diff --git a/PROTOCOL.md b/PROTOCOL.md
index 67f72b4..77a5577 100644
--- a/PROTOCOL.md
+++ b/PROTOCOL.md
@@ -58,6 +58,7 @@ Dispatch a user message to a session.
 | customInstructions | string? | Account-level instructions snapshotted onto this task. Updated daemons append this text to the Pi system prompt. |
 | disableSkills | boolean? | `true` disables Claude skill discovery and explicit skill file loading for the task. |
 | planCapability | PlanCapability? | Task-scoped bearer capability for Plan Mode tools. The daemon passes it to the Pi process as environment variables and never places it in the prompt. |
+| browserGrant | BrowserGrantContext? | Task-scoped browser grant context. Cloud creates the grant before dispatch; the daemon opens the local browser lazily on the first browser tool call. |
 
 `ContextRef`:
 
@@ -80,6 +81,18 @@ Dispatch a user message to a session.
 | expiresAt | string | ISO timestamp. |
 | snapshot | object? | Capability metadata snapshot used by cloud-side authorization. |
 
+`BrowserGrantContext`:
+
+| Field | Type | Notes |
+|---|---|---|
+| grantId | string | Browser grant record identifier. |
+| projectId | uuid | Project that owns the grant. |
+| sessionId | uuid | Session that owns the grant. |
+| taskId | uuid | Task that owns the grant. |
+| channelId | string | Browser channel that receives lifecycle events. |
+| machineId | uuid | Daemon machine expected to consume the grant. |
+| expiresAt | iso8601 string | Grant expiry. |
+
 `TaskDeadlines`:
 
 | Field | Type | Notes |
@@ -572,6 +585,17 @@ Daemon-to-browser lifecycle message for manual and automatic compaction.
 | previewWebSocketProtocols | boolean? | Daemon forwards requested WebSocket subprotocols. |
 | localServerDetection | boolean? | Daemon reports verified loopback web servers started by task tools. |
 | skills | boolean? | Daemon accepts `listSkills` and can pass explicit Claude skill files into Pi. |
+| browserRuntimeInstalled | boolean? | `gsd-browser` binary is present on the daemon machine. |
+| browserRuntimeVersion | string? | Installed `gsd-browser` version. |
+| browserRuntimeMinVersion | string? | Minimum runtime version required by the daemon. |
+| browserRuntimeMinVersionOk | boolean? | Installed runtime satisfies `browserRuntimeMinVersion`. |
+| browserRuntimePath | string? | Runtime binary path used by daemon probing and execution. |
+| browserRuntimeErrorCode | string? | Stable unavailable reason, e.g. `browser_not_installed`, `version_too_old`, `manifest_invalid`, or `chrome_missing`. |
+| browserRuntimeErrorMessage | string? | Human-readable unavailable reason. |
+| browserCloudMethodsVersion | int? | Cloud method manifest version reported by `gsd-browser cloud-methods --json`. |
+| browserChromeAvailable | boolean? | Chrome/Chromium is available to the runtime. |
+
+Old daemons omit browser runtime fields and browser lifecycle messages. Cloud treats omitted runtime fields as unknown or unavailable for ambient browser use.
 
 ### `welcome` (relay → daemon, response to hello)
 
@@ -830,6 +854,15 @@ Browser support is advertised in `hello.capabilities`.
 | browserIdentities | bool | Daemon can isolate browser state by identity scope and key. |
 | browserSensitiveActionApproval | bool | Daemon can pause browser tool execution for approval. |
 | browserMaxFrameBytes | int | Maximum encoded browser frame size the daemon can send. |
+| browserRuntimeInstalled | bool | `gsd-browser` binary is installed. |
+| browserRuntimeVersion | string | Installed `gsd-browser` version. |
+| browserRuntimeMinVersion | string | Minimum compatible runtime version. |
+| browserRuntimeMinVersionOk | bool | Installed runtime is compatible. |
+| browserRuntimePath | string | Runtime binary path. |
+| browserRuntimeErrorCode | string | Stable runtime unavailable code. |
+| browserRuntimeErrorMessage | string | Runtime unavailable detail. |
+| browserCloudMethodsVersion | int | Cloud method manifest version. |
+| browserChromeAvailable | bool | Chrome/Chromium is available. |
 
 ### Lifecycle
 
@@ -1135,7 +1168,7 @@ to the approved loopback target.
 
