diff --git a/workspace-server/internal/handlers/agent_message_persistence_gate_test.go b/workspace-server/internal/handlers/agent_message_persistence_gate_test.go
new file mode 100644
index 00000000..07998112
--- /dev/null
+++ b/workspace-server/internal/handlers/agent_message_persistence_gate_test.go
@@ -0,0 +1,177 @@
+package handlers
+
+import (
+	"go/ast"
+	"go/parser"
+	"go/token"
+	"os"
+	"path/filepath"
+	"sort"
+	"strconv"
+	"strings"
+	"testing"
+)
+
+// TestAgentMessageBroadcastsArePersisted is a forward-looking AST
+// gate: every function in this package that broadcasts an
+// `AGENT_MESSAGE` WebSocket event MUST also call
+// `INSERT INTO activity_logs` somewhere in its body.
+//
+// The reno-stars production data-loss bug (CEO Ryan PC's long-form
+// onboarding-friction message visible live but missing on reload)
+// happened because mcp_tools.go:toolSendMessageToUser broadcast WS
+// without a paired INSERT — while the HTTP /notify sibling DID
+// persist. The fix added the INSERT; this gate prevents the regression
+// class from re-emerging in any future chat-bearing tool.
+//
+// Why an AST gate vs a code-review checklist (per memory
+// feedback_behavior_based_ast_gates.md): "pin invariants by what a
+// function calls, not what it's named". The shape that loses data is:
+//
+//	BroadcastOnly(_, "AGENT_MESSAGE", _) without an INSERT companion
+//
+// Any new tool that emits AGENT_MESSAGE must persist or the next
+// canvas refresh drops the message — same shape as reno-stars. A
+// reviewer can miss this; the AST walk can't.
+//
+// Allowlist: empty by intent. If a future use case genuinely needs
+// fire-and-forget broadcast (e.g., transient typing indicators that
+// should NOT survive reload), add an entry here AND document why.
+// "Doesn't need to persist" is rarely the right answer for chat —
+// the canvas history is the source of truth.
+func TestAgentMessageBroadcastsArePersisted(t *testing.T) {
+	wd, err := os.Getwd()
+	if err != nil {
+		t.Fatalf("getwd: %v", err)
+	}
+	entries, err := os.ReadDir(wd)
+	if err != nil {
+		t.Fatalf("readdir %s: %v", wd, err)
+	}
+
+	type violation struct {
+		file string
+		fn   string
+	}
+	var violations []violation
+
+	for _, ent := range entries {
+		name := ent.Name()
+		if ent.IsDir() || !strings.HasSuffix(name, ".go") || strings.HasSuffix(name, "_test.go") {
+			continue
+		}
+		path := filepath.Join(wd, name)
+		fset := token.NewFileSet()
+		file, err := parser.ParseFile(fset, path, nil, parser.ParseComments)
+		if err != nil {
+			t.Fatalf("parse %s: %v", path, err)
+		}
+
+		for _, decl := range file.Decls {
+			fn, ok := decl.(*ast.FuncDecl)
+			if !ok || fn.Body == nil {
+				continue
+			}
+			if !funcEmitsAgentMessageBroadcast(fn) {
+				continue
+			}
+			if !funcInsertsIntoActivityLogs(fn) {
+				violations = append(violations, violation{file: name, fn: fn.Name.Name})
+			}
+		}
+	}
+
+	if len(violations) > 0 {
+		sort.Slice(violations, func(i, j int) bool {
+			if violations[i].file != violations[j].file {
+				return violations[i].file < violations[j].file
+			}
+			return violations[i].fn < violations[j].fn
+		})
+		var buf strings.Builder
+		for _, v := range violations {
+			buf.WriteString("  - ")
+			buf.WriteString(v.file)
+			buf.WriteString(":")
+			buf.WriteString(v.fn)
+			buf.WriteString("\n")
+		}
+		t.Errorf(`function(s) broadcast `+"`AGENT_MESSAGE`"+` without persisting to activity_logs:
+
+%s
+This is the reno-stars data-loss regression class: live message
+visible to the user, but missing on reload because activity_log was
+never written. Every chat-bearing broadcast MUST be paired with:
+
+  INSERT INTO activity_logs (workspace_id, activity_type, method,
+    summary, response_body, status)
+  VALUES ($1, 'a2a_receive', 'notify', $2, $3::jsonb, 'ok')
+
+See activity.go:Notify and mcp_tools.go:toolSendMessageToUser for
+the canonical shapes. Don't add an allowlist entry without a
+documented reason — the canvas chat history is the source of truth
+and silently dropping messages is a P0 user trust break.`,
+			buf.String())
+	}
+}
+
+// funcEmitsAgentMessageBroadcast walks fn.Body for any CallExpr that
+// looks like `*.BroadcastOnly(_, "AGENT_MESSAGE", _)`.
