fix: sanitize workspace agent logs before insert (#24028)

Workspace agent logs could still fail after the earlier invalid UTF-8
fix because NUL bytes are valid Go/protobuf strings but are rejected by
Postgres text columns. The legacy HTTP log upload path also bypassed the
old sanitization entirely, and both server insert paths computed
logs_length from the unsanitized input.

Add a shared log-output sanitizer in agentsdk, use it in the protobuf
conversion path and both server-side insert paths, and compute
OutputLength from the sanitized string so overflow accounting matches
what is actually stored. This keeps the old invalid UTF-8 behavior while
also handling embedded NUL bytes consistently across DRPC and HTTP log
ingestion.

Refs [#23292 ](https://github.com/coder/coder/issues/23292)
Refs [#13433 ](https://github.com/coder/coder/issues/13433)

coderd/agentapi/logs_test.go

@@ -139,6 +139,59 @@ func TestBatchCreateLogs(t *testing.T) {
 		require.True(t, publishWorkspaceAgentLogsUpdateCalled)
 	})
 
+	t.Run("SanitizesOutput", func(t *testing.T) {
+		t.Parallel()
+
+		dbM := dbmock.NewMockStore(gomock.NewController(t))
+		now := dbtime.Now()
+		api := &agentapi.LogsAPI{
+			AgentFn: func(context.Context) (database.WorkspaceAgent, error) {
+				return agent, nil
+			},
+			Database: dbM,
+			Log:      testutil.Logger(t),
+			TimeNowFn: func() time.Time {
+				return now
+			},
+		}
+
+		rawOutput := "before\x00middle\xc3\x28after"
+		sanitizedOutput := agentsdk.SanitizeLogOutput(rawOutput)
+		expectedOutputLength := int32(len(sanitizedOutput)) //nolint:gosec // Test-controlled string length is small.
+		req := &agentproto.BatchCreateLogsRequest{
+			LogSourceId: logSource.ID[:],
+			Logs: []*agentproto.Log{
+				{
+					CreatedAt: timestamppb.New(now),
+					Level:     agentproto.Log_WARN,
+					Output:    rawOutput,
+				},
+			},
+		}
+
+		dbM.EXPECT().InsertWorkspaceAgentLogs(gomock.Any(), database.InsertWorkspaceAgentLogsParams{
+			AgentID:      agent.ID,
+			LogSourceID:  logSource.ID,
+			CreatedAt:    now,
+			Output:       []string{sanitizedOutput},
+			Level:        []database.LogLevel{database.LogLevelWarn},
+			OutputLength: expectedOutputLength,
+		}).Return([]database.WorkspaceAgentLog{
+			{
+				AgentID:     agent.ID,
+				CreatedAt:   now,
+				ID:          1,
+				Output:      sanitizedOutput,
+				Level:       database.LogLevelWarn,
+				LogSourceID: logSource.ID,
+			},
+		}, nil)
+
+		resp, err := api.BatchCreateLogs(context.Background(), req)
+		require.NoError(t, err)
+		require.Equal(t, &agentproto.BatchCreateLogsResponse{}, resp)
+	})
+
 	t.Run("NoWorkspacePublishIfNotFirstLogs", func(t *testing.T) {
 		t.Parallel()