 ### Tool Calls
 
-`browserToolCall` and `browserToolResult` represent agent browser tool execution. The daemon validates active grant state before executing each call.
+`browserToolCall`, `browserToolCallStarted`, `browserToolCallUpdated`, `browserArtifactCreated`, and `browserToolResult` represent agent browser tool execution. The daemon validates active grant state before executing each call and sends only redacted safe result data to Cloud/model consumers.
 
 #### `browserToolCall`
 
@@ -1149,6 +1182,57 @@ to the approved loopback target.
 | method | string |
 | paramsJson | json? |
 
+#### `browserToolCallStarted`
+
+| Field | Type |
+|---|---|
+| type | "browserToolCallStarted" |
+| browserId | string? |
+| grantId | string? |
+| sessionId | uuid |
+| channelId | string |
+| taskId | uuid? |
+| toolUseId | string? |
+| method | string |
+| category | string? |
+| summary | string |
+| intent | string? |
+| metadata | json? |
+| at | iso8601 string |
+
+#### `browserToolCallUpdated`
+
+| Field | Type |
+|---|---|
+| type | "browserToolCallUpdated" |
+| browserId | string? |
+| grantId | string? |
+| sessionId | uuid |
+| channelId | string |
+| taskId | uuid? |
+| toolUseId | string? |
+| status | string |
+| summary | string? |
+| metadata | json? |
+| at | iso8601 string |
+
+#### `browserArtifactCreated`
+
+| Field | Type |
+|---|---|
+| type | "browserArtifactCreated" |
+| browserId | string |
+| grantId | string? |
+| sessionId | uuid |
+| channelId | string |
+| taskId | uuid? |
+| artifactId | string |
+| kind | string |
+| title | string? |
+| url | string? |
+| metadata | json? |
+| createdAt | iso8601 string |
+
 #### `browserToolResult`
 
 | Field | Type |
@@ -1156,11 +1240,18 @@ to the approved loopback target.
 | type | "browserToolResult" |
 | browserId | string |
 | grantId | string |
+| sessionId | uuid? |
+| channelId | string? |
 | taskId | uuid |
 | toolUseId | string |
 | ok | bool |
-| resultJson | json? |
+| resultJson | json? — Redacted safe result data only. |
 | error | string? |
+| errorCode | string? |
+| recoveryHint | string? |
+| sensitivity | string? |
+| redactionStatus | string? |
+| localArtifactPointer | string? |
 
 ### Sensitive Actions
 
diff --git a/envelope.go b/envelope.go
index b380d5a..8366a6c 100644
--- a/envelope.go
+++ b/envelope.go
@@ -211,6 +211,12 @@ func payloadForType(msgType string) (any, error) {
 		return &BrowserToolCall{}, nil
 	case MsgTypeBrowserToolResult:
 		return &BrowserToolResult{}, nil
+	case MsgTypeBrowserToolCallStarted:
+		return &BrowserToolCallStarted{}, nil
+	case MsgTypeBrowserToolCallUpdated:
+		return &BrowserToolCallUpdated{}, nil
+	case MsgTypeBrowserArtifactCreated:
+		return &BrowserArtifactCreated{}, nil
 	case MsgTypeBrowserControlClaim:
 		return &BrowserControlClaim{}, nil
 	case MsgTypeBrowserControlRelease:
diff --git a/messages.go b/messages.go
index 1aa8c60..e21ce55 100644
--- a/messages.go
+++ b/messages.go
@@ -83,6 +83,9 @@ const (
 	MsgTypeBrowserAction                  MessageType = "browserAction"
 	MsgTypeBrowserToolCall                MessageType = "browserToolCall"
 	MsgTypeBrowserToolResult              MessageType = "browserToolResult"
+	MsgTypeBrowserToolCallStarted         MessageType = "browserToolCallStarted"
+	MsgTypeBrowserToolCallUpdated         MessageType = "browserToolCallUpdated"
+	MsgTypeBrowserArtifactCreated         MessageType = "browserArtifactCreated"
 	MsgTypeBrowserControlClaim            MessageType = "browserControlClaim"
 	MsgTypeBrowserControlRelease          MessageType = "browserControlRelease"
 	MsgTypeBrowserUserInput               MessageType = "browserUserInput"
@@ -145,6 +148,16 @@ type PlanCapability struct {
 	Snapshot   json.RawMessage `json:"snapshot,omitempty"`
 }
 