+func funcEmitsAgentMessageBroadcast(fn *ast.FuncDecl) bool {
+	var found bool
+	ast.Inspect(fn.Body, func(n ast.Node) bool {
+		call, ok := n.(*ast.CallExpr)
+		if !ok {
+			return true
+		}
+		sel, ok := call.Fun.(*ast.SelectorExpr)
+		if !ok || sel.Sel.Name != "BroadcastOnly" {
+			return true
+		}
+		// BroadcastOnly(workspaceID, eventType, payload) — the second
+		// arg is the event name. Match by string-literal value.
+		if len(call.Args) < 2 {
+			return true
+		}
+		lit, ok := call.Args[1].(*ast.BasicLit)
+		if !ok || lit.Kind != token.STRING {
+			return true
+		}
+		raw := lit.Value
+		if unq, err := strconv.Unquote(raw); err == nil {
+			raw = unq
+		}
+		if raw == "AGENT_MESSAGE" {
+			found = true
+			return false
+		}
+		return true
+	})
+	return found
+}
+
+// funcInsertsIntoActivityLogs walks fn.Body for any STRING BasicLit
+// whose body contains `INSERT INTO activity_logs` (the SQL literal
+// passed to ExecContext). Matches the substring rather than a strict
+// regex because we don't care about the exact INSERT shape here —
+// only that the function persists. Specific shape pinning lives in
+// the per-handler test (see TestMCPHandler_SendMessageToUser_*).
+func funcInsertsIntoActivityLogs(fn *ast.FuncDecl) bool {
+	var found bool
+	ast.Inspect(fn.Body, func(n ast.Node) bool {
+		lit, ok := n.(*ast.BasicLit)
+		if !ok || lit.Kind != token.STRING {
+			return true
+		}
+		raw := lit.Value
+		if unq, err := strconv.Unquote(raw); err == nil {
+			raw = unq
+		}
+		if strings.Contains(raw, "INSERT INTO activity_logs") {
+			found = true
+			return false
+		}
+		return true
+	})
+	return found
+}
diff --git a/workspace-server/internal/handlers/mcp_test.go b/workspace-server/internal/handlers/mcp_test.go
index 7db2849c..6ede0c2c 100644
--- a/workspace-server/internal/handlers/mcp_test.go
+++ b/workspace-server/internal/handlers/mcp_test.go
@@ -11,6 +11,8 @@ import (
 	"os"
 	"testing"
 
+	"errors"
+
 	"github.com/DATA-DOG/go-sqlmock"
 	"github.com/Molecule-AI/molecule-monorepo/platform/internal/db"
 	"github.com/gin-gonic/gin"
@@ -629,6 +631,107 @@ func TestMCPHandler_SendMessageToUser_Blocked_WhenEnvNotSet(t *testing.T) {
 	}
 }
 
+// TestMCPHandler_SendMessageToUser_DBErrorLogsAndStill200s pins the
+// "best-effort persistence" contract: when the activity_log INSERT
+// fails (DB hiccup, constraint violation, transient connection drop),
+// the tool MUST still return success to the agent because the WS
+// broadcast already succeeded — the user has seen the message.
+//
+// This matches /notify (activity.go) behavior. Returning an error
+// here would cause the agent to retry and re-broadcast, double-
+// rendering the message in the user's live chat panel for every
+// retry until the DB recovers.
