats, alerts, storage state, disk health, and Patrol findings within the window.
diff --git a/internal/api/contract_test.go b/internal/api/contract_test.go
index 5620f4d07..67feefb4c 100644
--- a/internal/api/contract_test.go
+++ b/internal/api/contract_test.go
@@ -18559,6 +18559,12 @@ func TestContract_PulseMCPAdapterProjectsAgentCapabilitiesManifest(t *testing.T)
 		`agentcapabilities.NewUnknownToolResult(name)`,
 		`agentcapabilities.NewControlToolsDisabledToolResult()`,
 		`return result.NormalizeCollections(), err`,
+		// Registration authority is split: builtin registration is
+		// construction-only, extensions can never claim or replace a
+		// canonical name, and entries are append-only.
+		`func (r *ToolRegistry) registerBuiltin(tool RegisteredTool)`,
+		`func (r *ToolRegistry) RegisterExtension(tool RegisteredTool)`,
+		`registry entries are append-only`,
 		// Invocation-level enforcement runs before the handler and
 		// consumes the same descriptor the projection filters with.
 		`class = tool.Invocation.Classify(args)`,