+type BrowserGrantContext struct {
+	GrantID   string `json:"grantId"`
+	ProjectID string `json:"projectId"`
+	SessionID string `json:"sessionId"`
+	TaskID    string `json:"taskId"`
+	ChannelID string `json:"channelId"`
+	MachineID string `json:"machineId"`
+	ExpiresAt string `json:"expiresAt"`
+}
+
 type PlanningEvent struct {
 	Type              MessageType     `json:"type"`
 	EventID           string          `json:"eventId"`
@@ -254,30 +267,31 @@ const (
 
 // Task is sent from the browser to the daemon to dispatch a user message.
 type Task struct {
-	Type               string          `json:"type"`
-	TaskID             string          `json:"taskId"`
-	SessionID          string          `json:"sessionId"`
-	ChannelID          string          `json:"channelId"`
-	AttemptID          string          `json:"attemptId,omitempty"`
-	AttemptNumber      int             `json:"attemptNumber,omitempty"`
-	LeaseExpiresAt     string          `json:"leaseExpiresAt,omitempty"`
-	DeadlineProfile    TaskDeadlines   `json:"deadlineProfile,omitempty"`
-	TurnKind           TurnKind        `json:"turnKind,omitempty"`
-	Prompt             string          `json:"prompt"`
-	Engine             string          `json:"engine,omitempty"`   // "pi"; empty defaults to pi
-	Provider           string          `json:"provider,omitempty"` // Pi provider; empty defaults to claude-cli
-	Model              string          `json:"model"`
-	Effort             string          `json:"effort"`
-	PermissionMode     string          `json:"permissionMode"`
-	CWD                string          `json:"cwd"`
-	ClaudeSessionID    string          `json:"claudeSessionId,omitempty"` // passed to --resume
-	RequestID          string          `json:"requestId,omitempty"`
-	Traceparent        string          `json:"traceparent,omitempty"` // W3C trace context
-	ImageURLs          []string        `json:"imageUrls,omitempty"`   // user-attached image URLs
-	ContextRefs        []ContextRef    `json:"contextRefs,omitempty"`
-	CustomInstructions string          `json:"customInstructions,omitempty"`
-	DisableSkills      bool            `json:"disableSkills,omitempty"`
-	PlanCapability     *PlanCapability `json:"planCapability,omitempty"`
+	Type               string               `json:"type"`
+	TaskID             string               `json:"taskId"`
+	SessionID          string               `json:"sessionId"`
+	ChannelID          string               `json:"channelId"`
+	AttemptID          string               `json:"attemptId,omitempty"`
+	AttemptNumber      int                  `json:"attemptNumber,omitempty"`
+	LeaseExpiresAt     string               `json:"leaseExpiresAt,omitempty"`
+	DeadlineProfile    TaskDeadlines        `json:"deadlineProfile,omitempty"`
+	TurnKind           TurnKind             `json:"turnKind,omitempty"`
+	Prompt             string               `json:"prompt"`
+	Engine             string               `json:"engine,omitempty"`   // "pi"; empty defaults to pi
+	Provider           string               `json:"provider,omitempty"` // Pi provider; empty defaults to claude-cli
+	Model              string               `json:"model"`
+	Effort             string               `json:"effort"`
+	PermissionMode     string               `json:"permissionMode"`
+	CWD                string               `json:"cwd"`
+	ClaudeSessionID    string               `json:"claudeSessionId,omitempty"` // passed to --resume
+	RequestID          string               `json:"requestId,omitempty"`
+	Traceparent        string               `json:"traceparent,omitempty"` // W3C trace context
+	ImageURLs          []string             `json:"imageUrls,omitempty"`   // user-attached image URLs
+	ContextRefs        []ContextRef         `json:"contextRefs,omitempty"`
+	CustomInstructions string               `json:"customInstructions,omitempty"`
+	DisableSkills      bool                 `json:"disableSkills,omitempty"`
+	PlanCapability     *PlanCapability      `json:"planCapability,omitempty"`
+	BrowserGrant       *BrowserGrantContext `json:"browserGrant,omitempty"`
 }
 