+func TestMCPHandler_SendMessageToUser_DBErrorLogsAndStill200s(t *testing.T) {
+	t.Setenv("MOLECULE_MCP_ALLOW_SEND_MESSAGE", "true")
+	h, mock := newMCPHandler(t)
+
+	mock.ExpectQuery("SELECT name FROM workspaces").
+		WithArgs("ws-err").
+		WillReturnRows(sqlmock.NewRows([]string{"name"}).AddRow("CEO Ryan PC"))
+
+	// INSERT fails — must NOT abort the tool response.
+	mock.ExpectExec(`INSERT INTO activity_logs.*'a2a_receive'.*'notify'`).
+		WillReturnError(errors.New("transient db error"))
+
+	w := mcpPost(t, h, "ws-err", map[string]interface{}{
+		"jsonrpc": "2.0",
+		"id":      100,
+		"method":  "tools/call",
+		"params": map[string]interface{}{
+			"name": "send_message_to_user",
+			"arguments": map[string]interface{}{
+				"message": "should not be lost from the live chat",
+			},
+		},
+	})
+
+	var resp mcpResponse
+	if err := json.Unmarshal(w.Body.Bytes(), &resp); err != nil {
+		t.Fatalf("response was not valid JSON-RPC: %v", err)
+	}
+	// Tool response is success — INSERT failure logged, broadcast
+	// already succeeded.
+	if resp.Error != nil {
+		t.Errorf("tool response should be success on DB error (broadcast won), got JSON-RPC error: %+v", resp.Error)
+	}
+	if err := mock.ExpectationsWereMet(); err != nil {
+		t.Errorf("expected DB calls in order: %v", err)
+	}
+}
+
+// TestMCPHandler_SendMessageToUser_ResponseBodyShape pins the
+// response_body JSON shape stored in activity_logs. This shape MUST
+// match what the canvas hydrater (extractResponseText in
+// historyHydration.ts) reads — specifically `{"result": "<text>"}`.
+// Any drift in the JSON shape silently breaks chat history without
+// failing the INSERT.
+//
+// Caught the same drift class flagged in
+// feedback_assert_exact_not_substring.md: a substring match on
+// "result" would pass even if the field were renamed; we assert the
+// exact JSON shape.
+func TestMCPHandler_SendMessageToUser_ResponseBodyShape(t *testing.T) {
+	t.Setenv("MOLECULE_MCP_ALLOW_SEND_MESSAGE", "true")
+	h, mock := newMCPHandler(t)
+
+	const userMessage = "Hi there from the agent"
+
+	mock.ExpectQuery("SELECT name FROM workspaces").
+		WithArgs("ws-shape").
+		WillReturnRows(sqlmock.NewRows([]string{"name"}).AddRow("CEO Ryan PC"))
+
+	// Capture the response_body argument and assert its exact shape.
+	mock.ExpectExec(`INSERT INTO activity_logs.*'a2a_receive'.*'notify'`).
+		WithArgs(
+			"ws-shape",
+			sqlmock.AnyArg(), // summary
+			// The response_body MUST be JSON `{"result": "<message>"}`.
+			// Any other shape (e.g., wrapping in a Task object) breaks
+			// the canvas hydrater's `body.result` extractor.
+			`{"result":"`+userMessage+`"}`,
+		).
+		WillReturnResult(sqlmock.NewResult(1, 1))
+
+	w := mcpPost(t, h, "ws-shape", map[string]interface{}{
+		"jsonrpc": "2.0",
+		"id":      101,
+		"method":  "tools/call",
+		"params": map[string]interface{}{
+			"name": "send_message_to_user",
+			"arguments": map[string]interface{}{
+				"message": userMessage,
+			},
+		},
+	})
+
+	if w.Code != 200 {
+		t.Fatalf("expected 200, got %d body=%s", w.Code, w.Body.String())
+	}
+	if err := mock.ExpectationsWereMet(); err != nil {
+		t.Errorf("response_body shape drift — would silently break canvas chat history: %v", err)
+	}
+}
+
 // TestMCPHandler_SendMessageToUser_PersistsToActivityLog pins the fix
 // for the reno-stars / CEO Ryan PC chat-history data-loss bug:
 // external claude-code agents using molecule-mcp's send_message_to_user