 type TaskLifecycle struct {
@@ -906,14 +920,66 @@ type BrowserToolCall struct {
 }
 
 type BrowserToolResult struct {
+	Type                 MessageType     `json:"type"`
+	BrowserID            string          `json:"browserId"`
+	GrantID              string          `json:"grantId"`
+	SessionID            string          `json:"sessionId,omitempty"`
+	ChannelID            string          `json:"channelId,omitempty"`
+	TaskID               string          `json:"taskId"`
+	ToolUseID            string          `json:"toolUseId"`
+	OK                   bool            `json:"ok"`
+	ResultJSON           json.RawMessage `json:"resultJson,omitempty"`
+	Error                string          `json:"error,omitempty"`
+	ErrorCode            string          `json:"errorCode,omitempty"`
+	RecoveryHint         string          `json:"recoveryHint,omitempty"`
+	Sensitivity          string          `json:"sensitivity,omitempty"`
+	RedactionStatus      string          `json:"redactionStatus,omitempty"`
+	LocalArtifactPointer string          `json:"localArtifactPointer,omitempty"`
+}
+
+type BrowserToolCallStarted struct {
+	Type      MessageType     `json:"type"`
+	BrowserID string          `json:"browserId,omitempty"`
+	GrantID   string          `json:"grantId,omitempty"`
+	SessionID string          `json:"sessionId"`
+	ChannelID string          `json:"channelId"`
+	TaskID    string          `json:"taskId,omitempty"`
+	ToolUseID string          `json:"toolUseId,omitempty"`
+	Method    string          `json:"method"`
+	Category  string          `json:"category,omitempty"`
+	Summary   string          `json:"summary"`
+	Intent    string          `json:"intent,omitempty"`
+	Metadata  json.RawMessage `json:"metadata,omitempty"`
+	At        string          `json:"at"`
+}
+
+type BrowserToolCallUpdated struct {
+	Type      MessageType     `json:"type"`
+	BrowserID string          `json:"browserId,omitempty"`
+	GrantID   string          `json:"grantId,omitempty"`
+	SessionID string          `json:"sessionId"`
+	ChannelID string          `json:"channelId"`
+	TaskID    string          `json:"taskId,omitempty"`
+	ToolUseID string          `json:"toolUseId,omitempty"`
+	Status    string          `json:"status"`
+	Summary   string          `json:"summary,omitempty"`
+	Metadata  json.RawMessage `json:"metadata,omitempty"`
+	At        string          `json:"at"`
+}
+
+type BrowserArtifactCreated struct {
 	Type       MessageType     `json:"type"`
 	BrowserID  string          `json:"browserId"`
-	GrantID    string          `json:"grantId"`
-	TaskID     string          `json:"taskId"`
-	ToolUseID  string          `json:"toolUseId"`
-	OK         bool            `json:"ok"`
-	ResultJSON json.RawMessage `json:"resultJson,omitempty"`
-	Error      string          `json:"error,omitempty"`
+	GrantID    string          `json:"grantId,omitempty"`
+	SessionID  string          `json:"sessionId"`
+	ChannelID  string          `json:"channelId"`
+	TaskID     string          `json:"taskId,omitempty"`
+	ArtifactID string          `json:"artifactId"`
+	Kind       string          `json:"kind"`
+	Title      string          `json:"title,omitempty"`
+	URL        string          `json:"url,omitempty"`
+	Metadata   json.RawMessage `json:"metadata,omitempty"`
+	CreatedAt  string          `json:"createdAt"`
 }
 
 type BrowserControlClaim struct {
@@ -1050,22 +1116,31 @@ type BrowserSensitiveActionResponse struct {
 
 // HelloCapabilities describes optional daemon protocol support.
 type HelloCapabilities struct {
-	Stop                           bool `json:"stop,omitempty"`
-	Terminal                       bool `json:"terminal,omitempty"`
-	AgentTerminalJobs              bool `json:"agentTerminalJobs,omitempty"`
-	ContextRefs                    bool `json:"contextRefs,omitempty"`
-	PreviewTunnel                  bool `json:"previewTunnel,omitempty"`
-	PreviewMaxFrameBytes           int  `json:"previewMaxFrameBytes,omitempty"`
-	PreviewChunkBytes              int  `json:"previewChunkBytes,omitempty"`
-	PreviewWebSocketProtocols      bool `json:"previewWebSocketProtocols,omitempty"`
-	LocalServerDetection           bool `json:"localServerDetection,omitempty"`
-	Skills                         bool `json:"skills,omitempty"`
-	BrowserSessions                bool `json:"browserSessions,omitempty"`
-	BrowserFrameStream             bool `json:"browserFrameStream,omitempty"`
-	BrowserUserControl             bool `json:"browserUserControl,omitempty"`
-	BrowserIdentities              bool `json:"browserIdentities,omitempty"`
-	BrowserSensitiveActionApproval bool `json:"browserSensitiveActionApproval,omitempty"`
-	BrowserMaxFrameBytes           int  `json:"browserMaxFrameBytes,omitempty"`
+	Stop                           bool   `json:"stop,omitempty"`
+	Terminal                       bool   `json:"terminal,omitempty"`
+	AgentTerminalJobs              bool   `json:"agentTerminalJobs,omitempty"`
+	ContextRefs                    bool   `json:"contextRefs,omitempty"`
+	PreviewTunnel                  bool   `json:"previewTunnel,omitempty"`
+	PreviewMaxFrameBytes           int    `json:"previewMaxFrameBytes,omitempty"`
+	PreviewChunkBytes              int    `json:"previewChunkBytes,omitempty"`
+	PreviewWebSocketProtocols      bool   `json:"previewWebSocketProtocols,omitempty"`
+	LocalServerDetection           bool   `json:"localServerDetection,omitempty"`
+	Skills                         bool   `json:"skills,omitempty"`
+	BrowserSessions                bool   `json:"browserSessions,omitempty"`
+	BrowserFrameStream             bool   `json:"browserFrameStream,omitempty"`
+	BrowserUserControl             bool   `json:"browserUserControl,omitempty"`
+	BrowserIdentities              bool   `json:"browserIdentities,omitempty"`
+	BrowserSensitiveActionApproval bool   `json:"browserSensitiveActionApproval,omitempty"`
+	BrowserMaxFrameBytes           int    `json:"browserMaxFrameBytes,omitempty"`
+	BrowserRuntimeInstalled        bool   `json:"browserRuntimeInstalled,omitempty"`
+	BrowserRuntimeVersion          string `json:"browserRuntimeVersion,omitempty"`
+	BrowserRuntimeMinVersion       string `json:"browserRuntimeMinVersion,omitempty"`
+	BrowserRuntimeMinVersionOK     bool   `json:"browserRuntimeMinVersionOk,omitempty"`
+	BrowserRuntimePath             string `json:"browserRuntimePath,omitempty"`
+	BrowserRuntimeErrorCode        string `json:"browserRuntimeErrorCode,omitempty"`
+	BrowserRuntimeErrorMessage     string `json:"browserRuntimeErrorMessage,omitempty"`
+	BrowserCloudMethodsVersion     int    `json:"browserCloudMethodsVersion,omitempty"`
+	BrowserChromeAvailable         bool   `json:"browserChromeAvailable,omitempty"`
 }
 
 // Hello is the first frame sent by the daemon after connecting.
diff --git a/messages_test.go b/messages_test.go
index c440762..4f8dc24 100644
--- a/messages_test.go
+++ b/messages_test.go
@@ -3,6 +3,7 @@ package protocol
 import (
 	"bytes"
 	"encoding/json"
+	"strings"
 	"testing"
 	"time"
 )
@@ -32,6 +33,15 @@ func TestEnvelopeRoundTrip(t *testing.T) {
 			Traceparent:        "00-4bf92f3577b34da6a3ce929d0e0e4736-00f067aa0ba902b7-01",
 			CustomInstructions: "Always talk like a pirate.",
 			DisableSkills:      true,
+			BrowserGrant: &BrowserGrantContext{
+				GrantID:   "grant_123",
+				ProjectID: "project_123",
+				SessionID: "22222222-2222-2222-2222-222222222222",
+				TaskID:    "11111111-1111-1111-1111-111111111111",
+				ChannelID: "ch-1",
+				MachineID: "machine_123",
+				ExpiresAt: "2026-05-01T12:00:00Z",
+			},
 		}},
 		{"stream", &Stream{
 			Type:           MsgTypeStream,
@@ -56,9 +66,14 @@ func TestEnvelopeRoundTrip(t *testing.T) {
 			OS:            "darwin",
 			Arch:          "arm64",
 			Capabilities: &HelloCapabilities{
-				Stop:              true,
-				Terminal:          true,
-				AgentTerminalJobs: true,
+				Stop:                       true,
+				Terminal:                   true,
+				AgentTerminalJobs:          true,
+				BrowserRuntimeInstalled:    true,
+				BrowserRuntimeVersion:      "0.1.19",
+				BrowserRuntimeMinVersion:   "0.1.19",
+				BrowserRuntimeMinVersionOK: true,
+				BrowserCloudMethodsVersion: 1,
 			},
 			ActiveTasks: []string{"task-a", "task-b"},
 		}},
@@ -200,6 +215,61 @@ func TestEnvelopeRoundTrip(t *testing.T) {
 			Method:     "navigate",
 			ParamsJSON: json.RawMessage(`{"url":"https://example.com"}`),
 		}},
+		{"browserToolResult", &BrowserToolResult{
+			Type:            MsgTypeBrowserToolResult,
+			BrowserID:       "browser_123",
+			GrantID:         "grant_123",
+			SessionID:       "session_123",
+			ChannelID:       "channel_123",
+			TaskID:          "task_123",
+			ToolUseID:       "toolu_123",
+			OK:              true,
+			ResultJSON:      json.RawMessage(`{"url":"https://example.com","title":"Example Domain"}`),
+			Sensitivity:     "public",
+			RedactionStatus: "not_needed",
+		}},
+		{"browserToolCallStarted", &BrowserToolCallStarted{
+			Type:      MsgTypeBrowserToolCallStarted,
+			BrowserID: "browser_123",
+			GrantID:   "grant_123",
+			SessionID: "session_123",
+			ChannelID: "channel_123",
+			TaskID:    "task_123",
+			ToolUseID: "toolu_123",
+			Method:    "navigate",
+			Category:  "navigation",
+			Summary:   "Navigate to https://example.com",
+			Intent:    "inspect page",
+			Metadata:  json.RawMessage(`{"url":"https://example.com"}`),
+			At:        "2026-05-01T12:00:00Z",
+		}},
+		{"browserToolCallUpdated", &BrowserToolCallUpdated{
+			Type:      MsgTypeBrowserToolCallUpdated,
+			BrowserID: "browser_123",
+			GrantID:   "grant_123",
+			SessionID: "session_123",
+			ChannelID: "channel_123",
+			TaskID:    "task_123",
+			ToolUseID: "toolu_123",
+			Status:    "ok",
+			Summary:   "Navigate to https://example.com",
+			Metadata:  json.RawMessage(`{"statusCode":200}`),
+			At:        "2026-05-01T12:00:01Z",
+		}},
+		{"browserArtifactCreated", &BrowserArtifactCreated{
+			Type:       MsgTypeBrowserArtifactCreated,
+			BrowserID:  "browser_123",
+			GrantID:    "grant_123",
+			SessionID:  "session_123",
+			ChannelID:  "channel_123",
+			TaskID:     "task_123",
+			ArtifactID: "artifact_123",
+			Kind:       "snapshot",
+			Title:      "Example Domain",
+			URL:        "https://example.com",
+			Metadata:   json.RawMessage(`{"snapshotId":"snap_123"}`),
+			CreatedAt:  "2026-05-01T12:00:02Z",
+		}},
 		{"browserSensitiveActionRequest", &BrowserSensitiveActionRequest{
 			Type:      MsgTypeBrowserSensitiveActionRequest,
 			BrowserID: "browser_123",
@@ -1345,6 +1415,106 @@ func TestParseEnvelopeRejectsUnknownType(t *testing.T) {
 	}
 }
 
+func TestParseEnvelopeBrowserLifecycleCompatibility(t *testing.T) {
+	cases := []struct {
+		name        string
+		messageType MessageType
+		raw         string
+	}{
+		{
+			name:        "browserToolCallStarted",
+			messageType: MsgTypeBrowserToolCallStarted,
+			raw: `{
+				"type":"browserToolCallStarted",
+				"browserId":"browser_123",
+				"grantId":"grant_123",
+				"sessionId":"session_123",
+				"channelId":"channel_123",
+				"taskId":"task_123",
+				"toolUseId":"toolu_123",
+				"method":"snapshot",
+				"summary":"Snapshot page",
+				"unknownFutureField":"ignored",
+				"at":"2026-05-01T12:00:00Z"
+			}`,
+		},
+		{
+			name:        "browserToolCallUpdated",
+			messageType: MsgTypeBrowserToolCallUpdated,
+			raw: `{
+				"type":"browserToolCallUpdated",
+				"browserId":"browser_123",
+				"grantId":"grant_123",
+				"sessionId":"session_123",
+				"channelId":"channel_123",
+				"taskId":"task_123",
+				"toolUseId":"toolu_123",
+				"status":"ok",
+				"summary":"Snapshot page",
+				"unknownFutureField":"ignored",
+				"at":"2026-05-01T12:00:01Z"
+			}`,
+		},
+		{
+			name:        "browserArtifactCreated",
+			messageType: MsgTypeBrowserArtifactCreated,
+			raw: `{
+				"type":"browserArtifactCreated",
+				"browserId":"browser_123",
+				"grantId":"grant_123",
+				"sessionId":"session_123",
+				"channelId":"channel_123",
+				"taskId":"task_123",
+				"artifactId":"artifact_123",
+				"kind":"snapshot",
+				"unknownFutureField":"ignored",
+				"createdAt":"2026-05-01T12:00:02Z"
+			}`,
+		},
+		{
+			name:        "browserToolResult",
+			messageType: MsgTypeBrowserToolResult,
+			raw: `{
+				"type":"browserToolResult",
+				"browserId":"browser_123",
+				"grantId":"grant_123",
+				"sessionId":"session_123",
+				"channelId":"channel_123",
+				"taskId":"task_123",
+				"toolUseId":"toolu_123",
+				"ok":true,
+				"resultJson":{"snapshotId":"snap_123"},
+				"unknownFutureField":"ignored"
+			}`,
+		},
+	}
+
+	for _, tc := range cases {
+		t.Run(tc.name+" accepts unknown fields", func(t *testing.T) {
+			env, err := ParseEnvelope([]byte(tc.raw))
+			if err != nil {
+				t.Fatalf("ParseEnvelope: %v", err)
+			}
+			if env.Type != tc.messageType {
+				t.Fatalf("type = %q, want %q", env.Type, tc.messageType)
+			}
+			data, err := json.Marshal(env.Payload)
+			if err != nil {
+				t.Fatalf("marshal payload: %v", err)
+			}
+			if bytes.Contains(data, []byte("unknownFutureField")) {
+				t.Fatalf("unknown field survived round trip: %s", data)
+			}
+		})
+		t.Run(tc.name+" rejects invalid type", func(t *testing.T) {
+			raw := strings.Replace(tc.raw, string(tc.messageType), string(tc.messageType)+"Invalid", 1)
+			if _, err := ParseEnvelope([]byte(raw)); err == nil {
+				t.Fatal("expected invalid type error")
+			}
+		})
+	}
+}
+
 func TestHelloOmitsEmptyActiveTasks(t *testing.T) {
 	h := &Hello{
 		Type:          MsgTypeHello,